"What is the theory for decreased contact/NFC calls as the night wears on?"
I thought one hypothesis(?) was that in the middle of the night the birds are actually too high to be able to hear? Has anyone ever tested empirically what elevation birds migrate at? I would think this would be relatively easy to do by placing several microphones at different elevations on large manmade structures (turbines/radio towers) or the top of ridge/valley and then compare how loud the nfc calls are. Some of this might already be published. On Mon, Sep 9, 2013 at 12:01 PM, Christopher T. Tessaglia-Hymes < c...@cornell.edu> wrote: > A quick observational browse through last night's recording data results > in these highlights: > > 4 Black-billed Cuckoos > 2 Hooded Warblers > 1 Black-and-white Warbler > 2 Lincoln's/Swamp Sparrows > > Nothing really Earth-shattering as far as rarity, but it was definitely an > active night. > > Recently, I've been resting at night with a single earbud headphone > plugged into one ear in order to listen in on the general nighttime > activity. Last night, there were tons of calls from about 9pm through about > 2am, then a gradual tapering to only sporadic calls the rest of the night. > The morning thrush descent was very minimal at my location. There was one > small descending flock around 5:34am, which included some Rose-breasted > Grosbeak calls. There were some very distant thrush calls around 5:50-ish > and a single close flyover Rose-breasted Grosbeak calling around 6:05am, > but everything was pretty much shut down by 6:00am. > > Thrush descent can be entirely hit-or-miss depending upon where the birds > are during migration, just before the start of morning civil twilight > (today it was at 6:10am). > > I'd say that Rose-breasted Grosbeak was the species that dominated the > night, followed by Swainson's Thrush. Early in the night, there was also a > good passage of Green Herons. Throughout the night there were several > Chestnut-sided Warblers. > > After listening to the recent nights' migrations, I have been wondering > about vocal activity vs actual birds in flight. Early in the night, birds > are calling – seemingly everywhere. By the latter part of the night > migration, vocal activity seriously drops off. > > Why is this? I mean, even after a very quiet latter 3 1/2 hours, we can > have a surprisingly actively vocal thrush descent. What is the theory for > decreased contact/NFC calls as the night wears on? Are they all established > in their individual flight patterns in the sky? Are they conserving energy > by not vocalizing? Is there a relationship between very cold nights and > decreased calling rates vs warm nights and consistent calling rates? If > birds were descending earlier in the night we should observe decreased > target density on RADAR; however, as Dave Nicosia mentioned, RADAR was > still displaying active targets in the air as of 6am at our local station > (BGM). Is there a generally accepted theory for decreased vocal activity > into the night? > > It has been fascinating to listen to and observe the gradual exodus of > neotropical and other migrants from northern North America. > > Thanks for any insight and good night-listening! > > Sincerely, > Chris T-H > > --**** > Christopher T. Tessaglia-Hymes**** > Field Applications Engineer**** > Bioacoustics Research Program, Cornell Lab of Ornithology**** > 159 Sapsucker Woods Road, Ithaca, New York 14850**** > W: 607-254-2418 M: 607-351-5740 F: 607-254-1132**** > http://www.birds.cornell.edu/brp > > -- > *NFC-L List Info:* > Welcome and Basics <http://www.northeastbirding.com/NFC_WELCOME> > Rules and Information <http://www.northeastbirding.com/NFC_RULES> > Subscribe, Configuration and > Leave<http://www.northeastbirding.com/NFC-L_SubscribeConfigurationLeave.htm> > *Archives:* > The Mail Archive<http://www.mail-archive.com/nfc-l@cornell.edu/maillist.html> > Surfbirds <http://www.surfbirds.com/birdingmail/Group/NFC-L> > BirdingOnThe.Net <http://birdingonthe.net/mailinglists/NFCL.html> > *Please submit your observations to eBird<http://ebird.org/content/ebird/> > !* > -- > -- NFC-L List Info: http://www.NortheastBirding.com/NFC_WELCOME http://www.NortheastBirding.com/NFC_RULES http://www.NortheastBirding.com/NFC-L_SubscribeConfigurationLeave.htm ARCHIVES: 1) http://www.mail-archive.com/nfc-l@cornell.edu/maillist.html 2) http://www.surfbirds.com/birdingmail/Group/NFC-L 3) http://birdingonthe.net/mailinglists/NFCL.html Please submit your observations to eBird: http://ebird.org/content/ebird/ --
