Crow Trends in West Virginia
In a recent post about corvids, John of A DC Birding Blog commented about the susceptibility of American Crows to West Nile Virus (WNV). Using information from the Christmas Bird Count, he demonstrated a decline of about 50 percent in early-winter abundance in the Mid-Atlantic States of Delaware, Maryland, and Virginia, from about 14 birds/party-hour in 1992 to about 7 birds/party-hour in 2005.
In striking contrast, early-winter populations of American Crows in West Virginia (as indicated by the number of birds counted/party-hour) have increased dramatically over the same time period, especially since 2002, and an apparent 5-fold increase since the mid-1990s (left-click on the graph below to enlarge). Also, crows appear to be relatively more abundant in West Virgina by an order of magnitude.
The same general trend is also evident when we graph the actual number of birds counted (below).
The reason(s) for the dramatic differences in population trends between the two adjacent regions is not obvious, but would certainly seem to merit additional investigation. Are the birds wintering in these regions from different breeding grounds in which susceptibility to WNV differs? Have crows shifted their wintering grounds westward for reasons unrelated to WNV? Is WNV less prevalent in West Virginia than in the Mid-Atlantic States? As is so often the case, this comparison raises many more questions than answers.
In striking contrast, early-winter populations of American Crows in West Virginia (as indicated by the number of birds counted/party-hour) have increased dramatically over the same time period, especially since 2002, and an apparent 5-fold increase since the mid-1990s (left-click on the graph below to enlarge). Also, crows appear to be relatively more abundant in West Virgina by an order of magnitude.
The same general trend is also evident when we graph the actual number of birds counted (below).
The reason(s) for the dramatic differences in population trends between the two adjacent regions is not obvious, but would certainly seem to merit additional investigation. Are the birds wintering in these regions from different breeding grounds in which susceptibility to WNV differs? Have crows shifted their wintering grounds westward for reasons unrelated to WNV? Is WNV less prevalent in West Virginia than in the Mid-Atlantic States? As is so often the case, this comparison raises many more questions than answers.
Labels: crows
posted by John L. Trapp at
11/02/2006 02:35:00 PM
5 Comments
