April 2007


 Caspian Terns occur fairly regularly in Southwest Ohio, but generally only in onesies and twosies. Larry Gara called me yesterday afternoon (18 Apr 07) to tell me that he had found ten on the beach at Cowan Lake State Park. (See the post immediately following for a description and an interactive map.) I went out to the lake immediately and found seven still present. I was able to get a photo with five Caspian Terns in the same frame.

Note the size relationship with the Ring-billed Gulls.

In stalking the birds to get better pictures of the birds, I managed to spook them, but my ineptitude resulted in a couple of nice flight pictures.

Note the usual pattern of very light upper surfaces of the wing with the very dark lower surfaces.  This can be a good mark in distinguishing Caspians from Royals in flight, should we ever be so lucky as to be in that position here in Ohio.

Larry reports that none were found this morning.

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.

In the April edition of the Ornithological Newsletter (organ of the Ornithological Societies of North America), there is an announcement of a new service provided by USGS, the Raptor Information Service (RIS). The RIS contains citations on over 38,000 items concerning raptors, including “gray literature” reports and unpublished government reports. It is available to all comers here

I gave it a test drive this morning and the results were mixed. I entered “merlin ohio” as keywords and the system quickly found five items that matched those criteria, one of them going back to 1909. I picked up a copy of the winter 2006 issue of the Journal of Field Ornithology that happened to be lying around the lab, and entered “white-throated hawk Argentina” to see if the system would return an article in that journal. It did so in about 10 seconds, along with seven other articles on White-throated Hawks in Argentina. This indicates that the database is certainly extensive. I haven’t tried it on any Old World species, though.

That’s the good news. The bad news is that the citation is all you get. There is no information on where you might by able to find the referenced article, even when the journal is available online. Ideally, a mouse click should take you to the article. The inclusion of gray literature is laudable, but the whole difficulty with gray literature is that it is almost impossible to find. The people who put it into the database had to have found it somewhere; it would have been really nice to have included that information in the database.

(White-throated Hawk by Christian Gonzalez Bulo) 

This is not my first attempt at a blog, but I sincerely hope it will be the last.  The idea is to share some of my thoughts (and, hopefully, insights) on the natural world.  Some of these thoughts will be ruminations on the past, which encompasses among other things almost fifty years of more or less serious birdwatching, a broad range of scientific endeavors in several fields, and some current research.  I am interested to see if this medium can allow an old dog to execute this new trick without straining its mind to learn yet another computer language.  My cranial hard disk is full and badly in need of defragging.  We’ll see.  I may have to become an HTML hacker after all.