The Comparative Feeding Rates of North American Sparrows and Finches

Data on the seed profitabilities (mass of seed ingested per unit time) of captive emberizine sparrows and cardueline finches were used to interpret the underlying factors promoting differences in their ecologies. Sparrows consume seeds that the approximately an order of magnitude smaller in size that those consumed by finches of similar body mass. Because sparrows consume such small seeds and because finches are much more efficient at handling large seeds, sparrows need to encounter seeds at rates that are one to two orders of magnitude greater than that required by finches. As a result, sparrows have to spend much more time foraging than do finches, and sparrows are not able to go for as long periods of time searching for new food patches as are finches. Consequently, sparrows are relatively sedentary and restricted to areas of dense seed concentrations, whereas finches are extremely vagile and move over very large geographic areas in search of new patches of food. Furthermore, resource partitioning is more pronounced among finches. Small and large finch species eat very different seed sizes, whereas the diets of small and large sparrows overlap greatly.