Hi all, Good discussion. I'll chime in further later on about the winds and migration - much to say about that. . .but on a more proximal note, an interesting assortment of calls from vocal migrants moving tonight in NYC including Hermit Thrush (4), Brown Creeper (2), Red-breasted Nuthatch (2), White-throated Sparrow (8), and Song Sparrow (5) among others. Not huge numbers (44 calls in the last 1.5 hours), but decent.
Best, Andrew On Wed, Mar 17, 2010 at 10:05 PM, David La Puma <woodcree...@gmail.com> wrote: > Winds are indeed interesting. Several questions arise: > > Do birds use surface winds to "decide" whether to go or not, or do they use > a combination of surface variables such as barometric pressure, rH, etc., > and/or how much do they "test the atmosphere" (we do know that this occurs, > where birds will take off, and then facing opposing winds soon afterward, > will return to the surface) given a range of surface wind conditions? > > I'm including surface winds in this preliminary model (actually, I'm using > wind vectors, to make linear an otherwise circular variable, which takes > into account both wind direction and speed to produce a variable that ranges > from head-wind to tail-wind). The initial model does show this as being > quite important in predicting migration intensity (high tail-wind vectors > appear to be good predictors of high density migration events). I plan to > include wind vectors aloft as well, as a separate variable, and yes, I > suspect they will be important predictors. > > Most nocturnal migration occurs within the first few thousand feet, so in > the case of tonight, it looks like birds are moving under SSW winds at the > surface to W winds up to about 3000 feet ASL (according to the Wallops > Island radiosonde). These winds are averaging 10kts, which is a nice tail > wind given a southerly component, and is still quite manageable with a > westerly cross wind. On average, birds moving over the mid-Atlantic in > spring take a SW->NE trajectory, so some west in the wind can still > contribute to a tailwind. I suspect that had the winds been more northerly > at 900mb (~3000ft) but all else remained constant, you'd still see birds > moving tonight albeit at a lower altitude. > > Cheers > > David > > ____________________________________________________ > David A. La Puma > Villas, NJ > > Websites: > http://www.woodcreeper.com > http://badbirdz2.wordpress.com > > Photos: > http://www.flickr.com/photos/woodcreeper > > > > > > > On Wed, Mar 17, 2010 at 9:46 PM, Bryan Guarente <dafekt...@yahoo.com> wrote: >> >> The question that I like to ask of all this is which level of winds >> matters the most when talking about migration? I am seeing that others are >> taking into account the surface wind direction (NWS observations and >> forecasts), but what about above that? The winds change direction >> dramatically with height quite often, especially in areas where the surface >> friction is high like large cities, so how much are the higher level winds >> taken into account? If the model predictions are right from this morning >> for tonight, then the winds in both of your locations about a kilometer up >> in the atmosphere should be out of the WNW. Shouldn't that hinder the >> movement of birds tonight? >> >> Bryan Guarente >> Meteorologist/Instructional Designer >> The COMET Program >> University Corporation for Atmospheric Research >> Boulder, CO > > -- 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/ --
