Plural breeding among unrelated females and other insights on complex social structure in the cooperatively breeding Variegated Fairywren

Abstract

Cooperatively breeding species vary widely in degree of social complexity, and disentangling relationships among group members can reveal the costs and benefits of cooperation. Here, we explore the social system of a relatively unstudied cooperatively breeding bird, the Variegated Fairywren (Malurus lamberti), and explore how social complexity and group dynamics may affect cooperation and conflict. We used a combination of field-based population monitoring and detailed social association observations to determine group membership annually across four breeding seasons (2014 -2017), and used a ddRAD-seq genotyping method to determine genetic relationships within social groups. Social groups ranged in size from 2 -8 individuals and nearly half of all social groups had multiple adult individuals of both sexes. Approximately two-thirds of those groups exhibited plural breeding, in which multiple females within the same social group nested individually on the same territory. Genetic relationships were diverse across social groups, and many consisted of a combination of relatives and non-relatives of each sex. Notably, although related females often were present within a social group, co-breeding females in the same social group were never closely related to each other. Given extensive variation in relatedness among group members, cooperation in the Variegated Fairywren is likely maintained by a combination of direct and indirect fitness benefits..

A photographic guide for determining egg incubation stage in the Superb Fairy-wren (Malurus cyaneus)

“…This study was conducted on the western side of Lake Samsonvale (27°16ʹS, 152°51ʹE), in Southeast Queensland, Australia, between August and December 2023. Superb Fairy-wren breeding biology is monitored at this site alongside closely-related Red-backed (M. melanocephalus) and Variegated (M. lamberti) Fairy-wren populations (Baldassarre et al, 2014, Boersma et al, 2023, Welklin et al, 2021. The field site is characterized by eucalypt woodland with partial remnant dry tropical forest.…”

“…Determining when eggs are laid is often an important aim of field-based avian population monitoring projects (Double et al, 2005, Boersma et al, 2023. Ideally, a nest is found while it is being built, so that the exact lay date(s) can be determined during subsequent monitoring.…”

“…Amazona amazonica), current methods of candling eggs for determining incubation stage for species used in field research are less well established. (Brach et al, 1982;Delany et al, 1999;Hanson and Kossack 1957;Weller 1956) Here, we present a photographic guide for assessing embryo development using candling methods in the Superb Fairy-wren (Malurus cyaneus), a species that is the focus of several long-term population monitoring studies (Boersma et al, 2023;Cockburn et al, 2016;Colombelli-Négrel et al, 2022;Feeney et al, 2013;Mulder and Magrath, 1994;Peters et al, 2002) but, for which, no such resource has been published. Additionally, we outline a method that we developed to candle passerine eggs using readily available materials that can be easily modified for use in other species.…”