Breeding Habitat:N/A
Nest Type:N/A
Migration Status:Short distance migrant
Nest Location:N/A
BBS trend estimates for Turkey Vultures should be viewed with some caution. These soaring birds tend to be under-represented on early morning surveys, which are completed at a time when vultures are just becoming active. Additionally, the appearance or disappearance of vulture roosts can markedly influence the counts along individual routes and obscure trends in local populations.
Turkey Vultures tend to be counted in relatively small numbers throughout most of their range. Along BBS routes, they are most numerous in Texas and Florida (Relative Abundance Map). Vulture populations are generally increasing throughout their range, although local declines are evident in all regions of the continent (Trend Map).
The long-term trend estimates are similar. Significant increases are indicated for populations in the Eastern BBS Region, United States, Canada, and the entire continent (Trend List). Most significant trends in states and strata are increases, although local declines are evident in portions of the southern U.S. and Oregon. These increases generally occur after 1980, when most significant trends are in a positive direction. There are relatively few significant trends during 1966-1979, and these trends are nearly equally divided between increases and decreases.
The continental indices show no temporal patterns in trends, a result of the low numbers of vultures counted along most BBS routes (Survey-wide Annual Indices). However, temporal patterns are more apparent in statewide populations. For example, increases after 1980 occur in a number of states such as Kansas and Ohio (Kansas Annual Indices). (Ohio Annual Indices). Where these vultures have been decreasing, such as Florida, their populations have experienced rather consistent declines throughout the survey period (Florida Annual Indices).
Turkey Vultures expanded northward in portions of southern Canada and the northeastern United States during the twentieth century (Bagg and Parker 1951, 1953; Cadman et al. 1987). This range expansion is also apparent in the BBS data. Other analyses of Turkey Vulture trends concluded that their populations are reasonably stable, although some local increases and decreases have been reported (Coleman and Fraser 1989, 1990; Mossman 1991; Pattee and Wilbur 1987). The BBS trends are generally positive after 1980, indicating that some populations are increasing during recent years. Causes for the range expansion and recent increases are unknown, but may include more favorable climate and increased food supply (Coleman and Fraser 1989). Additionally, vulture reproductive success may have been reduced by pesticide contamination (Kiff et al. 1983), and recent increases may reflect recovery from pesticide-induced declines during the 1950s and 1960s.
Bagg, A.M., and H.M. Parker. 1951. The Turkey Vulture in New
England and eastern Canada up to 1950. Auk 68:315-333.
Bagg, A.M., and H.M. Parker. 1953. Further information on the
Turkey Vulture (Cathartes aura) in New England and eastern
Canada. Auk 70:490-491.
Cadman, M.D., P.F.J. Eagles, and F.M. Helleiner, eds. 1987. Atlas
of the breeding birds of Ontario. Univ. Waterloo Press,
Waterloo, Ontario. 617pp.
Coleman, J.S., and J.D. Fraser. 1989. Black and Turkey vultures.
Pp. 15-21 in B.G. Pendleton, ed. Proceedings of the northeast
raptor management symposium and workshop. Natl. Wildl. Fed.
Scien. Tech. Ser. No. 13.
Coleman, J.S., and J.D. Fraser. 1990. Black and Turkey vultures.
Pp. 78-88 in B.G. Pendleton, ed. Proceedings of the southeast
raptor management symposium and workshop. Natl. Wildl. Fed.
Scien. Tech. Ser. No. 14.
Kiff, L.F., D.B. Peakall, M.L. Morrison, and S.R. Wilbur. 1983.
Eggshell thickness and DDE residue levels in vulture eggs.
Pp. 440-458 in S.R. Wilbur and J.A. Jackson, eds. Vulture
biology and management. Univ. California Press, Berkeley, CA.
Patee, O.H., and S.R. Wilbur. 1987. Turkey Vulture and California
Condor. Pp. 61-65 in B.G. Pendleton, ed. Proceedings of the
western raptor management symposium and workshop. Natl.
Wildl. Fed. Scien. Tech. Ser. No. 12.