[texbirds] Re: Tropical Mockingbird - missing back toe nail on right foot
- From: Clay Taylor <Clay.Taylor@xxxxxxxxxxxxxxxxx>
- To: "'jay@xxxxxx'" <jay@xxxxxx>, Texbirds <texbirds@xxxxxxxxxxxxx>
- Date: Mon, 28 May 2012 10:03:54 -0400
Jay -
Good thoughts, to which I will add in the obvious follow-up - the Tropical
Mockingbird arrival coincided with the appearance of the Black-whiskered Vireo
at Sabine Woods. I sincerely doubt that BWVI is a commonly-kept cage bird in
whatever region caged wildbirds are commonly kept (not overly pretty, not a
sweet singer), and have never heard anyone question the provenance of recent
BWVI sightings on TexBirds.
So, when we discuss the probability of such-and-such a bird *naturally*
occurring in a location, if another low-probability bird arrives at the same
place and same time, are the *coincidence factors* additive, do we multiply
them, or are they on some sort of a logarithmic scale? Too bad the
Double-toothed Kite did not make another appearance this year.
Clay Taylor
TOS Life Member
Calallen (Corpus Christi), TX
Clay.taylor@xxxxxxxxxxxxxxxxx<mailto:Clay.taylor@xxxxxxxxxxxxxxxxx>
From: texbirds-bounce@xxxxxxxxxxxxx [mailto:texbirds-bounce@xxxxxxxxxxxxx] On
Behalf Of Jay Packer
Sent: Saturday, May 26, 2012 10:48 PM
To: Texbirds
Subject: [texbirds] Re: Tropical Mockingbird - missing back toe nail on right
foot
I'm sitting in a restaurant east of Houston, having just seen the Tropical
Mockingbird a couple of hours ago, off and on from 4-6 this afternoon.
Sadly, I was not observant enough to notice the missing toenail. Eric's email
makes me want to comment on the bird's origin though. Let me begin by saying
that in the absence of further evidence, I don't think anyone can definitively
say anything about the bird's origin. That said, I think the circumstances are
entirely plausible, and perhaps even more likely, for a natural origin.
When I think of the probabilities of caged birds showing up in Texas, the odds
are very low if we pick a spot on the map at random. (It seems reasonable to
assume that the odds are slightly higher along the border, where smuggled birds
cross.) On the other hand, migrants that cross the Gulf of Mexico are not
randomly distributed, which is why Sabine Woods is so much better for warblers
than Abilene, TX in migration. So when I ask myself "what's the probability of
a caged / escaped Tropical Mockingbird showing up at a migrant trap like Sabine
Woods?" the odds seem exceedingly low. Now a vagrant, having crossed the Gulf,
and deciding to stop at the first chunk of habitat encountered? This at least
seems entirely plausible. We know this happens with birds like Greenish Elania,
Yucatan Vireo, and others I'm probably forgetting.
To Eric's point about the toenail, I find this interesting but hardly helpful
in resolving the question of the bird's origin. Take me for example. I have a
toenail that's half missing and regrowing right now. Is this evidence that I've
been in a cage recently or an accident? :) Before I accept the "cage
hypothesis," I want to know why I should discount an accidental loss of a
toenail. Occam's Razor demands it. As Eric admitted, we know some percentage of
birds are going to have little anomalies like this. It just doesn't seem
sufficient to write off the bird as unnatural in origin.
Finally, the worn plumage too isn't conclusive, as everyone has been pointing
out. From the pictures that Martin Reid sent of other Tropical Mockingbirds at
this time of year to the worn plumage of the Northern Mockingbird at Sabine,
this feature is within the expected range of normal plumage wear and tear.
Given that it's theoretically *possible* for almost any vagrant to be present
because of humans moving them around, if we discount the Tropical Mockingbird,
perhaps we should discount all of three following too: unusual raptors
including Gryfalcon (due to falconry), all rare ducks (due to zoos and private
collections), and any songbird that fits in a cage (which is to say all of
them). In almost all cases, we don't truly know the providence of a rare bird.
I say we accept them unless we have a strong reason to believe they are of
unnatural origin or their natural occurrence simply defies belief. (A kiwi
isn't going to swim to Texas for example...)
This is just my two cents, and I look forward to someone showing the
foolishness of my logic.
--
Jay Packer
(sent from my phone)
On May 26, 2012 4:45 PM, "Eric Carpenter"
<ecarpe@xxxxxxxxx<mailto:ecarpe@xxxxxxxxx>> wrote:
Please start sending your posts to
texbirds@xxxxxxxxxxxxx<mailto:texbirds@xxxxxxxxxxxxx>
Texbirders,
The Sabine Woods Tropical Mockingbird is certainly puzzling and the
debate about origin/provenance is not an easy one to have an answer
for. It has been pointed out by many and is obvious in many photos
that there are worn (but not broken) feathers on the bird's tail.
What has not been noticed or mentioned at all is a very keen
observation that Eivind Vamraak shared with me a couple days ago. If
you look at any photos that show the bird's right foot, you should be
able to notice that the back toe nail on that foot is completely
missing. If you go back to photos from the original observations in
the last half of April, this toe nail has been missing from the
beginning.
With both the worn feathers and the missing toe nail, one can argue
for both natural and unnatural (captive) causes. If you scrutinize
enough wild birds to this same degree, it is likely you can find
similar wear & tear and abnormalities so I'm not passing a judgement
here but feel it would be wise to pass on this astute observation that
Eivind Vamraak shared with me.
--
Eric Carpenter
Austin
Edit your Freelists account settings for TEXBIRDS at
//www.freelists.org/list/texbirds
Other related posts:
