Effects of sociality on short‐distance, female‐biased dispersal in tropical wrens

Abstract

Summary 1.Dispersal from the natal area, or between breeding sites, marks a critical transition for individual animals, and a fundamental demographic and genetic process. Limitations on dispersal in natural populations are important in predicting population dynamics and structure. Tropical habitats that can be naturally patchy are also being fragmented rapidly, and these habitats harbour many social species. 2. We studied dispersal in cooperatively breeding stripe-backed wrens ( Campylorhynchus nuchalis ) in the Venezuelan savanna, using 20 years of data from marked populations over 40 km 2 . We test the hypotheses that dispersal is limited by competition for social position and that such limitation is sex-specific. 3. Dispersal is strongly female-biased, and results mainly in attainment of breeding status in neighbouring groups. Reproductive success is determined by the structure of the breeding group, and is concentrated in a small minority of individuals. 4. Natal dispersal is delayed, and represents a dramatic shift from indirect contribution to kin production (helping) to the direct approach of breeding. Monogamy limits breeding opportunities, compared to other social species, and both natal and breeding dispersal are constrained to short distances, particularly when compared to noncooperative breeders. 5. Males are more philopatric compared to females, for which more frequent and distant dispersal leads to greater reproductive success. Competition for breeding status in an established social order impedes dispersal, in part because experience and previous familiarity are important, particularly in males that rarely disperse to productive large groups. 6. Diverse patterns of sex bias in dispersal among cooperatively breeding birds can be explained by the comparative diversity of reproductive alternatives available to males and females. A 'breeding diversity' hypothesis is illustrated by comparison with malebiased dispersal in brown jays. 7. Social resistance to movement establishes a brake on gene flow and demographic interaction among populations that has important implications for population viability.

Sex-bias and timing of natal dispersal in cooperatively breeding Puff-throated Bulbuls Alophoixus pallidus

“…Unlike dispersing males who frequently occupy neighbouring territories, observed female PBUs never dispersed to neighbouring territories. Our results differ from findings in other studies where females are reported to move to neighbouring groups as a staging post (Cockburn et al 2008;Eikenaar et al 2008) or to acquire breeding status in neighbouring territories (Curry and Grant 1990;Yáber and Rabenold 2002). While dispersal is presumably underestimated beyond the 30-ha plot because most territories fall within two territories of a plot edge, we did search outside the core area and we recorded all observed off-plot dispersal events.…”

Fine-scale movement decisions of tropical forest birds in a fragmented landscape

“…We calculated home ranges for two antshrikes that returned at 0.58 and 0.30 ha (mean ¼ 0.44 ha, radius if circular ¼ 37 m) and for four wrens at 0.33, 0.31, 0.36, and 1.20 ha (mean ¼ 0.55, radius if circular ¼ 42 m) (Gillies and St. Clair 2010). These are similar to published results for congeners of both species, where home range radius was ;60 m for a congener to the antshrike in Brazil (T. caerulescens; Duca et al 2006) and ;75 m for a congener to the wren in Venezuela (Campylorhynchus nuchalis; Yaber and Rabenold 2002). Riparian corridors were typically 50-150 m wide.…”

Estimating Sex-Specific Dispersal Rates With Autosomal Markers in Hierarchically Structured Populations

“…Although inbreeding or kin competition might often be avoided by short moves, greater distances are normally required to escape crowding conditions or to colonize vacant territories. Furthermore, dispersal distances, just like dispersal rates, may differ among sexes (Blundell et al 2002;Yaber and Rabenold 2002). Although short-distance dispersal is expected to display sex biases if kin avoidance plays an important role at a local scale, longdistance dispersal should not if colonization processes constitute the prevailing ultimate cause at this scale.…”