The effects of an "El Nino" southern oscillation event on reproduction in male and female blue-footed boobies, Sula nebouxii

This study attempted to determine endocrine correlates of reproductive succ ess in relation to major deleterious environmental conditions. In 1992, an El Nino southern oscillation event resulted in complete reproductive failur e in a colony of blue-footed boobies, Sula nebouxi, on Isla Isabel in the P acific Ocean off San Bias, Nayarit, Mexico (21.5 degrees N, 105.5 degrees W ). In 1993, the Fl Nino event had waned and reproductive success was high. The mean sea surface temperature in 1992 was 26.69 degrees, the warmest yea r for 11 years of data (mean, 25.63 degrees). In. 1993 mean sea surface tem perature was 25.75 degrees. Plasma levels of testosterone were highest duri ng the egg-laying period in 1993 and declined markedly during incubation. T here were no differences between males and females. Comparisons of testoste rone levels between 1992 and 1993 (egg-laying time point removed for 1993) showed no significant differences. Thus reproductive failure during an Fl N ino year was not related to testosterone levels. Baseline plasma levels of corticosterone did not change over the nesting cycle in either sex. There w as a trend for plasma levels of corticosterone to be higher in males and fe males during the earlier stages of breeding in 1992 compared with 1993, and if all levels were combined within years then females showed significantly higher plasma levels of corticosterone in the Fl Nino year. Plasma levels of corticosterone showed marked increases following capture and handling in both sexes and at every stage of the breeding cycle in each year. There wa s no variation in the adrenocortical responses to stress with year or stage of nesting in males. However, in females, maximum corticosterone levels we re greatest during the parental phase of 1992, the El Nino year, when all n ests ultimately failed. Comparisons of the dynamics of corticosterone chang es during the capture stress protocol revealed no correlations with body ma ss in 1992 or 1993. These data suggest that although massive reproductive f ailure in the Fl Nino year was not related to testosterone levels, baseline circulating concentrations of corticosterone may have a role in inhibiting onset of breeding. In contrast, after the nesting cycle has been initiated , increased adrenocortical sensitivity to acute stress may be involved in n est abandonment. (C) 1999 Academic Press.