[CT Birds] snowy owls and stress
elphick at sbcglobal.net
Wed Dec 7 19:36:42 EST 2016
Fear not, I am not going to prolong the debate about snowy owl reporting as Roy has said all that needs to be said.
But I do want to address the notion that the snowy owls that migrate south are "stressed" as this is a common belief that is not well founded. A few years ago, when there was a big irruption, I dug into the scientific literature on the topic and as best I can tell there is no evidence at all for the claim. Certainly birds often move south to find food because it has become scarce farther north, but that is likely true for pretty much everything that migrates, and is not necessarily a problem. People who catch and band snowy owls - i.e., those who are in a position to objectively assess their condition - generally report that they are in good shape, and emerging data from birds that have had transmitters attached so that individuals can be tracked, tend to suggest that the birds are doing fine too. Of course, there are occasional cases when an individual does turn up emaciated and dies. But that is going to be true in any population of wild animals - it is normal for most birds to only have a 50:50 chance of surviving the year (probably higher in owls, but a moderate level of mortality remains normal).
Related to this is the idea that big irruption years are a sign that the birds are in trouble. Again, this idea is not well founded. Instead, irruptions tend to happen after really good breeding seasons - i.e., when things are going well for owls. It is because there are large numbers of individuals that we see more birds coming south in those years.
If anyone is interested in more detail I think I cited the scientific papers in a post on this topic a couple of years ago, so dig back in the archive and you may find it. If that fails you, I can try to find the information again.
Incidentally, the other big snowy owl myth is that they can be reliably aged/sexed by plumage in the field. There are average differences, and they appear to be useful much of the time, but data from banding and captive birds suggests that there is almost complete overlap in plumage features. So, for any given individual it will be hard to be certain. Again, I think I gave the citations in a post on this list a couple of years ago, but this document summarizes some of the key info:http://www.dvoc.org/OrnithStudy/Presentations/Presentations2012/Snowy%20Owl%20plumages.pdf
Chris Elphick @ssts
elphick at sbcglobal.net
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