Double-crested Cormorant (Phalacrocorax auritus) populations have rapidly increased in the Great Lakes and in wintering areas in the southeast USA since the mid-1970s, resulting in conflicts with humans. To increase understanding of their population biology, band-recovery models were used to estimate temporal trends in hatch year (HY), second year (SY), and after second year (ASY) survival of cormorants banded in the Great Lakes from 1979 to 2006. SY and ASY annual survival varied among years with no apparent trend. HY annual survival exhibited a negative log-linear trend. Lack of clear temporal patterns in SY and ASY survival suggested that increases in cormorant abundance subsequent to 1979 did not impact survival in these age-classes, whereas HY annual survival declined as abundance increased. In addition, issuance of depredation orders in 1998 and 2003 appeared to have a small negative effect on HY survival, but no clear effect on SY and ASY annual survival. The percentage of band returns reported from cormorant control operations generally increased over time, and greatly during the depredation orders. Mean ± SE annual survival from 1979 to 2006 was 0.446 ± 0.022 for HY, 0.835 ± 0.026 for SY, and 0.884 ± 0.020 for ASY individuals. Although increases in cormorant abundance did not appear to be related to increases in annual survival, the relatively high average annual survival rate of ASY cormorants may have been responsible for rapid population growth in the 1980s and 1990s in the Great Lakes.
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Vol. 35 • No. sp1