Friday, 10 December 2010

Grip and cryptic tick?

We were stopped by the Yosemite National Park Police in mid-April this year. At night. In a blizzard.

"Could I ask why you haven't fitted your snowchains?"

Easy answer, of course... "we don't have any..."

Now I am not advocating travelling in Yosemite without snowchains - it turns out it costs hundreds of dollars to get an emergency set fitted in Yosemite. At night. In a blizzard.

And my Monterey Bay pelagic had been cancelled that same day due to the same terrible weather...

To top it all a snow plough (or snow plow, I suppose) passed just as we had the chains fitted and completely cleared the inch of slush from the road. The brand new chains then slapped and ground against the wet tarmac all the way to Yosemite Lodge, and we never needed to use them after that...

...until, of course, this week in Edinburgh. On Monday of this week in a far worse blizzard than we experienced in Yosemite, it turned out the snowchains were worth their weight in gold!

As expected, the scenery of Yosemite was fantastic, and especially so with the snow blanket. Over the next couple of days the skies cleared to reveal a truly awe-inspiring landscape.

With the snow cover we were able to do some mammal tracking. In both of the cases below we had had the advantage of seeing their owner before we saw their tracks - which kind of defeats the purpose of tracking I suppose.

The Black Bear (left) walked past our accommodation as we were unpacking the car in the dark. This unexpected visit was pretty hair-raising at the time – we didn't hang around to photograph it but instead ran screaming to our room...

Next day, we jammed in on seeing a Bobcat (right). It sprang in a beautiful arc from a fallen tree trunk that was lying partway across a river. It leapt from what appeared to be a standing start several metres across the water and then slinked away into the undergrowth. A brief but spectacular sighting.

Birdwise, Yosemite was quiet, as can be expected at the time of year, given the altitude and the difficult weather conditions. The weather also changed our plans and restricted our movements. I was pretty gripped off not to be able to fit in a trip to try to see Great Grey Owl, one of my 'most-wanted' birds.

The corvids, on the other hand, were of good value, with both Steller's Jay and Common Raven both being relatively tame and sufficiently abundant for regular sightings. There are several subspecies of Steller's Jay and the form found in California (Cyanocitta stelleri frontalis) is distinguished by the blue streaks on the forehead.

The Raven would be of the subspecies Corvus corax principalis, which has a large bill and very glossy plumage. However, mitochondrial and chromosomal DNA evidence indicates that the 'Californian Raven' clade is a cryptic species that shares a more recent common ancestry with the Chihuahuan Raven rather than with the Holarctic clade of the Common Raven elsewhere in the Northern hemisphere. This DNA evidence suggests that the two clades of Common Raven split about 2 million years ago (which would coincide with the onset of an ice age), and the ancestors of the Chihuahuan Raven then splitting from the 'Californian Raven' about 1 million years ago. Subsequent to this it appears that while the more recent split has resulted in clear speciation between Chihuahuan and Californian birds, the Holarctic and Californian clades are now re-merging through interbreeding.

Whether the above individual is a 'Californian Raven' or not I do not know... according to the original paper (top link below) there is a chance of 27 in 28 based on their 28 samples. That said, they also speculate that the Californian clade may have been a low altitude and desert dwelling form and the Holarctic form a high altitude mountain form. The above bird was certainly photographed in the latter habitat.

The following bird, on the other hand, was photographed along the spectacular coast at Point Reyes. This lowland location makes this bird more likely to be a 'Californian Raven'. Note that this individual has clearly been used in a radio-tracking study by the Point Reyes Bird Observatory. Now, I wonder whether anyone has DNA tested this bird?...

A subsequent study (second link below) has also found strong support for the relationships described above between the Holarctic clade and the Californian and Chihuahuan clade. What is more, it found that the Holartctic clade of Common Ravens also includes the ancestors of the Pied Crow.

So, in summary, the Common Raven, below left (photographed on Islay with Common Jackdaws for scale!), shares a more recent ancestry with the Pied Crow, below right (photographed in South Africa), than it does with the 'Californian Raven' above. Similarly the 'Californian Raven' shares a more recent ancestry with the Chihuahuan Raven. Yet, despite this, the Common Raven and the 'Californian Raven' have not diverged sufficiently to prevent successful breeding between the two clades.

Finally, here is a scan of a photograph that I took in Lanzarote, Canary Islands in the pre-digital era.

This is a 'Canary Island Raven' (Corvus corax tingitanus), which is small, brown and oily rather than glossy. Mitochondrial DNA evidence suggests that this could well be a distinct species from the Holarctic clade of Common Raven. So that looks like a cryptic 'tick'...

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