Monitoring Avian Productivity and Survivorship (Maps): A Sharp, Rather than Blunt, Tool for Monitoring and Assessing Landbird Populations

Abstract

Information on avian population trends derived from survey data traditionally has been the major tool used to monitor large-scale, long-term changes in avian populations, and to assess both habitat quality and the responses of birds to both management practices and natural and human-caused environmental changes. Data on population trends alone, however, cannot provide the critical information needed to test competing hypotheses regarding the causes of observed population changes, or even to determine the stage(s) in the life cycle at which the changes are taking place. Moreover, population density may not correlate well with either productivity or survivorship, and thus, may inaccurately assess both habitat quality and the response of avian populations to management practices or environmental changes. Because populations of many landbird species (particularly neotropical migrants) are declining (Robbins et al. 1989), and because Earth’s biosphere and its landbird populations are facing a growing number of global environmental threats of ever increasing severity (Brown 1991), an additional tool for accurately assessing changes in avian productivity and survivorship is critically needed. The Monitoring Avian Productivity and Survivorship (MAPS) program has been designed to fill this need. It is a cooperative effort among North American bird banders that utilizes constant-effort mist netting and banding during the breeding season at a continent-wide network of stations. For target landbird species, the MAPS program provides annual, regional indices of post-fledging productivity from the number and proportion of young birds captured, and annual, regional estimates of adult survivorship, recruitment into the adult population and adult population size from capture-recapture data on adult birds. The MAPS program was established in 1989 and 1990 when 17 and 38 stations, respectively, were operated across the continent. Post-fledging productivity in 1990, as determined by the number of young birds captured, decreased significantly (P< 0.02) from 1989 by an average of 32.8% at the 10 stations operated in both years. Because this measure of productivity previously has been shown to be highest in years of relatively “average” weather conditions and to decrease markedly in years of extreme weather conditions (DeSante and Geupel 1987), and because 1990 was a year of extreme weather conditions across the continent (and the year of the highest average global temperature on record), it is suggested that the productivity data from these 10 MAPS stations may be representative of trends across the continent.