We don’t normally post more than once a day on the blog but this just came through on one of the listserves from my friend Bill Evans from Ithaca, NY, about what may be a massive southward nocturnal migration of Boreal birds that will take place in southern Canada and the eastern U.S. over the next couple of nights. Any of you “birdheads” from the area may want to get out and listen tonight and the next few nights and get out during the day to see if the birds are dripping from every bush and tree!
Here's what Bill sent:
Greetings all,
We are in one of those situations in the northeast where connoisseurs of nocturnal bird migration are in an especially heightened physiological state. I know of no specific word for it, but it is when the anticipated flight is looking so huge that it affects your adrenal function days in advance. In tonight's case it is not simply the next cold front passage, but potentially a movement of relatively large & perhaps historic proportions.
Here in deep interior northeastern US we haven't had a significant nocturnal bird movement since the night of August 26-27. That's 12 nights without a major flight. I looked back in my records of the last 20 years and there is no similar event. The longest comparable string of nights around this time of year without a significant nocturnal migration event is all the way back in 1992 when hurricane Andrew made landfall in Louisana and stalled out in the mid-Atlantic states -- there was an associated period of about 10 days (Aug 20-30) of largely southerly winds across much of the northeast. A notable dynamic that season was a temporal delay in the Veery flight while the Swainson's Thrush flight came through right on time. This translated into a record late high ratio of nearly 4-to-1 Veery to Swainson's Thrush flight calls on the night of Sep 7-8, 1992 documented across a broad front at acoustic stations near Watkins Glen, NY and another in Alfred, NY. Typically the bulk of the Veery flight has passed south by then and the flight call ratio for these species in central NY is 1-to-1 or lower. For example in fall 1991 at the same two acoustic stations, the ratio was already down to 2-to-1 in the big flight the night of Sep 4-5 that year.
The present delay in migration across the northeast is occurring later in the season than the 1992 event, so the species effects will be different. I would guess that half the Veerys are still north of central NY and that they will be a regular caller across NY in tonights flight amidst the first substantial numbers of Swainson's. I wouldn't be surprised if Veerys are more abundant than Swainson's across upstate NY tonight and perhaps also in Thursday night's flight. Certainly by the next cold front passage Swainson's will be the dominant thrush call.
Going back to Dave Nicosia's recent posts, I agree that northeast winds are relatively rare in the interior northeastern US. That wind direction would seemingly be ideal for the dominant fall flight direction of passerines in the interior northeast based on recent radar studies. Clearly these birds have to traverse this region with less than ideal winds. Even a wind out of the north would impart some crosswind on this southwest-bound movement. But the abundance of SW winds we've had recently are direct headwinds for this flight. For a species like Wilson's Warbler that wants to fly toward the southwest in fall across the interior northeast, I speculate that their flight has been delayed this year and that tonight (and perhaps even more so tomorrow night) may reveal relatively large numbers of their flight calls. The graph below is historic flight call data from Alfred, NY showing the proportion of Wilson's Warbler flight calls in the mix of all warbler and sparrow calls (Tseep software flight call detections).
Click to enlarge
Incidentally, the most Wilson's Warbler flight calls that were documented in any of the nights noted in the graph above was 31 in nine hours of nocturnal flight call monitoring on Sep 4-5, 1992 (post hurricane Andrew). That figure considers calls within one minute of one another as a single call event and a theoretical individual passing (there were 33 total WIWA calls that night). Ted Floyd noted yesterday that he and his son heard WIWA flight calls at a rate of 80/hr a few nights ago in Lafayette, CO. Such a rate would be unprecedented in the east, though the timing of the flight appears to be parallel. The good news for the typically WIWA-starved folks in southern New Jersey is that if there were ever a weather situation that would amplify your chances of recording WIWA night flight calls, this is it and the next two nights should deliver.
In conclusion, I have to reiterate what Dave Nicosia said about the uncertainties in predicting weather -- the same goes for bird migration. Everything I know suggests to me that tonight (and tomorrow night) look to be huge nocturnal flights across northeastern US. The spring is set as tight as for any early September night I've seen in the past 20 years. Theoretically there is an uncommonly large number of birds ready to fly, and we are in the time when peak numbers of neotropical migrants typically move across the region. Given that the numbers of night migrants in eastern North America are undoubtedly getting smaller annually due to increasing numbers of man-made fatality sources (windows, towers, etc) and habitat loss, this may well be the largest early September nocturnal migration event we have the opportunity to experience in the remainder of our lives. If you live in northeastern US or thereabouts, you might want to consider taking the next few nights and days off.
Turn on, tune in, bird out,
Bill E
p.s. for those within 100 miles south of Lake Ontario (e.g., Ithaca and west), it is likely that the numbers of birds ready to fly south of the Lake have leaked southbound over the past week and a half. We may have to wait for the wave of birds crossing the Lake (e.g., after 11PM for Ithaca area) to experience any kind of substantial migration magnitude via auditory or other.
