Today I learnt about dimorphism!

We Aussie blokes have noticed that sheilas look different....

I read today that this is called sexual dimorphism. Birds demonstrate this as well of course but some species demonstrate non-sexual dimorphism.

I had always been aware that the Eastern Reef Egret had dark and light forms known as morphs. Up 'till now I had only ever seen the dark morph (living down south) but this month on the Sunshine Coast I believe I have seen both.

This prompted a little exploration about how this dimorphism works with particular reference to this species. I read:

1. Wikipedia's pages Eastern Reef Egret and sexual dimorphism
2. Eremaea's listing for Eastern Reef Egret
3. Birdlife Australia re Eastern Reef Egret
4. Same for Birds in Backyards

Eastern Reef Egret (Egretta sacra) Dark morph, Noosa Heads headland

Eastern Reef Egret, light morph, Caloundra

This photo from Thailand hosted by Wikipedia at their Eastern Reef egret page claims to have both forms in the one frame:

Birders look away (instagram warning):

Black-shouldered kite, Wedge-tailed eagle, Eastern spinebill