Seasonal changes of the adrenocortical response to stress in birds of the Sonoran desert

Abstract

Many avian species of the North American Sonoran desert, e.g., the black-throated sparrow, Amphispiza bilineata, cactus wren, Campylorhynchus brunneicapillus, and curve-billed thrasher, Toxostoma curvirostre, can potentially breed from March/April to August. It is possible that, at least in summer, intense heat and aridity may have inhibitory effects on breeding by precipitating a stress response. Stress typically results in a rise in secretion of adrenocorticosteroid hormones that then inhibit reproduction by suppressing release of gonadal hormones. However, we found that plasma levels of corticosterone were not higher during summer, compared with winter, even in 1989 when summer temperatures were higher than normal. In June 1990, temperatures were also above normal and soared to the highest level recorded in Arizona (50 degrees C). Plasma levels of corticosterone during June were high in black-throated sparrows, but less so in two other species (Abert's towhee, Pipilo aberti, and Inca dove, Scardafella inca) found in more shady riparian and suburban habitat with constant access to water. The adrenocortical response to stress (as measured by the rate of corticosterone increase following capture) was reduced in the hottest summer months in black-throated sparrows, cactus wrens, and curve-billed thrashers, but less so in Abert's towhee an Inca dove. These data suggest that at least some birds breeding in the open desert with restricted access to water are able to suppress the classical adrenocortical response to stress. The response is then reactivated in winter after breeding has ceased. It is possible that this stress modulation may allow breeding to continue despite severe heat. Analysis of plasma from these species indicated that the apparent modulation of the adrenocortical response to stress was not an artifact of reduced affinity or capacity of corticosterone binding proteins.

The effects of neonatal handling on adrenocortical responsiveness, morphological development and corticosterone binding globulin in nestling American kestrels (Falco sparverius)

“…Indeed, Adams et al [1] felt that the reduced stress response they observed in grey-faced petrels was due to habituation. However, while we cannot rule out habituation as an explanation for our results, we believe that our findings (and possibly those of Adams et al [1] may reflect developmental differences between the handled and unhandled birds because the blood sampling technique used to induce the adrenocortical response [66] differs markedly from the daily handling procedures to which the birds were exposed. That is, during blood sampling the birds were immobilized, serially bled from a wing vein, and held in cloth bags in between sampling events, none of which the birds experienced during the daily handling protocol.…”

“…A few days prior to fledging, when the kestrels were 26 days old, we performed a standard capture and handling stress series [65]. From each next box we collected baseline blood samples from one randomly selected nestling within 3 min of opening the box.…”

“…Total plasma CORT levels were determined by direct radioimmunoassay (RIA) following Wingfield et al [66]. Samples were assayed in duplicate.…”

“…However, very little is known about whether handling itself affects avian phenotypic development (but see [53]). Love et al [36] examined handling in American kestrels in the sense that they explored the effect on corticosterone (CORT) secretion of three applications of a standard capture and handling protocol [65], a procedure that involves collecting blood samples over a prescribed period of time with the birds typically placed in cloth bags in between sampling periods. They found that repeated experience with this paradigm results in lower corticosterone (CORT) levels than in birds sampled for the first time, probably due to familiarity with the procedure.…”

Social environment affects testosterone level in captive male blue–black grassquits

“…Sufficient plasma for T assays was obtained from 40 males, totaling 388 blood samples during 12 months. The T concentration was measured by the method of radioimmunoassay, using an antibody for T (reference #RDI-TRK2T2) from Research Diagnostics Inc. (Flanders, USA) and following the procedure described by Wingfield et al (1992). The cross-reactivities provided by the supplier are 16% for 5-α-dehydrotestosterone, 1% for androstendiol, 0.4% for androstendione, b0.1% for androsterone, b0.1% dehydroepiandrosterone, b0.1% for progesterone, b0.01% for estradiol/estriol, and 0.01% for cortisol/ pregnenolone.…”