Following that: Taking the information of “In both IOC and Clements Brown Goshawk and Collared Sparrowhawk are not each other’s closest relatives” If that is actually correct (I don’t mean whether these have been quoted correctly but whether the idea is correct). That still raises that these two species have separately evolved into both juvenile and adult plumages of exactly the same pattern, from something presumably different. It would make sense that they evolve into something like the typical patterns for the genus (because presumably that colour pattern matches the woodland hawk lifestyle) but why go so much further than this to become almost identical? That it has happened on the same continent would suggest there has been some benefit in this convergence. Maybe it is mutual mimicry. Is there maybe some territorial benefit to both species or reducing disputes between them that the male Brown Goshawk is about the same size and appearance as the female Collared Sparrowhawk? I have no idea how that would work.
If they are similar in appearance because they have both evolved from an earlier double invasion of one ancestor species, that would require that they are each other closest relatives (assuming that the ancestor species no longer exists in that form). If so the changes that have occurred are in size and anatomy.
About “But before considering that, the question might well be why *should* these animals look obviously different?” Well if they are not each other’s closest relatives then their basic patterns would I assume show more connection to their separate origins, unless there is something driving the similarity.
As for the white morph of the Grey Goshawk that question is unrelated. Yes the aspect of mimicry of cockatoos is a plausible advantage. Or there might something else selected with the white gene. Or some advantage in investing energy by not producing pigment.
As for : Does anyone know if these two hawks have sufficiently distinct diets (say prey items of substantially different sizes) to make them pretty much non-competitive in the same landscape? I would have thought that is pretty obviously established.
Philip
