Investigating stopover habitat usage by songbirds at Tommy Thompson Park, a man-made urban peninsula
Thanks to their high mobility and visibility, birds are a model system for both migratory research and conservation efforts, especially in light of recent declines in songbird populations. However, despite the steady increase in urbanization along migration corridors, artificially-created habitats have not been well studied compared to other types of migration stopover sites. Using bird banding data collected at Tommy Thompson Park, a man-made peninsula located in Toronto on the northern shore of Lake Ontario, we are asking how different groups of songbirds make use of the various habitats. Construction of the peninsula began in 1959 and current habitats represent a range in succession from grasslands to cottonwood forests; thickets and wetland habitats are also present. In total, 53,984 birds of 124 species were banded during standardized spring and fall banding operations from 2003-2014, of which, 75 species with n≥25 individuals sampled were used for multivariate analyses. Habitat measures for the 15 mist nets used to capture the birds in the study area include shrub density, canopy and ground cover, canopy height, direction and proximity to water, while the sizes, taxonomic divisions, and both feeding and breeding guilds of the focal bird species were considered in the analyses.
Results show that 51 out of 75 focal species were caught more often (p<0.05) in some nets relative to others. Notable patterns include: (i) omnivorous, ground-foraging thrushes were found mostly in closed-canopy stands; (ii) granivorous ground-foraging sparrows were typically caught in open-canopy shrubby habitat next to the shoreline; (iii) woodpeckers, blackbirds and insect-gleaning kinglets were mainly found in shrubby areas further back from shore; and (iv) various species of lower-canopy insectivorous warblers, vireos and flycatchers were found in all three habitat types. Including rare species (n<25), nets in medium to high-density grass and shrubland with open canopies caught the greatest diversity and numbers of birds. These results indicate that, in order to make a stopover site useful to as many generalist and habitat-specific songbirds as possible, various microhabitats are necessary with low-level shrubs and grasses as the predominant feature and both open- and closed-canopy stands of trees present. As human land use continues to expand, migratory birds will become increasingly reliant on patches of urban wilderness for survival, including artificially-created stopover sites like Tommy Thompson Park, and studies such as this one will provide recommendations for creating and managing these habitats effectively.