Testing the environmental buffering hypothesis of cooperative breeding in the Seychelles warbler

Abstract

Species are facing environmental challenges caused by rapidly changing environments. Globally, extreme weather events, like droughts or extreme rainfall, are increasing in frequency. Natural selection usually acts slowly, while adaptations through phenotypic plasticity are limited. Therefore, organisms may utilise other mechanisms to cope with such rapid change. Cooperative breeding is hypothesised to be one such mechanism, as helpers could increase survival probabilities of offspring, especially in harsh years. Rainfall is a cue for onset of breeding in many tropical species, to ensure young are born when food abundance is highest. Using 21 years of data, we investigate the effect of rainfall on social behaviour and life history in the insectivorous Seychelles warbler (Acrocephalus sechellensis), a facultative cooperative breeder. We found that low rainfall is associated with reduced reproductive output and possibly with decreased survival. However, there were no statistical differences in response between groups with helpers, groups with only non-helping subordinates, and breeding pairs without subordinates. With low rainfall, more sons (the sex less likely to help) were produced, and those subordinate males already present were less likely to help. Thus, in contrast to expectations, cooperative breeding does not seem to buffer against harsh environments in Seychelles warblers, indicating that group living may be costly and thus not a mechanism for coping with changing environments. Our study showed that the interaction between the environment and life histories, including social behaviour, is complex, but that this interaction is important to consider when studying the impact of changing environments on species survival.

Environmental quality mediates the ecological dominance of cooperatively breeding birds

“…Here, we provide a formal mathematical framework for understanding precisely how cooperation could lead to ecological dominance in some taxa but not in others. Our model results also suggest that species that cooperate in harsh and/or fluctuating environments (Firman et al, 2020; Jetz & Rubenstein, 2011; Kocher et al, 2014; La Richelière et al, 2022; Lukas & Clutton‐Brock, 2017; Martin et al, 2020; Rubenstein & Lovette, 2007; Sheehan et al, 2015) will be less vulnerable to climate change than both non‐social species and those that cooperate against intraspecific competitors in benign and/or stable environments (Borger et al, 2023; Choe & Crespi, 1997; Cornwallis et al, 2017; Costa, 2006; Gonzalez et al, 2013; Solomon & French, 1997). This framework linking the ecological causes and consequences of cooperation can thus be used to explore a range of topics relevant to the changing world in which we now find ourselves, including the fluctuation and resilience of species abundances of social and non‐social species over evolutionary and ecological timescales, as well as range size shifts in relation to changes in social behaviour under different climate change scenarios.…”

Helpers don’t help when it’s hot in a cooperatively breeding bird, the Southern Pied Babbler

“…Recent research on Southern Pied Babblers Turdoides bicolor (hereafter “pied babblers”) has shown that larger group sizes do not buffer against the negative impacts of high temperatures or low rainfall on reproductive success ( Bourne et al, 2020c , 2020b , 2020a ; Bourne, Ridley, McKechnie, et al, 2021b ; reviewed in Ridley et al, 2021 ). Similarly, recent empirical studies have not detected a buffering effect of larger group size in Superb Starlings Lamprotornis superbus ( Guindre-Parker and Rubenstein 2020 ), Sociable Weavers Philetairus socius ( D’Amelio et al 2022 ), Greater Ani Crotophaga major ( Riehl and Smart 2022 ), Seychelles Warblers Acrocephalus sechellensis ( Borger et al 2022 ), or Meerkats Suricatta suricatta ( van de Ven, Fuller, et al 2020 ). However, there is empirical evidence in support of a buffering effect of larger group size in some studies, for example, in a concurrent study on Meerkats ( Groenewoud and Clutton-Brock 2021 ) and recent research on White-browed Sparrow-weavers Plocepasser mahali ( Capilla-Lasheras et al 2021 ).…”

Ecogeography of group size suggests differences in drivers of sociality among cooperatively breeding fairywrens

“…For example, social benefits of group living may buffer the negative effects of harsh and unpredictable environments on individuals when helpers contribute to breeder reproduction, offspring care and increased survival of group members (social benefits hypothesis; [9][10][11][12]). Conversely, environmental factors also influence the availability of opportunities for independent breeding and, when such opportunities are limited, can promote the formation of extended family groups through delayed dispersal of young (ecological constraints hypothesis; [2,[13][14][15][16]).…”