Hello Vermont Birders:
All this Snowy Owl activity is terribly exciting. If you haven't had a
chance to get out looking for one yet or if you haven't lucked into seeing
one despite your efforts, don't worry, more are on the way.
Bruce MacTavish reported to the Newfoundland listserv yesterday a
conservative count of *over 200* in a single party outing along the eastern
shore! Based on previous efforts and weather, he felt confident these were
newly arriving birds. Obviously, we aren't on the East Coast and so are not
as likely to get "those" Snowy Owls or concentrations of that magnitude,
but clearly there are more Snowy Owls on the move.
A friend and former colleague of mine at Hawk Mountain, Jean-Francois
Therrien, conducted his Ph.D. research on Snowy Owls in NE Canada. He
continues to spend time in northern Quebec in the summer doing research.
There are several aspects to Snowy Owl behavior and plumage which seem to
get debated frequently so I reached out to JF for some clarity. I thought
some members of this birding community might be interested in his reply.
In regards to plumage, most sources are in agreement that males tend to be
whiter/lighter than females and immature birds tend to be darker than
adults but these are just gross trends. There is a high degree of variation
among individuals and some birds have been documented as getting darker
with age. The darkest males can be darker than the lightest females.
Thankfully, many birders are reporting to east coast listservs their
sightings of Snowy Owls. Often the details include "immature male" or
"adult female." Personally, I am cautious to label most Snowy Owls but I
thought maybe I was missing something so I asked JF. Here is his reply:
"Concerning age/sex classes: there is no specific criterion to tell them
apart objectively (as of yet). Some folks have developed a way to tell sex
among chicks at nest (see attachment), but in the field, especially in
winter at low latitude, it is pretty much a guess in all cases. The only
group that we can identify with confidence is adult males. For the rest,
(except when you are facing a nest and you can tell female from male
easily), it relies on feelings! People have long thought that snowies were
getting whiter with age. This was mostly based on captive birds. We got
lucky and photograph the same female wearing a satellite transmitter in 2
winters (2008 and 2010). That female actually got significantly darker! We
were amazed. A specialist of plumage coloration and molt in birds said he
was unable to understand the actual pattern in snowies (since the number of
wild bird being captured remains low). So, a lot more debates to come!"
"(see attachment)" refers to a PDF JF sent me of a paper published in the
Journal of Raptor Research in 2011. (I can forward the PDF if you contact
me directly - not via the listserv). Researchers accurately predicted the
sex of 140 nestlings 100% of the time by studying the remiges and retrices.
Secondaries were best but outer primaries and central/deck tail feathers
worked as well. The dark "spotting" on the flight feathers of the nestlings
were comprised of pigmentation running the width of the feathers creating
bars and circles of pigmentation on either side of the rachis not reaching
the edges creating spots. Males had more spots than bars and females had
more bars than spots. So if you feel compelled to label the birds you find,
be sure to study/photograph the open wing and spread tail carefully. *Note
- The paper does not talk about the effectiveness of using this protocol on
anything older than a juvenile so you have to accurately age the bird
first. It might work but has yet to be studied.
The other area of discussion is the cause of the irruptions. Nobody debates
the predator-prey connection. Lemmings make up the bulk of the diet on the
breeding grounds and their populations are cyclical. The size of a Snowy
Owl clutch is variable. Females assess how successful their mate is at
bringing her lemmings at the beginning of the breeding season and she lays
eggs accordingly. In years with lots of lemmings, she will lay lots of
eggs. Debate comes in when the birds irrupt southward. So, has the lemming
population crashed and starving birds are forced to migrate or do we see
them down here when the Snowy Owls have big breeding seasons and there are
lots of young birds dispersing? I posed this question to JF as well:
"As for the irruption, you are quite right. Almost every year that we see a
good reproduction in the eastern Arctic, we have some sort of winter
irruption down in QC and New England. Last summer was fantastic in Northern
Quebec. I was there at the tip of the province and we found several nests,
all of which having large clutches and several lemmings piled up on the
surrounding. We expected to see some irruption because all of those chicks
are starting to wander around, and they are now reaching our latitudes."
Die-offs eventually follow these spikes as nature corrects itself but I for
one will be riding the high this winter.
Enough out of me.