Variable Mating System of a Sedentary Tropical Duck: The White-Cheeked Pintail (Anas bahamensis bahamensis)

Abstract

I studied the breeding chronology, courtship activities, pair-bond relation-ships, and parental-care behavior of a sedentary population of White-cheeked Pintails (Anas bahamensis bahamensis) in the Bahamas from 1985 to 1987. The timing and duration of breeding seasons was variable and associated with variation in the onset and amount of winter and spring rainfall. Year-around courtship, mate switches, courtship of brood females, and the formation of extrapair liaisons all reflected intense and continuous competition for quality mates. Most White-cheeked Pintails paired monogamously, but a low level of polygyny occurred regularly: each year, 4 to 9% of paired males had two mates during the breeding season, despite a strongly skewed sex ratio in favor of males (1.45:1). Polygynous males were particularly effective at guarding their mates during the breeding season, an important de¬terminant of female breeding success. The term "male-quality polygyny" is proposed to characterize this form of polygyny. Both long-term pair bonds and mate changes between years were recorded: I0 of 23 marked pairs (43%) stayed together for two or more breeding seasons, while 13 pairs (57%) divorced. Mate retention in the second year was not related to breeding success in the first year. Only females provided parental care, but some males continued to escort and guard their mate for at least part of the brood-rearing period. Although highly variable, male attendance declined with both hatch date and duckling age. Some birds associated as pairs year around, and several pairs stayed together during the wing molt. The sedentary lifestyle in this subtropical climate and the potential for variable and extended breeding seasons appear to be the key ecological factors influencing the complex and variable mating system of this species.