Birds on birth control: The effects of 17alpha-ethinylestradiol on zebra finch (Taeniopygia guttata) courtship behavior, parental care, and stress physiology

Abstract

Hormones are key regulators of behavioral expression and reproductive investment. Individual behavioral expression can also reflect environmental influences, such as contaminant exposure. Many environmental contaminants can specifically disrupt the endocrine system by binding to hormone receptors, thereby mimicking hormones or blocking hormone production. 17-Ethinylestradiol (EE2), found in oral contraceptives, is considered an endocrine disrupter and is often detected in sewage effluent. Both aquatic and terrestrial animals can be exposed to EE2 in the environment with potential effects on behavior and physiology. I observed the effects of EE2 on courtship, parental care, offspring growth, reproductive success and stress response in captive zebra finches (Taeniopygia guttata). I used three levels of EE2 exposure, 0 ng (control); 4 ng, which is a level found in streams near wastewater effluent sites; and 100 ng, which serves as a higher level not recorded in nature. Birds were exposed to their respective treatments every other day for three weeks before behavioral and stress tests. Treatment was continued through nest building and incubation. In Chapter II of my dissertation, I conducted mate choice trials on both males and females choosing between control and EE2 treated birds of the opposite sex. I found that on average focal bird preference was not influenced by EE2 treatment of choice birds. In Chapter III, I observed the effect of EE2 on male courtship behaviors over 48 hours, male parental care via incubation and whether offspring and reproductive effort were influenced by paternal treatment. EE2 decreased the amount of male pair bonding behaviors directed towards females during incubation and significantly decreased brood size in pairs with 100 ng EE2 treated males but male EE2 treatment did not significantly affect courtship behaviors, offspring growth or additional reproductive success. Finally, in chapter IV, I tested the effects of EE2 on baseline and stress-induced corticosterone (CORT) levels, a hormone released in response to stress, in males and females and the indirect effects of EE2 on offspring of treated males. I induced the stress response by fasting the birds for 4 hours and I collected pre-and post-fasting blood samples to analyze baseline and stress-induced CORT. I found that baseline CORT responses were increased in 4 ng EE2 treated females in comparison to control females and 100 ng EE2 treated females. Males and offspring were not influenced by EE2 treatment. My dissertation research shows that EE2 can affect some aspects of behavior, reproductive outputs and CORT levels in zebra finches, thereby, providing novel information on the potential for EE2 to influence avian behavior and physiology.