Date of Graduation

5-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Biology (PhD)

Degree Level

Graduate

Department

Biological Sciences

Advisor/Mentor

Smith, Kimberly G.

Committee Member

James, Douglas A.

Second Committee Member

Huxel, Gary R.

Third Committee Member

Loiselle, Bette

Keywords

Biological sciences; Psychology; Amazon; Foraging; Glyphorynchus; Home range; Mixed species flocks; Woodcreeper

Abstract

The wedge-billed woodcreeper (Glyphorynchus spirurus) is a common understory suboscine passerine of lowland Neotropical rainforests. It frequently joins mixed-species understory flocks but also regularly forages alone, and thus is an excellent model species on which to conduct comparative behavioral observations to examine the hypothesized costs and benefits of flock-following. Individuals exhibit variable flocking propensities (proportion of time spent with flocks), and thus observing the correlations between flocking propensity and physical and environmental factors can provide further insight into the importance of flock-following to the ecology of this species. Despite its abundance at many sites and its wide geographic range, surprisingly few studies have focused on the ecology and behavior of this species; previous observations suggested that this species occupies large, overlapping home ranges, which has important implications for intraspecific interactions and flock-following behavior. This study had three primary objectives: 1) to compare the foraging behavior and movement patterns of the wedge-billed woodcreeper in and out of flocks to examine the importance of hypothesized costs and benefits of flock-following for this species; 2) to determine which physical and environmental factors have the greatest influence on individual flocking propensity; and 3) to quantify the extent of home range overlap among individuals and to examine the influence of this overlap on space use and flock-following behavior. Wedge-billed woodcreepers used more open microhabitats in flocks than alone, supporting an anti-predator hypothesis for the benefit of flocking behavior. A decrease in time spent per trunk in flocks than alone, and a decrease in time spent with a flock with increasing movement rate, suggests an energetic cost associated with following flocks. Average flocking propensity was 32% in 2011 and 20% in 2012, considerably lower than previously reported in the literature and predicted under the assumption that individuals always join a flock when one is present in the home range. Body mass was the strongest predictor of individual flocking propensity, with larger individuals spending more time in flocks, and the correlation between the differences in body mass and flocking propensities of overlapping neighbors suggests that larger individuals may exclude smaller individuals from flocks. The distribution of flock-following locations was not influenced by the space use of larger neighbors, although a rigorous examination of simultaneous space use, coupled with a genetic analysis to determine if any overlapping neighbors are genetically related, would be necessary to provide a robust test of this hypothesis. Home ranges overlapped extensively in this study, thus the wedge-billed woodcreeper does not appear to defend exclusive home ranges at this site, unlike most other understory insectivores including other woodcreepers. Finally, in order to provide additional information about the behavior and natural history of this species, this dissertation includes a chapter that describes a previously known display behavior and provides notes about incubation and fledgling care.

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