Biological Sciences, School of
Date of this Version
I examined how pinyon jays (Gymnorhinus cyanocephalus) assess and determine the risk of pilferage to their caches. Jays were allowed to cache in an open room while alone or while being observed by a conspecific. In a counterbalanced design, jays cached in the opposite treatment once they had finished recovering their caches. I compared birds’ behaviors between treatments in order to determine whether jays consider the presence of an observer in measuring the local competitive environment. Once all jays had completed alone- and observed- treatments, I ran the experiment once more to determine if individuals were consistent in their cache protection strategies. Results from this experiment reveal that pinyon jays did not respond to audience effects. Birds showed distinct patterns of behavior, but individuals were consistent in their behavior across treatments and replications. Jays serving as observers were tested for their ability to recover caches they had watched being made. These birds were able to accurately recover observed caches, though not as reliably as cachers.
I then used base levels of cache protection activity as assessed from the first experiment to divide birds into two groups so each had similar mean levels of cache protection behaviors. To evaluate whether pinyon jays directly assess pilferage through cache-loss, I removed 50% of the seeds cached for birds receiving the cache-removal treatment, while birds receiving the non-removal treatment were allowed to recover all the seeds they cached. Birds that participated in the non-removal treatment later participated in a cache-removal treatment so I could compare the responses to cache-removal between the two groups. To assess whether experience pilfering might influence caching decisions, I compared responses between previous observers and previous cachers. Jays that had their caches removed ate fewer seeds and cached fewer seeds when compared to the non-removal group. Of the seeds they cached, more of those seeds were cached behind shielding landmarks. These behavioral patterns were not evident in the group that participated in both treatments. Birds with experience as pilferers were more exploratory, ate more food, and expressed higher levels of cache protection behaviors during the removal treatment.
Adviser: Alan C. Kamil
A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Biological Sciences, Under the Supervision of Professor Alan C. Kamil. Lincoln, Nebraska: July, 2011
Copyright 2011 Christine L. Keefe