SCHOECH, S. J.*; BOWMAN, R.; REYNOLDS, S. J.; U. of Memphis, TN; Archbold Biol. Stn., Venus, FL; U. of Birmingham, Edgbaston, UK: Interactions Between Nutrition, Corticosterone, and Reproduction in Florida Scrub-Jays
In variable environments animals often exhibit interyear variation in the timing of breeding. Study of two populations of Florida Scrub-Jays (Aphelocoma coerulescens) in the suburbs and �wildlands� found that suburban jays breed earlier than wildland jays. We hypothesize that this is due to human-provided food in the suburbs. Prior study suggests that wildland jays are protein-limited. This was assessed from 2000-2002 by providing supplements to wildland jays that were high in fat and protein (HFHP) or high in fat (HFLP): unsupplemented jays were controls (CNT). Both treatments advanced laying, though the low variance about the mean in the HFHP suggested that fat and protein acted in synergy. To assess the mechanism whereby laying was advanced, we measured testosterone (T), estradiol (E2), and corticosterone (CORT). HFHP males had higher T than HFLP and CNT males. Treatment did not affect E2 of females. There was an overall significant treatment effect on CORT levels with HFHP jays tending to have lower CORT. In 2003 we stopped using the HFLP supplement in wildlands and increased the number of territories supplemented with HFHP diet. Also, because pilot data suggested that suburban jays had very low basal CORT levels, we increased sampling of CORT in the suburbs in that year. Suburban jays had CORT levels that were more than two-fold lower than CNT wildland jays and HFHP wildland jays had intermediate levels. We postulate that the observed differences in the timing of breeding, both between suburban and wildland populations and between experimental groups in the wildlands, result from differential availability of food and further, that nutrient availability, levels of CORT, and initiation of reproduction are inextricably linked. These findings are intriguing and further manipulative studies are clearly needed and planned
