Characterizing complex mixed-species bird flocks using an objective method for determining species participation.
Farley, Elizabeth*,1, Sieving, Kathryn 1, Contreras, Thomas1, 1 University of Florida, Gainesville, FL, USA
ABSTRACT- We are working to understand mechanisms underlying the formation and dynamics of mixed-species foraging flocks (MSFs) that form around the Eastern Tufted Titmouse (Baeolophus bicolor) in north-central Florida during winter. To facilitate scale-extensive studies, we developed low-effort sampling and analysis methods to categorize species with respect to degree of flock participation (standard methods, developed for more stable Neotropical flocks, proved intractable). We paired 60-minute flock observations with 10-min point counts, conducted in place immediately after flocks left the area. During January--February 2004 and November 2004--March 2005, we observed 55 mixed-species flocks, recording 40 species associating with MSFs to some degree. The flocks averaged 12.4 spp. (range 3-20), 26.3 individuals (range 8-60), and 3.1 titmice (range 1-7) per flock. Twenty-six species were observed frequently enough (>10% of sampling occasions) to be included in analyses. Controlling for species' relative abundances, regression tree (RT) analysis was applied to determine groupings based on flocking propensity. The RT model divided species into 3 major groups: "Nuclear/Regular Associate" (high/moderate flocking propensity), "Occasional Associate" (moderate/low), and "Non-joiner/Accidental" (low/none). Our method classifies species in a way similar to those determined by more intensive methods, yet can be readily applied across different habitats used by titmice where abundance and species composition of associated species can vary widely. Our method may be reliably applied in other, especially complex, flocking systems, thereby facilitating learning about interspecies relationships.
Key words: interspecific groups, methodology, birds
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