Behavioral Diversity in Mixed-Species Flocks

Mixed-species groups are known to provide foraging and anti-predator benefits to group members. These benefits may be due to an increase in behavioral diversity unique to mixed-species groups. This dissertation examines boldness behavioral differences among individuals in mixed-species flocks of Carolina chickadees (Poecile carolinensis) and tufted titmice (Baeolophus bicolor). The studies in this dissertation applied the Behavioral Syndromes framework (personality-like components of correlated behaviors), principal component analysis, cluster analysis, and multiple-response permutation procedures to examine group differences in behavioral variability between species and flock composition conditions (mixed- vs single-species flocks). These identified behavioral types became predictors for individual behavior involving a novel foraging task, an approach that differs with more typical single-test predictive models common in the literature. Finally, to test for differences in social-context versus isolated-context behavioral testing, a Novel Environment Test was given to two different sets of individual tufted titmice, one set surrounded by a familiar flock and one set removed from theirs. Results indicated that mixed-species groups do show greater variability in their boldness principal component scores, with chickadees in mixed-species groups showing substantially more variation in their boldness behaviors than either titmice or single-species chickadee flocks. These same principal component scores out-performed all single-test predictors of novel foraging behaviors, finding that the two species differed slightly in the types of neophilia that correlated positively with novel foraging success. Between-group comparisons confirmed that the Novel Environment test depended on social/asocial context, possibly due to effects of sudden isolation and social inhibition. These findings confirm the expected condition of increased behavioral diversity in mixed-species flocks and effects of isolated testing, helping to explain the apparent diversity effect in novel foraging efficiency found in previous studies.