S.L. Vehrencamp | Geology Reports

USGS1991

Seasonal pattern of reverse mounting in the groove-billed ani (Crotophaga sulcirostris)

We observed reverse mounting behavior in a color-banded population of Groove-billed Anis (Crotophaga sulcirostris) in Costa Rica. Sex was determined with measurements and laparotomies. Reverse mounting appeared nearly identical to mounting by males. Of 27 mountings in which at least one bird was banded, 15 were reverse mountings. Only reverse mountings (11 observations) were observed in the pre-breeding period. During the breeding season males mounted females in 12 of 16 mountings; one of the reverse mountings followed nest predation. The timing of reverse mounting in anis suggests that it has an adaptive function in courtship. The proximate mechanism may be differential timing between partners in the development of breeding condition or of sexual motivation.

Condor↗

USGS1989

Dispersal in the communally breeding groove-billed ani (Crotophaga sulcirostris)

We studied dispersal in a color-banded population of the Groove-billed Ani (Crotophaga sulcirostris) in Costa Rica. Eight percent of the young alive at the end of the breeding season bred on their natal territories the next year and 4% remained but did not breed. Thirteen percent dispersed successfully within the study area and bred in communal groups or simple pairs. The remaining 75% of the young birds disappeared from the study area. Young males remained in the study area as breeders more frequently than did young females. Breeding dispersal occurred, with at least 9% of the adult population moving to a new territory each year.We used a demographic model to estimate the following dispersal fates for young birds. For both males and females, 62% of the young alive at the end of the breeding season in which they hatched obtained a breeding position the next year. Of those that dispersed from their natal territories, 59 to 70% of the males and 64 to 74% of the females obtained breeding positions. Of those that bred the year after they hatched, 22% of the males and 2% of the females bred in their natal units, 34% of the males and 6% of the females bred within the study area but outside their natal units, and 44% of the males and 92% of the females bred outside the study area. We estimated that all of the males and 28% of the females that bred the year after they hatched were within three territories of their natal sites.

Condor↗