His site offers the definitive breakdown of the situation, but I thought I'd recount my own experience too. I ID'ed my first Fish Crow last February on a trip to Florida to visit my Dad, who lives in Highlands County in the central part of the state (about 90 miles south of Orlando). While biking around his neighborhood (which is in a relatively rural area with new housing developments), I saw a number of black birds which I simply called "crows", meaning American Crow, until they spoke up. I heard the nasal caw-caw, just as depicted in this audio file, and once I heard several individuals with the same tonality, I felt confident that it wasn't simply a begging call from an American. The timbre just wasn't right for an American - more than just nasal, actually, it's...well, I call it "constricted", as if the bird almost sounds like it's being choked. Once I heard it, I actually found it quite distinct, and will never confuse it with any American call again.
I got another chance for skill reinforcement in October on another visit to see my Dad. This time the Fish Crows were all around his backyard, which was quite convenient since I now had a nice digital SLR with telephoto handy.
As you can see, they are very similar looking at first blush to American Crow, and without their frequent calling, it would be very hard to separate them. McGowan cautions on discerning the species based on physical characters in the field given their subtlety, and based on my own experience I would have to agree. As much as I wanted to, I was not able to use size difference at all - it is just so difficult to judge that in the field, especially if the birds aren't side-by-side. I mean, sure, sometimes they do kinda look a little small, but that's in no way reliable. Even looking for the "shorter legs" was more problematic than I would have thought, just from consulting Sibley.Another difficult character McGowan mentions is the relative lengths of P5 and P9 in the Fish vs. the American. I have a couple photos of the bird in flight, and offer one here.
Stills of birds in flight must be carefully interpreted, since the appearance of feather length can be distorted by momentary flexure of the wing and the observer's viewing angle. Those caveats aside, both my pictures show P9 to be at least as long or much longer than P5. (I know that P9 isn't actually significantly longer than P5, but I would submit that it is much more likely to appear so, and to appear lengthier in a Fish Crow than in an American, under similar flight postures.) By comparison, this photo by Bill Schmoker of an American with wings outstretched suggests P9 to be about the same length as P5.Another piece of supportive circumstantial visual evidence was the ruffling of the throat feathers during calling that McGowan mentions.
You can see that in my pic on the left of another Fish Crow individual, taken shortly after the one above. Also note his bent-over posture - again, not exactly diagnostic, but given the other data, at least supportive of the Fish Crow ID.In the end, the calls are always your best bet. Thankfully, crows are rarely bashful or reserved, and can usually be counted on to give themselves away without much cajoling. May your Fish Crowing be as educational as mine.
tags: birds crows
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