Date of Award
Open Access Thesis
Master of Science (MS)
David R. Brown
Charles L. Elliott
Little is known about how variation in nestling begging intensity influences the behavior of adult raptors and how responses of adult males and females to such variation might differ. My objective was to manipulate the begging intensity of nestling American Kestrels (Falco sparverius) and examine the responses of adult males and females. I studied 12 pairs of kestrels nesting in nest boxes from 1 March to 1 July 2014 at the Blue Grass Army Depot, Madison County, Kentucky. Nest boxes were modified with a separate compartment for a camcorder to record nestling behavior, and a second camcorder was placed outside of nests to monitor adult behavior. To manipulate nestling hunger levels, 12 to 26-day-old nestlings in six nests were deprived of food for 24 hours and those in the other six nests were fed until satiated. At each nest, I alternated control (no treatment) and treatment (fed or food-deprived) days (control, treatment, control, and treatment) over a four-day period to minimize the possible effect of nestling age on adult and nestling behavior. Each day, nestlings and adults were video-recorded for four hours. Recordings were subsequently reviewed and, to quantify begging behavior, I: (1) determined the proportion of nestlings in broods begging when adults arrived at and left nests, (2) categorized begging intensity of each nestling as 0 (no gaping), 1 (gaping), 2 (gaping with neck extended), or 3 (wings flapping vigorously) when adults arrived at and left nests, and (3) noted how long nestlings continued to utter begging calls after adults left nests. I also determined the provisioning rates of adult males and females. Analysis revealed that the proportion of nestlings begging when adults arrived at nests did not differ among treatments (food-deprived, fed, and control; P = 0.057), but did differ at adult departure (P = 0.0002), with a smaller proportion of nestlings in the fed-treatment nests begging after being fed. Nestling begging intensity differed among treatments both when adults arrived at (P = 0.0011) and left nests (P < 0.0001), with nestlings in food-deprived nests begging with greater intensity after food deprivation and those in fed-treatment nests begging with less intensity after being fed. In addition, food-deprived nestlings continued uttering begging calls longer (P = 0.007) after deprivation than during control periods. Adult male and female kestrels fed nestlings at similar rates (P = 0.10), and they fed nestlings (P = 0.0009) at higher rates after food deprivation than during control periods and at lower rates after fed treatments than during control periods. Adults provisioned food-deprived nestlings (mean = 4.2 visits/nestling/hour) at nearly four times the rate of satiated nestlings (mean = 1.1 visits/nestling/hour). My results suggest that the begging behavior of nestling American Kestrels varies with hunger level and is an honest signal of need, and that adult kestrels respond to changes in nestling hunger levels by adjusting provisioning rates. Although the responses of adult kestrels to variation in nestling begging behavior suggest that natural selection might favor ‘dishonest’ begging by nestlings, i.e., begging with greater intensity to obtain more food, the potential costs of ‘dishonest’ begging may outweigh any possible benefit, e.g., increased likelihood of attracting predators and loss of indirect fitness benefits if increased begging has negative impacts on the condition of siblings and parents.
Copyright 2015 Katheryn Ann Watson
Watson, Katheryn Ann, "Effect of variation in nestling hunger levels on the begging behavior of nestlings and the provisioning behavior of adult American Kestrels" (2015). Online Theses and Dissertations. 327.