Hi, please see refs. They are not all herons, but you may be able to get away with saying herons. Does your text specify the exact bird species? Or maybe you could look it up.

Noun 1. family Ardeidae - herons; egrets; night herons; bitterns

http://www.thefreedictionary.com/family Ardeidae

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Note added at 17 mins (2008-02-25 12:24:22 GMT)
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Ardeidae
The herons are wading birds in the Ardeidae family. Some are named as egrets or bitterns.
http://www.123exp-life.com/t/01134139029/

Sorry, I realise I was not very explicit above. I meant if your text specifies they are only herons, perhaps you could use that or look up on the Internet which bird species are actually in this area to say herons and bitterns, for example, rather than using the scientific name Ardeidae, which may not suit your text.