Delayed dispersal and the costs and benefits of different routes to independent breeding in a cooperatively breeding bird

Abstract

Why sexually mature individuals stay in groups as nonreproductive subordinates is central to the evolution of sociality and cooperative breeding. To understand such delayed dispersal, its costs and benefits need to be compared with those of permanently leaving to float through the population. However, comprehensive comparisons, especially regarding differences in future breeding opportunities, are rare. Moreover, extraterritorial prospecting by philopatric individuals has generally been ignored, even though the factors underlying this route to independent breeding may differ from those of strict philopatry or floating. We use a comprehensive predictive framework to explore how various costs, benefits and intrinsic, environmental and social factors explain philopatry, prospecting, and floating in Seychelles warblers (Acrocephalus sechellensis). Not only floaters more likely obtained an independent breeding position before the next season than strictly philopatric individuals, but also suffered higher mortality. Prospecting yielded similar benefits to floating but lower mortality costs, suggesting that it is overall more beneficial than floating and strict philopatry. While prospecting is probably individual‐driven, although limited by resource availability, floating likely results from eviction by unrelated breeders. Such differences in proximate and ultimate factors underlying each route to independent breeding highlight the need for simultaneous consideration when studying the evolution of delayed dispersal.

Subordinate females in the cooperatively breeding Seychelles warbler obtain direct benefits by joining unrelated groups

“…However, similar to what was found in Kingma, Bebbington, et al. () and Kingma et al. (), male floaters suffer higher mortality when floating compared to male dispersers that obtain a dominant position directly.…”

Oxidative status and fitness components in the Seychelles warbler

“…Birds were caught using mist nets between 06.30 and 19.00 h throughout the breeding season (see Kingma et al . b; for description of the catching protocol). A blood sample (c. 100 μL) was taken immediately after catching by brachial venipuncture.…”

“…dominant or subordinate) of all independent individuals (≥3 months old) was based upon field observations combined with the available long-term data. A 'dominant' male and female were identified in each territory, while the term 'subordinate' included all other independent individuals resident in the territory (Richardson, Burke & Komdeur 2002;Kingma et al 2016a). Subordinates are often independent young from previous breeding attempts, and are normally younger than the dominant individuals (Komdeur 1994b).…”

Compensatory and additive helper effects in the cooperatively breeding Seychelles warbler (Acrocephalus sechellensis)

“…Dominant birds, defined as the pair-bonded male and female in a territory based on their behavioral interactions and nesting behavior (Richardson, Burke, & Komdeur, 2002), form long-term pair bonds. Groups may contain 0-5 sexually mature (>5 months old) subordinates, which are usually retained offspring (Groenewoud et al, 2018;Kingma et al, 2016;Richardson et al, 2002) and typically produce one clutch per season of a single egg (87%; range 1-3 eggs). Nestlings fledge 18-20 days after hatching and become independent around 88 days of age (Komdeur, 1991).…”

“…Seychelles warblers live in groups that occupy stable territories that are defended yearround (Komdeur, 1991). Groups consist of a pair-bonded dominant male and female and 0-5 subordinate individuals of either sex that may or may not provide help with provisioning nestlings and fledglings (Kingma, Bebbington, Hammers, Richardson, & Komdeur, 2016;Komdeur, 1994). The presence of subordinate helpers and nonhelping subordinates provides the opportunity to disentangle the impact of helping and group size (Woxvold & Magrath, 2005).…”