Hi Greg and Nikolas,
Brown Falcon plumages are very complicated, but they do have actual morphs. The
morphs change with age (i.e they have phases within morphs). What's more, the
morphs also vary geographically and there are slight difference between the
sexes in adult plumage.
there are three morphs, brown, black and rufous. The downy young of all morphs
are the same. The juveniles are similar (brown above and on the thighs and
flanks with buff centre of breast and underparts) but the rufous morph has
broader rufous fringes (scaling) to the upperparts and the dark morph has very
little buff below. In adult plumages of the brown morph the buff becomes cream
and the upperparts become slightly duller and mottled; the rufous morph gets
rufous upperparts and cream underparts, while the dark morph resembles a Black
Falcon. In this way the juveniles are intermediate between the rufous morph
and dark morph, and the former get paler with age while the latter get darker
and the brown morphs don't change so much..
Brown morph predominates in the SE (and is the only morph in Tassie), rufous
morph predominates in the interior and west, dark morph is most common in the
tropics but is comparatively rare (generally, the more humidity, the darker the
plumage, but with exceptions). The distributions are difficult to determine
precisely because there is lots of variation and lots of birds intermediate
between rufous and brown morphs,, Also, the changes with age and differences
between sexes make it even more confusing.
However, the rufous morph probably does not breed on the east coast, so the
bird Greg saw likely was from inland, but not necessarily from very far inland.
Also, in the most arid central deserts there is a very pale version of the
rufous morph that is quite similar to Nankeen Kestrel females, and could be
named the kestrel morph. In HANZAB, I didn't accept any subspecies in
Australia, but previously 5 were recognised. Birds in the SW (all rufous morph,
I think) are slightly smaller than those elsewhere, so you colud separate them
as subspecies occidentalis.
There are more details in HANZAB.
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