Family living sets the stage for cooperative breeding and ecological resilience in birds

Abstract

Cooperative breeding is an extreme form of cooperation that evolved in a range of lineages, including arthropods, fish, birds, and mammals. Although cooperative breeding in birds is widespread and well-studied, the conditions that favored its evolution are still unclear. Based on phylogenetic comparative analyses on 3,005 bird species, we demonstrate here that family living acted as an essential stepping stone in the evolution of cooperative breeding in the vast majority of species. First, families formed by prolonging parent–offspring associations beyond nutritional independency, and second, retained offspring began helping at the nest. These findings suggest that assessment of the conditions that favor the evolution of cooperative breeding can be confounded if this process is not considered to include 2 steps. Specifically, phylogenetic linear mixed models show that the formation of families was associated with more productive and seasonal environments, where prolonged parent–offspring associations are likely to be less costly. However, our data show that the subsequent evolution of cooperative breeding was instead linked to environments with variable productivity, where helpers at the nest can buffer reproductive failure in harsh years. The proposed 2-step framework helps resolve current disagreements about the role of environmental forces in the evolution of cooperative breeding and better explains the geographic distribution of this trait. Many geographic hotspots of cooperative breeding have experienced a historical decline in productivity, suggesting that a higher proportion of family-living species could have been able to avoid extinction under harshening conditions through the evolution of cooperative breeding. These findings underscore the importance of considering the potentially different factors that drive different steps in the evolution of complex adaptations.

Generalists are the most urban‐tolerant of birds: a phylogenetically controlled analysis of ecological and life history traits using a novel continuous measure of bird responses to urbanization

“…Urbanization also appears to select against insectivorous species (Chace and Walsh , Evans et al ). The degree of sociality was also generally positively associated with urbanization, as found elsewhere (Coleman and Mellgren , Jokimäki and Suhonen , Kark et al ), likely a result of cooperative breeding being a successful life history strategy in variable environments (Griesser et al ). However, our study also highlighted differences with global norms.…”

Looking for unity in diversity: human cooperative childcare in comparative perspective

“…This final transition towards help by offspring may have been facilitated, as in birds, by an increase in the variability in food availability [29]. In sum, in birds, where 55% of species are pair living [3], family living appeared to be the critical precondition for the transition to cooperative breeding. In mammals by contrast, where 95% of species show female-only care [49], it was more likely male parental care and the accompanying increased female reproductive investment that was the critical precondition (figure 2a,b).…”

“…Cooperative breeding among birds probably arose in two steps [3]. First, in pair-living species, offspring began to stay with their parents beyond nutritional independence, leading to family living.…”

“…In mammals by contrast, where 95% of species show female-only care [49], it was more likely male parental care and the accompanying increased female reproductive investment that was the critical precondition (figure 2a,b). However, in both birds and mammals, high average relatedness in the social units was a precondition and thus kin selection responsible for the evolution of cooperative breeding in most cases [2,3].…”

“…Sometimes newly evolved, derived traits in one lineage are functionally similar to traits in other lineages, a phenomenon called evolutionary convergence. Examples include the evolution of flight, warning coloration, complex eyes [1] or cooperative breeding [2,3]. However, the underlying genetic basis of these convergently evolved traits will only rarely be identical [1].…”