[texbirds] Re: Tropical Mockingbird - missing back toe nail on right foot
- From: Jay Packer <jay@xxxxxx>
- To: Texbirds <texbirds@xxxxxxxxxxxxx>
- Date: Sat, 26 May 2012 21:48:27 -0500
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> wrote:
> Please start sending your posts to 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
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>
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