Sources of variation in baseline and stress-induced blood glucose levels in two free-living tropical passerine species

Abstract Blood glucose plays an essential role in the body’s energy metabolism. However, the sources of variation in baseline and stress-induced change in glucose concentrations remain poorly understood in tropical passerines. This study assesses intra-annual variation in baseline and stress-induced change in glucose concentrations in two common free-living Afrotropical passerines, the Village Weaver (Ploceus cucullatus) (Müller, 1776) and the Black-crowned Waxbill (Estrilda nonnula) (Hartlaub, 1883) captured around Dschang, western Cameroon, using intrinsic (sex, body mass, moult, and breeding status) and environmental (season, temperature, and rainfall) variables as predictors. We found that, in the Black-crowned Waxbills, baseline glucose was significantly elevated in the dry season, with the same trend observed in the Village Weaver. Stress-induced change in glucose concentrations was elevated in the Black-crowned Waxbills in the dry season but only when temperature was fitted as a covariate. Village Weaver females showed higher stress-induced change in glucose compared to males. Body mass, and moulting were not predictors of baseline or stress-induced change in glucose concentrations. This study reveals that some of the fluctuations in glucose levels may be mediated by seasonal changes in temperature (but not rainfall), sex, and breeding status.