Tuesday, December 19, 2006

More on Waterfowl

After some more thought on last night's post, and the relative lack of waterfowl on Sunday's count, I decided to check into the results from past Christmas Bird Counts from Lower Kent County. The historical results section of Audubon's CBC website provides an easy way to do this. I generated a few graphs of species that seemed to be out of line with previous counts. The numbers are interesting.

For starters, here is the tundra swan graph.

This one charts scaup and canvasbacks.

This one shows buffleheads.

This shows long-tailed ducks (known previously as oldsquaw).

This one shows black ducks.

The breaks in the tables may indicate years in which counting was canceled due to bad weather. Eastern Neck NWR is the main spot for waterfowl within the count circle. The refuge is only accessible by a bridge, and when weather conditions are hazardous, the bridge is closed. I chose the 59th CBC as a starting point because it appears to be the earliest Lower Kent CBC in the database.

A few things are apparent in these graphs. One is that tundra swans really have declined over the past ten or fifteen years, at least in the upper Chesapeake Bay area. During the eighties, tundra swans seemed to have a base winter population around 5,000 to 7,000; that number has shrunk to about 1,000. Perhaps this is due to mute swan competition or worsening conditions in the bay's underwater vegetation.

The second is that the sample species I picked out have 2006 numbers largely in line with those of the past decade. Numbers fluctuate from one year to the next, but seem to be relatively stable. Canvasbacks are probably the most out of line with recent years, but there does appear to be some precedent for this.

My third observation is that each of these species have had major spikes in recent years: tundra swans and black ducks in the early and mid-eighties, scaup and long-tailed ducks after 2000, buffleheads and canvasbacks in the nineties. The peak years for tundra swans and scaup must have been particularly spectacular. Perhaps some of the impression that 2006 has been a poor year for waterfowl is due to local memories of these peak years.