Date: 4/27/26 6:42 pm From: Mike Thompson <mt...> Subject: Re: [cobirds] Mexican Ducks in summer
Thanks Owen - With the limitations outlined below, experienced and
inexperienced birders alike cannot reliably distinguish MEDU and hybrids
from deceptive MALL without excellent looks and documentation. And
experienced birders will more frequently report MEDU/MALL from May through
October, when MALL plumage deteriorates.
I can think of several good reasons for a dip in MEDU reports that are not
due to lack of effort:
1. The plumage discussion mentioned below; leading to cautious reporting.
2. The uncertainty of Mottled Duck in the mix of eastern ducks
3. Harsh, high-angle spring and summer light producing miserable shimmer
in long distance views. Compared with low-angle fall and winter light,
which is generally more favorable in the scope.
4. Seasonal behavior patterns of dabblers. It is far more feasible to
find a MEDU outlier in a flock of dabblers concentrated in a one-acre
feedlot pond which may be the only unfrozen water for miles. Contrasted
with the scattered, widespread nature of dabblers from May-October.
5. MEDU are expanding their range northward, making a comparison with
long term fixed populations in AZ and TX moot. We do not have a handle on
their seasonal movement but which does seem to resemble seasonal frequeny
of MALL. The following graphs illustrate this point:
Check out the statewide frequency graph for MALL and how it resembles the
same patterns as MEDU and MEUDxMALL.
[image: image.png]
[image: image.png]
[image: image.png]
Now check out MEDU/MALL:
[image: image.png]
The peak frequency of MEDU/MALL reports occurs during the lull of MEDU and
MEDUxMALL reports - mas o menos. From my perspective, that's awesome
hand-in-glove data. It strikes me that collectively, we aren't really
missing anything. MEDU researches using our data will be aware of reporting
limitations during nonbreeding season and can connect the dots on either
side.
With all that said, I fully support encouraging "well-documented and
unimpeachable Mexican Duck records" around the clock. Amen to that. The
best way to do that in my mind is to educate folks on ID points and the
data will fall into place naturally.
Thank you for bringing up the issue, it's very interesting.
Mike
On Mon, Apr 27, 2026 at 6:08 PM Owen Robertson <owen.k.robertson...>
wrote:
>
> Mike,
>
> Thanks for your response. I want to clarify that I’m not in favor of
> reckless/undocumented Mexican Duck reports - such a program would not
> improve this gap in data I’m describing. I’m simply saying that in addition
> to overreporting of MEDU, underreporting (as a result of a lack of observer
> effort) is perhaps an even greater problem. There will always be Anas
> ducks that trip us up (the Waneka bird last year is a great example) no
> matter how well-photographed they are, or how many experienced observers
> chase them, but such birds will be problematic regardless of season.
> Conversely, the many well-documented and unimpeachable Mexican Duck records
> that Colorado possesses should be acceptable as such in June just as much
> as in January. And similarly, a dubious Mexican Duck in January should not
> be accepted simply because it is January - Mallard molt timing is variable,
> and odd plumages can occur at any time of year. I firmly believe that the
> kind of data gap we see in late summer is fixable - perhaps not to the
> levels of certainty that we have about MEDU in other times of year, but it
> is not unimprovable. This improvement, in my opinion, can most strongly
> begin with observers taking the time to thoroughly check Anas flocks in
> summer, documenting oddballs, and reporting them - either as MEDU, a
> hybrid, or as MEDU/MALL (or, perhaps, Anas sp.). If errors are made in
> identification, they can be corrected, but a lack of effort is not so easy
> to remedy. If experienced observers can separate MEDU reliably (albeit with
> care) from odd Mallards, then our goal should be to get birders out there
> checking duck flocks and learning about the ID, rather than giving up the
> ghost from the start. Perhaps we’re in total agreement about that, but
> treating an ID like something that cannot be done, or is reserved for those
> with decades of experience, is (in my opinion) deeply harmful, both to the
> Colorado birding community and to the eBird data we’re both striving to
> improve.
>
> Best,
>
> Owen
>
>
>
> On Mon, Apr 27, 2026 at 6:11 PM Mike Thompson <mt...> wrote:
>
>> Owen - from a review perspective this is a rather risky approach. Youth
>> and exuberance can often confuse laziness with wisdom and caution.
>>
>> I have a completely different perspective from Montezuma County where
>> MEDU are more abundant in our waterways than anywhere else in Colorado: the
>> dip in the graph reflects careful birders and a solid, accountable review
>> team. Not the other way around. Wise summertime submissions of MEDU/MALL
>> easily fill the dip in the graph.
>>
>> And you did not mention the most problematic ID issue with local
>> summertime Anas; young male MALL, not eclipse MALL, are typically quite
>> dark and give a strong vibe for the MEDU-complex. Young male MALL are the
>> primary confusion issue with summertime MEDU reports, not eclipse MALL. And
>> both young and eclipse MALL are confusion issues for hybrids. Yes an
>> experienced birder can separate them, but not usually as carefully as
>> needed in a distant scope view.
>>
>> A message from a review perspective to all observers is to always
>> positively identity what you can, get the best documentation possible, and
>> use extra caution when reporting MEDU and MEDUxMALL during non-breeding
>> season.
>>
>> Mike Thompson
>>
>> <mt...> mobile
>>
>>
>> On Mon, Apr 27, 2026 at 15:48 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]
>>>
>>>
>>>
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>>
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