…. but an example of how species emerge. And this is not just a newly discovered species (indeed, not that new, it was discovered a few years ago). It is a species that is believed to have evolved recently as well. And it’s a North American Bird.

From a press release:

Julie Smith, now at Pacific Lutheran University, and her former graduate advisor, Craig Benkman at the University of Wyoming, have uncovered strong evidence that coevolution has led to the formation of a species of bird new to science in the continental United States. Benkman discovered in 1996 what appears to be a new species restricted to two small mountain ranges in southern Idaho (the South Hills and Albion Mountains). This species is a morphologically and vocally distinct “call type” of red crossbill (Loxia curvirostra complex), which is a group of seed-eating finches specialized for extracting seeds from conifer cones.

[source]

The research is reported in American Naturalist (reference below).

Here’s the story. In most places where there are lodgepole pines (Pinus contorta latifolia … common in the Northern Rocky Mountains) squirrels out-compete birds, including crossbills, for access to the pine seeds. Therefore, these seeds are not a major part of the diet of these birds. In addition, the overall seasonal timing of activity, which needs to account for when to mainly feed, when to seek mates, when to lay eggs, etc., is shaped by many factors including food sources, but not by the availability of these seeds.

However, in the South Hill crossbills (Loxia curvirostra Complex) there is an absence of pine squirrels (Tamiasciurus hudsonicus). Why are they absent? The paper (and the press report) do not indicate the reason, but it is the case that they are almost everywhere but on some isolated mountains. These areas are places where there are lodgepole pine (and crossbills) but they are small habitats separated from the more continuous habitats in which the squirrels are found. So, I’m guessing it is a habitat limitation combined with some historical bad luck.

Anyway, in the absence of these squirrels, the crossbills feed on the pine tree seeds, and thus, the pine trees evolve anti-predator defenses specific to the crossbill seed predation. This would be different from the defenses they would evolve against he squirrels.

(This is a common trope in seed/animal co-evolution. What defends a plant against a mammal is different than what defends a plant against a bird. This is why you can put cayenne pepper in your bird seed to keep the squirrels away, while at the same time not bothering the birds … cayenne is from a plant that benefits from bird dispersal but also benefits from avoiding mammal predation/dispersal. We are the odd mammal in that we like to spice our food with it … which in turn is probably because we are a primate that eats and stores more meat than other primates, and are thus liable to become ill from rotten food. Cayenne is an antibiotic and serves as a meat preservative. Of course, women who are pregnant will tend to avoid such spices … they have an elevated sensitivity to such things, known as “morning sickness” … which is good because the antibiotic effect may also cause birth defects if consumed in the first several weeks of pregnancy… the fact that rotten meat may be bad for these women is then perhaps handled by a cultural innovation … food taboos against meat during early pregnancy and at certain other times… but I digress. Digress my ass off there, I’d say.)

So, the interaction between the crossbills and the pine trees is such that both evolve in a kind of red queen effect “evolutionary arms race” scenario. Thus, the crossbills entire life history pattern, having to do with the timing of mating, mainly, changes. So these crossbills then become reproductively isolated from the other crossbills.

This, of course, are the conditions under which many new species evolve. And that is what has happened here, apparently.

It is estimated that this reproductive isolation has been going on for about 5,000 to 7.000 years. And a new species has emerged.

How cool is that?

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Smith, Julie W. and Craig W. Benkman, 2007. “A coevolutionary arms race causes ecological speciation in crossbills” American Naturalist 169:455-465.