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 bird’s 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.