The Effects of Global Change on Avian Biodiversity

Abstract

Avian biodiversity is under threat from many concurrent and interacting forms of change. My research uses various long-term monitoring datasets to understand and anticipate these changes. First, I quantified differences in reporting rates across eBird and the North American Breeding Bird Survey (BBS) and assessed the sources of these biases to understand how each dataset can best be used to monitor bird populations. While more species are reported to eBird, there are generally lower counts of each species in eBird. Species associated with water habitats are severely underrepresented in the BBS, likely due to the roadside BBS routes, which undersample these habitats. eBird observers report popular and rare species at higher rates than BBS observers. Species that are typically identified by sound are reported at higher rates in the BBS. These differences are probably because of differences in observer behavior and expertise. Identifying and understanding the sources of these biases can help with integration of these two datasets in future analyses.Next, I examined how winter climate and food availability interact to influence local bird abundances. During winter, temperature influences the metabolic costs associated with thermoregulating and therefore food requirements, while snow cover and daylight influence foraging ability. Consequently, food has the potential to mediate the sensitivity of bird populations to winter climate. I found that among small species, abundance responses to temperature tend to be amplified by food, meaning these species are more food-limited in mild conditions. Among large species, abundance responses to temperature are constant across food. Food generally did not mediate responses to daylight and snow cover, which influence foraging ability. These results demonstrate that a full understanding of how bird populations respond to climate change requires accounting for how these responses are mediated by food.Finally, I implemented a novel modeling framework to identify relationships between species abundances that can inform management. First, I identified species at risk of nest parasitism from Brown-headed Cowbirds, an obligate brood parasite. Because cowbird parasitism can reduce the reproductive success of the host species, some rare and endangered species have been managed with cowbird removals. I found that there are fewer cowbirds than expected based on the environment on the breeding grounds of the rare Kirtland's Warbler, likely due to decades of cowbird removals. Conversely, the breeding grounds of Bell's Vireos contain more cowbirds than expected, putting them at high risk of nest parasitism. Second, I used relationships between abundances of Atlantic Cod and other fish and invertebrate species to improve predictions of Atlantic Cod, whose populations have declined dramatically. These improved predictions can enhance management and reduce bycatch of cod. In each of these cases, quantifying relationships between species abundances improves ecological understanding to help inform management.