Red Crossbill Taxonomy

honest question, for anything other than statistics-driven genetic based hard science population studies what is the point of distinguishing these? Why would we use iNat for this? There are tons of independent populations of plants that look identical but are coherent populations but we don’t track them on iNat as separate entities


Red Crossbills are a pretty amazing adaptive radiation, they are like the Galapagos finches of North America.

There is great evidence that the Cassia Crossbill (AKA South Hills AKA type 9) is reproductively isolated from the others, and its coevolution with Lodgepole Pine is one of the best examples of coevolution out there: it lives where Red Squirrels are absent, which means that the crossbills are the main seed predator of the pines in their range. Without needing to defend against squirrels, the pines have evolved cones that are harder for crossbills to open. As a result, the crossbills there evolved bigger bills to open those tricky seeds. Other crossbill types that wander into the Cassia Crossbill’s range have a very hard time surviving there since their bills are not adapted to those seeds, even though they look very hard to distinguish to our eyes.

The rest of the Red Crossbills are very shallowly diverged, which is not surprising since the different ecotypes probably couldn’t have arisen until after the glaciers retreated and coniferous forests spread widely cross the landscape in the last 11,000 years or so (for reference, most North American bird species pairs are at least 100,000 years diverged). They are probably in the “grey zone” of what we would consider species, so studying the can provide great insight into the process of speciation, but they haven’t had enough time to evolve to be very different (genetically or in terms of appearance) despite playing different ecological roles.

A great reference about the crossbills is “Genome divergence and diversification within a geographic mosaic of coevolution” (

One reason is that some of the ecotypes might not be doing very well, and so distinguishing them is important for their conservation. For example, the most distinct ecotype, the Cassia Crossbill is probably critically endangered. Whether people care about conserving taxa that look so similar is another question, but since the ecotypes have different ecological roles I think it would be best to lean on the side of caution and try to understand them before it is too late.


i guess my point isn’t that they shouldn’t ever be studied and certainly not that the full genetic diversity shouldn’t be conserved, rather, is iNat ever going to work as a place to divide taxonomy to this detail given there’s no real way to verify them on here?

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Fair point, and observations with just photos should probably remain as just Red Crossbill. Luckily it is very possible to ID the call types, so observations with recordings can still be identified to ecotype with reasonable confidence. One reason this could be valuable is that since crossbills are so nomadic and widespread, it is hard for scientists to study their distributions, making citizen science data really valuable for understanding their distributions and movements. Right now eBird is mainly used for that, but encouraging the addition of call type information on iNat can add to the available knowledge base.


Photos are more or less unidentifiable but if recordings are obtained they can be identified. Biggest problem will encounter is, iNat does not provide spectrographs for those recordings, as I’m a person who prefers to use to identify by visual representations of the call. But we need to consider how many users are submitting crossbill calls but do not participate in eBird. As a person who uses both, I find it surprising how many non-eBirders submit rare sightings and the biggest database for avian sightings does not receive those reports. So yes, I believe iNat can help.

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This seems like a good use of observation fields.


The Cassia Crossbill is usually split as its own species nowadays.

Why can’t you verify them on here if you can upload audio?

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Yep, the evidence of it being a full species is pretty good.

Agree to disagree I guess. To my eyes, this is different from using an observation field to identify hawk morphs or Lawrence’s/Brewster’s Warblers. That’s because those are examples of polymorphism not potentially diverging populations. Though they are distinctly identifiable, they are nothing more but variation of the same taxonomic unit and are not likely to diverge into a sympatric population, or new subspecies.

I will also mention another problem and that is Evening Grosbeak also have call types as well. There are 5 known types but only 3 subspecies on iNat to recognize them. Unlike the crossbill, the named subspecies’ ranges match pretty well with the known call types ranges. However, Matt Young seems pretty confident that two subspecies previously synonymized with others matches the remaining call types based on specimen localities. The grosbeaks are less nomadic than crossbills so specimens are much more likely to be that resident subspecies.

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