Hi, Bryan et al. Bryan, thanks for the great response. > In these maps, I see an area of weak frontal passage or at > the least frontgenesis (front "birthing" area) just south of Pittsburgh > running ese to wnw. The winds behind the frontal zone are directly > from the north or slightly west of north. 12Z is just before sun-up > that time of year, so about the time I would expect Ted was out > huckin' papers. With the frontal passage overnight, I would expect > the bird numbers to be piled up behind the front in the preferable > wind field. I would suspect that the morning was cloudy with maybe > a light drizzle based on the frontogenesis. Based on the sounding > from that morning, there was possibly some fog or very low clouds > that morning (Sounding <http://tinyurl.com/2fxclby> ). I would expect that this made the conditions > even better, pushing some of the birds lower. It seems like a perfect
> day to me for a nice night flight... Hold that thought for just a moment. You'll see why... > but wait... > > Ted's dates were Sept 21-22, 1985, so we have been looking at > the morning before the flight occurred not the night of it. > > [...] > > These winds are not preferable for what one might want to see for an > NFC kind of night. Winds from the south or SSW. I am hoping that > the answer to this is that Ted has the wrong dates recorded, but that is > for him to decide. I checked again, and the date is correct. The big flight was in the 5am hour of Sunday, September 22nd, 1985. (Nautical dawn in Pittsburgh doesn't start till 6:08 a.m. on that date, so this was a full-on night flight.) Anyhow, this brings me to something I've been pondering a fair bit the past few months: Maybe active nocturnal migration is a lot "leakier" than we imagine. Let me explain. Although there is undeniably a general relationship between big night flights and big weather events (e.g., the recent "monumental nocturnal migration," well predicted, I hasten to point out, by Bill Evans), I doubt it's a perfect relationship. I mean, nothing in ecology is perfect; everything is messy; if you're statistically inclined, r-squared is always less than 1.0. Sure, we tend to remember the textbook-perfect events: great hawk flights when the winds are "perfect," great shorebird fallouts in miserable weather, "monumental" night flights of passerines on the heels of favorable conditions for flying, etc. But what about all the times when we go out in "great" conditions only to find few if any "good" birds? Conversely, what about all the times we are surprised by good birding, despite seemingly poor conditions? A little while ago, I posted to NFC-L about a non-existent night flight in Colorado that was followed by a very heavy (practically "monumental") dawn flight. Details here: http://tinyurl.com/2eyuena. I hypothesized that the birds "leaked out" at dawn, as soon as they could see enough to migrate close to ground level, below the nasty south winds. What I did NOT mention in my post--because I didn't know it at the time--is that Mark Peterson observed the exact same phenomenon about 150 miles to my southeast, the same day. He had been out overnight and heard nothing. Then he observed a very heavy dawn flight. By "dawn," I mean that it got underway during "dawn"--both of us started to detect this movement toward the end of "nautical dawn," and we observed that it continued well past sunrise. I used to think--and I still think it's the "conventional wisdom"--that good night flights are precipitated by events at or before sunset the night before. By why is that necessary? (And if it IS necessary, then you need to look at conditions at sunset at the source--hundreds of miles away in the case of strong fliers like thrushes. Aside to Bryan: What were conditions like at sunset the night before, a few hundred miles nw. of Pittsburgh?) Recently, we've learned that nocturnal migrants do strange things few of us ever anticipated. For example, some of them don't sleep--at all. Swainson's Thrushes and White-crowned Sparrows undergo dramatic physiological changes at the onset of migration--changes that basically enable them to forego sleep, day and night, during spring and fall migration. Even wilder is that sustained flight is paradoxically *less* metabologically demanding for a migrating Gray-cheeked Thrush than is hanging around at daytime stopovers (when the birds are relatively cold, and therefore losing energy). An emerging paradigm is that birds have a lot more leeway--a lot more flexibility, or "plasticity"--with regard to migratory strategies than we'd ever imagined. (Read the Euro literature on migratory Blackcaps! It's unreal.) Back to the morning of Sept. 22, 1985. Could it be something of a wild goose chase to analyze conditions at sunset on Sept. 21st a few hundred miles north of Pittsburgh? Instead, might the birds have responsed to changing conditions, on location, as they happened? They're not sleeping, anyhow! So why not just get up and go? That would be consistent with the data provided by Bryan. The bottom line is, There was an amazing movement pre-dawn that morning. That phenomenon doesn't seem to fit the classic model, as Bryan persuasively points out. But maybe it's consistent with the emerging idea that birds adapt to local conditions as they are happening? ------------------------------- Ted Floyd Editor, Birding Follow Birding magazine on Twitter: http://twitter.com/BirdingMagazine <http://twitter.com/BirdingMagazine> ------------------------------- -- NFC-L List Info: http://www.NortheastBirding.com/NFC_WELCOME http://www.NortheastBirding.com/NFC_RULES ARCHIVES: 1) http://www.mail-archive.com/nfc-l@cornell.edu/maillist.html 2) http://birdingonthe.net/mailinglists/NFCL.html 3) http://www.surfbirds.com/birdingmail/Group/NFC-L Please submit your observations to eBird: http://ebird.org/content/ebird/ --
