Our Li\inf; Rcsdurces — Hiinuiii Inllmnccs 



40i 



Disease 



Cause Species 



First occurrence in species Major 

 Location expansion 



Year 



Current status 



Widespread: maior problem 



Widespread; major problem 



Expanding 



Expanding 



Stable 



Major problem of urban environments (bird feeders) 



Widely distnbuted 



Continuing spread norlbv^ard from southeastern U.S. 



Ma|or geographic spread; increased frequency of occurrence 



Table 1. Changes in patterns of 

 diseases affecting wildlife. 



occurrence during the 2()th century. Changes in 

 disease patterns in wild birds are consistent with 

 such changes in other species, including 

 humans, and reflect environmental changes that 

 foster the eruption of disease and the spread of 

 infectious agents (Tables I and 2). 



Magnitude of Losses 



Changes over time in the frequency of wild 

 bird die-off s and losses from disease cannot be 

 precisely determined because no appropriate 

 data base exists. Also, changes in surveillance 

 and reporting confounds inteipretation of exist- 

 ing data. Nevertheless, with the exception of 

 rare catastrophic events, available information 

 suggests that substantially greater numbers of 

 wild birds are dying from diseases now than in 

 earlier periods of the 2()th century. The yearly 

 average of 55.066 reported waterfowl deaths 

 from disease during 1930-64 (Friend 1992) has 

 been exceeded or nearly exceeded by single 

 events since 1964. Several disease outbreaks, 

 for example, have killed between 25.000 and 

 100.000 waterfowl: die-offs of 5,000 to 10,000 

 waterfowl are common. 



The number of avian die-offs in the NWHC 

 data base with reported mortality of 1,000 or 

 more is sufficient to suppoit the contention of 

 increased numbers of birds dying from disease 

 compared with the period before 1965. The 

 annual number of avian die-offs is an addition- 

 al indicator of the relatively high frequency of 

 avian disease during the late part of the 20th 

 century (Fig. 5). 



Habitat and Human 

 Interactions 



Causes of major bird die-offs during the past 

 decade and their geographic distribution are 

 shown in Table 3. Composite data indicate a 

 relation between bird concentrations and the 

 occurrences of avian disease. Those states with 

 large concentrations of migratory birds on 

 migrational staging and wintering areas tend to 

 have the most disease outbreaks. Preliminary 

 assessments suggest that habitat quantity and 

 quality are important factors in this relation. 



Suspected 

 Confirmed 



I 



Pacific 



Central Mississippi Atlantic 



I 



Total 



Table 2. Emerging diseases of 

 wildlife. 



1990-93 



Fig. 4. Number of duck plague 

 outbreaks in waterfowl in the 

 United States, by tlyway (suspect 

 cases have pathology consistent 

 with duck plague but lack isola- 

 tion of the virus to confirm the 

 diagnosis), and total number of 

 outbreaks by decade. 



