Tom,
I will take a shot at the last part of your question, not that this is likely
to be a complete answer. You asked:
An example of an edge case would be why do some rarities stick around all
winter while some just pass through in a 24-hour period. I understand the
basics of why but am wondering if there’s something more or is it simply food
and breeding. Maybe that’s what I’m looking for, the nuances / edge cases.
There are a number of factors to consider when thinking about if or why a
vagrant bird will overwinter. The first question to answer centers on, is the
bird actively migrating? Many species are still actively on the move southbound
in December and for other species the northbound migration may start before
what we consider to be the spring migration window. If a bird first appears at
the margins of the winter season it may be on the move. If the first sighting
of a rarity occurs during the early December window the bird may not have
settled into a site where all of its winter needs will be met, thus it is a
one-day wonder. Another question to ponder is, what is the latitude where this
species normally winters? In other words, should I expect it to stop at my
latitude? This is often demonstrated by strays from Asia and Europe. When they
end up on the wrong side of the ocean they tend to stop and winter at a
latitude similar to the one where they normally winter. Good examples of this
are some of the Siberian strays that have wintered in Baja.
As you noted in framing your question, food availability plays a big role in
where birds winter, along with supplies of fresh water, suitable cover/roost
sites, and safety from predators. Sometimes a bird will show up in early winter
and be reliable at a site for a period of weeks and then suddenly it disappears
in mid-winter. Odds are that it did not decide to move on in the middle of the
season. It's more likely that the bird starved, froze, or fell victim to a
predator. Once a songbird finds a site that checks all of the boxes above
(reliable food, water, cover, safety from predation) they generally seem to
settle in for the season and can be reliably refound at a site until the normal
time for their spring migration arrives.
Of course there are all sorts of variables that add nuance and mystery to our
understanding of why birds do what they do. The Sibley book several of us
recommended may help in answering basic questions about bird behavior that to a
degree translate to what a particular speices might do when it strays off
course. As Rich suggests, the "Rare Birds of North America" is probably a
better reference if you trying to better understand the behaviors of wayward
birds and what factors influence whether or not they stick around. Someday I
hope to have better answers to these questions, perhaps resulting in a better
success rate in finding these vagrants. I'm sure I am not alone in that regard.
Dave Irons
Beaverton, OR
________________________________
From: obol-bounce@xxxxxxxxxxxxx <obol-bounce@xxxxxxxxxxxxx> on behalf of Tom
Wnuk <dmarc-noreply@xxxxxxxxxxxxx>
Sent: Wednesday, March 8, 2023 2:36 AM
To: Oregon Birders OnLine <obol@xxxxxxxxxxxxx>
Cc: Tom Wnuk <twnuk@xxxxxx>
Subject: [obol] Bird Behavior Recommendations
Anyone have recommendations for an in-depth look at Bird Behavior across the
Bird Families?
I had taken the Cornell Ornithology home study course in the late 90’s but
between multiple moves seem to have lost that material and now it’s online and
has been updated; so, I’d have to purchase again. It also doesn’t go deep into
behavior.
I’m looking for a more in-depth look not the basic info. Birds of the World
has a good overview but still doesn’t go deep enough.
An example of an edge case would be why do some rarities stick around all
winter while some just pass through in a 24-hour period. I understand the
basics of why but am wondering if there’s something more or is it simply food
and breeding. Maybe that’s what I’m looking for, the nuances / edge cases.
There are many resources on Amazon for instance but they all seem to be general
info.
thanks
-tom *******
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