Dimorphic Egret is, to my eyes, indistinguishable from Little Egret. It exists in white & dark phase morphs as does Western Reef Heron & (allegedly) Little Egret (though I've never knowingly seen a Dark phase Little Egret). However there are behavioural differences. Dimorphic Egret is an entirely marine species which is closely allied to Little Egret & to the Western Reef Heron with the three almost comprising a superspecies.

Little Egrets stalk the (usually freshwater/brackish) shallows vigorously waving their bright yellow feet to disturb small fish, whilst the coastal Western Reef Herons rush back & forth in the surf spearing anything that breaks cover.
So what do Dimorphic Egrets do? Well in Mida Creek at least they play follow my leader with the Sacred Ibises.

During my short visit to Mida Creek I watched 5 different Dimorphic Egrets & all were, at some point, partnered up with a Sacred Ibis. The pattern was that an Egret would fly in & land beside a feeding Sacred Ibis & then follow it. Whenever the Ibis probed an area of wet mud the Egret would be at its shoulder constantly picking off small crabs, shrimps & often small fish. The Ibises seemed mainly to be taking molluscs & worms though were also observed eating crabs.

Whilst the Egret clearly benefits from this arrangement I could see no obvious advantage for the Ibis. Despite having tidbits stolen from under their beaks the Ibises seemed very tolerant of their shadowing Egrets. My guide confirmed that this odd couple arrangement was standard behaviour with no other species ever involved.

I have been unable to find any reference to this behaviour in the literature or on the internet though it is clearly known to the local birding/wildlife guides.