AOU Updates, 2020 Edition


Northwestern Crow with dead fish_FedWayWA_20090920_LAH_0904

We’re approaching mid-summer, the time that nestlings fledge, birders wilt, and ornithologists announce updates to lists of North American birds. As is common in these days of DNA analysis, most of the changes involve taxonomic reordering and changes in genus. That’s fascinating for those interested in taxonomy, but for most birders, it’s the lumps and splits that claim our attention. When species are lumped, we stand to lose a lifer. When subspecies are split into two or more full species, we can celebrate a longer list. There are three changes this year that will affect our North American life list totals.

Great Blue Heron_EvergladesNP-FL_LAH_9771
Great Blue Heron in the Everglades

If you’ve been to Florida (or some other Caribbean islands) you may have seen a Great White Heron, considered a type of Great Blue Heron since 1973. Now the Great White Heron (Ardea occidentalis) has once again been recognized as a separate species.

This is nothing new. Up until 1973, the two birds were considered distinctive species. Then, the AOU lumped them, based on anecdotal reports of mixed breeding. Besides, the only morphological difference is plumage color, and intermediates (called Wurdemann’s Herons) are occasionally spotted.

Now, studies[i] have revealed that the herons are divided genetically—one group includes three subspecies of the Great Blue Heron (fannini, herodias and wardi), while the Great White Heron is separate. Wurdemann’s Herons have been confirmed as hybrids between these two groups.

More conclusive is the discovery that most pairs mate according to color, with very few mixed pairs—and those are likely due to a scarcity of matching mates, as Great Blue Herons are relatively uncommon in Florida. Moreover, the two groups mate at different times. Finally, the two groups occupy different habitats, with the blue herons choosing sites with fresh-to-brackish water and the white herons opting for mangroves and turtle grass beds.

Now I need to go convince my husband that a return to Florida is in his future. I have yet to see a Great White Heron.

The next change caused me to lose a lifer, but it makes so much sense, I really don’t mind. With the discovery that there are no purebred Northwestern Crows, the species has finally been merged with the American Crow. I wrote about Northwestern Crows a couple of years ago, if you want to learn more.

Northwestern Crow_DumasBaySanctuary-WA_LAH_9524r
Just another American Crow

Well, you lose some, but you gain some. Much to my delight, the Mexican Duck has finally been split from the Mallard, joining all the other Mallard-like species such as Mottled Duck, American Black Duck, and Hawaiian Duck. Again, they were considered separate until 1973, which seems to be a big year for lumps. New DNA data showing minimal mixing between the two was enough to convince the scientists to once again recognize the species as separate.

Mexican Ducks all look like female Mallards, so identification can be a bit tricky. Look for a duck with female Mallard plumage, but a male (all yellow) Mallard bill. An article by the ABA, “The Bird We Always-Never Knew” has some helpful tips. Unfortunately, I wasn’t able to get a photo of the one I saw (in Arizona), so you’ll have to settle for these two relatives instead: a lovely female Mallard and a Mottled Duck.

If you’ve birded in Central America, you’ll want to peruse the remaining changes, especially those involving the emerald hummingbirds, as they may impact your life list.

Puerto Rican Emerald_Maricao-PR20100525_LAH_6857
The Puerto Rican Emerald is still Chlorostilbon maugaeus—a hummingbird endemic to Puerto Rico.

[i] McGuire, H.L., Taylor, S.S. & Sheldon, F.H. (2019) Evaluating the taxonomic status of the Great White Heron (Ardea herodias occidentalis) using morphological, behavioral and genetic evidence. The Auk, 136(1):uky010.

The answer to last week’s quiz is Mountain Bluebird (female).

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