I reckon it is pretty good Ken!
Given the randomness of wether a bird is pooping as it passes or has decided that your car is the worst threat ever and needs aimed bombardment and what it has had for lunch it can be a variety of shapes, colours and sizes.
As birds (and for that matter Platypus and Echidnas) don't wee, their fecaes can have a grey/brown/green middle with white element which is the urea deposit that we mammals would pee.
It can be more solid or jelly like, but unless you are going to make a lifetimes study on the subject, or are going to exhibit at a convention of bird poo experts then fret not:OD