Our Liviiif; Resources — Birds 



69 



States). Status determination is complicated hy 

 the low density of nesting birds and fluctuations 

 in breeding associated with cycles of prey abun- 

 dance. It remains in Category 2. i.e.. possibly 

 appropriate lo propose to list but a\ailable data 

 are not conclusive for threatened or endangered 

 status. 



Falcons 



American peregrine falcon {Faico pt'rci;rlnu.s 

 anatwn) populations declined as a result of con- 

 tamination by DDT and other organochlorine 

 pesticides. The species was extirpated as a 

 breeding bird in the eastern United States and 

 declared endangered elsewhere. Peregrine 

 recovery has been accomplished in the eastern 

 United States and supplemented in the West 

 (except Alaska) by release of hundreds of pere- 

 grines bred in captivity. Now several generations 

 originating from released peregrines have sur- 

 vived and produced young in the wild. In some 

 locales (e.g.. parts of California), however, 

 young are still not produced at nomial rates. In 

 Alaska nesting numbers of the Arctic subspecies 

 increased naturally, and it was downlisted to 

 threatened status in 1984. Now the Anic pere- 

 grine falcon is propo.sed for removal from the 

 Endangered Species List. 



Owls 



The distribution of the ferruginous pygmy 

 owl (Glaucidium brasilianinn cactorum) 

 extends north only into southern Arizona and 

 southern Texas, and concern exists about its sta- 

 tus because of the fragmentation and loss of 

 deciduous riparian woodlands and remnant 

 mesquite habitat. The subspecies occurring 

 there, the cactus ferruginous pygmy owl. was 

 elevated from Category 2 as of March 1993 and 

 is being considered for listing as threatened. 



The spotted owl (Slrix occidentalis) is being 

 surveyed extensively and studied because the 

 northern and Mexican subspecies are threat- 

 ened. In the Pacific Northwest the threat to 

 these owls is loss of old-growth forest, and in 

 the Southwest, general loss of forest habitat. 

 The attention focused on spotted owls has 

 resulted in the only standardized, broad-scale 

 survey of an owl species. Since 1968 the num- 

 ber of known owl nesting areas in Oregon has 

 increased from 27 records (9 sightings, 18 spec- 

 imens) to about 2.700 separate sites known to 

 be occupied by pairs or single birds sometime 

 within the last 5 years (E. Forsman, U.S. Forest 

 Service, personal communication). This does 

 not reflect an increase in owls; rather, it reflects 

 our ignorance of owl numbers and distribution, 

 largely resulting from lack of survey effort. 



Conclusions 



Raptors, as top predators, naturally occur at 

 low densities relative to many other organisms. 

 As a group, raptors are poorly surveyed and 

 there are few quantitative data with which to 

 determine their population status and trends. A 

 summary of our assessment of the status and 

 population trends of the 60 species and sub- 

 species of raptors we considered (Table) 

 includes the following: 2 are declining in num- 

 bers and 5 are increasing; 16 (27%) are thought 

 lo be stable; 19 (32%) are classified as stable, 

 but this assessment is qualified because of local 

 or regional concerns or poor information; the 

 infomiation for 12 (20%) is so poor that we 

 could not determine their status; 7 (12%) of 

 these species or subspecies are endangered or 

 threatened; and 9 (15%) are in Category 2 or 3. 

 reflecting recent concern that they might be 

 endangered or threatened. 



We must learn more about the distribution 

 and population dynamics of all our raptor 

 species. With knowledge of their status and 

 trends and information about their distribution 

 and habitat requirements, we can avoid expen- 

 sive, disruptive, last-resort management of these 

 birds. With knowledge of their ecology, we can 

 conserve biodiversity. 



References 



Bowerman. W.W. 1993. Regulation of bald eagles 



[Haliaeetus leucocephalus) productivity in the Great 



Lakes Basin: an ecological and toxological approach. 



Ph.D. dissertation. Michigan State University. East 



Lansing. 291 pp. 

 Johnsgard. P.A. 1988. North American owls: biology and 



natural history. Smithsonian Institution Press, 



Washington. DC. 295 pp. 

 NWF. 1988. Proceedings of the Southwest Raptor 



Management Symposium and Workshop. Scientific and 



Tech. Series 11. National Wildlife Federation. 



Washington. DC. 395 pp. 

 NWF, 1989a. Proceedings of the Western Raptor 



Management Symposium and Workshop. Scientific and 



Tech. Series 12. National Wildlife Federation. 



Washington. DC. 320 pp. 

 NWF 1989b. Proceedings of the Northeast Raptor 



Management Symposium and Workshop. Scientific and 



Tech. Series 13, National Wildlife Federation, 



Washington, DC. 356 pp. 

 NWF. 1990. Proceedings of the Southeast Raptor 



Management Symposium and Workshop. Scientific and 



Tech. Series 14, National Wildlife Federation. 



Washington, DC. 248 pp. 

 NWF. 1991. Proceedings of the Midwest Raptor 



Management Symposium and Workshop. Scientific and 



Tech. Series 15, National Wildlife Federation. 



Washington, DC. 290 pp. 

 Palmer. R.S., ed. 1988. Handbook of North American birds. 



Vols. 4 and 5. Yale University Press, New Haven, CT. 



433 pp. and 462 pp. 

 White, CM. 1994. Population trends and current status of 



selected western raptors. Studies in Avian Biology 



15:161-172. 



For further information: 



Mark R. Fuller 



National Biological Service 



Raptor Research and Technical 



Assistance Center 



3948 Development Ave. 



Boise. ID 83705 



