Date of Award
5-2024
Document Type
Thesis
Degree Name
Master of Science (MS)
College/School
College of Science and Mathematics
Department/Program
Biology
Thesis Sponsor/Dissertation Chair/Project Chair
J. A. Smallwood
Committee Member
L. C. Hazard
Committee Member
M. L. Aardema
Abstract
Declining populations often undergo changes in reproduction and/or body size linked to reductions in resource abundance or quality. American Kestrels have been exhibiting long-term declines throughout their North American range. Several studies have examined these declines through the use of nest box programs, migration surveys, the USGS Breeding Bird survey, and the National Audubon Society's Christmas Bird Count. Using the nest box surveys, researchers are able to collect detailed morphometric and breeding data about breeding populations. Here we present data from a northwestern New Jersey nest box program, 1997 through 2023, reporting the trends in the reproductive output and the body sizes of adult and fledgling kestrels during the period of decline. We found that study year was significantly correlated with size variables in chicks and breeding variables in adults. Adult body size of both sexes was significantly correlated with clutch size, with large adults producing bigger clutches. In addition, the survival rate of chicks was significantly higher for large adult females. In chicks, there was significant evidence that size dimorphism within broods is increasing; females are getting larger and males are getting smaller. Degree of sexual dimorphism in adults, an indicator of the proportion of avian prey in raptor diets, showed no significant changes over the study period nor was it significantly associated with the breeding variables. The results of our study indicate that the decline of kestrels may be related to changes in breeding habits. For body size trends, there is emerging evidence that chicks are starting to display increased dimorphism that may aid their post-fledging survival. Future study is recommended to continue monitoring the population status and morphometric trends.
File Format
Recommended Citation
Walker, David Michael, "Breeding and Morphometric Trends in a New Jersey Population of American Kestrels (Falco Sparverius)" (2024). Theses, Dissertations and Culminating Projects. 1434.
https://digitalcommons.montclair.edu/etd/1434