Theses and Dissertations

Date of Award


Document Type


Degree Name

Master of Science (MS)



First Advisor

Dr. Karl S. Berg

Second Advisor

Dr. Julie A. Mustard

Third Advisor

Dr. Richard J. Kline


Songbirds learn songs during a plastic phase in vocal development, similar to human vocal babbling. Research has focused on male song learning, a process influenced by gonadal steroids. Like humans, parrots are very plastic vocal learners and both sexes learn vocalizations throughout life. It is unclear how the endocrine system mediates environmental information with developing phenotypes in parrots. Corticosterone (CORT) is a sex-neutral hormone that can affect cognitive development, but its role in vocal development has not been experimentally tested in wild parrots. I quantified vocal babbling from nestling Green-rumped Parrotlets (Forpus passerinus) recorded in Venezuela. Nestlings received oral CORT-oil supplements, oil, or nothing starting 21 days post-hatch, and lasting one week. Nestlings produced 28 vocalization types. CORT-treated nestlings produced less frequency modulation than controls. A significant interaction effect indicated CORT affected acoustic structure post-treatment. Results provide experimental evidence that stress during development influences learning programs in both sexes.


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