KeywordsDung Beetle Water Bird Fishing Technique Bait Fishing Considerable Individual Difference
The active placement or manipulation of edible or inedible items, to attract or distract potential prey, facilitating prey capture.
Bait fishing is a rare form of tool use that has been observed primarily among herons (family Ardeidae), as well as a small number of other water birds (Ruxton and Hansell 2011). It involves the placement of a buoyant object on the surface of a body of water, which serves to attract or distract fish, and potentially increases the chance of capturing prey when fishing. The objects used as bait are often food items – such as insects or bread – that are highly attractive to fish, but small inedible items, including sticks or feathers, can also be used. In clear instances of bait fishing, birds will bring items to the water that they found elsewhere (Lovell 1958), or they will keep the floating item within striking distance by actively repositioning the item before it drifts out of reach.
To date, although bait fishing has been observed in a number of different species, it remains an uncommon behavior. No individuals have been observed to rely solely on bait fishing to obtain food, and this behavior has only been observed in a proportion of individuals within a population. Analogous behaviors have been observed among a few other species of animal, where bait has been used to attract different types of prey (discussed in more detail below). These behaviors are most commonly described using the term “baiting” rather than bait fishing.
Bait Fishing by Water Birds
Bait fishing was first anecdotally observed and reported in the 1950s (Lovell 1958). Lovell, throwing bread to birds at a lake in Florida, observed a green-backed heron (Butorides striatus) fishing from a small wall. When Lovell threw bread toward the heron, the bird took the bread to the water’s edge, and then, rather than eating it, the heron placed the bread in the water. When the bread began to drift away the heron repositioned it closer to the wall. After a few moments Lovell observed a fish begin to nibble on the bread, and, suddenly, the heron successfully speared the fish. Lovell remained at the lake and observed the heron performing this behavior repeatedly over a number of days.
To date, bait fishing has been observed in the wild or in captivity among at least seven different heron species, as well as two species of gull and one species each of kite, sun bittern, and kingfisher (reviewed in Ruxton and Hansell (2011) and Shumaker et al. (2011)), and reports of this behavior in additional species continue to amass. Bait fishing has been studied most extensively among the green-backed herons – in which the behavior was first identified – which have been observed to fish with bait in multiple locations around the world, including southern America, Japan, and parts of western Africa (Higuchi 1988). Note that green-backed herons are sometimes classified into two species (the green heron, B. virescens and the striated heron, B. striatus) but are now most commonly considered to be a single species.
The items that are used as bait appear to vary across locations. At sites studied in Japan, green-backed herons have been observed to use almost any nearby items as bait, including bread, popcorn, flies, insects, sticks, leaves, feathers, and berries (Higuchi 1986), while in other areas the items observed to be selected as bait have been more restricted. On a few occasions, herons have been observed to break a large stick into a smaller piece and then use this as bait, which can be considered a form of tool manufacture (Higuchi 1986; Shumaker et al. 2011). Given the differences that might exist in attracting fish, some researchers draw a distinction between bait fishing using edible and inedible items, referring to the latter as “lures” (Ruxton and Hansell 2011).
This bait-fishing behavior can be viewed as an extension of a more conventional fishing technique – the stand-and-wait method – where a predator remains stationary until prey comes within reach then delivers a rapid strike to capture their prey. In this context, provisioning bait is expected to increase the bird’s success, by enticing fish to swim within the bird’s striking distance more often than would occur without bait. However, although there are some indications that bait fishing can be an efficient technique, the prediction that bait fishing is more effective than alternative fishing tactics, not involving bait, has yet to be explicitly tested. In one of the most systematic observational studies, Higuchi recorded the success rate of adult and juvenile green-backed herons engaging in bait fishing using a range of different baits and lures. Adult herons were highly successful when using flies as bait, catching a fish on 86% of observed attempts and on 56% of attempts when using other insects. In contrast they obtained a fish on only 29% of attempts using sticks and 25% when using berries, both items that were commonly placed onto the water by the birds. Juveniles were substantially less successful than adults, typically only placing inedible objects on to the water’s surface (Higuchi 1986). These results demonstrate that fishing with edible bait was more profitable than using inedible lures, but it remains unclear how bait fishing compares to other fishing tactics. A detailed observational study of three herons indicated that considerable individual differences could be found in both the propensity to engage in bait fishing and the chances of success, which may have been linked to features of the birds’ territories (Higuchi 1988). Thus, one possible explanation for the rarity of this behavior is that bait fishing may rarely be more effective than other fishing techniques (Ruxton and Hansell 2011).
Origins of Bait Fishing
Relatively little is known about the origins of bait-fishing behavior. It is plausible that passive bait fishing – where birds wait near bait or lures already present on the water’s surface – could have acted as a precursor either behaviorally or evolutionarily to active bait fishing (Gavin and Solomon 2009; Lovell 1958). Other researchers have suggested that “dunking” behaviors, where food is dipped into water before it is eaten, could have preceded the placement of bait, by enabling a bird to form an association between placing items in water and the presence of fish (Ruxton and Hansell 2011). Given that bait fishing is rare, but has been observed in a number of different locations, it has likely arisen a number of times independently. Thus, this behavior may have a variety of different origins. Although some researchers have speculated that bait fishing requires special cognitive abilities (reviewed in Ruxton and Hansell (2011)), much like other instances of tool use, there is currently no reason to believe that bait fishing depends on advanced cognition (Shumaker et al. 2011).
Baiting Behaviors in Other Species
In addition to the behavior of water birds, using bait to catch fish has also been observed among one group of brown capuchin monkeys, a species known for its wide range of tool-use behaviors (Mendes et al. 2000). Here, capuchin were observed to catch fish with their hands, and on several occasions an individual threw food items into the water, or held the food under the surface with one hand, potentially to attract fish. Analogous baiting behaviors have also been noted in a small number of other species (see Shumaker et al. (2011) for a comprehensive list). As one example, assassin bugs have been reported to use the carcasses of termites as bait to entice other termites out of their nests (McMahan 1982). Of particular note, burrowing owls have been observed to place mammalian dung close to their burrows, which appears to functions as bait for dung beetles, a major component of these birds’ diet (Levey et al. 2004). By experimentally manipulating the presence or absence of dung in front of a number of owls’ burrows, Levey and colleagues demonstrated that the owls consumed far greater quantities of dung beetles when the dung was present, indicating that the dung does attract dung beetles. Burrowing owls regularly replace dung when it is removed, demonstrating that they engage in active baiting.
Recently, it has been suggested that crocodiles and alligators also perform a form of baiting. Dinets and colleagues report anecdotal evidence that crocodilians – residing in areas with large populations of egrets and other wading birds – often lie in shallow water with sticks positioned across their snouts (Dinets et al. 2015). On one occasion a crocodile was observed to catch an egret as it approached one of the sticks, suggesting that this behavior potentially functioned to attract birds seeking scarce nest material. In a systematic study, crocodiles were observed with sticks on their snouts a number of times (n = 11 observations); however, the researchers did not observe birds attempting to take the sticks, nor did they observe successful predation of birds. Thus, whether this behavior is an example of baiting is not yet known.
In conclusion, bait fishing is a rare form of tool use, where buoyant items are actively placed by an animal on the surface of the water to attract or distract potential prey. This behavior has been most frequently observed among herons (Ardeidae), as well as in a small number other water birds. It can involve the placement of a range of different items to attract prey, with flies being one of the most successful types of bait. Analogous behaviors – often referred to as baiting – have been observed among other species, predominantly to catch invertebrate prey.
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