Date of Award


Degree Type


Degree Name

Master of Science




Dr. Scott MacDougall-Shackleton


Many songbirds use information from the environment to coordinate seasonal reproduction. American goldfinches (Carduelis tristis) demonstrate seasonal reproduction but differ from other songbird species by delaying reproduction until late- summer. Using correlational evidence collected from nesting cards across North America, I determined that timing of breeding for goldfinches was significantly related to ambient temperature and thistle blooming phenology. In a captive experiment, my results demonstrate that temperature and blooming thistle phenology significantly affect gonad recrudescence and testosterone levels. In summer temperature conditions, goldfinches exposed to blooming thistle plants had significantly higher levels of testosterone compared with birds shown a non-blooming thistle plant or no plant. Goldfinches may use blooming thistles as a predictor of abundant food availability and favourable breeding conditions which then gets them into breeding condition.



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.