Foraging preferences of songbirds at a feeding station
We investigated foraging preferences of songbirds at an artificial feeding station to examine the extent to which these ecologically similar granivores partition food resources via seed choice and spatial foraging preferences. A vertical feeding station was constructed with 4 movable platforms, each located at 0m, 2m, 4m, and 6m heights from the ground. Each platform had 4 treys attached, each filled with one of the following seed types: black oil sunflower seed, millet, cracked corn, or thistle. The station was located at the edge (< 5 m) of a deciduous woodland in a suburban landscape in Media, Delaware County, PA. We observed birds from 0700-0900 hrs, from late-May thru mid-June during the 2011, 2012, and 2014 breeding seasons. We determined seed selectivity by recording the number of times each bird species ate from a specific seed tray. Interactions between avian species and foraging preferences (e.g., foraging height and seed type) were examined using hierarchal log-linear analysis. Contingency tables were used to compare height and food preference of each the bird species.
Our analysis revealed a significant interaction between bird species and seed type (X2= 6899.210, p=0.0001) and bird species and foraging height preference (X2=1477.474, p=0.0001). Seed type preferences varied for each species. For example, Blue Jays exhibited a preference for cracked corn (81% of feedings), while other species exhibited varying degrees of preference for sunflower seed. For example, the American Goldfinch fed upon thistle on 91% of visits and while most visits (39%) were at 4m. The Black-Capped Chickadee foraged mostly upon sunflower seed (97% of visits) and the preferred height was 6m (58% of visits). 81% of Blue Jay visits were to cracked corn and with a preferred feeding height of 2m (51% of visits). The Northern Cardinal preferred to eat at the 2m height 57% of feedings and ate sunflower seed 69% of the time. The Tufted Titmouse ate sunflower seed 99% of visists and at 6m height 49% of visits. 93% of all visits by the White Breasted Nuthatch were to the sunflower seed and 47% to the 2m height. Our study documents that these ecologically similar, granivorous birds exhibited foraging preferences that may function to reduce competition with other species during the time of year when food is presumably readily available.