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Egretta is a genus of medium-sized herons, mostly breeding in warmer climates.
The genus name comes from the Provençal French for the little egret, aigrette, a diminutive of aigron, "heron".

1/ Pacific reef heron (Cò đen, Egretta sacra), also known as the eastern reef heron or eastern reef egret
2/ Little egret (Cò trắng, Egretta garzetta) 
The species epithet garzetta is from the Italian name for this bird, garzetta or sgarzetta.
3/ Chinese egret or Swinhoe's egret (Cò trắng Trung Quốc, Egretta eulophotes)

Little egret 
(Cò trắng, Egretta garzetta) 
The little egret (Egretta garzetta) is a species of small heron in the family Ardeidae. 

Pacific reef heron 
(Cò đen, Egretta sacra), also known as the eastern reef heron or eastern reef egret

The Pacific reef heron (Egretta sacra), also known as the eastern reef heron or eastern reef egret, is a species of heron found throughout southern Asia and Oceania.

Ardeidae, Ardea: the Latin word ardea meaning "heron".
The genus name comes from the Provençal French for the little egret, aigrette, a diminutive of aigron, "heron".
In Latin, "sacra" is a plural noun referring to "sacred things" or religious rites.