Well of the top of my head I'm not up with all those terms but there certainly
are differences and I'm not sure that these words describe them. Where do they
come from? Your question may be about birds or may be about words.
In a broad comment, most bird orders differ between them and other orders in
the arrangement of their toes and are generally consistent within the order.
The features are how many toes they have per foot, (Ostrich has two, other
birds have three or four) whether they have two, three or four toes facing
forward, whether the hind toe, if they have one, separates from the foot at the
same level or higher than the other toes (as in in humans the big toe separates
at the same point, but our thumb does not), whether the foot is webbed or toes
joined and if so how many toes are enclosed, whether the toes are webbed but
the web does not join the toes.
Syndactyl means joined toes, as in the Coraciiformes: kingfishers, rollers etc.
They have their forward toes joined for part of their length. Strangely the
only passerines with syndactylous (joined) toes are the Australian
Treecreepers. As for webbed feet, I'm not sure which of those words is used.
Anyway it should describe eg. ducks and pelicans, although in ducks only three
toes are webbed. The Pelecaniformes have all four toes joined in a web, but
that does not mean all four toes face forward. The web is very broad and so the
outer toes (1 and 4) face pretty much inwards and outwards. Zygodactyl is two
toes forward and two back, as in parrots, cuckoos and owls, although in owls
one toe can be either way. Heterodactyl would suggest to me variability. As
noted in my quiz, mousebirds have very mobile toes but I don't know if that is
included in the list of words.
Philip
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