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text-dec --_000_13C76C679C2947138C219D1420E4E127dalca_ Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Hi John, Thanks for the interesting and informed response =97 of course, some are si= mply diurnal migrants, why didn=92t I think of that? No corresponding pred= ator threat for nocturnal migrants because no way to locate prey (no echolo= cation), rather like the state in WWI (no night-fighter plane action becaus= e no radar yet, compared to WWII when radar detection of =91prey=92 availab= le and effective night fighters developed). I was thinking that the night calls must be used to promote cohesion with a= migrating group, perhaps helping the poorer navigators (first year migrant= s?) stick with the more experienced birds and not drift off course. The re= dstart work recognizing sex but not age seems not to support this. Perhaps= it=92s a bit like the seemingly complex daytime visual coordination in the= large flocks of peeps and starlings, but which apparently now can be mostl= y explained if an individual pays attention just to its immediate neighbour= s and has fast coordination responses. Some earlier German work found tha= t male fly 1 chasing male fly 2 could commence executing a following turn r= esponse within about 12 milliseconds of fly 2 initiating an evasive turn, b= ut birds being much bigger probably are not that fast =97 much longer nerve= conduction pathways. There must be some cost to flight calling, so one would expect some associa= ted benefit. An extreme case is that of a diurnal Australian cicada that h= as to sing very loudly to reach females isolated in other local vegetation = =91islands=92 several kilometers away, and has to devote around 50% of its = metabolism to support this, as well as exposing itself to predation. Steve On Oct 25, 2016, at 8:16 AM, John Kearney <john.kearney@ns.sympatico.ca<mai= lto:john.kearney@ns.sympatico.ca>> wrote: Hi Steve and all, American Goldfinches are diurnal migrants. Since my equipment records betwe= en civil sunset and civil sunrise, their migration would not be captured in= my data. As an experiment this year, I left a couple of my recorders runni= ng for an additional 3 hours after the beginning of civil sunrise. I haven= =92t analyzed those recordings yet but it should give me information about = diurnal movements. Finch movements often begin in earnest during the last t= wo weeks of October. In the American Goldfinch, the extent of their migrati= on appears to vary from year to year. For nocturnal migration, there are species that have no known flight calls.= This is the case for vireos, and while flycatchers may have some flight ca= lls, they are seldom heard. Other nocturnal migrants tend to call more ofte= n than others. For example, White-throated Sparrows seem to call often whil= e Dark-eyed Juncos infrequently. Most warbler species seem to call often (b= ut Yellow-breasted Chat has no known flight call). Recently studies in the field of aeroecology have begun to explore some of = the complexity of bird distribution, behaviour, and interactions when in fl= ight. Acoustic monitoring is currently limited to capturing sounds within 3= 00 meters of the ground. Radar can sample much higher. Depending on the ang= le of the radar, it could be sampling quite a different group of migrants f= rom the acoustic sample. Since radar enables us to determine the speed of t= he echoes, it is possible at least to distinguish between certain groups of= migrating birds, such as shorebirds or warblers and then compare this to t= he acoustic data. It would be very instructive to do more combined radar/ac= oustic studies that address some of the questions you are raising. We also are just beginning to understand the complexity of vocal interactio= ns among birds in flight. One study published this year on American Redstar= ts showed that these birds may be able to distinguish the calls of birds of= different sexes but not different ages. The most surprising finding was th= at there was statistical evidence for uniqueness in the calls of individual= birds. In other words, American Redstarts might be able to identify an ind= ividual by his/her nocturnal flight call. With this kind of individual vari= ation as a possibility, it is no wonder that the identification of night fl= ight calls is such a challenge. Thanks for your thought provoking questions, John From: naturens-owner@chebucto.ns.ca<mailto:naturens-owner@chebucto.ns.ca> [= mailto:naturens-owner@chebucto.ns.ca]On Behalf Of Stephen Shaw Sent: October-25-16 00:57 To: naturens@chebucto.ns.ca<mailto:naturens@chebucto.ns.ca> Subject: Re: [NatureNS] Nocturnal migration for the 3rd Week of October Hi John, I=92ve seen a couple of groups of ~20-30 Am Goldfinches passing through our= yard in Halifax recently, feeding high in the trees plus visiting feeders,= twittering away, then moving on after a half hour or less. I had assumed = that these were migrating groups en route, but this species never seems to = figure in your flight call lists. Does this mean that they really are in the business of migrating now but do= so silently so you miss recording them? Alternatively does it mean that t= hey are just wandering around locally for food in groups, but are not =91in= tending=92 to migrate at all? Generally, are there a lot of species that migrate silently that you would = obviously miss recording? Perhaps the ratio of flight calls to radar image= s at the same site would be instructive, if possible to make these and if t= hey can be quantified usefully (for instance, do the radar images cover mor= e spatial volume than the acoustic recordings reach, and if so could you co= mpensate for the difference)? Presumably the flight calls are thought of as a coordination process to pro= mote keeping that species group bunched together to collectively improve na= vigation, or are there some other benefits?=97 calling while migrating must= have an additional otherwise unwanted metabolic cost. Steve On Oct 24, 2016, at 2:12 PM, John Kearney <john.kearney@ns.sympatico.ca<mai= lto:john.kearney@ns.sympatico.ca>> wrote: Hi All, Nocturnal migration was down to 88 flight calls at Carleton, Yarmouth Count= y, this week. The estimated minimum number of individual migrants was 78. T= he most common species was White-throated Sparrow (23 calls) and Yellow-rum= ped Warbler (11). Sparrows accounted for 63% of all calls, warblers for 25%= , and Kinglets for 7%. Straggl