The El Niño – Southern Oscillation dramatically influences the probability of reproduction and reproductive rate of a tropical forest bird

Abstract

Although climate change has been implicated in population declines of tropical forest birds, there is a critical lack of data on the mechanisms underlying these declines. Attempts to link climatic factors to variation in adult survival, fecundity or nest success have been largely inconclusive. Recent community‐scale analyses have suggested that tropical birds may be less likely to breed under adverse conditions, but long‐term data on individual reproduction are needed to test this hypothesis. Here we leverage 12 years of data on a lowland forest bird, the greater ani Crotophaga major, to investigate how demographic parameters vary with phase of the El Niño – Southern Oscillation (ENSO), a major driver of climatic conditions in tropical wet forest. The likelihood of breeding and annual reproductive rate both decreased dramatically in El Niño‐like years, with only 37.5% of adults attempting breeding in 2015 (a strong El Niño year). For birds that did breed, however, clutch size and daily nest predation rate were unaffected by climate. Of the local climate variables investigated, dry season length and the frequency of high temperatures were most closely associated with reproductive failure. These results indicate that El Niño conditions alter the demography of greater anis by reducing the likelihood of reproduction, a response that may be more widespread than currently recognized. We suggest that reduced reproduction under adverse conditions represents an important and understudied aspect of the life histories of tropical forest birds.

Long-term monitoring reveals widespread and severe declines of understory birds in a protected Neotropical forest

“…Recent evidence suggests that adults of tropical forest bird species are able to survive El Niño events or seasonal drought (e.g., refs. 42 and 57 ) but may modulate or forego breeding entirely in favor of self-maintenance during periods of low rainfall and/or low food availability ( 43 , 58 , 59 ), thereby driving reduced population growth rates. Future studies that directly measure food resources in relation to climate and bird abundance (e.g., ref.…”

Full Issue

“…For example, the islands of Kabaena and Wawonii have distinctly different underlying geology (ultramafic) and associated plant communities (Galey et al 2017, Trethowan et al 2020, Ó Marcaigh et al 2021. The entire study area is also strongly influenced by El Niño-Southern Oscillation cycles, which exert influence on breeding probability and phenology (Duursma et al 2018, Smart et al 2021. Thus, breeding patterns on different islands, and in extreme El Niño/La Niña years, may produce distinctive patterns that our data are unable to reveal.…”

Ecological correlates of alternative reproductive tactics: conspecific brood parasitism rates vary with nest predation and seasonal effects influenced by climate change

“…Adverse conditions in tropical locations are often associated with unpredictable and extreme precipitation patterns (Stutchbury and Morton 2023). Decreased proportions of adults attempting breeding have been recorded under extreme drought conditions in the Neotropics leading to decreased population-level reproductive success (Smart et al 2021). El Niño -La Niña dynamics have recently been accelerating and contributing to inter-annual fluctuations in precipitation, but these oscillations affect different geographic regions with opposing effects of heavy rains and drought.…”