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Index of Subjects
rows accounted for 63% of all calls, warblers for 25%, and Kinglets for
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Hi Steve and all,
American Goldfinches are diurnal migrants. Since my equipment records
between 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 running for an additional 3 hours after the beginning of civil
sunrise. I haven't analyzed those recordings yet but it should give me
information about diurnal movements. Finch movements often begin in earnest
during the last two weeks of October. In the American Goldfinch, the extent
of their migration 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
calls, they are seldom heard. Other nocturnal migrants tend to call more
often than others. For example, White-throated Sparrows seem to call often
while Dark-eyed Juncos infrequently. Most warbler species seem to call often
(but 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
flight. Acoustic monitoring is currently limited to capturing sounds within
300 meters of the ground. Radar can sample much higher. Depending on the
angle of the radar, it could be sampling quite a different group of migrants
from the acoustic sample. Since radar enables us to determine the speed of
the echoes, it is possible at least to distinguish between certain groups of
migrating birds, such as shorebirds or warblers and then compare this to the
acoustic data. It would be very instructive to do more combined
radar/acoustic studies that address some of the questions you are raising.
We also are just beginning to understand the complexity of vocal
interactions among birds in flight. One study published this year on
American Redstarts 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 that there was statistical evidence for uniqueness in
the calls of individual birds. In other words, American Redstarts might be
able to identify an individual by his/her nocturnal flight call. With this
kind of individual variation as a possibility, it is no wonder that the
identification of night flight calls is such a challenge.
Thanks for your thought provoking questions,
John
From: 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
Subject: Re: [NatureNS] Nocturnal migration for the 3rd Week of October
Hi John,
I've 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
they are just wandering around locally for food in groups, but are not
'intending' 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 images
at the same site would be instructive, if possible to make these and if they
can be quantified usefully (for instance, do the radar images cover more
spatial volume than the acoustic recordings reach, and if so could you
compensate for the difference)?
Presumably the flight calls are thought of as a coordination process to
promote keeping that species group bunched together to collectively improve
navigation, or are there some other benefits?- 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
<mailto:john.kearney@ns.sympatico.ca> > wrote:
Hi All,
Nocturnal migration was down to 88 flight calls at Carleton, Yarmouth
County, this week. The estimated minimum number of individual migrants was
78. The most common species was White-throated Sparrow (23 calls) and
Yellow-rumped Warbler (11). Sparrows accounted for 63% of all calls,
warblers for 25%, and Kinglets for 7%. Straggling warblers included a
Black-throated Green Warbler and a Black-throated Blue Warbler.
The weather radar in Caribou, Maine, indicated a similar low volume of
migratory activity based on the density of echoes in clear-air mode.
A summary table is given below and tables and charts can be seen
<http://www.johnfkearney.com/Carleton_YarmouthCounty_2016.html> here.
Estimated
Call
Minimum
Species
Count
Individuals*
White-throated Sparrow
23
14
Unidentified Sparrow
11
11
Yellow-rumped Warbler
11
11
Savannah Sparrow
9
8
Song Sparrow
7
11
Golden-crowned Kinglet
6
3
Unidentified Songbird
5
5
Palm Warbler
5
5
Blackpoll Warbler
3
3
Lincoln's/Swamp Sparrow
3
3
Dark-eyed Junco
2
1
Black-throated Blue Warbler
1
1
Black-throated Green Warbler
1
1
Unidentified Warbler
1
1
Total
88
78
* Calls that are more than one minute apart plus calls that are less than
one minute apart divided by three and rounded up to nearest whole number
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