Breeding Biology of the Puerto Rican Sharp-Shinned Hawk (Accipiter Striatus Venator)

Abstract

Abstract We studied the breeding biology of the Sharp-shinned Hawk (Accipiter striatus venator ) in Maricao forest of western Puerto Rico from 1978 to 1985. Sharp-shinned Hawks are year-round residents and establish nesting territories only during the breeding season, which coincides with the dry and beginning of the wet seasons. Nesting sites were occupied in December and January every year and reoccupancy rates were 50% or higher. Prolonged and intense territorial conflicts between mated and unmated males were common. The onset of egg-laying was in late March or early April approximately 3-4 months after occupancy of nesting sites. Laying of first clutches peaked in early April and spanned 38 days (n = 19 clutches). Laying of second clutches occurred irregularly and spanned 55 days (n = 8 clutches). Females renested only after the initial clutch or brood was lost. The incubation period was 32 days (n = 13 clutches), similar to the duration reported in temperate North America. Nestling females attained larger asymptotic mass than males, but the latter grew faster; although the slopes of the regression lines were statistically homogeneous. Males fledged at an average age of 28.2 days and females at 32.1 days. Young were slightly heavier than adults at fledging, but the wing chord and tail lengths were approximately 50% shorter than those of adults. Fledging occurred at the peak of prey abundance. The breeding cycle in Puerto Rico was approximately 2 months longer than that recorded in Oregon and Utah. The time that elapsed from occupancy of nesting sites to egg laying accounted for the differences. Juveniles departed from nesting sites when prey was still abundant but delivery rates had declined considerably. A total of 105 eggs was laid in 40 nests (average clutch size 2.6), of which 63% hatched and 47% of the nestlings fledged. A total of 0.8 young fledged per breeding attempt. Overall nest success was 29%, 36% (n = 33 nests) in first nesting attempts and 0% in second nesting attempts (n = 9 nests). Most reproductive losses in 28 nests resulted from nestling mortality from Philornis sp. (Diptera, Muscidae) (n = 9) and desertion of clutches (n = 11). Fecundity and reproductive success was lower in Puerto Rico than in Oregon, Utah, and Wyoming. Despite low reproductive success in Maricao forest, the breeding population did not decline during our study.