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Message: <blockquote data-quote="Alexjh1" data-source="post: 3496855" data-attributes="member: 85555">From what I gather, not especially in non-breeding, though the average dimensions are different.  But that's not exactly unprecedented in herons - breeding plumage birds of for instance Chinese and Javan Pond Heron look totally different, while in non-breeding they're almost impossible to tell apart.The problem is that just because the difference between two species isn't obvious in the field to a human, it doesn't mean it isn't to the birds themselves, which has a lot more to do with whether they are the same species or not.  Otherwise Marsh/Willow Tits or Willow Warbler/Chiffchaff would have to always move in close enough to each other to inspect the minutiae or have a brief awkward conversation to work out if they were the right species or not.</blockquote>