Delayed Dispersal as a Route to Breeding: Territorial Inheritance, Safe Havens, and Ecological Constraints

Abstract

The relative roles of ecological constraints, the benefits of philopatry, and the role of life history continue to be debated in the evolution of natal philopatry and cooperative breeding. We compare three routes to breeding: departing to search for territories as a floater, staying and queuing to inherit the natal territory, or queuing and eventually shifting to a neighboring vacancy. Our model assumed a dominance-structured population. It quantifies the benefits of philopatry for varying-rank subordinates and contrasts it against the benefit of dispersal. We apply the model to data on Siberian jay Perisoreus infaustus, a species in which retained offspring do not help at the nest. The results indicate that territorial inheritance plays a small role in this species (presumably due to inbreeding avoidance), and territory acquisition is less constrained for dispersing than philopatric offspring. Nevertheless, small family groups-one or, at the most, two same-sex queuers-are predicted to form because philopatric offspring gain nepotistic benefits that improve their survival. This fits with data on group sizes and supports the idea of the natal territory as a safe haven for waiting for breeding opportunities. We also discuss our predictions in the light of ecological constraints and clarify recent confusingly different predictions on the role of habitat saturation as an explanation for delayed dispersal and cooperative breeding. We argue that "ecological constraint" is too wide a term to yield useful predictive power and that it is more appropriate to examine the consequences of specific life-history traits on the success of dispersers.

Male-male competition is not costly to dominant males in a cooperatively breeding bird

“…By enlarging group size, competitive male subordinates provide a range of benefits: improved nestling survival and condition at fledging, higher chick mass and foraging abilities at independence, better foraging rates for all group members via decreasing the need for vigilance and early successful dispersal probabilities of helped chicks (Radford and Ridley 2007;Raihani and Ridley 2007;Ridley and Raihani 2007;Hollén et al 2008). Dominant males may also gain indirect benefits from tolerating related competitive subordinate males because babbler subordinate males benefit from staying in the natal group until they successfully disperse as breeding dominants Raihani et al 2010), MJN-F, unpublished data), similar to subordinates in other cooperatively breeding species (Kokko and Ekman 2002;Griesser et al 2006). In the southern pied babbler, especially considering that male competition is not itself costly, these benefits may compensate tolerant dominant males for the small risk of lost paternity and any mate guarding costs.…”

Nepotism and subordinate tenure in a cooperative breeder

“…Dominant males gain both indirect and direct benefits from tolerance of their related male subordinates. We suggest that dominant males gain indirect fitness benefits when their own relatives (sons and/or brothers) are nepotistically prioritized in the queue of males waiting in the 'safe haven' of the group for local dominance opportunities [16]. Nepotistic tolerance also allows related subordinate males to inherit the dominant position in the event that the dominant male dies, provided the dominant female is unrelated and the subordinate male is the oldest such male [8].…”

Individual contributions to territory defence in a cooperative breeder: weighing up the benefits and costs

“…Yearling and adult subordinate males were also expelled from their groups within the first week after the successful immigration of a prospecting male. The threat of losing the safe haven from which to conduct forays in search of mating and dispersal opportunities [34] may explain why older subordinate males led chases of prospectors at rates similar to those of dominants. Subordinate individuals of both sexes are also expected to gain greater indirect fitness benefits from helping to raise offspring fathered by the dominant male rather than by the extra-group males, as he is typically their own father [19,32].…”