PARENT SESSION
Oral Session # 10: Predator-Prey Ecology I: Terrestrial I: Theory and Cues.
Presiding: A Liebold
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 202.

Winter flocking for foraging or predation benefits, or both?

Sieving, Kathryn ^*,1, Contreras, Thomas¹, ¹ Wildlife Ecology and Conservation, Gainesville, Florida, USA

ABSTRACT- The relative importance of foraging and predation-related benefits is variously weighted in discussions of principal selective forces generating and maintaining multi-species bird flocks. We hypothesize that life history characteristics related to reducing predation risk and increasing foraging efficiency are both important; specifically, that one of the factors by itself is probably not sufficient to generate flock participatory behavior. To test our hypothesis we compared the anti-predation and foraging traits of two groups of understory bird species in north-central Florida; those that participate as satellite species in organized winter flocks with Eastern Tufted Titmice (Baeolophus bicolor) vs. those species that vigorously participate in predator-mobbing aggregations, but do not follow titmice while foraging (35 species total). Our central prediction is that flocking and mobbing species should not be distinguishable on the basis of anti-predation related traits (assuming they share potential predators since flock satellites also mob), but that they would diverge in foraging-related traits (assuming that mobbing only species do not gain foraging efficiency by flocking). Using logistic regression, we tested for the ability of 2 predation-related variables (body mass and escape tactic (4 categories)) and 3 foraging-related variables: foraging location (3 categories), foraging tactic (4 categories, and diet breadth (5 categories) to predict group membership (either flock satellites or mobbing aggregations). Supporting our central prediction, foraging tactic was the principal predictor of group membership (model chi-square = 20.15, P < 0.001; -2LLR = 24.1), providing 92.3% correct identification of flocking species, and 75% for mobbing-only species. Most flock species are foliage gleaners, and most mobbing only species are ground gleaners. Body mass was secondarily important in predicting group membership with mobbing-only species being heavier (p<0.05) but all birds weigh significantly less than the reported mean weights for potential avian predators in the study region.

Key words: mobbing, foraging, flocking, predation