[Maine-birds] more info on Snowy Owls

Hello Maine Birders:

The timing of Stella Walsh's question about Snowy Owl irruptions coincides nicely with a post I sent to the Vermont listserv earlier today. We are enjoying some Snowy Owls over here on the west coast of New England but nothing like you are seeing in Maine. The information is relevant regardless of location so I thought I would post it here:

A friend and former colleague of mine at Hawk Mountain, Jean-Francois Therrien, conducted his Ph.D. research on Snowy Owls in NE Canada recently. 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!"

When JF wrote: "see attachment" he was referring to a PDF 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 with older birds but it 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.

Good birding,

Eric Hynes

Hinesburg, VT

--------------------

www.fieldguides.com

http://fieldguides.com/guides/eric-hynes

--
Maine birds mailing list
maine-birds@googlegroups.com
http://groups.google.com/group/maine-birds
https://sites.google.com/site/birding207
---
You received this message because you are subscribed to the Google Groups "Maine birds" group.
To unsubscribe from this group and stop receiving emails from it, send an email to maine-birds+unsubscribe@googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.