Puerto Rican Sharp-shinned Hawk

Accipiter striatus venator

Description

The Accipiter striatus (sharp-shinned hawk) is a polytypic species with nine subspecies distributed in the western hemisphere, from Alaska to Canada south to Argentina and to the West Indies (Cuba, Hispaniola and Puerto Rico). The Puerto Rican sharp-shinned hawk was first discovered in 1912 in the Maricao Commonwealth Forest, and described as a distinct subspecies, Accipiter striatus venator (1914). The Puerto Rican sharp-shinned hawk is a small hawk measuring approximately 11-13 in (28-33 cm). The dark slate gray upper parts and heavily barred rufous underparts of the adults are distinctive. Immatures are brown above and heavily streaked below. It has short, squared tail, often appearing notched when folded, and small head and neck. In flight, the short, rounded wings and long, narrow tail are characteristic.

Behavior

Studies on breeding and nesting habitat of this species, in 1986 discovered that the sharp-shinned hawk population in Maricao nests in both natural and modified Calophyllum plantation habitats. Plantation nest sites tended to have large canopy trees and fewer understory than natural forest nest sites. Sharp-shinned hawks appear to select plantation and natural forest nest sites with similar vegetative structure and topography. Results suggested that vegetation structural requirements (closed canopies and dense stands) are sought by the Puerto Rican sharp-shinned hawks in the selection of nest sites in Maricao and apparently in other parts of its range in Puerto Rico. Furthermore, these authors reported low reproductive success, high desertion of eggs, and high nestling mortality due to parasitism by the warble fly Philornis spp.

Habitat

The center of sharp-shinned hawk courtship and territorial activities in Maricao forest was located in the north-central and eastern parts, within the sub-tropical lower montane wet forest and subtropical wet forest life zones. In the Carite Forest, territorial and courtship activities occurred in the northeastern and north-central parts, within the caimitillo-granadillo forest types. In Toro Negro, these activities took place in the elfin woodland, sierra palm, caimitillo-granadillo and tabonuco forest types. In the Caribbean National Forest, the only two sharp-shinned hawks sighted (a solitary territorial pair) were detected in the south-central part of the forest, confined to the palo colorado forest type of the lower montane forest life zone.

Distribution

Extant breeding populations of the Puerto Rican sharp-shinned hawk were located in the mountain forest of the Maricao Commonwealth Forest, Toro Negro Commonwealth Forest, Guilarte Commonwealth Forest, Carite Commonwealth Forest and Caribbean National Forest. Sixty individuals were counted in island-wide surveys conducted in 1983 and a breeding density of 1.9 hawks per sq mi, 0.73 hawks per sq km, was estimated. In 1985, 72 individuals were counted and a breeding population of 2 hawks per sq mi, 0.76 hawks per sq km, (230-250 island-wide) were estimated in island-wide surveys. In 1992, 110 sq mi (285.6 sq km) censuses yielded 82 sharp-shinned hawks; 40 in Maricao, 30 in Toro Negro, 10 in Carite and two in Caribbean National Forest. An overall population of 129 individuals has been estimated for these forests in 1992. Although the Guilarte Forest population was not censured in 1992, a population of 25 individuals was estimated for the forest in 1985. Although the sharp-shinned hawk was previously known from the karst region of Rio Abajo and Guajataca Commonwealth Forests in 1986, there was no evidence of its presence in these areas. Fossil evidence indicates that the species was once more widespread in the karst region. In 1986 sharp-shinned hawks were searched for but not sighted in Cambalache, Vega, Susua, and Guanica forests. 1994 observations indicate the hawk does exist in and around the Susua Forest.

Threats

Timber harvest and management practices that would result in a reduction in numbers or in the diminishing of habitat quality of species already limited in their abundance and distribution could be detrimental. In 1986, 50% of the nesting areas in the Maricao forest were in plantations of maria (Calophyllum brasiliense ). The timber harvest and management practices could have negative effects on sharp-shinned hawks if vegetation structural features, such as high stem density and canopy closure, were not maintained. Adequate nest site habitat in the Maricao forest is considered to be in limited supply. Any activities that modify required structural features of vegetation in sharp-shinned hawk nesting areas could result in the reduction of the effective population size. Sharp-shinned hawks showed a strong nest site tenacity and returned year after year to the same nesting areas. In the Maricao forest, the Puerto Rico Energy Power Authority has a power substation located in the lower montane wet forest life zone, the center of sharp-shinned hawk nesting habitat. Many kilometers of aerial power lines run through forest lands. The access road for the substation is located adjacent to sharp-shinned hawk habitat in the subtropical wet forest life zone. The construction of this access road resulted in the destruction of approximately 6.4 acres (2.6 hectares) of sharp-shinned hawk habitat. The construction of new or the enlargement of the existing communication infrastructure could potentially eliminate important sharp-shinned hawk habitat. The mortality of sharp-shinned hawk nestlings due to parasitism by the warble fly Philornis spp. has been documented. Studies conducted in Maricao forest attributed 61% of nestling mortality to Philornis parasitism. The Puerto Rican sharp-shinned hawk has experienced a 40% decline in a period of seven years. The potential for alteration of the species' habitat, human disturbance, illegal shooting, and nestling parasitism by warble flies constitute serious threats to the continued survival of the species.

Conservation and Recovery

The U.S. Fish and Wildlife Service published a Recovery Plan for the Puerto Rican sharp-shinned hawk in 1997. It only survives in the Maricao, Toro Negro, Guilarte, and Carite Commonwealth Forests (managed by the Commonwealth of Puerto Rico), and in the Caribbean National Forest (U.S. Forest Service). Its survival is absolutely dependent on the protection of its habitat in these areas of remnant forest. This can be accomplished by conserving these forests against destructive uses in forestry, road-building, and other threatening developments. In addition, the endangered hawk must be strictly protected against any shooting. The populations of the Puerto Rican sharp-shinned hawk should be monitored, and research undertaken into its biology and habitat needs.

Contacts

U. S. Fish and Wildlife Service
Boqueron Ecological Service Field Office
P.O. Box 491
Boqueron, Puerto Rico 00622
Telephone: (809) 851-7297

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

References

U.S. Fish and Wildlife Service. 9 Sept. 1994. "Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Puerto Rican Broad-Winged Hawk and the Puerto Rican Sharp-Shinned Hawk." Federal Register http://endangered.fws.gov/r/fr94550.html

U.S. Fish and Wildlife Service. 1997. "Puerto Rican Broad-winged Hawk and Puerto Rican Sharp-shinned Hawk Recovery Plan." U.S. Fish and Wildlife Service, Atlanta, Georgia.