Subject: [Tweeters] Hooded Mergansers and Rough Skinned Newts
Date: Oct 7 12:37:36 2008
From: Dennis Paulson - dennispaulson at comcast.net


Hi, Don and Sandi.

I looked in my old notes from when I taught vertebrate zoology, and I
had juvenile Pied-billed Grebe and Mallard listed as birds that had
died after eating Rough-skinned Newts. I can't recall where I got the
Mallard info, but the grebe is a specimen in the Slater Museum
collection that was found dead shortly after the observer saw it eat
a newt. It was an albino, one of the reasons the observer was sure it
was the same bird.

Some populations of Common Garter Snakes are immune to the newts'
toxins, but populations of the same species in areas where the newts
don't occur are not. Newt toxicity, on the other hand, definitely
varies from population to population, so I suppose it is possible
that the Orcas Island ones aren't among the most poisonous. Are
garter snakes common at this pond? Natural selection, with
differential predator pressure in different areas, could easily lead
to differences in toxicity in different populations. That's probably
why rattlesnakes are less dangerous in Washington than in Arizona.

So there are three possible alternatives. 1) Your newts aren't toxic.
2) The mergansers get rid of most of the skin toxins by their
actions. 3) Hooded Mergansers, at least these birds, are immune to
tetrodotoxin. A lot of data would have to be gathered to distinguish
among these hypotheses. It's amazing how many observations in nature
lead to more questions than answers!

Dennis

On Oct 7, 2008, at 12:03 PM, tweeters-
request at mailman2.u.washington.edu wrote:

> Date: Mon, 6 Oct 2008 18:59:41 -0700
> From: Don McVay <dmcvay at cmc.net>
> Subject: [Tweeters] Hooded Mergansers and Rough Skinned Newts
> To: Tweeters <tweeters at u.washington.edu>
> Message-ID: <E1A14850-307E-4650-9204-BD1708E2DC21 at cmc.net>
> Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes
>
> Hi Tweets,
>
> On Orcas Island in a small fresh water pond near Deer Harbor Saturday
> afternoon we made another observation of a Hooded Merganser eating a
> Rough Skinned Newt (Taricha granulosa). We posted this behavior on
> Tweeters for the first time in the Spring of 2003.
>
> The Merganser was a juvenile accompanied by an adult female. The
> behavior of the Merganser was similar to other observations of this
> feeding behavior. The Merganser manipulated the Newt with its beak,
> methodically rolling and passing the Newt between the mandibles and
> then rapidly swishing the newt in the water. It did this for several
> minutes before swallowing the newt. Both Mergansers were observed
> about an hour later resting among the cattails with no apparent ill
> effects.
>
> The toxicity of this newt is well documented. Several years ago an
> Oregon college student died, when on a dare, he swallowed a rough-
> skinned newt. The tetrodotoxin or TTX is a dangerous neurotoxin to
> mammals and is similar to that found in puffer fish and the blue-
> ringed octopus. The toxin in one newt has been estimated to be
> sufficient to kill several humans.
> See: http://www.calacademy.org/calwild/sum98/eye.htm
>
> Once again this behavior raises several questions from the previous
> post:
>
> 1. Are rough skinned newts a common dietary regime of the HOME?
> Apparently they are since we have observed this feeding behavior of
> Hoodies on several occasions.
> 2. Do other diving ducks feed on rough-skinned newts?
> 3. Was the rolling in a serrated beak and washing of the newt a
> behavior of the HOME to remove the toxin from the newts surficial
> poison glands?
> 4. Are HOME and other birds immune to tetrodotoxin? Some reptiles
> have been observed eating Rough Skinned Newts. (Garter Snakes)
> 6. Is there a geographic difference in Newt toxicity?
> 5. How do they do that?
>
> Don and Sandi McVay
> Queen Anne & Deer Harbor
> dmcvay at cmc.net

-----
Dennis Paulson
1724 NE 98 St.
Seattle, WA 98115
206-528-1382
dennispaulson at comcast.net



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