Drought disrupts year-round breeding readiness in a tropical songbird

Abstract

Climate change is expected to increase the prevalence and severity of extreme weather events like drought. For many opportunistically breeding tropical bird species, precipitation serves as a primary cue for onset of breeding, and sustained drought can have major impacts on reproductive fitness. The physiological effects of drought are poorly understood, but understanding physiological responses can help resolve the mechanisms underlying effects of drought on population demography. We used physiological data collected on a year-round breeding New Guinea endemic passerine, the White-shouldered Fairywren (Malurus alboscapulatus), during years with persistent rainfall and during the 2015-2016 El Niño drought event to assess patterns of breeding readiness, body condition, and molt. Many males lost their cloacal protuberances, a sperm storage organ they typically maintain year-round, during the drought period. Body molt, which also occurs year-round in this species, was higher in males during the drought period. Using a sliding-window statistical model approach, we identified a critical precipitation window of 0-40 days prior to capture for cloacal protuberance volume and a window of 8-53 days for molt, with lower precipitation associated with smaller cloacal protuberances and greater molt. Plasma androgens were predictive of variation in male cloacal protuberance volume and molt, thus potentially mediating transitions between life-history stages in response to environmental conditions. Female molt, androgens, and male mass varied with photoperiod, with longer but decreasing day lengths characteristic of the austral summer associated with increasing molt and decreasing androgens. Collectively, our results indicate the potential for photoperiod to cue some life-history stages, whereas reduced rainfall impacts male but apparently not female reproductive physiology and readiness to breed. Improving our understanding of environmental regulation of life-history transitions in tropical taxa is essential for identifying which taxa are most at risk under a changing climate. La sécheresse perturbe la préparation à la nidification tout au long de l'année chez un passereau tropicalRÉSUMÉ. On prévoit que les changements climatiques augmenteront la prévalence et la gravité des phénomènes météorologiques extrêmes tels que la sécheresse. Pour de nombreuses espèces d'oiseaux tropicaux qui nichent de façon opportuniste, les précipitations sont le principal indice du début de la nidification, et une sécheresse prolongée peut avoir des répercussions importantes sur la capacité de reproduction. Les effets physiologiques de la sécheresse sont mal connus, mais la compréhension des réponses physiologiques peut aider à résoudre les mécanismes sous-jacents aux effets de la sécheresse sur la démographie des populations. Nous avons utilisé les données physiologiques recueillies chez un passereau endémique de Nouvelle-Guinée se reproduisant toute l'année, le Mérion à épaulettes (Malurus alboscapulatus), au cours d'années avec des précipitations ...

Does capacity to elevate androgens underlie variation in female ornamentation and territoriality in White-shouldered Fairywren (Malurus alboscapulatus)?

“…Both subspecies of White-shouldered Fairywren tested in this study breed opportunistically, with both sexes showing breeding readiness year-round except for in cases of extreme drought (Boersma et al, 2022b); Enbody et al 2019). Whereas most males responded to GnRH challenges by elevating androgens in relation to their pre-GnRH sample (N = 47 of 68 males, 69%), comparatively fewer females elevated androgens following GnRH challenge (N = 15 of 54 females, 28%).…”