Date of Award
Open Access Thesis
Master of Science (MS)
David R. Brown
Charles L. Elliott
The alarm calls of some birds are functionally referential and may provide nestlings with information about the threat posed by potential predators. However, few investigators have examined the responses of nestlings in cavity nests to the anti-predator vocalizations of adults. Therefore, the objectives of my study of cavity-nesting Eastern Bluebirds (Sialia sialis) were to examine (1) the vocal responses of adult Eastern Bluebirds to different predators, and (2) the behavioral responses of nestlings to those adult vocalizations. My study was conducted from April - July 2013 at the Blue Grass Army Depot in Madison County, Kentucky. Pairs of Eastern Bluebirds nesting in nest boxes were exposed to four potential nest predators, including taxidermy mounts of a raccoon (Procyon lotor) and an eastern chipmunk (Tamias striatus), a study skin of an American Kestrel (Falco sparverius), and a rubber model of a black rat snake (Pantherophis obsoletus). My control was a study skin of a Mourning Dove (Zenaida macroura). To assess responses during 3-min trials, predators or the control were placed adjacent to or on nest boxes with 12-19-day-old nestlings. During trials, adult vocalizations were recorded and the behavior of nestlings was simultaneously recorded with a camcorder. I conducted 48 trials at 27 nest boxes. Adult bluebirds did not respond vocally during 10 trials (20.8%), but did call during all 12 trials with the raccoon. In addition, adult bluebirds uttered alarm calls and chatter calls that were significantly longer in duration at significantly higher rates in response to the raccoon. Adult bluebirds uttered significantly more chatter calls and alarm calls during trials when nestlings responded (23 of 39 trials [59%], excluding control trials) by crouching (21 trials), climbing the walls of the nest box (one trial), or fledging (one trial). Crouching may reduce the risk of predation by predators too large to enter the nest cavity, but potentially able to reach into a cavity. Remaining in a nest cavity is likely advantageous because premature fledging by young unable to fly or fly very well when a predator is nearby would increase the risk of mortality. My results indicate that adult Eastern Bluebirds do not produce predator-specific, functionally referential alarm vocalizations, but, by varying call characteristics and call rates, appear to provide nestlings with information about potential predators that generates appropriate anti-predator responses.
Copyright 2014 Erin E. Grabarczyk
Grabarczyk, Erin E., "Vocal responses of adult Eastern Bluebirds (Sialia sialis) to potential nest predators and the behavioral responses of nestlings" (2014). Online Theses and Dissertations. 263.