Once you’ve got to grips with shape, size, colour, seasonality, sexual dimorphism and the elusive “gis” you may feel confident about identifying all the birds familiar to you. However a final curve ball is thrown into the equation with the addition of colour morphs. Albinism, a complete lack of pigment, is characterised by white hair, feathers or scales and pink eyes and is a pretty rare phenomenon in the natural world. Certainly, when you consider most animals evolved their colouration to avoid being seen; to avoid being eaten or to hide while hunting, its a surprise that any bright white animal survives in the wild.
Melanism is the condition when dark pigments are overly displayed, giving a brown or black animal. In some species, such as the adder, this trait has become the normal in some races. In snakes which live within the arctic circle, black adders are the standard. The black colour gives.them an advantage in heat absorbtion in the weak arctic sun. A black adder, and no baldrick in sight!
A colouring that is seen regularly, especially in urban birds, is called leucesism (loo-se-sism). Leucistic animals show partial colour absence, or white patches to some or all of their body. In some cases the animal looks like an albino. But a dark iris confirms this isn’t the case.
Black birds, including blackbirds, are particularly obvious owners of a leucistc gene, and reports regularly get sent through of birds with white wings or chest feathers. I have read speculation that this apparent increase in leucesism could be due to an urban bird’s diet; that by scavenging through fast food waste, birds increase the liklihood of passing on the trait. I suspect he truth will be somewhat less exciting, but possibly more sobering. The natural order of thing, predator prey relationships don’t exist in our urban jungle, so animals that stand out don’t get picked off by the number of predators which could be present if we weren’t.
This picture of dunnock, the quintessential little brown job or LBJ, shows a small amount of white, unlikely to cause any serious harm to the bird. However it can play havoc when attempting to identify a bird, especially if you tend to base your ID on a brief glimpse followed by a trawl through the illustrations of a bird guide. Which brings me on to one of my favourite subjects, field notes.
The reason not to take expensive glossy ‘field’ guides into the field is that they are glossy and expensive. Perversely the place for a field guide is in the home! Take notes, sketches and close observations.
A quick glimpse of a bird will provide about 1% accuracy, with the remaining 99% filled in by your brain. Sorry to say, but most of what we ‘see’ is made up, pure works of fiction, unconsciously extrapolated by your in-board supercomputer.
Bear this in mind when you are next out on a walk. Everything is worth a closer look.