Possible relationship between vocal communication system and fat reserve in wintering birds: a test of the optimal body mass theory
Fat reserve is a key adaptation in wintering small birds for maximizing individual fitness in a variable environment. Optimal body mass models suggest that winter fat reserve maximizes winter survival by balancing costs, such as greater predation risk, and benefits, such as ability to withstand food scarcity, of fat deposition. Flocking integration may be important in determining the fat reserve of birds. I am testing the hypothesis that if bird species have a complex vocal repertoire, then they will have high communication efficiency (which reduces predation risk) and this allows a high fat reserve. I tested this hypothesis by recording vocalizations of the Dark-eyed Junco (DEJU) and American Tree Sparrow (ATSP) in Kansas. The junco is fatter in winter than the tree sparrow and is predicted to have a larger vocal repertoire within its winter flocks. A Marantz digital recorder with a Sennheiser directional microphone was used to record vocalizations at winter feeding stations. Raven software was used to describe vocalizations within each species. Consistent with the hypothesis, DEJU produced more than one call type in every observation period, while ATSP produced only one call type throughout the observations. Even though ATSP had a mean call rate of 1.62 calls / bird / minute whereas DEJU had a mean call rate of 0.12 calls / bird / minute a significant difference was not detected. ATSP frequently gave false alarm calls (alarm calls with no predators in the vicinity) at the winter feeding station providing deceptive information to flock mates and potentially impeding flock integration. These results support the hypothesis that communication ability plays a significant role in determining interspecific variation in fat levels of small wintering birds.
Thesis (M.S.)--Wichita State University, Fairmount College of Liberal Arts and Sciences, Dept. of Biological Sciences