Demography and population trends of Whooping Cranes
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Previous studies of Whooping Crane demography used estimates of fecundity rates based on females in captivity, and breeding success was estimated based on either the number of unbanded pairs nesting or the number arriving in wintering areas with chicks. We analyzed demographic data from 12 cohorts of banded Whooping Cranes (Grus americana) from the Aransas National Wildlife Refuge/Wood Buffalo National Park (ANWR/WBNP) population that had not been compiled previously into a single data base and had not been included in previous population analyses. We estimated age-specific survival and natality, parameterized an age-structured density-dependent model, and projected population sizes assuming two different estimates of wintering ground carrying capacity. Sixty-seven of 132 birds banded between 1977 and 1988 formed nesting pairs, females first produced hatchlings when 3 to 7 yrs old, and the annual proportion of mature females that reproduced successfully ranged from 0.566 to 0.606. Population projections indicate that the down-listing criterion of reaching a population size of 1000 individuals might be attained considerably later than the target year (2035) indicated in the Whooping Crane recovery plan. Even assuming that all suitable habitat within a ~100-km radius of their current winter range could be occupied, projections suggest that population size may be ~700 in 2035, and might not reach 1000 individuals until the mid-2060s. Based on their territorial behavior on the wintering grounds, long generation time and faithfulness to their migratory route, we suspect that the population growth rate may decrease markedly in the near future and the ANWR/WBNP population may remain below the target down-listing size of 1000 individuals. 2012 The Authors. Journal of Field Ornithology 2012 Association of Field Ornithologists.
