Thursday, April 19, 2007

Re: Forster's Tern dates in Ohio

I'm grateful to Bill Whan and Vic Fazio for going to so much effort to confirm that I was correct in my comments about the timing of Forster's Tern arrival. To recap: they pointed out that there are a few records at the end of March (notably early) and more for the first week of April (on the early side), so that multiples in northwest Ohio on April 12th would be, as I wrote earlier, right on time.

As birders, we often have a tendency to focus on early and late records rather than on the normal timing of migration. These extreme records are more fun, but from a biological standpoint they're not as important. As an example of the "fun" aspect: last fall, as I reported on this listserve, I found a Yellow-billed Cuckoo at Metzger Marsh on October 31 (not Nov. 1, as reported in the Ohio Cardinal). That cuckoo was a very late bird. It didn't set a record -- the species has been found in Ohio in November a number of times -- but these occurrences notwithstanding, the important thing to note is that the vast majority of Yellow-billed Cuckoos have departed for the south before the middle of October. We know that because a lot of observers have gathered a lot of information over multiple years. This points up the great value of keeping notes and recording the numbers of individuals that we find each day, not just the extreme dates for each species, to try to get a picture of peak numbers and the actual span of the typical migration season for each bird.

When we talk about timing of migration, we have to avoid falling into the trap of making generalizations about the state of Ohio as a whole. There are substantial differences in timing in different regions of the state. In spring, some migrants have returned to southern Ohio in numbers before there's any hint of them in the northern tier of counties. But even at the
same latitudes, there can be differences. In looking at two local publications, Birds of the Cleveland Region (by Larry Rosche) and Birds of the Toledo Area (by Matt Anderson et al.), I frequently find that they give slightly different timing for the migration of a given species. Part of that may be coincidence, with the data skewed by a few odd records, but part of it may reflect genuine differences between northwestern and northeastern Ohio. And in an era of changing climate, the timing of migration may change in unpredictable ways in the future. It's always worthwhile for birders to keep detailed records on the occurrences of birds in their own area, and not just assume that the important stuff already has been determined elsewhere.

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