Late last week a comment of a Facebook post in a Rare Bird Alert group caught my eye; the post itself highlighted a Fork-tailed Flycatcher that had been found in Atlantic County, New Jersey and the comment was quite simple: “what the heck is going on with tyrannids this year?” I thought about it for a moment and found myself emphatically agreeing, what is going on with tyrannids this year?
Take a step back: across much of the US, from the Canadian shore of the Great Lakes east through New England there are two main stretches of time when tyrannids (and other flycatchers) from the south and west are expected to surge out of their normal range. One of them falls in late spring into early summer, the stretch we are in now; the other is in the fall and is a bit of a wider window. Depending on where exactly you are latitudinally and in relation to the coast, it could be anywhere from mid-to-late August through the end of November. These somewhat predictable movements are highlighted by the spectacular-and-showstopping Scissor-tailed and Fork-tailed flycatchers. However other species are often part of the ensemble; three of the yellow-bellied kingbirds—Western, Tropical, and Couch’s kingbirds are also often involved and Gray Kingbirds also contribute some records.
There have certainly been many sightings this year; in addition to the aforementioned Fork-tailed Flycatcher, there have been several out-of-range Scissor-tailed Flycatchers (around twelve according to eBird), a handful of Tropical Kingbirds, and a handful-and-a-half of Western Kingbirds in odd places (around 10, again going off of eBird data). The interesting thing is that when looking back with a broad and long historical lens, this does indeed seem to be a lot of birds. However, when compared to the past two years, it is roughly on par with what we have seen recently. Just last year, for instance, Fork-tailed Flycatchers turned up twice out of range and in 2017 there were a startling five notable sightings in eBird. By comparison, this years flight of one has been fair-to-poor. Compared to the prior two years, the other tyrannid suspects show a similar pattern. Scissor-tailed Flycatcher numbers are about average, or maybe just a tad high; the distribution is a bit more coastal than in other years, but again, the difference isn’t terribly dramatic. The kingbirds are holding more-or-less even, as well.
These tyrannids pose an interesting conundrum for students of avian status and distribution; while changes in vagrancy of southern and western birds is often credited to changes in the breeding distributions of those birds, the case is a bit less clear-cut with tyrannids. There has certainly been some shift in the range of a few species, but it hasn’t been widely connected to a change in patterns of dispersal—at least not yet. One question, and one that might be very answerable but which I have not delved into, is whether the vagrancy patterns are changing in the fall as well, or whether it is primarily the spring/summer window being altered.
As June wraps up and especially as fall migration picks up in late July and August, keep an eye out for any wandering tyrannid flycatchers. With these observations fresh in our minds, perhaps we can begin to piece together why our southern and western tyrannids are dispersing north and east with such frequency.