About | HeinOnline Law Journal Library | HeinOnline Law Journal Library | HeinOnline
LOG IN
LOG IN

12 Endangered Species Tech. Bull. 1 (1987)

handle is hein.animal/endanspb0012 and id is 1 raw text is: January 1987 Vol. XII No. 1 - __ U U U U W~ U U U - - - m_ U T Be Department of Interior. U.S. Fish and Wilditfe Service Endangered Species Program, Washington D.C. 20240 Two Animals Proposed for Listing During December 1986, the Fish and Wildlife Service (FWS) proposed to add two animals a bird and a toad-to the U.S. list of Endangered and Threatened species. If the proposals are later made fi- nal, protection under the Endangered Spe- cies Act will be extended to these taxa: Black-capped Vireo (Vireo atricapillus) Once a widely distributed bird, the black- capped vireo bred from north-central Kansas through Oklahoma and Texas to central Coahuila, Mexico (with an outlying, possibly temporary, colony in Nuevo Leon, Mexico). Its wintering range was from Sonora to Oaxaca, with most activity in Sinaloa and Nayarit. Unfortunately, however, this small but attractive songbird is disappearing. Habitat loss and the spread of a competing bird species have eliminated the black-capped vireo from most of its breeding territories in the U.S., and it likely faces similar problems in Mex- ico. In an effort to prevent its extinction, the FWS has proposed to list this species as Endangered (F.R. 12/12/86). Black-capped vireos require a specific type of habitat consisting of a few small trees scattered among separated clumps of many shrubs or bushes. The clumps of bushes are in the open, surrounded by bare ground, rocks, grasses, or wild- flowers. Bushes with low-reaching foliage are particularly important for breeding be- cause the nests are usually only 18 to 40 inches (0.5 to 1.0 meter) above ground and need to be screened from view. These specific habitat characteristics have proved to be highly vulnerable to damage or destruction from certain land use practices. Urbanization has com- pletely eliminated many former vireo breeding areas. Elsewhere, grazing sheep, goats, and other exotic herbivores remove the vegetation cover near ground level that is necessary for vireo nesting. Range management also can be a factor when it involves the removal of low, broad- leaved bushes. On the other hand, natural vegetational succession can overwhelm the clumped habitat needed by the vireo. In the past, overgrown areas periodically would be opened by such events as wild- fires; now, however, the amount of avail- able habitat has been drastically reduced. Competition is another big problem for the black-capped vireo. The extensive human-related changes in the landscape and land-use patterns-in particular, the opening up of forested areas and the spread of cattle and grain fields in North America over the past 150 years-appear to have favored the spread of the brown- headed cowbird (Molothrus ater). This more adaptable bird seems to be increas- ing in numbers as well as in range. (It threatens not only the black-capped vireo but also a related subspecies in California, the Endangered least Bell's vireo, Vireo bellii pusillus.) Cowbirds parasitize vireo nests, laying their eggs before the vireo clutches are completed. The cowbirds eggs hatch 2 to 4 days before the vireos and, by the time the vireos do hatch, the cowbird nestlings outweigh them tenfold. A 1961 study found that in all places where a cowbird nestling occupied the nest, no black-capped vireo chicks survived. Based on extensive field surveys over the past decade, the FWS believes that the black-capped vireo is a candidate for extinction. Trends in all parts of the spe- cies' range are downward; the vireo has disappeared from Kansas, is gravely en- dangered in Oklahoma, and no longer oc- curs in several parts of its former range in Texas. Its current breeding range is from central Oklahoma (Blaine County) south through Texas (Dallas, the Edwards Plateau, and Big Bend National Park), to at least the Sierra Madera in central Coahuila, Mexico. The largest remaining breeding population, which occurs near Austin, Texas, could lose its breeding hab- itat as a result of proposed development and road construction projects. The city of Austin, which endorses listing the vireo, is considering ways to protect this habitat. A proposed designation of Critical Hab- itat was not included in the listing proposal for the black-capped vireo because this bird occurs in scattered, small areas that can vary over time due to vegetational suc- (continued on page 9) Adult male black-capped vireos are olive green on the upper surface and white un- derneath, with faintly yellowish-green flanks. Their crown and the upper half of the head is black with a partial white eye ring and lores. Adult females are duller in color, with a slate gray crown and underparts washed in greenish-yellow. ENDANGERED SPECIES TECHNICAL BULLETIN Vol. XII No. 1 (1987)

What Is HeinOnline?

HeinOnline is a subscription-based resource containing thousands of academic and legal journals from inception; complete coverage of government documents such as U.S. Statutes at Large, U.S. Code, Federal Register, Code of Federal Regulations, U.S. Reports, and much more. Documents are image-based, fully searchable PDFs with the authority of print combined with the accessibility of a user-friendly and powerful database. For more information, request a quote or trial for your organization below.



Contact us for annual subscription options:

Contact Us

Already a HeinOnline Subscriber?

Log In

profiles profiles most