Ohio has the misfortune of sitting between two major flyways. Despite this, forty species of waterfowl (Anseriformes) are known to occur in Ohio and large numbers of ducks and geese regularly pile up along the state’s 150 miles of Lake Erie shoreline. However, large flights of waterfowl in the interior of the state are much less prevalent. In an attempt to shed some light on waterfowl migration patterns in the interior, I have embarked on a program of systematically counting the ducks and geese using a large lake in southwestern Ohio. This article reports the result of 2005, the first year of the study.
Cowan Lake is a 700 acre lake about seven miles southwest of Wilmington in Clinton County. The lake was formed in 1950 by damming Cowan Creek. It is the centerpiece of Cowan Lake State Park. A full description is here. The DeLorme map reference is p.77 D5. An interactive, annotated map is here.
This season (winter 2005) I tried with some success to count the waterfowl on Cowan Lake every day that weather permitted. Cowan Lake is small enough that all the birds on the lake can be counted in six stops along the south shore, accessible from OH 350. Counting usually took about an hour and I tried to time my visits for the last hour before sunset. I included grebes and cormorants in the counts because they are not Anseriformes, they do seem to follow the same migration patterns. The waterfowl numbers given below are a summary of those counts.
Cowan’s contribution to waterfowl migration was limited by the constraints of open water conditions during the early weeks and by human use when the weather warmed up. Before 15 Feb there was too much ice for the counts to be representative. On the other hand, waterfowl concentrations are very sensitive to human use of the lake. Waterfowl numbers nose-dived with even three or four boats on the lake. After 5 Apr, human traffic on the lake precluded use by more than a handful of waterfowl, and most of those were the Canada Geese and Mallards that breed there.
Aggregating the numbers of waterfowl gives a partial picture of the main thrust of waterfowl migration. In the chart above, aggregated numbers are plotted on against a linear scale. Plotting the data against a semilog scale, as below, gives a better picture of usage. From this chart it is easy to see that during the period there were usually several hundred waterfowl on the lake on days that were conducive to taking data. Note that a zero on this chart indicates that no count was made on that date. From these charts, it is evident that two big pushes occurred, one between 8 Mar and 16 Mar and one between 23 Mar and 31 Mar.
It is also interesting to plot the number of species observed each day. From the chart below, I conclude that the on days where there are a lot of birds, there are also a lot of species. Apparently, a good migration day is good for most species. However, in general, the number of species is a somewhat less variable than the number of individuals. This is partly because some species tend to migrate a little earlier or a little later than others. No good trends emerge from this one year’s data, but as I replicate this study in future years, this picture should become clearer.
13 Apr 07 at 0021
is the third graph up there by mistake? it looks the same as the second graph. did you mean to graph no. of species?
it would be interesting to have a reference number of waterfowl species known to migrate through Ohio to judge what “a lot of species” is at Cowan vs. the state as a whole.
13 Apr 07 at 0808
Thanks for the catch, Scribbler. It is great to have the free services of a great copywriter. Note changes.
16 Apr 07 at 2028
Hello VN, Aphriza suggested I come to you with this question about migrating shorebirds: today at Wood Neck Beach in Woods Hole, I spied a flock of what I have tentatively identified as mostly sanderlings with a few dunlins. Do you know when these species molt into breeding plumage? Both birds looked like they were still in winter plumage. The sanderlings had pale throats and breasts, and the dunlins had pale bellies.
16 Apr 07 at 2245
Welcome back to the USA, Moley. You are almost certainly correct in your identifications, Sanderling and Dunlin being probably the two most numerous wintering shorebirds on the eastern seaboard. They should begin molting in three weeks or so and you should see at least a couple in full breeding plumage before they depart for the far north, especially the Dunlin. Breeding plumaged Sanderlings are harder to come by, as they tend to molt on the move.
The Dunlin will pretty much all go north, but you will probably continue to see sanderlings around all summer long. These are first year birds who are not yet sexually mature. They will continue to look like first winter birds.
Keep prowling the beaches. The shorebird migration is just cranking up.
DISCLAIMER: This is an extrapolation of my experience along the coasts of the states of the Old Confederacy. Your results may differ.