Date of Award

January 2018

Degree Type

Open Access Thesis

Document Type

Master Thesis

Degree Name

Master of Science (MS)


Biological Sciences

First Advisor

Luke E. Dodd

Department Affiliation

Biological Sciences


Among birds, the rapid growth rates of altricial young help reduce mortality by reducing the amount of time spent in the nest. However, in species where a high degree of maneuverability and speed is required (i.e. aerial insectivores), it is important that nestlings not gain excess weight. Nestlings in some species must attain an efficient wing loading just prior to fledging to facilitate mobility for hunting and evading predators. My objective was to examine the mass of nestling American Kestrels (Falco sparverius) during the mid- to late nestling period and specifically to determine the possible effects of attaching small lead weights (3gm and 6gm) to some nestlings. If wing loading at fledging is important for nestling kestrels, then the mass of nestlings with and without weights attached might differ at fledging whereas wing-loading values should be similar. My study was conducted during the 2016 breeding season at the Blue Grass Army Depot in Madison County, Kentucky. Nestling kestrels (n = 40) in 12 broods were divided into three treatment groups: control (n = 12), half-weighted (n = 14), and full-weighted (n = 14). At day 15 post-hatching, half-weighted nestlings received 3-g lead weights and weighted nestlings received 6-g weights, representing 2.5% and 5% of mean adult body mass. I used video recordings to monitor parental provisioning behavior and nestling begging behavior. After subtracting the mass of the lead weights, there were no differences among the treatment groups in mass or wing loading prior to fledging. Over the course of the nestling period, there was no change in the amount of prey biomass delivered per nestling per hour. However, there was a difference in the begging intensity, percent time begging, and activity levels by the nestlings in the days prior to fledging. These results suggest that the asymptotic mass of nestling kestrels is not due to parental behavior. Instead, a combination of physiological processes and nestling behavior may be influencing the asymptotic mass. The lack of difference in mass and wing loading among treatment groups may be due to the greater flexibility in wing loading required by predatory birds. These results also suggest that achieving optimum wing loading prior to fledging is less critical for American Kestrels than for smaller insectivorous birds.