Winter Foraging Habits of Communal Flocking Birds John Rudolph Winter Field Ecology, Spring 2010 Mountain Research Station, University of Colorado at Boulder

Species in Flock

Introduction How do birds that flock together in the winter forage in a group without competing with each other for food? How do birds that flock together in the winter forage in a group without competing with each other for food? It goes against common sense that birds would group up to forage in winter when there is less food It goes against common sense that birds would group up to forage in winter when there is less food

Observation Location My house – Fourmile Canyon My house – Fourmile Canyon Ponderosa Pine dominate woods Ponderosa Pine dominate woods Riparian – Fourmile Creek, lots of large cotton woods and willows Riparian – Fourmile Creek, lots of large cotton woods and willows Feeder on the 2 nd flood porch Feeder on the 2 nd flood porch

Observation Methods Early morning observation Early morning observation Record bird’s location of foraging by voice Record bird’s location of foraging by voice Feeder time vs. Tree foraging Feeder time vs. Tree foraging 2 minute intervals 2 minute intervals

WBN and BBC foraging locations 3 – Tree trunk 2 – Tree Branch 1 – Feeder

Observation Results WBN – even in locations with feeders it still primarily feed on the trees WBN – even in locations with feeders it still primarily feed on the trees The WBN rarely ventured off the trunk when foraging The WBN rarely ventured off the trunk when foraging

WBN Foraging Patterns Only foraged large branches near the trunk that had rough bark, similar to the trunk Only foraged large branches near the trunk that had rough bark, similar to the trunk Special adaptations to walk on trunk Special adaptations to walk on trunk No preference for foraging height in tree No preference for foraging height in tree

Compare to BC Chickadee Constantly going back and forth from feeder to twigs on the trees Constantly going back and forth from feeder to twigs on the trees Caches from the feeder in nooks all over tree, usually where branches split Caches from the feeder in nooks all over tree, usually where branches split When foraging on cottonwoods, it stays When foraging on cottonwoods, it stays on the twigs almost exclusively, on the twigs almost exclusively, feeding on buds feeding on buds

Forage Niche Separation WBN & BCC foraging location in unique to that species WBN & BCC foraging location in unique to that species Lets birds flock together in winter, but not directly compete for food Lets birds flock together in winter, but not directly compete for food I was unable to tell a difference in I was unable to tell a difference in foraging locations on the trees between male and female WBN

Works Cited On Sex-Specific Foraging Behavior in the White-Breasted Nuthatch Thomas C. Grubb, Jr. Journal of Field Ornithology, Vol. 53, No. 4 (Autumn, 1982), pp Cornell Lab of Ornithology breasted_Nuthatch/id breasted_Nuthatch/id breasted_Nuthatch/id