Meeting Abstract
52.2 Saturday, Jan. 5 An Investigation of Male Age, Provisioning Rate, and Physiological Costs in Florida Scrub-Jays WILCOXEN, T.E.*; SCHOECH, S.J.; BRIDGE, E.S.; BOUGHTON, R.K.; University of Memphis; University of Memphis; University of Memphis; Archbold Biological Station twilcoxn@memphis.edu
Life-history theory predicts that as animals age they should increase the energy expended towards the care of offspring while investing less in themselves, for they face decreased probability of survival to the next breeding attempt. Therefore, the tradeoff between current and future reproduction should be skewed towards current effort in older individuals. If such tradeoffs occur, then we predict that, when compared with younger males, older male Florida Scrub-Jays (Aphelocoma coerulescens) will provision the brooding female and nestlings at greater rates, exhibit a decreased immune function, be in poorer body condition, and be more stressed, as characterized by higher corticosterone (CORT) levels. Provisioning rates were calculated as the amount of food delivered over time as determined by focal watches. We used an in vitro test of the ability of whole blood to kill a bacterial strain to assess immune function. Body condition was estimated using a standard process that regresses multiple linear size measures against mass. Provisioning rate was positively correlated with both male age and immune capability. There was a significant difference between years in the mean percentage of bacteria killed and in CORT concentrations, but there was no difference in the patterns. No relationships were found among provisioning, CORT, or body condition. We suggest that older birds are not compensating for increased provisioning rates at the cost of other physiological functions. Instead, the birds that survive to older ages are in no worse condition, do not show elevated stress levels and have greater immune function. This is supported by the differences between an average year for reproduction and survival and a poor year for reproduction and survival.
