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Simultaneous decline in Steppe Eagle (Aquila nipalensis) populations and Levant Sparrowhawk (Accipiter brevipes) reproductive success: coincidence or a hernobyl legacy?
Abstract
Visual migration surveys,
especially at bottlenecks, can be a vital tool to evaluate population
fluctuations in environmentally sensitive species. Raptors are considered to be
important bioindicators that can help identify environmental catastrophes. Substantial
proportions of the global population of Steppe Eagles (Aquila nipalensis)
and Levant Sparrowhawk (Accipiter brevipes) concentrate at Eilat,
Israel, during the spring and autumn migrations, but counts from seven autumn
and seven spring migration surveys indicate a constant decline in Steppe Eagle
numbers. Further, the number of juveniles observed in these counts dropped
steadily from 30% in the early 1980s, to 1.4% in 2000. The numbers observed at
Eilat are well below the range of the numerical fluctuations observed in
previous surveys. In Levant Sparrowhawks, no decline in total numbers is
evident, but a significant change in the adult to juvenile age ratio was noted
between the population trapped in the 1980s and that sampled in the late 1990s.
The cumulative evidence of the decrease in the total numbers of Steppe Eagles,
the decreasing proportion of subadults within the population, and the decrease
in adult:young ratio in the Levant Sparrowhawk population trapped leads us to
suggest that the Chernobyl accident on 26 April 1986 may have negatively
affected wildlife populations, not only to the west with the spread of the
radio-active plume, but farther east than previously assumed.
Ostrich 2004, 75(1&2): 20–24
especially at bottlenecks, can be a vital tool to evaluate population
fluctuations in environmentally sensitive species. Raptors are considered to be
important bioindicators that can help identify environmental catastrophes. Substantial
proportions of the global population of Steppe Eagles (Aquila nipalensis)
and Levant Sparrowhawk (Accipiter brevipes) concentrate at Eilat,
Israel, during the spring and autumn migrations, but counts from seven autumn
and seven spring migration surveys indicate a constant decline in Steppe Eagle
numbers. Further, the number of juveniles observed in these counts dropped
steadily from 30% in the early 1980s, to 1.4% in 2000. The numbers observed at
Eilat are well below the range of the numerical fluctuations observed in
previous surveys. In Levant Sparrowhawks, no decline in total numbers is
evident, but a significant change in the adult to juvenile age ratio was noted
between the population trapped in the 1980s and that sampled in the late 1990s.
The cumulative evidence of the decrease in the total numbers of Steppe Eagles,
the decreasing proportion of subadults within the population, and the decrease
in adult:young ratio in the Levant Sparrowhawk population trapped leads us to
suggest that the Chernobyl accident on 26 April 1986 may have negatively
affected wildlife populations, not only to the west with the spread of the
radio-active plume, but farther east than previously assumed.
Ostrich 2004, 75(1&2): 20–24
