Breeding ecology and nest-site selection of Song Wrens in central Panama

We describe nest-site selection and report measures of breeding productivit y from a population of Song Wrens (Cyphorhinus phaencephalus) in central Pa nama. We studied 31 pairs from 1995 to 1998 and collected data on nest pred ation from 1996 to 1998. Song Wrens are year-round residents that build bre eding nests for reproduction and dormitory nests for roosting. Twenty-five of 50 Song Wren breeding nests produced fledglings (dairy nest survival rat e = 0.968). Song Wrens usually (78%) placed their breeding nests in ant-def ended acacias (Acacia melanoceras). However, nests placed in acacias did no t experience lower rates of nest predation than nests placed in sites not d efended by ants. The population-wide breeding season was seven months long, but individual pairs often bred within a span of only 2.5 months. Modal cl utch size was two (n = 42), but the frequency of three-egg clutches was hig h (greater than or equal to 27%). Pairs that lost eggs or chicks renested m ore quickly than pairs that fledged young and attempted a second brood. Obs erved annual production of young was 1.4 fledglings per pair. Compared with other wrens, Song Wrens had a much longer breeding season and longer inter vals between broods. The annual productivity of Song Wrens was the lowest r ecorded for any wren, which may have been due to smaller clutch sizes, long intervals between broods, and the correspondingly low number of nesting at tempts per pair per year.