Waterfowl and Wetland Birds

Abstract

The future of wetland bird habitat and populations is intrinsically connected with the conservation of rangelands in North America. Many rangeland watersheds are source drainage for some of the highest functioning extant wetlands. The Central and Pacific Flyways have significant overlap with available rangelands in western North America. Within these flyways, the importance of rangeland management has become increasingly recognized by those involved in wetland bird conservation. Within the array of wetland bird species, seasonal habitat needs are highly variable. During the breeding period, nest survival is one of the most important drivers of population growth for many wetland bird species and rangelands often provide quality nesting cover. Throughout spring and fall, rangeland wetlands provide key forage resources that support energetic demands needed for migration. In some areas, stock ponds developed for livestock water provide migration stopover and wintering habitat, especially in times of water scarcity. In the Intermountain West, drought combined with water demands from agriculture and human population growth are likely headed to an ecological tipping point for wetland birds and their habitat in the region. In the Prairie Pothole Region, conversion of rangeland and draining of wetlands for increased crop production remains a significant conservation issue for wetland birds and other wildlife. In landscapes dominated by agricultural production, rangelands provide some of the highest value ecosystem services, including water quality and wetland function. Recent research has shown livestock grazing, if managed properly, is compatible and at times beneficial to wetland bird habitat needs. Either directly, or indirectly, wetland bird populations and their habitat needs are supported by healthy rangelands. In the future, rangeland and wetland bird managers will benefit from increased collaboration to aid in meeting ultimate conservation objectives.

1 Introduction

Rangeland systems and the wetland birds using them vary across western North America. This chapter addresses three groups of birds dependent on wetlands: waterfowl, shorebirds, and waterbirds. Many wetland bird conservation plans recognize the significant influence rangelands have on associated wetlands, including the North American Waterfowl Management Plan (NAWMP 2018), U.S. Shorebird Conservation Plan (Brown et al. 2001), Canadian Shorebird Conservation Plan (Donaldson et al. 2000), and North American Waterbird Conservation Plan (Kushlan et al. 2002). Wetland birds typically exhibit large-scale mobility, including seasonal migration across North America capitalizing on ecoregional resources to meet their annual cycle needs. Wetland birds breeding in northern latitudes take advantage of primary productivity associated with extended summer daylight but as winter nears, they seek resources at more southerly latitudes. Wetland bird migrations have heralded seasonal change for societies over human history. Connected wetland networks sustain migrations by providing rest and food resources and have demographic consequences for populations.

Within seasonal home-ranges, wetlands birds can be highly mobile, and a single wetland or wetland type can rarely meet daily, seasonal, or annual needs. Seasonal wetlands tend to have high biological productivity, whereas wetlands with stable water levels typically have reduced biological productivity. Because wetlands are dynamic, their availability and quality as habitat can be highly variable. Consequently, wetland birds generally select landscapes with a diversity of wetlands to maximize resources. Diversity within a complex of wetlands is a key strategy for resource managers throughout North America (Baldassarre and Bolen 2006). Wetland bird conservation has been coordinated across migration corridors (i.e., flyways) and regions. Rangelands cover significant areas of the Great Plains and the West (Fig. 13.1; Table 13.1 [avian scientific names presented]). Throughout this chapter ecoregional terminology is used consistent with wetland bird conservation and management plans.

Fig. 13.1

Major wetland bird ecoregions of rangeland systems in North America

Table 13.1 Major wetland bird ecoregions within central and western North America with subregions and regions of western rangelands

Previous reviews have provided important information on the ecology and management of waterfowl (e.g., Smith et al. 1989; Batt et al. 1992; Baldassarre and Bolen 2006; Baldassarre 2014), shorebirds (Helmers 1992; Iglecia and Winn 2021), and other waterbirds (Beyersbergen et al. 2004; Ivey and Herziger 2006). Available research addressing rangeland management has focused on waterfowl, with less empirical information for shorebirds and waterbirds. Therefore, this chapter relies heavily on science addressing waterfowl and rangeland relationships. We provide overviews of life history, regional variation, and population dynamics of wetland birds that may be influenced by rangeland management and conservation.

2 Wetland Systems

Wetlands occupy a relatively small footprint in many rangelands. However, wetlands, riparian systems, and mesic habitats are often vital to the productivity, function, and biodiversity of rangeland systems (Johnson 2019, Chap. 7). Wetlands provide substantial ecosystem services and structure biological communities well beyond their immediate footprint (Mitsch and Gosselink 2015; Donnelly et al. 2016; Johnson 2019). Wetlands are transitional areas with characteristics of both aquatic and terrestrial ecosystems in addition to their own unique ecological conditions. Wetlands typically occur where groundwater is at or near the surface or land is covered by collection of water through runoff of surface water within a watershed (Cowardin et al. 1979; Mitsch and Gosselink 2015). Wetlands have dynamic hydrology resulting in conditions ranging from near-terrestrial to fully aquatic. Availability of habitat can vary temporally and is subject to variation in response to climate patterns. Identifying jurisdictional (i.e., subject to legal authority) wetlands includes a combination of key factors: (1) presence of shallow water or moist soil for 14–21 days during the growing season, (2) water-adapted plants (i.e., hydrophytic vegetation), and (3) hydric soils influenced by anaerobic conditions of saturation (Cowardin et al. 1979; Weller 1999). Not all wetlands are considered jurisdictional or subject to legal protections. For example, some wetlands in more arid environments are ephemeral, in some cases inundated only once or twice over years.

Hydrology and water budget determine wetland type and associated ecological processes (Mitsch and Gosselink 2015). Wetlands are commonly classified by hydroperiod (Cowardin et al. 1979; Table 13.2). Hydrologic conditions such as water depth, flow patterns, and flood frequency and duration (i.e., hydroperiod) influence abiotic and biotic components. The hydroperiod is determined by water inflows and outflows. Hydroperiod, largely dictates resource availability for wetland birds, other wildlife, and livestock. For example, recharge wetlands are solely dependent upon surface runoff linking hydroperiod to precipitation patterns. Conversely, discharge wetlands have hydroperiods based on groundwater. Hydroperiod is more dynamic in recharge versus discharge wetlands. Small hydrologic fluctuations can lead to significant changes in plant and animal composition (Mitsch and Gosselink 2015). Wetlands referenced in this chapter are either palustrine (i.e., marshy fresh or inland saline waters or vegetated margins of large water bodies; Cowardin et al. 1979), or lacustrine wetlands (i.e., relatively shallow, open, freshwater lakes or their sparsely vegetated margins).

Table 13.2 Definitions of inland wetland hydroperiods

Wetland bird use tends to vary by water depth, vegetation characteristics, and size (Laubhan and Gammonley 2000; Weller 1999; Ma et al. 2010). There are five general types of wetland plant associations: submerged plants, floating-leaved plants, emergent plants, moist-soil plants, and woody plants. Submerged aquatic vegetation (SAV) communities provide important food sources for wetland birds—especially waterfowl—through their seeds, tubers, and leafy materials as well as associated aquatic macroinvertebrates. Light penetration and turbidity affect subsurface photosynthesis and influence establishment and productivity of SAV. Floating-leaved communities include both rooted and free-floating aquatic plants and provide little value to most wetland birds. Function and productivity within rangeland wetlands is primarily provided by emergent plants. These plants range from dense, robust emergents such as cattail (Typha spp.), and bulrushes (Scirpus spp.), to relatively shorter emergents with varying flood tolerances including sedges (Carex spp.), rushes (Juncus spp.), spike-rushes (Eleocharis spp.), and water-tolerant grasses such as cordgrass (Spartina spp.), panic grasses (Panicum spp.), and whitetop (Scholochloa festucacea). Many emergent wetland species can be common livestock forages (Kirby et al. 2002). Moist-soil plants include annuals or perennials that germinate following drying events on exposed mudflats and provide abundant food via seeds and aquatic invertebrates (Fredrickson and Taylor 1982; Haukos and Smith 1993; Anderson and Smith 2000). Common moist-soil plants in western rangelands include smartweeds (Polygnum spp.), barnyardgrass (Echinochloa crus-galli), spike-rushes, curly dock (Rumex crispus), goosefoots and Lamb’s quarters (Chenopodium spp.), and alkali bulrush (Scheonoplectus maritumus; Kadlec and Smith 1989; Haukos and Smith 1993; Dugger et al. 2007). Management of moist-soil habitats has been extensively applied to wetland complexes providing forage for waterfowl (Fredrickson and Taylor 1982; Baldassarre and Bolen 2006). Periodic drying can temporarily reduce wetland bird use, but is essential for cycling nutrients, succession of plant communities, and maintaining productivity (Harris and Marshall 1963; Murkin et al. 1997).

2.1 Flyway Wetlands

Flyways including Atlantic, Central, Mississippi, and Pacific are useful constructs for the administration of migratory bird management (Anderson et al. 2018; Roberts et al. 2023), with rangelands primarily overlapping the Central and Pacific Flyways. The Central Flyway includes prairie potholes, playas, and coastal marshes. Central Mixed-Grass Prairie and Tallgrass Prairie regions in the southern Central Flyway provide key wetland habitats during migration (Smith et al. 1989; DU 2021; Hagy et al. in review). Millions of pothole wetlands occur in the Northern Mixed-Grass Prairie, northwestern Tallgrass Prairie, and Aspen Parklands within the Prairie Pothole Region (PPR; Fig. 13.1). High wetland density with associated grasslands makes the PPR unique and ecologically important in North America, and globally, for breeding and migrating wetland birds (Baldassarre and Bolen 2006; Niemuth et al. 2010). The PPR is known as the “Duck Factory” producing between half to two-thirds of all ducks in North America (Smith et al. 1964; Batt et al. 1989; Baldassarre and Bolen 2006) along with important water and forage resources for livestock (Johnson 2019). Playas are shallow, ephemeral, recharge wetlands abundant on the High Plains of Central and Southern Shortgrass and Mixed-Grass prairies. Playas’ hydroperiods are highly variable and inundation can range from days to years. Playas are drivers of biodiversity in the region and the primary source of Ogallala Aquifer recharge (Haukos and Smith 1994; Smith et al. 2012; Gitz and Brauer 2016). Millions of wetland birds use playas during migration and winter (Haukos and Smith 1994; Moon and Haukos 2008; Smith et al. 2012). Coastal marshes, tidal freshwater swamps, and adjacent lagoons are defining features of the Gulf Coast. Freshwater and brackish marshes generally support the most valuable habitats for wetland birds, particularly waterfowl (Chabreck et al. 1989; Davis 2012). Coastal wetlands of Louisiana and Texas are wintering grounds for millions of wetland birds (Baldassarre and Bolen 2006; Vermillion 2012; Henkel and Taylor 2015).

The Pacific Flyway includes the Intermountain West with a variety of wetlands comprising < 10% of the area (McKinstry et al. 2004; Donnelly and Vest 2012). Many seasonal wetlands have been converted to irrigated pastures and hay meadows for production agriculture (McKinstry et al. 2004) and water management is generally complex and controversial (Downard and Endter-Wada 2013; Donnelly et al. 2020; Lovvorn and Crozier 2022). Within the region, wetlands are critical to sustaining wetland birds, other wildlife, and agricultural-based economies (Sketch et al. 2020; Donnelly et al. 2021, 2022; King et al. 2021). For most wildlife species, wetlands are part of their annual life cycle (McKinstry et al. 2004). The region provides migration, breeding, and wintering habitats for > 10 million wetland birds (Donnelly and Vest 2012; IWJV 2013). Due to precipitation patterns, wetlands experience high annual variability in availability and productivity maintaining a network of functional wetlands is critical to wetland bird conservation (Haig et al. 1998; Mackell et al. 2021; Donnelly et al. 2020, 2021, 2022).

3 Life History, Annual Cycle, and Population Dynamics

The diverse taxa comprising wetland birds span a continuum of life-history strategies that prioritize different fitness components (e.g., fecundity versus survival). However, management occurs primarily at population levels and key vital rates that shape population dynamics allow for some generalizations (Koons et al. 2014). Life histories vary from short-lived and high reproductive rates (i.e., more R-selected) to long-lived and lower reproductive (i.e., more K-selected) strategies (Stearns 1992). Accordingly, adult survival will have more influence on population growth rate for species with moderate-to-long generation times, like geese, compared to species with faster life histories, like teal, where reproductive success is more impactful (Koons et al. 2014). Overall, both reproduction and survival of wetland bird populations are influenced by environmental and habitat conditions. Sustaining functional wetland networks, especially within rangelands, across flyways provides resiliency against environmental stressors for wetland bird populations (Albanese and Haukos 2017; Haig et al. 2019; Donnelly et al. 2020).

3.1 Nest and Female Survival

Nest survival, the probability that ≥ 1 egg hatches, is one of the primary drivers of duck population growth rate and often the focus of management (Hoekman et al. 2002; Reynolds et al. 2006). Duck population growth rates can also be sensitive to adult female survival with increased predation risk for nesting females (Hoekman et al. 2002). Nest survival is generally higher for larger species like geese and swans averaging ≥ 70%, whereas ducks average 15–20% (Hoekman et al. 2002; Baldassarre and Bolen 2006; Baldassarre 2014). Clutch sizes range from 4 to 6 eggs for geese and swans and 8–12 eggs for ducks, whereas shorebirds typically lay 4 eggs and some other waterbird clutches may only have 1 egg (e.g., sandhill cranes). Waterfowl and shorebirds that commonly nest in rangelands tend to be solitary nesters, but semi-colonial behavior may occur where nest densities are high (e.g., islands). Nest initiation starts in mid-April for early nesters like mallards and northern pintail, to late June for late nesters like gadwall in high elevation systems (Baldassarre 2014). Growing season interacts with environmental conditions dictating nesting phenology and the propensity for renesting (Baldassarre 2014; Raquel et al. 2016).

Some wetland birds are generalists (e.g., mallards) that will nest in uplands, emergent vegetation in wetland margins, artificial nest structures, or woody vegetation along riparian areas (Baldassarre 2014). Others, like inland populations of snowy plovers, nest exclusively in specialized habitat (e.g., unvegetated shorelines and sandbars; Anteau et al. 2012). Agricultural lands can become ecological traps, such as when northern pintail select cropland resulting in low nest survival (Buderman et al. 2020). Waterfowl nesting habitat has three broad categories: (1) uplands including grasslands, shrublands, and agriculture lands, (2) overwater vegetation such as cattails and bulrushes or man-made platforms, and (3) cavities in trees or nest boxes.

Ducks select nesting cover based on species, local conditions, and availability. For example, mallards tend to select denser cover whereas northern pintail typically select shorter, less dense vegetation (Baldassarre 2014). Proximity to wetlands is important for upland nesting ducks but varies by species. Blue-winged teal have relatively small home ranges and nest closer to wetlands. Mallard and northern pintail can nest > 2 km from a wetland (Reynolds et al. 2006). Lesser scaup have limited mobility in uplands and nest very close to wetlands. When uplands lack cover, upland nesters tend to seek cover in dry wetlands at the emergent fringe (Lovvorn and Crozier 2022).

Most adult female mortality (i.e., 65–80%) of ducks occurs during the breeding season where nesting females are vulnerable to predators (Hoekman et al. 2002; Arnold et al. 2012). Providing quality nesting habitat helps increase both nest and female survival (Reynolds et al. 1995; Arnold et al. 2012). At the population level, nest survival is impacted by large-scale environmental factors and local nest-site characteristics; vegetation structure is more important than composition (Ringelman et al. 2018; Sherfy et al. 2018; Bortolotti et al. 2022). Nest survival generally increases with larger patch size and more perennial vegetation (Baldassarre and Bolen 2006; Bortolotti et al. 2022). The relationship of habitat and nest survival is complex, varies regionally, and difficult to differentiate among confounding factors like landscape characteristics, environmental changes, and predator communities (Clark and Nudds 1991; Horn et al. 2005; Walker et al. 2013a; Ringelman et al. 2018; Bortolotti et al. 2022; Pearse et al. 2022). Rangelands, with associated wetlands, generally provide extensive areas of perennial cover and reliably have high duck nest survival (Stephens et al. 2005; Walker et al. 2013a; Bortolotti et al. 2022). Increased nest survival in rangelands, compared to cropland landscapes, is likely due to reduced predator efficiency within large intact habitat and/or lower predator densities (Ball et al. 1995; Phillips et al. 2003; Horn et al. 2005). Large areas of intact rangelands may also support a greater abundance and diversity of other prey, reducing predation pressure on duck nests (Ackerman 2002). Although not fully understood at continental and population scales, intact rangelands are likely important in sustaining waterfowl in North America due to the potential for high nesting productivity (Higgins et al. 2002; PHJV 2021; PPJV 2017).

Nearly all shorebirds are ground nesters, but habitats and breeding behavior vary widely by species (Iglecia and Winn 2021). Before Euro-American settlement, breeding shorebirds in the Great Plains specialized in exploiting the diverse grassland mosaics left by bison (Bison bison) and fire (Eldridge 1992). Shorebird breeding habitat includes unvegetated beaches and salt/alkali flats to moderately tall and dense grasslands (Eldridge 1992; Iglecia and Winn 2021). Long-billed curlew, marbled godwit, willet, killdeer, and mountain plover all nest and forage in short (< 15 cm) grassland vegetation often far from wetlands. Wilson’s phalarope and upland sandpiper typically use taller (10–30 cm) and denser vegetation (Eldridge 1992). For species that rely on wetland invertebrates, proximity to wetlands is important when selecting nesting habitat (e.g., Wilson’s phalarope, American avocet, piping plover, snowy plover, marbled godwit, willet; Eldridge 1992; Specht et al. 2020). Drivers of shorebird nest survival may be similar to those of waterfowl due to shared nest predators (Specht et al. 2020).

Diving ducks and swans (Table 13.3) primarily build overwater nests from emergent vegetation such as bulrush, cattail, and sedges (Baldassarre 2014). These overwater nesters often have limited available nesting cover and are generally associated with semi-permanent and permanent wetlands (Baldassarre 2014). Overwater nests are more protected, and survival tends to be higher than upland nests, although predation rates can increase with decreasing water levels (Baldassarre and Bolen 2006). Across the PPR, mallards nest in emergent wetland vegetation and experience relatively higher nest survival rates compared to upland nests (Baldassarre and Bolen 2006; Baldassarre 2014). Other waterbird species also nest over water either in dense emergent vegetation (e.g., sandhill crane) or on floating mats of vegetation (e.g., grebes). Some waterbirds nest on islands (e.g., pelicans) and in trees (e.g., herons; Beyersbergen et al. 2004).

Table 13.3 Common waterfowl species in North America and their primary occurrence in rangelands, population size, trend, and conservation or management status in the United States

3.2 Juvenile Survival

Juvenile survival can also strongly influence population growth rate for wetland birds, especially dabbling ducks (Hoekman et al. 2002). Chick survival is lowest within the first two weeks post-hatch. Small size and lack of thermoregulation during this time makes chicks vulnerable to exposure (Bloom et al. 2012; Iglecia and Winn 2021) and a wide range of predators (Sargeant and Raveling 1992; Baldassarre and Bolen 2006). Females can move their brood long distances to find quality habitat, which includes abundant invertebrates for food and security cover. Brood occurrence and survival has been shown to correlate with the availability of perennial herbaceous vegetation and wetland area (Krapu et al. 2000; Walker et al. 2013b). Rangelands with abundant and diverse wetlands in both size and hydroperiod are essential to sustaining wetland bird populations in North America (Helmers 1992; Beyersbergen et al. 2004; Walker et al. 2013b).

Waterbird species have chicks that range from precocial to altricial. Sandhill crane colts leave the nest directly after hatching whereas loons, grebes, most rails, and coots rely on parental feeding at the nest for several days. Gull and tern chicks may quickly leave the nest but remain close to the nest site for several days. Ibis, pelicans, cormorants, and herons feed chicks in nests until mobility develops, which varies from 2 to 11 weeks (Weller 1999). Sandhill crane parents feed young for the first few weeks and colt mortality can be high at this time (Gerber et al. 2015). Sandhill cranes have the lowest recruitment of hunted avian species in North America (Drewien et al. 1995).

3.3 Post-breeding Survival and Migration

Post-breeding is bracketed by the reproductive and fall migration periods (Hohman et al. 1992). Most waterfowl molt flight feathers rendering birds flightless for 3–5 weeks (Baldassarre and Bolen 2006; Fox et al. 2014). Post-breeding waterfowl are vulnerable to habitat changes (e.g., drying, or de-watering of wetlands) that increase predation risk or limit access to food resources (Hohman et al. 1992). Molting has high nutrient demands like protein-rich foods (e.g., aquatic insects). Post-breeding waterfowl select habitats that lower predation risk and offer abundant food resources (Fox et al. 2014). Semi-permanent or permanent wetlands with emergent vegetation and open water are often selected post-breeding (Hohman et al. 1992; Fleskes et al. 2010). Such habitats also offer key migratory stopover areas when energetic demands increase and wetland bird diets transition to more carbohydrate-rich food sources such as wetland plant seeds, tubers, rhizomes, and agricultural grains (Baldasarre and Bolen 2006; Donnelly et al. 2021). Shorebirds will consume small amounts of plant material, but they primarily consume invertebrates for energy and some species may double their body mass prior to migration (Baker et al. 2014; Iglecia and Winn 2021).

Across rangelands, wetland availability is lowest during late summer and early fall (Johnson et al. 2010; Donnelly et al. 2019). Habitat availability is typically lowest during the post-breeding period when birds have high nutrient demands. Low nutrient reserves may negatively affect autumn survival (Sedinger and Alisauskas 2014). Additionally, diseases such as botulism, avian cholera, and avian influenza virus increase mortality risk, particularly for waterfowl, especially with decreased wetland availability (Friend et al. 2001; Baldassarre and Bolen 2006; Kent et al. 2022). Changes in land and water use, often in combination with drought, decrease wetland availability resulting in bird concentrations and recurring disease issues (Fleskes et al. 2010; Donnelly et al. 2022; Kahara et al. 2021). Similar to the breeding period, rangelands that provide wetland habitat during the post-breeding period are vital to wetland birds (Johnson et al. 2010; Gerber et al. 2015; Kemink et al. 2021; Donnelly et al. 2022).

Ideally, migration and wintering habitat provide key nutrients and energy (i.e., lipids) sources during migration and highlight the importance of available wetland complexes (Moon and Haukos 2006, 2009; Davis et al. 2014; Yetter et al. 2018). Selected food resources may change based on physiology and behavior and in response to environmental conditions. Narrow migration windows may or may not align with food availability. Donnelly et al. (2019) found that most seasonal wetlands were available during spring migration, whereas ≤ 20% were available for fall migration. In winter, freezing and snow accumulation can decrease food (e.g., grains) availability inhibiting migration.

Some wetland birds (e.g., waterfowl, coots, sandhill cranes and other rails) are hunted during fall and winter. Hunters, through harvest reporting (e.g., band returns, wing collections, surveys) and funding (e.g., duck stamp), have increased our understanding of population dynamics, movements, and conservation (Anderson et al. 2018). For example, adult female mallard survival during the non-breeding season has little impact on population growth rates relative to the breeding period and males have low natural mortality making them even more available for sustainable harvest (Hoekman et al. 2002). Consequently, hunting harvest is the primary mortality cause for male ducks (Hoekman et al. 2002; Riecke et al. 2022a). Female ducks generally experience lower harvest rates than males (Riecke et al. 2022a, b). Waterfowl harvest is carefully managed across flyways and represents one of the most successful examples of adaptive management in the world (Nichols et al. 2019).

Non-breeding habitat conditions can have carry-over effects to breeding success (Sedinger and Alisauskas 2014; Swift et al. 2020). Generally, birds in better nutritional state (i.e., body condition) during winter and spring may arrive in breeding areas earlier, nest earlier, and experience greater breeding success (Devries et al. 2008; Sedinger and Alisauskas 2014; Swift et al. 2020). Management that enhances nutritive resources in non-breeding habitats can also increase vital rates (Davis et al. 2014; Stafford et al. 2014). More information is needed to better understand shorebird vital rates and population dynamics, along with the impacts of migration and winter habitat. However, adult annual survival sustains populations for several arctic-nesting shorebirds during migration (Weiser et al. 2020). Like other wetland birds, wetland networks are critical (Albanese and Davis 2015). Wetlands within rangelands generally have less functional impairment than in croplands and are critical to wetland bird survival (Tsai et al. 2012; Collins et al. 2014; Albanese and Davis 2015; McCauley et al. 2015; Tangen et al. 2022).

3.4 Spring Migration

Spring migration is another critical time for wetland birds and includes additional energetic demands, like molt and courtship (Anteau et al. 2011; Stafford et al. 2014). Survival is usually high (Moon and Haukos 2006; Osnas et al. 2021), and habitat availability remains important (Anteau and Afton 2011; Sedinger and Alisauskas 2014). For many species, early arrival to breeding areas correlates with increased reproductive success. Shallow flooded wetlands are often the first to thaw and provide important food resources in spring. Overall, the timing, stop-over frequency, and duration of spring migration is influenced by weather conditions, habitat availability (i.e., food abundance), and initial body condition (Miller et al. 2005; Haukos et al. 2006; Stafford et al. 2014). Wetland networks are therefore needed to support migration survival and breeding success (Devries et al. 2008; Zarzycki 2017; Osnas et al. 2021).

4 Current Species Population Status and Monitoring

More than 200 million individuals of 280 species of wetland birds occur in North America (PIF 2021). Over half of these species have seasonal distributions that overlap with rangelands, comprising > 160 million wetland birds (Tables 13.4, 13.5 and 13.6). Wetland bird populations have increased between 1970 and 2017, primarily from waterfow and geese, but other wetland birds have declined (Rosenberg et al. 2019).

Table 13.4 Common shorebird species in North America and their primary occurrence in rangelands, population size, trend, and conservation or management status in the United States

Table 13.5 Common waterbird species in North America and their primary occurrence in rangelands, population size, trend, and conservation or management status in the United States

4.1 Monitoring Programs

Large-scale programs have been developed to monitor population status. Several are agency-led, particularly for hunted species, while some rely on citizen science efforts. Since 1955, the U.S. Fish and Wildlife Service (USFWS) and Canadian Wildlife Service (CWS) have conducted the Waterfowl Breeding Population and Habitat Survey (WBPHS) to estimate breeding populations in Alaska, Canada, and north-central United States (USFWS 2022). The WBPHS is used for estimates of multiple waterfowl species populations and wetland abundance. The USFWS, in coordination with state wildlife agencies, conducts an annual mid-winter waterfowl survey within each flyway to index waterfowl populations (USFWS 2023). Large-scale monitoring for shorebirds has been proposed, with implementation of some periodic, regional surveys (Cavitt et al. 2014). Secretive marsh bird surveys have been implemented in multiple regions (Johnson et al. 2009).

Publicly-sourced data collection has become increasingly important. The Breeding Bird Survey (BBS) is the main source of avian population status in North America and provides representative sampling of wetlands (Sauer et al. 2003; Niemuth et al. 2007; Veech et al. 2017). The BBS may not suffice for all species and formal evaluations are needed concerning wetland birds (Hudson et al. 2017). For many wetland birds, BBS data could be more useful if wetland habitat availability were included (Niemuth and Solberg 2003; Niemuth et al. 2009). For other species, targeted monitoring may be necessary. eBird, a global online database launched in 2002 (Cornell Lab of Ornithology), compiles public records of avian species detections with location and date (Sullivan et al. 2014). Biologists have used eBird data to assess migration chronology, distribution, abundance, and population trends (Walker and Taylor 2017; Horns et al. 2018; Fink et al. 2020).

International banding programs provide information on movements and demographics of many wetland bird populations. The U.S. Geological Survey Bird Banding Laboratory distributes about one million aluminum leg bands to managers and researchers in the U.S. and Canada each year and manages an archive of over 77 million banding records and 5 million band encounters (U.S. Geological Survey, Bird Banding Laboratory 2020). Hunter participation in waterfowl band reporting has been one of the longest and most significant information sources for waterfowl research and conservation. Mark-recovery methods (Brownie et al. 1985; Williams et al. 2002) are used to identify harvest distribution and associated breeding areas, estimate harvest rates, and survival rates for species, age, and sex (Smith et al. 1989). The USFWS and CWS conduct annual hunter surveys for hunted wetland birds (Martin and Carney 1977; Cooch et al. 1978; Martin et al. 1979). Harvest estimates can provide an index to population trends when other data sources are limited for some species. Banding and harvest survey data can be combined to estimate population abundance in some cases (Lincoln 1930; Alisauskas et al. 2009, 2014).

4.2 Waterfowl

As a group, there are fewer waterfowl species (n = 46) than either shorebird (n = 51) or waterbirds (n = 62), but waterfowl populations are more abundant. Waterfowl have also had more monitoring due to their gamebird status and associated socio-economic values (Anderson et al. 2018). Indices of breeding ducks from the WBPHS have fluctuated from lows of 25 million in the early 1960s and 1990s to nearly 50 million in 2014–2015. Duck populations show a cyclical pattern over time influenced largely by conditions in the PPR (Fig. 13.2; Baldassarre and Bolen 2006; USFWS 2022).

Fig. 13.2

Total duck population change 1955–2022 from the Traditional Survey Area of the Waterfowl Breeding Population and Habitat Survey (USFWS 2022)

Duck species that rely primarily on rangeland wetlands tend to have small populations or be in decline. Cinnamon teal are widely distributed across western rangelands. Mottled ducks occur primarily along the Gulf Coast. Cinnamon teal, mottled duck, and Mexican duck are among the least studied species with lower abundance and are identified as Species of Conservation Concern (Table 13.3; Baldassarre 2014). Northern pintails have declined since the early 1970s and remain below population objectives (NAWMP 2018; USFWS 2022). Rangeland conversion to row-crop production, especially in the PPR, has contributed to pintail declines (Baldassarre 2014; Buderman et al. 2020). Lesser and greater scaup have had similar population declines and status as pintails (NAWMP 2018; USFWS 2022). Most lesser scaup breed in the Western Boreal Forest, but at least 25% breed in rangeland wetlands where livestock grazing is a prominent land-use (Baldassarre 2014).

Goose and swan populations have generally increased since the 1970s, with overabundance of some goose populations (USFWS BMC 2011; Baldassarre 2014; USFWS 2022). The dramatic increase in snow geese is largely due to 4 factors: (1) increased food availability due to crop-conversion and enhanced fertilizer-based yields, (2) establishment of staging and wintering areas on refuges, (3) declines in harvest rates, and (4) climate change (Jefferies et al. 2003; Baldassarre 2014). Several Canada goose populations breed extensively in rangelands (Baldassarre 2014). The Hi-Line population in north-central Montana increased tenfold following their 1960s reintroductions concomitant with reservoir and stock pond development (Nieman et al. 2000; Baldassarre 2014).

4.3 Shorebirds

Shorebirds have experienced significant declines (i.e., 37%) since the 1970s (Fig. 13.2; Rosenberg et al. 2019; Smith et al. 2023). Most shorebirds are considered species of high conservation concern with 5 listed under the Endangered Species Act (1973; Table 13.4; U.S. Shorebird Conservation Plan Partnership 2016). Over 80% of breeding shorebirds migrate to Mexico, Central, and South America (Iglecia and Winn 2021). At least 16 species have significant breeding range overlap with rangelands and ~ 50% exhibit declining population trends (Table 13.4). Causes of shorebird declines are poorly understood.

4.4 Waterbirds

Waterbirds include > 180 species across 7 taxonomic orders that use marine and inland aquatic habitats (PIF 2021). More than 60 waterbird species inhabit rangelands (Table 13.5). Status of some waterbirds, especially secretive species, is poorly understood (Sauer 1999; Johnson et al. 2009), but survey information suggests variation in trends. Rosenberg et al. (2019) estimated a 22% decrease across 77 species. Sandhill crane populations have increased in recent decades (Seamans 2022).

5 Habitat Associations

A broad overview of functional habitat relationships across groups of wetland birds is provided herein. Habitat use varies by species, season, and time of day and habitat associations are available for most species (e.g., eBird, Birds of the World). Breeding and foraging characteristics are highly varied among waterbirds, shorebirds, and waterfowl. Heterogeneous habitat with assorted wetland types, water depths, vegetation density, and food support a diversity of wetland birds (Ma et al. 2010).

Table 13.6 General waterbird habitat associations based on amount of emergent vegetation, open water, and nesting habitat

5.1 Waterfowl

Puddle ducks, or dabblers, are associated with shallow wetlands foraging near the water surface by “tipping-up” to reach food items (Table 13.3; Fig. 13.3). However, they can perform shallow dives to avoid predators or reach food. Dabblers use seasonal and perennial wetlands with emergent vegetation for foraging and escape cover, particularly important during the brooding period (Walker et al. 2013b; Fig. 13.3). Seasonal wetlands are in overall decline (Collins et al. 2014; McCauley et al. 2015; Donnelly et al. 2022). In the Intermountain West, rangeland seasonal wetlands have been converted to flood-irrigated fields but can still provide important habitat (Fleskes and Gregory 2010; Donnelly et al. 2019; Mackell et al. 2021). Semi-permanent wetlands are habitat for dabblers and may be especially important during periods of water scarcity (McCauley et al. 2015; Donnelly et al. 2022). Dabblers also use open water as roosting habitat, especially when foraging habitat is nearby. During the breeding period, grass-dominated upland habitats are vital for dabbler nesting habitat. For example, nearly 90% of waterfowl in the PPR nest in uplands (PPJV 2017).

Fig. 13.3

Modified from Tori et al. (2002), Helmers (1992), and Richmond et al. (2012)

Preferred foraging depths of select wetland birds.

Pochards, or diving ducks, are adapted to deeper aquatic systems where they forage in the water column or benthic substrate (Figs. 13.3 and 13.4; Table 13.3). Common benthic forage includes bivalves, worms, and insect larvae (Baldassarre and Bolen 2006). Divers often use wetlands with SAV for foraging (e.g., pondweeds [Potamogetonaceae]). Sea ducks generally have high salinity tolerance, forage deeper, and are uncommon in rangelands (Table 13.3), though bufflehead and common goldeneye use rangeland wetlands (Baldassarre and Bolen 2006). Mergansers also use rangeland aquatic habitats and forage on small fish, often in deeper water systems.

Fig. 13.4

Modified from Krapu and Reinecke (1992)

Principal foraging habitats of various waterfowl groups with respect to water depth, plant communities, and wetland hydroperiod.

Swans use wetland habitat similar to diving ducks (Fig. 13.4). Swans use their long necks to access SAV. Breeding trumpeter swans use freshwater marshes, ponds, lakes, and occasionally slowly moving streams. Basic breeding habitat features include sufficient open water to take flight (about 100 m), SAV, stable water levels, structure for nest sites, and low human disturbance (Baldassarre 2014; Mitchell and Eicholz 2020). Both tundra and trumpeter swans can forage in upland agricultural areas during the non-breeding season. Migrating tundra swans show strong selection for wetlands with sago pondweed (Stuckenia pectinata) while nonforaging swans selected large open water areas (Earnst 1994).

Canada geese commonly occur in rangelands (Baldassarre 2014) and are primarily grazers of grasses and sedges, though non-breeding geese can be dependent on crops. Canada geese use a greater diversity of nest sites than other waterfowl (Baldassarre 2014). Common brood-rearing habitat includes gradually sloping ponds or river shorelines, abundant graminoids, and mudflats (Mowbray et al. 2020).

5.2 Shorebirds

Shorebirds use a variety of wetland and upland habitats throughout the year. Most shorebirds select shallow wetlands, wet meadows, shorelines, and open mud flats for foraging and avoid tall and dense vegetation (Iglecia and Winn 2021). For example, marbled godwits and willets select short sparse upland vegetation and wetland complexes for nesting and foraging (Niemuth et al. 2012; Shaffer et al. 2019a, b; Specht et al. 2020). However, these species can use taller and denser vegetation when brooding (Shaffer et al. 2019a, b). Some shorebirds use uplands for breeding, but shift to wetlands later (Shaffer et al. 2019a, c; Niemuth et al. 2012). Shorebirds exhibit varied wetland salinity tolerances. Some breeding shorebirds solely use uplands (Shaffer et al. 2019d, e, f; Iglecia and Winn 2021). During migration, shorebirds select shallow, sparsely vegetated wetlands often with mudflats. For example, shorebirds in the fall correlate positively with grazing pressure, and negatively with denser vegetation (Albanese and Davis 2015). Aquatic and terrestrial invertebrates are common shorebird foods, although seeds, vegetation, algae, and small fish are consumed opportunistically. Dominant invertebrate prey items include chironomids, flies (Diptera), beetles (Coleoptera), true bugs (Hemiptera), amphipods (Amphipoda), snails (Gastropoda), and clams and mussels (Bivalvia). Water depth, in combination with leg and bill length, determines food availability and habitat types used by different shorebirds (Fig. 13.3).

5.3 Waterbirds

Waterbirds exhibit diversity in morphology, life history, and habitat use. Species range from large and conspicuous cranes to secretive marsh birds such as bitterns and rails (Table 13.5). Waterbirds use various wetland types with assorted amounts of emergent vegetation, open water, water depth, and woody vegetation (Fig. 13.3; Table 13.6; Beyersbergen et al. 2004). Species use different areas within a wetland. For example, white-faced ibis nest on emergent vegetation in colonies and use shallow flooded areas to forage (Coons 2021; Moulton et al. 2022). Similarly, sandhill cranes nest on mounds in shallow water and use adjacent uplands for foraging (Austin et al. 2007; Ivey and Dugger 2008). Many other waterbirds use flooded areas in rangelands where management often mimics natural hydroperiods (Ivey and Herziger 2006).

6 Rangeland Management

Livestock production and wetland bird populations are linked by their dependence on rangelands and surface water (Bue et al. 1964; Richmond et al. 2012; Brasher et al. 2019). Grazing, burning, haying, and water management in wetlands and uplands often increase resources for wetland birds (Kadlec and Smith 1992; Naugle et al. 2000; Baldassarre and Bolen 2006). Response to management practices vary among species, spatial scales, biological parameters, season, and locale. Managers should consider objectives, seasonal habitat needs, and potential tradeoffs. Generally, management that provides a mosaic of upland and wetland habitat is best (Naugle et al. 2000; Baldassarre and Bolen 2006; Krausman et al. 2009; Ma et al. 2010).

6.1 Grazing

Upland nesting ducks generally favor dense cover within 4 km (~ 2.5 miles) of wetlands (Reynolds et al. 2006). Nest survival correlates positively with vegetation height (Baldassarre and Bolen 2006; Bloom et al. 2013) and the amount of adjacent grassland (Greenwood et al. 1995; Reynolds et al. 2001; Stephens et al. 2005), reinforcing the need to conserve rangelands. Lack of disturbance can negatively impact grassland, and duck productivity (Naugle et al. 2000; Dixon et al. 2019; Grant et al. 2009). Recent literature has demonstrated the compatibility of livestock grazing with waterfowl habitat (Naugle et al. 2000; Ignatiuk and Duncan 2001; Warren et al. 2008; Bloom et al. 2013; Rischette et al. 2021). Livestock grazing is a land-use that can ultimately support wetland birds (PPJV 2017; Brasher et al. 2019; PHJV 2021). However, localized impacts of grazing can depend on timing, intensity, duration, bird species, and demographics (Briske et al. 2011; Lipsey and Naugle 2017).

Managing grazing for residual cover (> 28 cm; Bloom et al. 2013) will enhance waterfowl nest survival (Warren et al. 2008; Rischette et al. 2021), which is highest when cover provides a physical barrier to predators. Grazing timing and intensity has complex interactions with nest density and survival, along with local and landscape conditions such as precipitation, site quality, and predator dynamics (Herkert et al. 2003; Stephens et al. 2005; Warren et al. 2008; Bloom et al. 2013; Ringelman et al. 2018). Mismanagement leading to overgrazing is detrimental to wetland birds and rangeland health (Kadlec and Smith 1992; Krausman et al. 2009). To maximize productivity, disturbances (e.g., grazing) should occur after or late in the nesting period (Barker et al. 1990; Naugle et al. 2000). From an operational viewpoint, when areas must be grazed, moderate to low stocking rates are preferred for waterfowl nesting cover (Bloom et al. 2013; Rischette et al. 2021).

Multiple grazing systems can support wetland birds while meeting rangeland health and producer objectives. Generally, systems that emphasize residual and dense grass cover are beneficial for waterfowl nesting habitat (Chap. 4; Table 4.2; Holechek et al. 1982; Barker et al. 1990; Ignatiuk and Duncan 2001; Murphy et al. 2004; West and Messmer 2006; Krausman et al. 2009). Studies have indicated that grazing systems with deferment, rotation, and rest (e.g., deferred rotation, rest rotation, deferred rest rotation, and high-intensity low-frequency) can increase residual cover and support wetland bird productivity (Gjersin 1975; Mundinger 1976; Barker et al. 1990; Ignatiuk and Duncan 2001; Murphy et al. 2004; Carroll et al. 2007; Emery et al. 2005; Shaffer et al. 2019a, b, d, e). Resting or deferring grazing in wetlands during the non-breeding season can maintain plant-based foods for waterfowl. Conversely, for many shorebird species, abundance correlates positively with increased grazing pressure, particularly in the non-breeding season (Holechek et al. 1982; Powers and Glimp 1996; Albanese and Davis 2015). In areas with longer growing seasons (e.g., Central Valley of California), grazing July–October supported forage for wintering geese and cranes along with nesting cover (Carroll et al. 2007). However, fall and winter grazing within shorter growing seasons may reduce initial residual cover, albeit with less influence on later nests due to vegetation growth. Evaluating contributions of local-scale management over the short-term (2–3 years) is challenging because productivity can also be influenced by large-scale and carry-over effects (Ringelman et al. 2018; Bortolotti et al. 2022).

Maintaining wetland vegetation structure and availability (Murkin et al. 1997; Masto et al. 2022) is key to nesting, foraging, and brood-rearing habitat for most species (Harrison et al. 2017). In wetlands dominated by robust and monotypic perennials (e.g., cattail) or invasives (e.g., reed canary grass [Phalaris arundinacea]), grazing can improve habitat structural diversity, especially in conjunction with practices such as fire, herbicides, and water-level manipulation (Stutzenbaker and Weller 1989; Schultz et al. 1994; Anderson et al. 2019; Bansal et al. 2019; Hillhouse 2019). Maintaining emergent vegetation is important for escape cover and food (Walker et al. 2013b). While reducing vegetation structure along shorelines may be better for shorebirds, excessive grazing can reduce habitat quality for other species (Hoffman and Stanley 1978; Harrison et al. 2017; Iglecia and Winn 2021). For nests along shorelines (e.g., snowy plover), restricting livestock access, or delaying grazing, can increase productivity (Iglecia and Winn 2021). Many wetland plants have high nutrition value and forage production generally exceeds uplands sites (Johnson 2019). Graminoids in mesic areas usually provide high forage quality for livestock (Hubbard 1988; Kirby et al. 2002).

In regions where available water is limited, livestock disproportionately select wet areas increasing the risk of habitat degradation. Historically, improper grazing has led to deterioration of wetlands and negatively impacted wetland birds (Tessman 2004). However, there is a paucity of research concerning grazing impacts on wetland bird survival and productivity, especially in the Intermountain West (Gilbert et al. 1996; Powers and Glimp 1996; Ivey and Dugger 2008; McWethy and Austin 2009). Risk of nest failure due to predation or trampling is generally associated with increased stocking rates (Littlefield and Paullin 1990; Bleho et al. 2014; Harrison et al. 2017; Shaffer et al. 2019d, e). Increases in water scarcity will likely exacerbate grazing impacts on wetland birds.

During the non-breeding period, moist-soil vegetation and seasonally flooded areas should be the focus of resource managers (Fredrickson and Taylor 1982; Smith et al. 1989; Haukos and Smith 1993; Hillhouse 2019). Moist-soil communities dominated by annual plants such as smartweed, common ragweed (Ambrosia artemisiifolia), and barnyardgrass, as well as perennials such as sedges, spike-rushes, giant bur-reed (Sparganium eurycarpum), and dock (Rumex spp.) offer high quality forage (Chabreck et al. 1989; Haukos and Smith 1993; Anderson et al. 2019). Consequently, factors that decrease seed production reduce food availability and carrying capacity. Grazing late summer can reduce seed production, whereas grazing until mid-summer may allow plants and seed production to recover (Chabreck et al. 1989; Anderson et al. 2019; Hillhouse 2019).

At landscape scales, livestock grazing helps maintain rangeland and wetland habitat, but negative effects can occur at smaller scales, although most issues can be addressed through management. For example, rotation and cross fencing can be used to control when and where grazing occurs and help maintain economic and ecological viability (Fynn and Jackson 2022). However, fencing can facilitate mesopredator movements and cause collisions for wetland birds, especially for species that fly close to the water surface or take flight by running across the water surface (Cornwell and Hochbaum 1971; Allen and Ramirez 1990).

6.2 Haying/mowing

Delaying haying until late nesting season helps minimize adult mortality and nest failure. However, optimal hay quality in some areas may occur earlier creating a challenge for livestock operations (Epperson et al. 1999; Gruntorad et al. 2021). Flushing bars mounted to haying equipment may help prevent adult mortality, but nests are still destroyed. Haying patterns that move concentrically out from the middle of the field may provide more opportunity for young birds to escape (Ivey 2011). Haying reduces residual vegetation the following nesting season and generally results in lower nest densities and productivity (Renner et al. 1995; Naugle et al. 2000; Rischette et al. 2021). Early nesting species (e.g., mallard, northern pintail) are impacted more by haying than later nesting species (Luttschwager et al. 1994; Renner et al. 1995). Ideally, haying should be late enough to minimize disturbance to nesting birds but early enough for precipitation and regrowth late in the growing season (Rischette et al. 2021).

Many wetland resources depend on irrigation with haying and grazing (Lovvorn and Hart 2004; Copeland et al. 2010; Donnelly et al. 2021). Early haying (e.g., mid-June) may cause nest failure and reduced foraging as well as mortality of unfledged waterbirds (Littlefield 1999; Ivey and Herziger 2006). Concomitantly, irrigated hayfields provide productive breeding habitat for species that select shorter and sparse vegetation (Hartman and Oring 2009; Shaffer et al. 2019d). The short-stature vegetation from haying (or grazing) can provide foraging habitat the following spring and summer when these areas are flooded (Fleskes and Gregory 2010; Donnelly et al. 2019).

6.3 Fire

Historically, fire was a principal driver of ecosystem structure throughout the Great Plains (Chap. 6). Burns reset succession to more productive states providing improved nesting and foraging habitat. Prescribed burns can be used to provide desired plant communities for wetland birds (Smith et al. 1989; Kadlec and Smith 1992; Anderson et al. 2019). Fire in marshes and prairie wetlands can reduce dense vegetation, increase food resources, promote desirable plants, provide new growth, and increase plant nutrition (Smith and Kadlec 1985, 1992; Chabreck et al. 1989; Stutzenbaker and Weller 1989; Naugle et al. 2000; Brennan et al. 2005; Venne and Frederick 2013; Anderson et al. 2019). Fire effects vary by location, season, and species needs. Because seasonal habitat requirements vary widely across wetland bird species, providing a mosaic of burned and unburned areas at multiple scales is likely ideal (Gray et al. 2013). If well-managed, fire can support broad ecological functioning (Hovick et al. 2017).

6.4 Water Management

Livestock operations in semi-arid rangelands have long used surface water developments. Inadequate water can lead to poor livestock distribution and utilization issues (Bue et al. 1964; Holechek et al. 2011). Water developments (e.g., stock ponds) for livestock can provide habitat for wetland birds (Forman et al. 1996; Pederson et al. 1989; May et al. 2002; Baldassarre and Bolen 2006). Stock ponds are dammed watercourses, excavated areas, or a combination of both. Excavated stock ponds in seasonal wetlands provide additional water accumulation, causing altered hydroperiods and less-preferred vegetation (Gray et al. 2013; Smith 2003; Baldassarre and Bolen 2006). Constructing terraces can provide shallow water and emergent vegetation (Gray and Bolen 1987). Selection of stock ponds is influenced by multiple factors including size, water depth, emergent and submergent vegetation, proximity to other wetlands, and adjacent nesting cover (Austin and Buhl 2009).

Stock ponds that provide various water depths and diverse vegetation will be attractive to multiple species (Ma et al. 2010). Surface area, shoreline complexity, and vegetation composition are key characteristics for breeding season selection (Flake et al. 1977; Austin and Buhl 2009). Shorebirds may benefit from grazed pond margins and adjacent uplands (Laubhan and Gammonley 2000; May et al. 2002). Irregular shorelines, improved water quality, and SAV are attractive to breeding ducks (Hudson 1983; Svingen and Anderson 1998; Austin and Buhl 2009). Ponds, and natural wetlands, that approximate a 50:50 ratio of emergent vegetation and open water (i.e., hemi-marsh) provide ideal conditions for many wetland birds, particularly waterfowl (Murkin et al. 1997; Smith et al. 2004). Stock ponds are common in areas with limited water availability. Rumble and Flake (1983) recommend ponds for waterfowl broods that have: (1) larger surface area, (2) shallow water supporting submersed and emergent vegetation, (3) grazing management fostering emergent vegetation, (4) adjacent upland cover, and (5) undrained nearby wetlands. Exclusion fencing in shallows may promote emergent and moist-soil plants for food and cover.

Water developments for livestock are also used during non-breeding periods. Approximately half of the ducks during 1997–2014 mid-winter surveys in Texas were detected on stock ponds (Texas Parks and Wildlife Department unpublished data; DU 2021). Medium-sized ponds (0.81–16.2 ha) had higher occupancy (32–51%) compared to smaller ponds (< 0.81 ha; 11–26%; Texas Parks and Wildlife Department unpublished data; Mason et al. 2013). Evidence suggests stock ponds may help offset reduced habitat availability during drought (DU 2021). Along the Gulf Coast, stock ponds provided wintering habitat and freshwater sources for waterfowl, shaping distribution, abundance, and foraging patterns (Adair et al. 1996; Ballard et al. 2010). Forage availability in stock ponds is currently not well understood, but likely highly variable (Kraai 2003; Clark 2016). Stock ponds may provide important refugia during non-breeding periods (Kraai 2003; K. Kraai, Texas Parks and Wildlife Department, personal communication).

The relationship between irrigation and wetlands is complex (Bolen et al. 1989; Lovvorn and Hart 2004; Bishop and Vrtiska 2008; Moore 2016; Donnelly et al. 2020; King et al. 2021). Donnelly et al. (2022) indicate rapid wetland decline in western North America may be approaching an ecological tipping point for wetland bird populations. In the West, most surface water rights are agricultural and used in irrigation systems (Kendy 2006; Downard and Endter-Wada 2013; Donnelly et al. 2020; King et al. 2021). In many areas, availability of wetland habitat follows irrigation schedules and further research is needed to better understand benefits and relative tradeoffs for wetland birds throughout the annual cycle (Copeland et al. 2010; Donnelly et al. 2019, 2020, 2021; Lovvorn and Crozier 2022). Water scarcity is intensifying socio-political pressures, including “use it or lose it” policies, to improve efficiency (Grafton et al. 2018; Sketch et al. 2020). However, more efficient irrigation practices (e.g., pressurized sprinklers) could lead to significant declines in flood irrigation and negatively impact wetland bird habitat and other ecosystem services (Baker et al. 2014; Moulton et al. 2016; Donnelly et al. 2020, 2021). Rapid wetland declines in the West may be approaching an ecological tipping point for wetland bird populations (Donnelly et al. 2020, 2022).

7 Ecosystem Threats

Wetland loss has been extensive, with > 50% declines in the western U.S. and Great Plains (Dahl 1990, 2014) and comparable losses (40–70%) in western Canada (Doherty et al. 2013), and Mexico (25–98%; Landgrave and Mereno-Casasola 2012). In the Great Plains, the most significant driver has been wetland drainage (e.g., tiling) tied to row-crop expansion, and loss of wetland legal protections (Dahl 1990, 2011; Lark et al. 2020). In the West, agricultural development and large-scale overexploitation of beavers in the 1800s led to widespread wetland losses (Dahl 1990; Lemly et al. 2000; McKinstry et al. 2001; Chap. 7). Intact wetlands and rangelands tend to be associated with livestock production and land owned by public agencies. Wetland bird conservation is therefore intrinsically linked to livestock production (Higgins et al. 2002; Anderson et al. 2018; Brasher et al. 2019). Climate change is predicted to exacerbate threats (Niemuth et al. 2014; Haig et al. 2019; Lark et al. 2020; Donnelly et al. 2021; Moon et al. 2021). Conservation of remaining wetlands, especially in rangelands, will be important to sustain wetland birds (Bartuszevige et al. 2012; Tsai et al. 2012; PPJV 2017; PHJV 2021; Donnelly et al. 2021).

7.1 Habitat Conversion and Alteration

Recent changes in row-crop agriculture, such as the development of drought-resistant crop varieties and increased farming efficiencies, provide incentives to convert rangeland and other marginal areas into crop production (Higgins et al. 2002; Doherty et al. 2013; Lark et al. 2020). Recently, the most extensive conversion has occurred in the PPR and High Plains (RWBJV 2013; Fields and Barnes 2019; Lark et al. 2020). Lark et al. (2020) found recently converted grasslands and wetlands in the PPR had 37% less nesting accessibility for ducks than non-converted areas, demonstrating the significant risk of agricultural conversion to wetland bird productivity. Along the Gulf Coast, human development, crop conversion, non-native grass pastures, and wetland draining has led to < 1% of native prairie remaining and significant loss to wetland bird nesting habitat (Smeins et al. 1991; Wilson and Esslinger 2002; Vermillion et al. 2008). The loss of ranching operations and subdivision of land ownership has contributed to habitat declines. Future development is expected to increase 72% over the next 80 years putting remaining rangeland and wetlands at further risk (Moon et al. 2021). In the Intermountain West, human population growth and water scarcity have intensified competition for water resources driving substantial land-use changes that impact wetland bird habitat (Hansen et al. 2002; Baker et al. 2014; Donnelly et al. 2021; King et al. 2021). Water-use is increasingly transferred from agricultural to municipal holdings for growing urban water demands, increasing the challenge of maintaining regional wetland networks (Brewer et al. 2007; Dilling et al. 2019; Donnelly et al. 2021). The accumulation of increasing threats within the Intermountain West has potential negative population-level impacts (Haig et al. 1998, 2019; Donnelly et al. 2020, 2021; Mackell et al. 2021).

7.2 Energy Development

Energy development continues to increase across rangelands (Ott et al. 2021). Collisions, habitat loss and degradation, and displacement are common impacts from energy development that threaten wetland bird populations (Shaffer et al. 2019g). Oil field wastewater developments in semi-arid rangelands are commonly mistaken as habitat by wetland birds resulting in mortality (Flickinger 1981; Flickinger and Bunck 1987; Trail 2006; Ramirez 2010). Oil spills and flowback water from fracking occur regularly and can contaminate wetlands. Brine contamination has been frequently reported in wetlands in the Bakken Formation and can negatively affect local aquatic invertebrates (Preston and Ray 2017; Blewett et al. 2017). The demand for biofuel, particularly corn ethanol, has accelerated grassland and wetland conversion of > 400,000 ha per year (Wright and Wimberly 2013; Lark et al. 2015, 2020). This conversion leads to increases in land values, affecting livestock operation sustainability, and portends challenges for ranching economies and associated ecosystem services (Johnson and Stephens 2011).

Indirect losses from energy development include fragmentation and displacement, which significantly increases the footprint of habitat loss (Johnson and Stephens 2011; Loesch et al. 2013). Indirect effects vary by species, seasons, and spatial scale of habitat (Shaffer et al. 2019g; Pearse et al. 2021). Lower breeding (Loesch et al. 2013) and wintering abundance (Lange et al. 2018) of ducks have been documented near wind energy facilities as well as avoidance during migration by whooping cranes (Pearse et al. 2021). Fragmentation and displacement from wind development are of greater conservation concern compared to direct mortality (Shaffer et al. 2019g; Hise et al. 2020). Larger wetland birds, such as sandhill cranes, are at greater risk of collision (Brown and Drewien 1995; Navarrete and Griffis-Kyle 2014; Murphy et al. 2016; Pearse et al. 2016; Hays et al. 2021).

7.3 Invasive Species

Invasive flora and fauna affect wetland birds in rangelands. Invasive aquatic plants reduce overall biodiversity and habitat quality for waterbirds. Native and non-native plant species such as cattail, common reed, reed canary grass, and creeping foxtail (Alopecurus arundinaceus) form dense monotypic stands that outcompete more desirable vegetation (Baldassarre and Bolen 2006; Hillhouse 2019; Johnson 2019). Cattail species have proliferated in the absence of natural disturbances (e.g., grazing and fire) and row-crop agriculture provides conditions that promote cattail establishment and vigor (i.e., nutrient runoff, sediment accumulation; Bansal et al. 2019). Dense stands of cattail can dominate wetlands, eliminate open-water, replace emergents and SAV, and preclude wetland bird species (Bansal et al. 2019). Similarly, common reed (i.e., phragmites) is a growing problem in the Intermountain West (Duncan et al. 2019; Rohal et al. 2019). Reed canary grass is widely used as livestock forage but can quickly form dense unproductive monotypic stands (Paveglio and Kilbride 2000; Evans-Peters et al. 2012; Hillhouse 2019).

Invasive animals also negatively affect waterfowl either directly through predation (e.g., northern pike (Esox lucius), or indirectly through habitat degradation. Common carp (Cyprinus carpio) are pervasive and degrade habitat quality and waterfowl productivity by consuming SAV and increasing turbidity that reduces forage availability (Ivey et al. 1998; Bajer et al. 2009). However, carp control is challenging, and success is often short-lived (Pearson et al. 2019). PPR wetlands evolved under isolated and intermittent drying conditions with only temporary surface-hydrologic connections. Wetland drainage has resulted in deeper, more stabilized hydrology, with interconnected basins that permit fish to persist (McLean et al. 2022). Similarly, fish are not endemic to playas in the High Plains but excavated ponds for irrigation support introduced fish, causing similar issues as above (Bolen et al. 1989; Smith et al. 2012).

7.4 Climate Change

The availability and function of wetlands are balanced by precipitation and evapotranspiration, making them sensitive to changes in climate (McKenna et al. 2021a). Climate change will likely have variable effects on wetland function and productivity throughout North American rangelands. Indirect climate change impacts on land-use are also conservation concerns for wetland birds (McKenna et al. 2019). In response to climate change, water availability and land-use patterns will increasingly challenge agricultural-based economies and wetland bird populations.

The PPR has received considerable attention for evaluating potential climate change effects on wetland birds. Recommendations for waterfowl conservation strategies have shifted as climate change has been increasingly understood. Areas that currently support the largest densities of intact wetlands and breeding populations will likely be most critical to future continental waterfowl populations (Loesch et al. 2012; Niemuth et al. 2014; Sofaer et al. 2016; McKenna et al. 2021a). Many of these wetlands overlap rangeland areas with ranch and livestock-based economies (PPJV 2017). In the southern PPR, a shift from winter to summer and fall precipitation-driven hydrology has occurred in recent decades (McKenna et al. 2017). More precipitation may initially seem beneficial, but wetland productivity and function can decline with less periodic drying (Euliss et al. 2004; McCauley et al. 2015). Under wetter conditions, wetlands would deepen and have more stable water levels promoting fish persistence and cattail domination (Anteau et al. 2016). Shorebirds that require exposed shorelines and mudflats would be less likely to find habitat (Anteau et al. 2016). Alternatively, prolonged dry periods can result in loss of seasonal wetlands and shrinking wetlands alter plant and invertebrate communities. Upland management, such as grazing and burning, adjacent to wetlands can help increase runoff into wetlands and reduce ponding loss during the breeding season (McKenna et al. 2021b).

In the Southern Great Plains, spring and summer are expected to become hotter and drier with fewer, but more intense and unpredictable, precipitation events (Londe et al. 2022). Recent models indicate a high likelihood that wetland networks will exhibit reduced connectivity, with playas especially at risk (Uden et al. 2015; Albanese and Haukos 2017; McIntyre et al. 2018; Verheijen et al. 2020; Londe et al. 2022). Loss of stopover habitat and forage can reduce survival during the non-breeding period (Moon and Haukos 2006) and subsequent reproductive success (Sedinger and Alisauskas 2014). Reduced summer wetland inundation also means less available water for livestock. Opportunities to introduce rangeland management practices, such as fire and/or grazing in Conservation Reserve Program lands, (Cariveau et al. 2011; Smith et al. 2011) may become increasingly important to address climate impacts.

The West is experiencing rising temperatures, reduced snowpack, and earlier runoff resulting in water scarcity (Kapnick and Hall 2012; Mote et al. 2018; Snyder et al. 2019). Snowpack runoff drives availability and function for most western wetlands. In recent decades, water surface area in wetlands have declined by 47% or more while important aquatic systems like the Great Salt Lake have declined by 27% (Donnelly et al. 2020). Terminal basins and lower portions of watersheds in the Great Basin (Kadlec and Smith 1989; Donnelly et al. 2020) are strongly influenced by upstream water management decisions (Moore 2016; Null and Wurtsbaugh 2020; King et al. 2021; Donnelly et al. 2022). Climate change brings increasing temperatures and evapotranspiration rates intensifying water scarcity and ultimately impacting wetland bird habitat in the region (Downard and Endter-wada 2013; Moore 2016; Haig et al. 2019; Donnelly et al. 2020, 2021, 2022).

Climate change has potential to affect Gulf Coast habitat through sea-level rise and intensification of tropical storms. Coastal wetlands are vulnerable to increasing salinity, which decreases primary production, altering habitat quality (Battaglia et al. 2012; Moon et al. 2021). Freshwater and irregularly flooded marshes (Chabreck et al. 1989; Wilson and Esslinger 2002), are projected to dramatically decrease (Moon et al. 2021). Inland prairie and agricultural wetlands are also at risk (Battaglia et al. 2012; Moon et al. 2021) but may continue to provide vital habitat to species like mottled duck (Moon et al. 2021).

8 Conservation and Management Actions

8.1 Addressing Loss and Fragmentation of Wetlands and Rangelands

Minimizing the conversion of wetlands and rangelands to cultivated agricultural production is one of the greatest conservation challenges and priorities for wetland birds. Unfortunately, increases in commodity prices and the slow pace of conservation actions are unlikely to reverse wetland bird habitat losses in rangelands or offset anticipated future losses (Higgins et al. 2002; Doherty et al. 2013; Lark et al. 2020). However, maintaining livestock production on rangelands decreases the likelihood of cropland conversion and other land use changes (Higgins et al. 2002). Therefore, sustaining grazing as part of the region’s socio-economic fabric will be vital for conserving wetland bird habitats (Higgins et al. 2002). Where grasslands have been lost, the maintenance and conservation of wetland basins supports wetland bird persistence (Reynolds et al. 2006; Niemuth et al. 2009). Nevertheless, keeping rangelands “green side up” and wetlands intact are primary conservation goals to sustain wetland bird populations.

Flood irrigation, beaver restoration, and low-tech riparian and wet meadow restoration (e.g., beaver dam mimicry or analogs, Zeedyk structures) offer opportunities to enhance natural water storage (Blevins 2015; Silverman et al. 2018; Moore and McEvoy 2022). Enhanced soil water storage capacity from such practices can increase watershed resilience to climate drivers, enhance wetland wildlife habitat, and increase livestock forage production (Silverman et al. 2018). Financial incentives, access to technical assistance, and local partnerships help managers implement restoration as well as maintain or upgrade flood irrigation infrastructure (Sketch et al. 2020; Donnelly et al. 2021; Moore and McEvoy 2022). Watershed and state-based partnerships will help managers navigate water management, water rights, and restoration techniques within the social-ecological systems of western watersheds (Downard and Endter-Wada 2013; Moore and McEvoy 2022).

8.2 Partnerships and Programs

Conserving wetland birds requires effective public–private partnerships at local, regional, and international scales (Anderson et al. 2018; Brasher et al. 2019). For example, the NAWMP acknowledges sustaining waterfowl populations is impossible without conservation on private lands and no single entity can solely address habitat loss. Conservation partnerships for wetlands and grasslands have historically focused on voluntary incentive programs such as those available through the federal Farm Bill (Hohman et al. 2014) for sustaining and growing wetland bird populations (e.g., Gray and Teels 2006; Reynolds et al. 2006; Bishop and Vrtiska 2008; Drum et al. 2015). More recent partnerships have focused on adaptive conservation projects in working rangelands, including the creation and maintenance of water sources that concurrently improve livestock grazing management and wildlife habitat. Effective wetland bird conservation includes a broad suite of short-term and long-term stewardship programs and incentives for livestock operations (Higgins et al. 2002; Brasher et al. 2019).

Numerous agency programs are available to assist with range improvements, grazing infrastructure, and wetland restoration and protection (Brasher et al. 2019). Prominent federal examples include Natural Resource Conservation Service (e.g., EQIP, WRE—including reserved grazing rights option) and the U.S. Fish and Wildlife Service Partners for Fish and Wildlife Program which can provide technical expertise and funding for wetland conservation projects that align with supporting producer objectives. Community-based conservation efforts can foster productive dialogue among stakeholders for meaningful conservation actions (Neudecker et al. 2011; Bennett et al. 2021). Voluntary conservation easements, including NRCS’s Agricultural Conservation Easement program, limit sub-division, development, and conversion of rangelands to other land-uses (Brasher et al. 2019; Bennett et al. 2021). Prioritization is needed to help distribute limited resources (Niemuth et al. 2022). Facilitating land-use changes, like the transition of expiring Conservation Reserve Program lands into grazed rangeland will sustain or improve habitat conditions for wetland birds, expand grazing opportunities, and improve landscape resilience by supporting sustainable ranching economies that keep grasslands and wetlands on the landscape (Higgins et al. 2002; PPJV 2017; NRCS 2021).

The growing awareness of ecosystem services provided to society through wetlands and rangelands are likely to generate additional public–private partnership opportunities and funding sources for conservation. Ecosystem services from rangelands and wetlands include flood control, water quality, groundwater recharge and discharge, carbon storage, and ecological resilience (Mitsch and Gosselink 2015). Focus on improved wildlife resources has been a primary message for conservation groups to date; however, helping people understand the life-sustaining ecosystem services provided by rangeland and wetlands may increase stakeholder interest and funding available for conservation (Bartuszevige et al. 2016; Humburg et al. 2018; Brasher et al. 2019).