[Tweeters] Hooded Merganser/Rough-skinned Newt update

[Dan McDougall-Treacy]

Sego, here's what Birds of the World has to say about HOME. (Not much):

Some descriptive information available (Appendix 1
<https://birdsoftheworld.org/bow/appendix/ACT1045304/APP1004690>). Most
quantitative studies have expressed diet as percent occurrence (i.e.,
number of samples in which food occurred divided by total number of
samples; Stewart 1962
<https://birdsoftheworld.org/bow/species/hoomer/cur/references#REF30453>),
or as percentages of total number of individual items in diet of all
individuals combined (Cottam and Uhler 1937
<https://birdsoftheworld.org/bow/species/hoomer/cur/references#REF12606>, Rawls
1954
<https://birdsoftheworld.org/bow/species/hoomer/cur/references#REF12621>).
In addition, prior to the 1970s, food habits research relied on
undifferentiated stomach or gizzard samples, a methodology known to bias
results against soft-bodied invertebrate foods in waterfowl (Swanson and
Bartonek 1970
<https://birdsoftheworld.org/bow/species/hoomer/cur/references#REF2290>).
Thus, the following information may be biased against some foods, does not
correspond to particular nutritional or life history stages, and does not
accurately reflect quantities of food items in the diet.

Diet of 138 birds sampled nationwide from Nov to Mar, expressed as the
percent of total number of items in all samples, found fish 44% (spp.
unknown), crayfish 22% (*Cambarus* spp.), aquatic insects 13%, other
crustaceans 10%, amphibians 6% (mostly *Ra**na* spp.), vegetation 4%, and
molluscs < 1% (Cottam and Uhler 1937
<https://birdsoftheworld.org/bow/species/hoomer/cur/references#REF12606>).
Using similar methodology, the diet of 11 birds at Reelfoot Lake, TN
contained 81% fish, 13% crustaceans, and 5% clams (Rawls 1954
<https://birdsoftheworld.org/bow/species/hoomer/cur/references#REF12621>).
In Michigan, percent occurrence of foods from 10 birds was crayfish 50%,
fishes 50%, insects 20%, frogs 10% (*n* = 10; Salyer II and Lagler 1940
<https://birdsoftheworld.org/bow/species/hoomer/cur/references#REF56481>).
Percent occurrence in stomach samples of 10 birds from Chesapeake Bay in
winter was fish 100%, crayfish 30%, dragonfly nymphs 20% (Odonata), mud
crab 10% (*Xanthidae*), and caddisfly larvae 10% (Trichoptera; Stewart 1962
<https://birdsoftheworld.org/bow/species/hoomer/cur/references#REF30453>).
Mammals not recorded in diet, although a captive bird killed a meadow
vole (*Microtus
pennsylvanicus*) by repeatedly biting the skull, but it was unable to
swallow the 83 mm vole (White 1975b
<https://birdsoftheworld.org/bow/species/hoomer/cur/references#REF12629>).

Vegetation reported in the diet; most authors consider its presence
incidental, although Salyer and Lagler (Salyer II and Lagler 1940
<https://birdsoftheworld.org/bow/species/hoomer/cur/references#REF56481>)
suggested the thick-walled gizzard of Hooded Mergansers (presumably thicker
than other mergansers) was evidence of an omnivorous diet. More likely a
strong gizzard helps grind the hard exoskeleton of crustacean (e.g.,
crayfish) prey.
Your observations certainly are noteworthy.

Dan McDougall-Treacy


On Fri, Mar 1, 2024 at 1:17 PM Sego Jackson <pond at whidbey.com> wrote:


> This morning, I (again) happened to see from our bedroom window that the

> Hooded Merganser was thrashing away at a Rough-skinned Newt. This time I

> was determined to see if it swallowed it or not. After watching for 10

> minutes, it drifted behind some vegetation on the near edge of the pond,

> and out of sight. So I ran outside and positioned myself where I could

> watch it and within 5 minutes it swallowed the newt.  So it is consuming

> them and not just playing around.

>

>

>

> And assuming it swallowed the first two times too, what I note is that

> from first noticing the merganser has a newt to it having “finished the

> job” has been about 15 minutes each time. I have no idea how long the

> merganser had hold of the newt before I noticed in each case.

>

>

>

> Anyone know what a merganser typically does with prey? Is the thrashing

> the prey about and time to get it down typical for other merganser prey?

>

>

>

> Sego Jackson

>

> Whidbey Island

>

>

>

> Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for

> Windows

>

>

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