Date: 4/27/26 6:32 pm From: Eric DeFonso <bay.wren...> Subject: Re: [cobirds] Mexican Ducks in summer
Hi Owen,
Just a few nitpicks about your otherwise engaging posting.
First, regarding the data used to illustrate interstate comparison....are
these the total number of individual human observations of confirmed MEDU
in each state, or the total number of instances of confirmed individual
MEDU in each state? I'm assuming the latter, in which case it's probably
also true that in Colorado at least the vast majority of initial
identifications of a persisting confirmed MEDU are made by very experienced
observers. Or, in the few cases where the observer is less experienced,
it's quickly confirmed by a very experienced observer or reviewer, and then
chased and photographed by less experienced observers in order to gain more
experience for the next rare occasion when a potential MEDU is located. How
do I know this? Well it's basically my own story. I've had to learn as I go
in tiny incremental steps on how to identify MEDU in the field, which also
requires knowing how to identify hybrids, but I'll get to that more in a
moment.
Second, it's worth noting that although the state box plots are all very
comparable-looking in terms of proportions of confirmed MEDU by season, the
y-axis is indeed dramatically different, and should not be overlooked. CO
MEDU number no more than 10% of the next least populous MEDU state (NM) in
these graphs, despite the significantly larger human population (and
birding population) of CO compared to NM. I would be careful about
extrapolating too much information about what MEDU movements are (or
aren't) in CO based on such small number statistics. Especially since CO is
the only state in this comparison where the species is out of range.
My last nitpick had to do characterizing MEDU ID as simple given how
"dramatically" different they are from MALL. Well, that type of hyperbole
understates the difficulty of the problem, and seeing as how ABA articles
have had to be written by esteemed Colorado birders (Mlodinow, Leukering,
Bushong) on how to identify MEDU, calling the process of separating the
MALL complex comparable to separating Northern Shovelers from American
Wigeons feels a bit denigrating to those of us who have been struggling for
years to do things correctly. Does the process of MALL/MEDU/MALLxMEDU
separation start to get easier and more straightforward the more you
observe and practice it? Certainly, and perhaps even to a point where an
experienced observer does feel as if the visual difference between these
birds is to them dramatic and obvious. But learning this is still a process
for the community as a whole and only keeps moving when we help each other
continually with how to separate these birds. I would argue that given the
already very low numbers of MEDU likely present in the state at any given
time, and given my previous argument that the MEDU-observers with ID skill
are already catching the majority of MEDU likely to be found anyway, it
probably serves the community better at this point to just assist them with
improving their ID skills instead of criticizing their past efforts.
Efforts which, as Mike Thompson aptly pointed out, are already being
reviewed by a solid and accountable review team. For my part, I want to
continue improving my own recognition of the field-identifiable traits, and
to improve communication of that information to the birding community. The
more confident birders can feel when looking over a distant MALL flock, the
more time they will actually spend doing so. It has less to do with
laziness and much more to do with encouragement. I also know this from
experience. :)
Eric
-------
Eric DeFonso
Boulder County, CO
On Mon, Apr 27, 2026 at 3:48 PM Owen Robertson <owen.k.robertson...>
wrote:
> Hi CoBirders!
>
> Perhaps there are few more dreaded phenomena in Colorado birding than late
> summer *Anas* duck identification. Mallards molt into their "alternate"
> plumage (it's still termed "alternate", even though the birds are dull)
> from roughly June-October, and during those months every pond in the state
> is teeming with brown-bodied, yellow-billed ducks that may or may not
> contain a smidgen of *diazi *DNA. I've been hearing about this problem
> for a while now (looking at you, Ted), and took the opportunity of a
> freeform statistics final project to do some analysis on the wonderful
> eBird data that you all have contributed to! I found that, despite no
> (known) seasonal movements in Mexican Ducks, they are reported almost half
> as often in late summer than they are elsewhere in the year. This pattern
> is extremely strong (p < 0.0001), holds true for all four states where MEDU
> are regular in the ABA (Texas, Arizona, New Mexico, and Colorful Colorado),
> and is really quite striking (check out the boxplots and line chart at the
> bottom of this email for a visualization).
>
> Which brings me to the (slightly) chastising part of this email: male and
> female Mexican Ducks are eminently identifiable *year-round* - they look
> dramatically different from any worn or molting Mallard you could imagine.
> So why are we not finding them? The answer is that *birders are lazy! *(And
> yes, I'm including myself in that statement). We see a flock of five dozen
> *Anas* drifting through the heat haze at John Martin Reservoir in August
> and plop them on the eBird list as Mallard, but in December that one
> chocolate brown male with a yellow bill really pops, and *bam* - Bent
> County pulls another MEDU. (By the way, the disparity in reports of male
> and female Mexican Ducks must be wild - somebody wanna check that out? And
> I don't even want to think about the *hybrids* in summer...) Since
> Mexican Ducks aren't known to undertake seasonal movements, they should be
> out there, ready and waiting to be found by the first birder (that's you!)
> to take a closer look. (And if they do turn out to migrate or disperse in
> some way, more rigorous eBird data could help confirm that!). In sum - *Mexican
> Ducks being overlooked in summer/fall is a real problem for eBird data, and
> the solution is wonderfully simple: just look for them!*
>
> Good birding!
>
> Owen
> [image: Screenshot 2026-04-27 at 5.40.42 PM.png][image: Screenshot
> 2026-04-27 at 5.22.35 PM.png]
>
>
>
> --
> --
> You received this message because you are subscribed to the Google Groups
> "Colorado Birds" group.
> To post to this group, send email to <cobirds...>
> For more options, visit this group at
> http://groups.google.com/group/cobirds > * All posts should be signed with the poster's full name and city. Include
> bird species and location in the subject line when appropriate.
> * Join Colorado Field Ornithologists https://cobirds.org/membership/ > ---
> You received this message because you are subscribed to the Google Groups
> "Colorado Birds" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to cobirds+<unsubscribe...>
> To view this discussion visit
> https://groups.google.com/d/msgid/cobirds/<73a81814-4348-4f8b-99e1-51fa1f0a1d65n...> > <https://groups.google.com/d/msgid/cobirds/<73a81814-4348-4f8b-99e1-51fa1f0a1d65n...>?utm_medium=email&utm_source=footer> > .
>
--
--
You received this message because you are subscribed to the Google Groups "Colorado Birds" group.
To post to this group, send email to <cobirds...>
For more options, visit this group at
http://groups.google.com/group/cobirds * All posts should be signed with the poster's full name and city. Include bird species and location in the subject line when appropriate.
* Join Colorado Field Ornithologists https://cobirds.org/membership/ ---
You received this message because you are subscribed to the Google Groups "Colorado Birds" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cobirds+<unsubscribe...>
To view this discussion visit https://groups.google.com/d/msgid/cobirds/<CAFjVA_a-T4ZHwx4G2Wt-kE4XhhzEZKhpCcawCLxo3ZJqXVHvgA...>
