Tannin
Common; sedentary.
However, photos contain a lot more features, and much more faithfully reproduce details, textures and colors.
If you are talking about:
- a particular individual bird
- at a particular time of year
- under particular lighting conditons
- in a particular pose
then I agree entirely.
But if you are talking about a generalisable image that fairly represents the normal and typical look of a species, then a decent artist will beat a photographer every time. A good field-guide illustration heightens the key ID features and generalises the typical range of variation such that you, the birdwatcher, are able to extract the recognition features from the illustration and apply them to the bird in your scope.
Bird illustration, in other words, is not about 100% life-like reproduction (we have cameras for that), it is about creating caricatures - drawings or paintings which are more life-like than life itself.
Think about your favourite political cartoonist: he can capture the essential essence of any of our noble leaders, and make them more recognisable than a photograph would be, with just a few strokes of the pen - bring out the eyebrows, for example, or outline the weak chin. Quality field guide illustrations do something rather similar, though much more subtle. This is why they work so effectively and why photographic guides will never be much more than a charming novelty.