Guam Broadbill

Myiagra freycineti

Description

The Guam Broadbill, Myiagra freycineti, is a small flycatcher with an iridescent bluish head and neck with gray lores and anterior forehead. The back and upper wing coverts are near green-blue with the rump grayer than the back. The chin and throat are white and the breast light cinnamon, fading to pale buff and white on abdomen and under the tail coverts. Tail color is bluish-slate with the tips of the tail feathers edged with white. The bill and feet are black and the iris is dark brown. Adult females are more gray-brown above with less of a metallic luster and tibias which are less brownish. Immature individuals resemble adults but with more brown and less blue on back and fluffier underparts than adults.

Behavior

Nests of the Guam broadbill have been recorded in all months except November and December. The number of clutches per year is unknown although one pair raised three clutches in ten months during 1980-1981. Both sexes incubate eggs and brood young. Two observed eggs were cream-colored with a band of brown splotches around the widest part of the egg.

During several hours of observation at one nest, the female performed most of the incubation, but the male also participated. The eggshells were consumed by an adult, probably the female. No data is available on length of incubation or nesting period.

Specimens have been observed or collected throughout the year and do not appear to migrate.

The Guam broadbill is apparently entirely insectivorous and feeds both by gleaning insects from twigs and foliage, and by hawking insects from the air during the day. When hawking insects it is rather tyrannic-like, making repeated sallies for prey and returning to the same, or sometimes, a different perch, where the bird bobs its tail to maintain balance.

Habitat

The Guam broadbill formerly appeared in all habitats on Guam with the exception of southern savannahs. The species has been recorded in woodland areas, forested areas with bushy undercover, areas dominated by Leucaena leucocephala, and in southern riparian habitats. Specimens have also been observed on coastal strand habitats and man-grove swamps in addition to forest habitats.

In 1979, the Guam broadbill seemed to have been restricted to the mature limestone forest of the relatively undisturbed northern cliffline and was rare in mixed woodlands and second growth forests in portions of Guam.

Distribution

Historically, the Guam broadbill was distributed throughout Guam island in all habitats except savannah. It was widely distributed in forest, scrub and agricultural areas until 1968 when it entered into decline because of the spread through the island of the accidentally introduced brown tree snake, after which time the species was restricted to the northern cliffline and adjacent northwestern portions of the northern plateau. A survey done in 1981 by the U.S. Fish and Wildlife Service and the Guam Aquatic and Wildlife Resources estimated 460 of the birds in northern Guam. The last individuals seen in Pajon Basin were in October 1983. The last two sightings on Guam of the species occurred in March 1984. In 1981 the total population was estimated at 2,000 birds and by 1983 was less than 100. By 1987 it was extirpated from the wild and currently only survives in a captive breeding program in Guam and in 16 zoos in the United States. Efforts are underway to establish a self-sustaining, experimental population on the nearby snake-free island of Rota in the Northern Mariana Islands.

Threats

The entire native forest avifauna on Guam has undergone a drastic decline. Introduced diseases and predation were considered as possible causes for the range reductions and extinctions. To date, no infectious organisms have been isolated on Guam that could account for the decline. Feral dogs, cats, and rats are a problem on all major islands in the Marianas, but the only predator unique to Guam is the brown tree snake, Boiga irregularis. Data indicates the snake is the major cause of the decline. There is a close correlation between the range expansion of the snake and the forest bird contraction, and through experiments, predation by snakes was shown to be high in areas where native forest birds had gone extinct locally.

Competition with the introduced black drongo, Dicrurus macrocerus, an adaptable bird, is unlikely because of the differences in habitat utilization, foraging techniques, and dietary preferences. The Guam broadbill may have suffered more from occasional predation by drongos rather than competition for food or by displacement from nesting sites.

The extensive use of pesticides in the past for agriculture and vector control could present a possible link to the general avian population decline, and they may have impacted certain bird populations in the past. An intensive pesticide survey conducted in 1981 concluded pesticides were not a significant factor at present.

Conservation and Recovery

The recent, drastic decline of forest bird populations on Guam has been one of the most alarming and challenging endangered species problems of modern times. Current evidence points to an efficient predator of small birds, the brown tree snake, as the culprit. Because hope still remains that a few birds may yet survive, the species is included in the Recovery Plan for the Forest Birds of Guam and Rota.

The plan states among its primary objectives to prevent extinction by initially establishing a sustainable population. In addition, it is imperative to develop methods of reducing predation by brown tree snakes; this action would then allow expansion of the wild population and reintroduction of captive birds back into their historic range. Down-listing to threatened status would occur once predation from snakes is under control and the Guam broadbill could reoccupy all essential habitat.

Contact

Regional Office of Endangered Species
U.S. Fish and Wildlife Service
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

Reference

U.S. Fish and Wildlife Service. 1985. "Recovery Plan for the Native Forest Birds of Guam and Rota, Mariana Islands." U.S. Fish and Wildlife Service, Portland, 110 pp.