American Birding Podcast



Happening NOW: Western Tanagers Invade the Midwest

There are some birds we think of as being inherently prone to irruptive behavior. The winter finches are a famous example, as are Snowy Owls, Rough-legged Hawks, and a handful of other, mostly northern species. Western Tanagers are not one of these species. While prone to vagrancy, the patterns of vagrancy they undergo tend to be fairly stable and predictable from year to year. So far this year, that has been thrown out the window.

In a typical May-June Period, eBird data suggests that the Midwest and eastern Great Plains see just below a dozen records a year. In some years that can be as low as 8 or so (as in 2016) while in others it may approach 12 (as in 2017). These records tend to be widely scattered: A few are usually on the eastern edge of the plains states, in the Dakotas, and northern Iowa, with often at least one in western New York or Pennsylvania or southern Ontario, and the others falling somewhere in between.

A review of the same eBird data in the current year shows something remarkable. There are at least 20 reports in eBird from this region; so far none have made it as far east as Ontario, Pennsylvania, or New York and records from the Dakotas and Nebraska are scarce, however Wisconsin alone has put nearly a dozen and Minnesota, Iowa, Illinois, and Michigan have all seen multiple birds.

In many of our posts we suggest theories to our readers about why we might be seeing these trends. In this case, I openly and readily admit that I don’t have a great explanation. It seems clear that something must be pushing birds out from the center of their breeding range and causing them to fan out into the Midwest. However, many questions remain. Why has the area of this dispersal been fairly limited? As stated earlier, in many years the eastern Great Lakes and eastern Plains states see some records and this year that has largely not been the case. And just how many birds are involved? Many of these birds have not been particularly long-staying so are just a couple of birds accounting for a large number of records as the roam? We may not be able to answer any of these right now; look to future issues of North American Birds for analysis, but in the meantime, get out and enjoy lovely western wanderers!