Noninvasive assessment of seasonal hormone profile in captive bald eagles (Haliaeetus leucocephalus)

Abstract

AbstractThe hypothesis was to test whether a ratio of estrogen:androgen in eagle feces would reflect gonadal activity, and whether our procedure for noninvasive hormone analysis of fecal steroids could be applied to assess seasonal reproductive function in four captive bald eagles (Haliaeetus leucocephalus). Total immunoreactive excretory estrogens (E) and testosterone (T) were analyzed and compared as an E/T ratio from ad libitum monthly stool collections during the 1980–81 breeding season of birds maintained in an artificial insemination (AI) project. Since active male gonads are known to secrete a preponderance of androgens into the peripheral circulation and that renal clearance filters steroid metabolites into the urine, it was reasonable to assume that a lowered excretory E/T profile would mimic major changes in male seasonal steroidogenesis; analogously, active female gonads would result in an increased excretion of urinary estrogens, in turn reflected by a seasonal elevation of E/T ratios. A serial profile of excretory E/T ratio data for two male bald eagles approximated unity values except for a midseason low (x < 0.4) in February, one month prior to semen collections, followed by a significant end‐of‐breeding season rise in E/T values (x > 2.5, P < 0.01). The average E/T profile from data of two female eagles were two‐ to sixfold higher than males except for a significant mid‐breeding season peak in E/T values during March (x > 13.5, P < 0.01). Despite the absence of nest building or egg production by either female, these preliminary observational data indicated seasonal patterns of gonadal activity in both female eagles that were synchronous with semen availability from adjacent males.