Songbirds

Photos by Laura Gooch and Tim Lenz.

Dietary competition in resident and migratory songbirds

Each winter billions of migratory birds travel to the tropics, dramatically increasing the number of birds in habitats formerly occupied by year-round residents. In the Caribbean, the annual peak in numbers of insectivorous birds coincides with the dry season, the time when their arthropod prey are least abundant. In collaboration with Luke Powell, Rob Fleischer, and Pete Marra at the Smithsonian Conservation Biology Institute, we are investigating if ecologically similar migrant and resident bird species are able to coexist via partitioning of food resources. We are using next-generation sequencing of the feces of resident birds (such as the yellow warbler, left) and migrant birds (such as the American redstart, above right) in Jamaica to obtain DNA sequences of diet items. We are then matching the sequences to a comprehensive database of DNA 'barcode' sequences for Jamaican arthropods, which we are building in collaboration with Delano Lewis at Northern Caribbean University. This is a critical step towards understanding the importance of interspecific competition as a mechanism influencing population processes in these birds. This is especially timely, because of the ongoing decline in numbers of many migrant species.

Urban Ecology

Urbanisation has transformed habitats across much of the world, leading to altered local environmental conditions, increased pollution, changes in community composition, and altered food availability. Some species are able to exploit these habitats (“winners”), while some are able to cope or adjust to a degree (“adapters”), and others are forced to either disperse away or suffer local population extinction (“avoiders”). Overall, a general pattern of lower species richness in urban areas has emerged. It is becoming increasingly important to understand what factors influence species’ success (or failure) in these ubiquitous environments in order to maintain biodiversity in a rapidly urbanising world.

The widely known garden bird, the blue tit (Cyanistes caeruleus), may initially appear to be a winner at successfully exploiting urban environments. Indeed, adult birds may benefit from warmer winter temperatures and supplemental food resources provided by humans. However, during the breeding season, cities may actually become “ecological traps” for blue tits because they have limited availability of fat and protein-rich caterpillars required in the specialist diets of rapidly growing chicks. Several studies have demonstrated that blue tits breeding in cities actually have lower reproductive success than birds breeding in forested sites, yet the causes of this pattern remain unclear.

We are working closely with Davide Dominoni from Glasgow University at long-term ecological research sites along an urbanisation gradient from the heart of urban Glasgow to an undisturbed oak forested research station. The goals of this study are to examine: 1) How the diets of nestling blue tits change along the urbanisation gradient, 2) How the diets and condition of parents varies along the gradient and throughout the year. Because of the previous difficulty in analysing diets in high resolution (e.g., diet items fed to chicks on video can only be crudely classified as caterpillar vs. non-caterpillar), hypotheses about the impacts of food availability on urban species’ reproductive success have largely been unexplored, and diet may provide a missing link in understanding species’ persistence and extirpation in cities. Thus, we are metabarcoding diet samples from adults during the breeding and non-breeding season as well as their chicks and measuring reproductive success and morphological traits.