26/11/02 Strange heron/egret seen near Inchclutha, near Balclutha

An unidentified heron/egret has been seen at, Inchclutha, near Balclutha, in the South Island of New Zealand, between 13th October - 14th November 2002. The following is a description written by Richard Schofield who is responsible for first seeing the bird.

Size: Very similar to adjacent cattle egrets Bubulcus ibis
Shape: As cattle egret, with very hunched posture, but more horizontal gait, bill longer and relatively slimmer, tapering more evenly. No jowl on underside of bill. Forehead not as steep as cattle egret.
Plumage: Entire neck rufous, forecrown pale grey, small whitish patch on chin, rest of plumage dark bluish-grey, perhaps a shade paler than reef heron Egretta sacra, though much darker than white-faced heron Ardea novaehollandiae. Some plumes visible on back and throat, and nape.
Bare parts: Bill - lemon yellow, greyish yellow towards base. Iris yellow, legs dull yellow, bare yellow patch on face between bill and eye, with black stripe below it.
Behaviour: When first seen, feeding actively amongst cattle (and cattle egrets). At one point chased a cattle egret. On subsequent occasions, usually accompanying one or more cattle egrets, also seen alongside white-faced heron.
Apart from colouration, appearance in flight was indistinguishable from accompanying cattle egrets - same size and shape, same flight action.

Further notes from Richard ,added 29 November.....

Some other observations on the bird (to muddy the waters even more?) The presence of plumes on the neck and back (which unfortunately don't show up in the photos) do not suggest an immature bird.

Reef Heron would surely appear larger than cattle egret, and there's plenty of more suitable habitat locally than a field full of cows.

The dark grey plumage of the body, wings and tail was completely uniform, with no hint of any paler areas, or even paler fringes to the feathers. Again, the neck was uniformly coloured, with no stripes or paler areas.

The bird appeared healthy at all times, feeding actively and frequently preening. Took flight readily with the cattle egrets.

I can find only two references to melanistic cattle egrets (India & Spain). No photos, but both these birds both had paler primaries. Also, the Inchclutha bird has a different feeding action & posture to the adjacent cattle egrets. A hybrid seems high on the list of possibilities, but of what...?

Current suggestions -

Green/striated heron

Reef egret

Melanistic cattle egret

Hybrid cattle egret/reef egret/white-faced heron