Harem Structure and Reproductive Behaviour of Pteropus tonganus In American Samoa.

We studied the reproductive biology of Pteropus tonganus on Tutuila, American Samoa from 1992 to 1994. Pteropus tonganus typically roosts in colonies consisting of harem groups averaging 5.3 females per male and peripheral single males and groups of males. The mating system appeared to have elements of both female defense polygyny and resource defense polygyny. The reproductive status of females within harems varied throughout the year so that some females appeared non-pregnant while others were pregnant or nursed large young (up to about 3/4 the length of the female). Post-partum mating was frequent, especially with females that had small dependent young. Mating, pregnancy, birthing, and young of all sizes occurred year-round. However, some evidence of bimodal peaks occurred during January and June- August.

The breeding behavior of Atlantic walruses, Odobenus rosmarus rosmarus, in the Canadian High Arctic

The breeding behavior of Atlantic walruses, Odobenus rosmarus rosmarus, overwintering at the Dundas Island polynya (76 °09′N, 94 °52′W) in the Canadian High Arctic was studied from 1981 to 1990. Approximately 25–65 walruses frequented the polynya area each winter; their distribution was determined by sea-ice features (e.g., thin annual ice, cracks) that ensured easy access to open water. The mating system of walruses breeding in the area is best described as female-defense polygyny. A large mature male had exclusive access to a herd of walruses containing several females for 1–5 days at a time. Although there were numerous males in the polynya capable of attending a herd during the breeding season, one or two males spent significantly more time with a herd. It was not evident that female preference was important in determining which male became the attending male. When attending a herd, a male continuously repeated a complex, stereotyped underwater song. Other sexually mature males in the area behaved as silent herd members, vocal satellite males, or, in some cases, both. The small number of walruses at the polynya, the sedentary nature of the population due to ice conditions, and the inherent gregariousness of female walruses appear to be important factors influencing the evolution of social behavior and the mating system in walruses