Fish Crow and White Ibis

This is an example of the type of predation Fish Crows are capable of. They are notorious egg thieves and with will take chicks as well.

This happens often enough when nature takes it's course(as this was the case).

This is just one of the reasons I won't approach my nesting colonies as closely when they are nesting as I will other times of year.

It only takes is a few seconds for a Black Crowned Night Heron or Fish Crow to raid a nest.
If you get to close and flush the adult birds, in many cases you have condemned the chicks to the above eventuality.

Now if the crow had a better head angle:).

I applaud you for not disturbing nesting birds!

Crows are clever enough to follow you into a nest to do a raid. One standard precaution when working in ibis and other colonies is to frequently change your route in to the nests.