Mystery Animal: Egret?

What is this mystery animal?

I photographed these birds at Bolsa Chica Ecological Preserve near Huntington Beach in Southern California. While feeding, these birds were sedate and the feathers on their heads were flat. However, suddenly the birds launched into this display. Do you have information? Here are my questions!

Is this love or war?

Are these Snowy Egrets?

How are egrets related to herons? There is a great deal of Celtic mythology related to herons, and I wonder if egrets are related.

Update! Scott and Alan, two individuals posting on both believe that these birds are Snowy Egrets. In addition, Scott thought it was a dispute over feeding territory. Thanks for the info!

The habitat is a muddy marshland with many species of birds. I observed these birds in early July.

Please send me an email with any thoughts on the identification of this animal, to provide insights, or to share birding experiences. Thank you so much for any help you can provide.