Oiii Liviiii; Hcxtiiiirex — Human Influences 



401 



Federal agencies can also provide substan- 

 tial, permanent conservation of the listed 

 species that have more than halt ot all occur- 

 rences on their lands. For example, most popu- 

 lations of both the white-haired goldenrod 

 (Solidago alhopilosu) and white birds-in-a-nest 

 (Machridca alhci) are on national forest lands. 



For many listed species with less than 50% 

 of their occuiTences on federal land, federal 

 agencies may still be able to provide important 

 protection and recovery opportunities. For 

 example, the Karner blue buttertly (Lycaeules 

 melissa samiielis). with less than one-quarter of 

 its occurrences on federal lands, still can sub- 

 stantially benefit from federal management 

 actions, such as restoration of the pine and oak 



savanna habitat on which this butterfly depends. 

 This study found, however, that fully 50% of 

 federally listed species are not known to occur 

 on federal lands, and that for all listed species, 

 64% of known occurrences are on nonfederal 

 lands. This strongly points to the need for devel- 

 oping and strengthening federal efforts for pro- 

 tecting these species through cooperative efforts 

 and incentive programs with state and local 

 agencies, private conservation organizations, 

 and private landholders. 



Reference 



Natural Heritage Data Center Network. 199.^. Perspectives 

 on species imperilment (revised priming). The Nature 

 Conservancy, Ariington, VA. 40 pp. 



For further information: 



Bruce A. Stein 



The Nature Conservancy 



1815 N.Lynn St. 



Arlington, VA 22209 



Changes in disease patterns and trends retlect 

 changing relationships between the affected 

 species (host) and the causes of disease (agent). 

 Host-agent interactions are closely linked to 

 environmental factors that either enhance or 

 reduce the potential for disease to occur. As a 

 result, wildlife disease patterns and trends are, 

 to a substantial extent, indicators of environ- 

 mental quality and changing host-agent interac- 

 tions within the environment being evaluated. 

 The types, distribution, and frequency of dis- 

 eases causing major avian die-offs have 

 changed greatly during the 20th century. Too lit- 

 tle is known to assess the changes of most avian 

 diseases that result in chronic attrition rather 

 than major die-offs, or about those that affect 

 reproductive success, reduce body condition, or 

 affect survival in other indirect ways. 

 Nevertheless, the changing patterns and trends 

 in highly visible avian diseases provide notice 

 of problems needing attention. 



Information on the status of disease in wild 

 birds was obtained from National Wildlife 

 Health Center (NWHC) evaluations of the 

 cause of death for more than 30,000 carcasses 

 from across the United States during the past 

 two decades, reports of avian mortality received 

 from collaborators, the scientific literature, and 

 NWHC field investigations of bird mortality. 

 Comprehensive assessments of causes of wild 

 bird mortality, magnitude of losses, and geo- 

 graphic distribution of specific diseases are not 

 possible from these data, although we can iden- 

 tify general relationships for waterfowl and 

 some other species. 



Changes in Disease Patterns 



The occurrence of disease involves three fac- 

 tors: a susceptible host, presence of an agent 

 capable of causing disease, and suitable envi- 

 ronmental conditions for contact between the 



host and agent in a manner that results in dis- 

 ease. Environment is often the dominant factor 

 in this relationship (Fig. 1 ). 



Avian Botulism 



The most dramatic example of geographic 

 expansion of a noninfectious indigenous disease 

 is avian botulism, caused by the bacterium 

 Clostridium botulimtm. In 1914 a Bureau of 

 Biological Survey researcher began investigat- 

 ing catastrophic die-offs that had begun in 1910 

 and in which millions of waterbirds along the 

 Great Salt Lake, Utah, had died. Later studies 

 revealed that avian botulism was responsible for 

 those die-offs. Historically, avian botulism was 

 referred to as "western duck disease" because of 

 its rather limited geographical distribution of 

 occurrence (Kalmbach and Gunderson 1934; 

 Fig. 2) 



Increased 

 Avian Diseases 

 With Habitat 

 Change 



by 



Milton Friend 



National Biological Service 



Fig. 1. Common factors required for disease to occur. Environmental factors greatly influence 

 occurrence of disease by changing the amount and type of host-agent interactions. 



