Dissertation Research Summary:
My research interests have focused on the early life of the Northern Mockingbird (Mimus polyglottos). During the last few years I have attempted to determine what factors influence early behaviors in the mockingbirds life cycle. Both endogenous and exogenous factors have and are being studied to determine what causes a young bird to first leave the nest and then at a later date leave the natal territory.
Physiologically I have determined that nestling mockingbirds emerge from the egg lacking the ability to respond to stress. The ability to respond to stress in birds typically is measured via the secretion of the steroid hormone corticosterone. Corticosterone is secreted and rises rapidly in the blood stream of birds following some type of external or internal perturbation. The increase in concentration of this hormone facilitates mobilization of energy reserves in order to help an animal through periods when it cannot gain access to normal food sources or carry out normal activities. It has also been shown that this hormone facilitates storage of energy reserves under certain conditions such as preparation for migration. I have shown that a peak in plasma concentrations of corticosterone occurs at the time of fledging in young mockingbirds. This increase may facilitate mobilization of energy reserves during this time of increased energetic demand. No such correlation was found at the time birds leave the natal territory although this could be due to the difficulty in capturing young birds immediately prior to dispersal.
In a captive study where young mockingbirds were hand raised to control for exogenous influences, I found no indication that the timing of natal dispersal or locomotor activity associated with dispersal have an endogenous component. Similarly, corticosterone was not found to increase significantly at the time captive birds were expected to disperse. Taken together these findings lead me to believe that dispersal behavior in young birds is not under primary endogenous control and may be very much under exogenous influence such as reduced feeding from parents or aggressive interactions with parents on the natal territory.
Currently I am conducting an experiment in which I intend to determine if the exogenous factor of food delivery rate to the nest influences the timing of fledging in nestling mockingbirds.
I hope that my research has provided insight into the early life of birds that may be used to aid researchers determining how territory quality influences early movement behaviors that ultimately result in the birdís success. I also hope that I have shown that the capture and handling of young birds does not have negative physical or physiological effects on the birds so that researchers interested in studying early life history of birds will not shy away in fear of harming study subjects.