The role of social environment on parental care: offspring benefit more from the presence of female than male helpers

Abstract

Summary1. Investment in offspring depends on the costs and benefits to the carer, which can vary with sex and social status. Investment also depends on the effort of others by allowing for compensation (load-lightening), with biparental care studies showing that this depends on the state and type of the other carer. By contrast, studies on cooperative breeders have solely focussed on the effects of group size rather than its composition (i.e. social environment). 2. Here we propose and provide the first test of the 'Social Environment' hypothesis, that is, how the characteristics (here the sex) of other helpers present in the group affect parental care and how this in turn affects offspring fitness in cooperatively breeding red-winged fairy-wrens (Malurus elegans). 3. Breeders provisioned nestlings at a higher rate than helpers, but there was no sex difference in provisioning rate. Compensation to increasing group size varied little with sex and status, but strongly depended on social environment. All group members reduced their provisioning rates in response to an increasing number of male (load-lightening), but not female helpers (additive care). 4. As a result, nestlings received more food and grew faster in the presence of female helpers. The increased nestling growth did convey a fitness advantage due to a higher post-fledging survival to adulthood. 5. Our study provides the first evidence that parental care can depend on social environment. This could be an important overlooked aspect to explain variation in parental care in cooperative breeders in general and in particular the enormous variation between the sexes, which we reveal in a literature overview.

Associations between changing climate and body condition over decades in two southern hemisphere passerine birds

“…Both species are sedentary, year-round residents, occupying territories that persist year-to-year [35,36]. Both are co-operative breeders, breeding during the austral spring and summer months, producing multiple clutches each season [35,37]. The species are long-lived: maximum age for red-winged fairy-wrens and white-browed scrubwrens in this study is 15 and 13 years respectively.…”

Multidimensional environmental influences on timing of breeding in a tree swallow population facing climate change

“…However, the similarity in coefficients for within‐ and between‐individual spring temperature components potentially suggests that the population trend observed can be explained by individual phenotypic plasticity (see Brouwer et al. and Gienapp and Brommer for similar interpretations when β W = β B ).…”

Indirect fitness benefits through extra‐pair mating are large for an inbred minority, but cannot explain widespread infidelity among red‐winged fairy‐wrens

“…Although female helpers benefit offspring growth more than male helpers (Brouwer et al. ), there was no indication that helpers of both sexes affected fitness differently (Fig. ) and thus we only modeled the total number of helpers to minimize the number of parameters in the model.…”

“…Second, if the benefits of extra‐pair paternity only become apparent under poor rearing conditions, we predict that EPO will outperform WPO when hatched in poor years (with lower than average reproductive success) or in the absence of helpers at the nest, because helped offspring are heavier and grow better, and larger offspring survive better in their first year of life (Brouwer et al. ). Third, we predict that the high philopatry of both sexes results in frequent inbreeding and inbreeding depression.…”