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Most North American sparrows forage almost exclusively on herbaceous seeds during the winter months. Limited amounts o f surface seed force some birds to employ a bilateral scratching behavior to extract seeds buried beneath soil, snow, or litter. Artificial seed trays were used to test the ability o f six different sparrow species to extract seed buried at different depths in soil. The results suggest three functional groups based on relative scratching ability. Strong scratchers, which included Eastern Towhee and Song and White-throated sparrows, met or exceeded their energetic requirements when foraging on seed buried at all depths (down to a maximum depth of 1.50-2.25 cm). A weak scratching species, Savannah Sparrow, scratched with the same frequency as the strong scratchers, but experienced negative energy budgets when forced to forage on sub-surface seed. Nonscratchers, which included Field Sparrow and Northern Cardinal, failed to secure any buried seed. Level of scratching ability may impact foraging efficiency in habitats with low surface seed. As a result, interspecific differences in scratching ability may promote habitat selection. Strong scratchers may be adapted to foraging near woody vegetation where intense resource competition and abundant litter limit the availability o f surface seed. Weak scratchers, on the other hand, may be forced to feed away from areas with little available surface seed. Since woody vegetation serves as a primary source of cover in early successional habitats, a tradeoff between foraging efficiency and the risk of predation may permit the local coexistence of species that differ in relative scratching ability and adaptations to evading predators. VARIATION BETWEEN SPARROWS IN ABILITY TO EXTRACT BURIED SEEDS

Variation Between Sparrows In The Ability To Extract Buried Seed