Reproduction and Social Organization of the Black-Capped Donacobius (Donacobius atricapillus) in Southeastern Peru
Abstract A color-banded population of Black-capped Donacobius (Donacobius atricapillus) on a Peruvian oxbow lake was studied during one breeding season and censused for 3 yr thereafter. Eighteen territories along a marshy shoreline were occupied by groups of 2-4 donacobius. Each group contained a mated pair and 0-2 helpers, apparently offspring produced during 1-2 preceding breeding seasons. Helpers participated in nest surveillance, territorial displays, and feeding nestlings. Displays occurred at territory boundaries and consisted of loud duetting by the pair or group. Breeding coincided with the rainy months, October through April, and peaked in November-January. Clutch size was always two. Egg and nestling periods each lasted 17-18 days. No correlation was demonstrable between group size and overall fledging success. Trios, however, accounted for all cases in which both young successfully fledged, whereas pairs never fledged more than one young. Annual survivorship of breeding adults averaged 71%. Cooperative breeding in donacobius is associated with limited opportunities for acquiring breeding territories, as in many other cooperative breeders. The relatively short period during which young serve as helpers (and the resulting small family sizes), however, suggests that at other times or places breeding territories are more readily available to young.