Date of Award
January 2015
Degree Type
Open Access Thesis
Document Type
Master Thesis
Degree Name
Master of Science (MS)
Department
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
Abstract
Anti-predator defense is an important adaptation in group-living organisms. Some species of flocking birds use referential calls to communicate predator presence and the level of threat posed by predators. Previous studies have revealed that two species in the corvid family, American Crows (Corvus brachyrhynchos) and Siberian Jays (Perisoreus infaustus), use referential calls to convey information about predator presence and level of threat. Because of their intelligence and flocking behavior, Blue Jays, like American Crows and Siberian Jays, may use referential calls to communicate raptor presence and threat. During the non-breeding seasons of 2014 and 2015, I recorded and subsequently analyzed the vocal responses of Blue Jays to study skins (N = 7) that varied in size and the level of threat they pose. Experiments were conducted at seven different locations in Madison County, Kentucky. The mean number of jays present was 2.6 (range = 1 – 6), and jays uttered five different vocalizations, with ditonal and monotonal jeers given most frequently. The rate at which jays uttered ditonal jeers differed significantly among trials (P < 0.001), with the highest rates during trials with an Eastern Screech-Owl (Megascops asio) and a Sharp-shinned Hawk (Accipiter striatus). I found no differences among trials in the characteristics (duration, low frequency, high frequency, and peak frequency) of either ditonal jeers or monotonal jeers. Assuming that calling rates vary relative to the degree of threat posed by aerial predators, my results suggest that Eastern Screech-Owls and Sharp-shinned Hawks represent the greatest potential threats to Blue Jays in my study area, and other raptors used in my experiments, including American Kestrels (Falco sparverius), Cooper’s Hawks (Accipiter cooperii), Red-tailed Hawks (Buteo jamaicensis), and Great Horned Owls (Bubo virginianus), pose lesser threats. Although Blue Jays in my study did respond differently to different predators, their vocal responses were not functionally referential, i.e., the same calls with the same characteristics were used when responding to different predators, only the calling rates differed among trials. Thus, rather than providing conspecifics with specific information about predation risk, Blue Jay calls, especially ditonal jeers, appear to be directed at predators and primarily serve to harass and provoke them into moving elsewhere.
Copyright
Copyright 2015 Julie Dahl
Recommended Citation
Dahl, Julie, "Vocal responses of Blue Jays (Cyanocitta cristata) to raptors that differ in predatory threat" (2015). Online Theses and Dissertations. 253.
https://encompass.eku.edu/etd/253
