Pp. Marra et Rl. Holberton, CORTICOSTERONE LEVELS AS INDICATORS OF HABITAT QUALITY - EFFECTS OF HABITAT SEGREGATION IN A MIGRATORY BIRD DURING THE NON-BREEDING SEASON, Oecologia, 116(1-2), 1998, pp. 284-292
During the non-breeding season, many species of territorial migratory
birds exhibit a non-random pattern of habitat distribution, with males
and females occupying different habitats. In this study, we examined
possible physiological consequences arising from such habitat segregat
ion in one migrant passerine species, the American redstart (Serophaga
ruticilla), on its nonbreeding grounds in Jamaica, West Indies. For 2
years, we measured concentrations of corticosterone, at the rime of c
apture (baseline) and 30 min after capture (profile of acute corticost
erone secretion), in redstarts in two distinct habitats, one occupied
predominately by males and one mostly by females. All redstarts in bot
h habitat types exhibited similar concentrations of baseline corticost
erone levels in fall (October), whereas in spring (March-April), redst
arts in female-biased habitat exhibited significantly higher baseline
levels regardless of age or sex. In fall, all individuals in both habi
tats exhibited significant increases in corticosterone concentration w
ith capture and handling, but in spring only redstarts (both sexes) in
male-biased habitat continued to exhibit acute corticosterone secreti
on. Redstarts in female-biased habitat had elevated baseline corticost
erone levels and reduced acute corticosterone secretion. In spring, ba
seline corticosterone concentration was negatively correlated with bod
y mass, suggesting muscle catabolism associated with high corticostero
ne concentrations or possibly that birds are leaner as a result of inc
reased foraging effort. These results indicate that redstarts (primari
ly females) in female-biased habitats suffered a decline in physiologi
cal condition, which could in turn influence their departure schedules
, migration patterns and even their condition and arrival schedules on
the breeding grounds. Thus, segregation of populations into habitats
of different quality during the nonbreeding period may have ramificati
ons throughout the annual cycle of such migratory species. Furthermore
, these results show the usefulness of plasma corticosterone levels as
indicators of physiological condition and thus habitat quality for bi
rds during the non-breeding period.