Avian Cooperative Breeders Research Articles

Helping is costly to young birds in cooperatively breeding white-winged choughs

Cooperative breeding among birds is at its most extreme in white-winged choughs ( Corcorax melanorhamphos ). Choughs have never been observed to breed successfully without helpers, and reproductive success increases linearly across all group sizes (maximum = 16). Further, helpers contribute to every aspect of reproduction, including nest building and incubation. Here we show that the contribution of young helpers (one year old and less) to incubation depends on the group in which they live. In small groups (3-5 birds), young helpers contribute as much to incubation as older birds, but in large groups they contribute little. In large groups, help increases sharply with age. Old birds contribute equally, regardless of group size. Although choughs generally do not lose body mass over incubation, young helpers lose mass in proportion to the amount of incubation they perform, independent of any effect of group size. This provides evidence that helpers in cooperatively breeding birds suffer costs from providing help additional to the costs incurred from remaining philopatric. It also demonstrates that the needs of the group influence whether young birds provide help.

Philopatry and dispersion in the cotton-top tamarin,Saguinus (o.) oedipus: An attempted laboratory simulation

Cotton-top tamarins [Saguinus (o.) oedipus,Callitrichidae] living in cooperatively breeding, mature families in a captive colony were given the chance to explore a new living area. The aim was to simulate choices of philopatry versus dispersion. Breeding adults tended to stay home, as did eldest sons and still-dependent young offspring, but eldest daughters tended to go prospecting. The latter also spent more time in the new area and did more looking around while there. This confirms impression of female dispersion gained from records of “evictions” of daughters by other family members. These findings agree with those from field study and show noteworthy parallels with an avian cooperative breeder, the Florida scrub jay, Aphelocoma coerulescens.

Shared paternity in the acorn woodpecker (Melanerpes formicivorus)

We investigated multiple paternity in acorn woodpeckers (Melanerpes formicivorus) from central New Mexico by starch-gel electrophoresis. Seven of thirty-one presumptive genetic loci were polymorphic. Multiple paternity was revealed in one of three multi-male groups sampled on the basis of offspring and adult electrophoretic phendtypes, and was suggested in the two other groups. This study provides the first documentation of multiple paternity for any avian cooperative breeder.