Date of Award

January 2016

Degree Type

Open Access Thesis

Degree Name

Master of Science (MS)


Biological Sciences

First Advisor

Gary Ritchison

Department Affiliation

Biological Sciences

Second Advisor

David R. Brown

Department Affiliation

Biological Sciences

Third Advisor

Charles L. Elliott

Department Affiliation

Biological Sciences


Fledglings of some aerial insectivores experience pre-fledgling mass recession, possibly to achieve an optimum wing loading by the time of fledging. However, studies of aerial insectivores to date have been limited to two species of swifts (Apodidae), and additional studies of species of aerial insectivores are needed to determine if factors contributing to pre-fledging mass recession vary among species. Thus, my objective was to examine factors contributing to pre-fledging mass recession by nestling Tree Swallows (Tachycineta bicolor). My study was conducted during the 2015 breeding season at the Blue Grass Army Depot in Madison County, Kentucky. Nestling Tree Swallows (n = 127) in 29 broods were divided into half-weighted (n = 32), full-weighted (n = 36), and control (n = 59) treatment groups. Lead weights weighing 2.5% (0.6 g) or 5% (1.2 g) of the nestling’s mass were glued to the back feathers of half-weighted and full-weighted nestlings, respectively, between 9 and 11 days post-hatching. Video recordings were used to monitor parental provisioning behavior and nestling begging behavior. I found no differences among treatment groups in mass at fledging, amount of mass lost, or wing loading at fledging. In addition, adult provisioning rates and the proportion of time spent begging by nestlings did not vary during the period from day 11 to day 19 post-hatching. These results suggest that mass loss by nestling Tree Swallows prior to fledging is not due to changes in either parental or nestling behavior, but, rather, is likely a physiological process resulting from the loss of water from maturing feathers and other tissues. In contrast, the results of studies of two species of swifts (Apodidae) suggest that changes in nestling behavior influenced the extent of pre-fledging mass recession such that weighted nestlings lost more mass than control nestlings, apparently to optimize wing loading at fledging. This difference between swifts and Tree Swallows in the apparent cause of pre-fledging mass recession may be due to differences in the duration of nestling periods (several days longer for swifts) and wing loading (higher in swifts than Tree Swallows). With greater wing loading, optimum mass as fledging may be more critical for swifts than for Tree Swallows.