| Publication Type: | Book Chapter |
| Year of Publication: | 2006 |
| Authors: | Clark, AB, Robinson, DA, McGowan, KJ |
| Book Title: | Ornithological Monographs No. 60Ornithological Monographs No. 60 |
| Series Title: | Ornithological Monographs |
| Volume: | No. 60 |
| Publisher: | American Ornithologists' Union |
| ISBN Number: | 0-943610-69-9 |
| Keywords: | Corvidae, Corvus, Corvus brachyrhynchos, Corvus corone |
| Abstract: | Abstract In a marked population of cooperatively breeding American Crows (Corvus brachyrhynchos) studied for 17 years in Ithaca, New York, the effect of West Nile virus (WNV) was local but dramatic during 2002-2003. In two consecutive years, >35% of American Crows in well-known families died or disappeared between late July and early October, the primary WNV season in the state of New York. West Nile virus was confirmed as the cause of death in nearly all tested birds. Risk of mortality did not differ with age, sex, or breeding status of birds, but adult mortality increased 10-fold and juvenile mortality 3-fold above normal levels for this population as measured during 1990-1998. Four times as many breeders died during August-October as disappeared during an entire year between 1995 and 1998. Social effects were assessed by comparing changes from 2001, before WNV was present, through 2005, two years after the high mortality of 2003. Although no significant decreases in group size, frequency of helping, average age of breeders, or territory density were observed after two years of WNV presence, the direction of most changes suggested that repeated years of WNV presence would likely affect social structure. Unusual social events, including female territory-budding and adoption of and subsequent helping by unrelated juveniles, were documented in 2004-2005. American Crows filled territory vacancies very slowly. The presence of breeding-age auxiliaries on territories may counter rapid social change and breeding declines in cooperatively breeding crow populations, but repeated years of such high mortality are likely to cause both significant social disruption and severe population declines among American Crows.Abstract In a marked population of cooperatively breeding American Crows (Corvus brachyrhynchos) studied for 17 years in Ithaca, New York, the effect of West Nile virus (WNV) was local but dramatic during 2002-2003. In two consecutive years, >35% of American Crows in well-known families died or disappeared between late July and early October, the primary WNV season in the state of New York. West Nile virus was confirmed as the cause of death in nearly all tested birds. Risk of mortality did not differ with age, sex, or breeding status of birds, but adult mortality increased 10-fold and juvenile mortality 3-fold above normal levels for this population as measured during 1990-1998. Four times as many breeders died during August-October as disappeared during an entire year between 1995 and 1998. Social effects were assessed by comparing changes from 2001, before WNV was present, through 2005, two years after the high mortality of 2003. Although no significant decreases in group size, frequency of helping, average age of breeders, or territory density were observed after two years of WNV presence, the direction of most changes suggested that repeated years of WNV presence would likely affect social structure. Unusual social events, including female territory-budding and adoption of and subsequent helping by unrelated juveniles, were documented in 2004-2005. American Crows filled territory vacancies very slowly. The presence of breeding-age auxiliaries on territories may counter rapid social change and breeding declines in cooperatively breeding crow populations, but repeated years of such high mortality are likely to cause both significant social disruption and severe population declines among American Crows. |
| URL: | http://dx.doi.org/10.1642/0078-6594(2006)60[65:EOWNVM]2.0.CO;2 |
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