Summary
Female Red-winged Blackbirds were observed to interact aggressively with conspecific females during the breeding season. Redwing females attempted to repel intruding females through the use of vocalizations, displays, and aggressive chases. Mapped positions of marked individuals indicated that female Red-winged Blackbirds recognized male territory boundaries and defended subsections of the male's territory against new intruding females and against harem mates. Female vocalizations advertising territory ownership were clumped in time early in the breeding season, suggesting that neighbouring individuals were interacting vocally. These results support the competitive version of the polygyny threshold model. The observed aggressive interactions, territorial behaviour, and vocal interactions suggest that female Red-winged Blackbirds attempt to deter further recruitment into harems.
Methodology
These studies were performed at the Queen's University Biological Station on Lake Opinicon north of Kingston, Ont. The study site was a small marsh (Cow Island Marsh) consisting primarily of cattails (Typha spp). with a border of alder (Alnus rugosa) and sweet gale (Myrica gale) between the cattail mat and the surrounding upland. All of the territorial males ( 10 in 198 1 and 9 in 1982) and most of the female Red-winged Blackbirds (9 of 15 in 1981 and 7 of 15 in 1982) were banded with unique colour combinations to allow the recognition of individual birds. Binoculars (8 X 40) and a 20-power spotting scope were used to identify Sand combinations.
General observations.
Females were difficult to observe since they were more discreet than the males and spent a large proportion of their time low in the cattails. Consequently, two elevated blinds were used for observations; in addition. a canoe positioned near the centre of the bay was frequently used. Most observations occurred between 0530 and 0900, and occasionally between 1800 and 2100 in May and June of 1981 and 1982.