Tuesday, 20 January 2015

Seeing evolution in action?

RobinThough I was some 10m or more away from the small bird, I recognized it immediately, even in poor lighting conditions. It was perched, looking away from me and I could not see its most distinctive feature. Despite that, as I approached the bird and it turned round my identification was confirmed, as I knew it would be. It was a Robin.

Though the Robin is probably the UK's most recognisable bird, identification can be difficult when you can't see its red breast. Long distance and poor lighting conditions make it even more tricky. So why was I so confident that I knew what this bird was? I was using something called jizz. It is a combination of factors that characterise a particular species. These might include the way it flies, its general shape, characteristic movements, habitat and location. Put together these can often point to a single species.

You can use jizz to look for rarely-seen birds. For instance, if I see something that has the distinctive jizz of a Robin but something is not 'quite right', I'd take a closer look and see if it could be one of its close relatives, like the Bluethroat, instead. This species does not breed in the UK but a handful pass through the country every year, especially in autumn or spring. But consider the odds. If I see a Robin that doesn't 'feel' right the chances are incredibly small that it will actually be a Bluethroat. On the vast majority of such occasions the bird will turn out to be a regular Robin. My feeling that the jizz is not right will be a result of my not being completely familiar with every possible aspect of the Robin's appearance and behaviour.

Now suppose I see some animal I don't recognise at all. It could be an anomalous 'out of place' or 'unknown' animal. However, as in the case of the Bluethroat, the chances are very high that it is actually a species native to the UK that I have either never seen before or don't recognise because I'm not completely familiar with its jizz.

It is not just birders and naturalists who use jizz to identify animals. Everyone does it without realizing what the process is. We all, even those people who have no interest in natural history, unconsciously absorb details of animal appearance and behaviour. But the process is error-prone. Encounters with wild animals are often fleeting and distant as most avoid human contact. So few people get a chance to build up a great familiarity with any particular species. I suspect many of the reports of 'out of place' or 'unknown' animals in the UK are misidentifications of native species, or pets, where the witness has little experience of their jizz.

And sometimes even familiar species can appear unfamiliar. I have previously reported several times on the crows at a nearby railway station (see here). They have started to behave more like street pigeons than wild crows. They allow people to approach them to within a metre, they walk off rather than fly away and are found in covered areas with no immediate access to the sky. All these behaviors are more typical of street pigeons than wild crows. If a local population of a familiar species starts to behave in an unusual way, it can easily make identification by jizz problematic. This could easily lead to the misidentification of such species as 'out of place' or 'unknown' animals.

There is a fascinating article in this week's New Scientist concerning evolution. Recent research suggests that species may adapt to new environmental conditions BEFORE any genetic mutation takes place. One dramatic experiment showed how fish could learn to walk if changes in their habitat demanded it, without any genetic change. It now seems that, in evolution, adaptation may precede genetic mutation.

It hadn't occurred to me before that the unusual behaviour in some of our local crows could actually be evolution itself in action. Pigeons have become adapted to life in close proximity to humans, forming a subspecies - the feral or street pigeon. So, are we witnessing the birth of a new subspecies of crow - the street crow? Will our city streets one day have as many crows as pigeons? If so, you read it here first! Well, maybe first ...

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