[NatureNS] Nocturnal migration for the 3rd Week of October

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From: Stephen Shaw <srshaw@Dal.Ca>
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Thread-Topic: [NatureNS] Nocturnal migration for the 3rd Week of October
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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