Why are there a a large number of surnames in English based on birds (Swan, Finch, Quail, Parrott, Woodcock, Peacock, Duck, Chicken and so on; perhaps also Swift, Swallow etc. but these might have other meanings) and in related languages (German has Pelikan for example), whereas the range of animal-based names is smaller (Fox is the only example that comes immediately to mind; I have never come across people with surnames like cow, sheep, pig,dog, cat)?