We’re going to start this post the same way I started out my last one. I have the afternoon off from work, I drive up to the Few’s Ford parking lot, and I exit my car. From the woods, I can hear an odd clucking, a cuckoo. I search for it, and before long it sits up on a bare branch allowing me to get photos. A dark, thin bill. A dull eyering. Small size. Everything points to one ID in my mind: Black-billed Cuckoo. But, as the discussion of the bird continued, it became clear this was actually a young Yellow-billed Cuckoo. And everything I know is wrong.
My mistake? Relying on field marks. On some level in one’s birding career, they stop using field marks to identify a bird. Instead, you rely on the overall impression of a bird, and by gestalt you immediately know its ID. Every once in a while, a bird throws you for a loop, and you begin to register field marks to try and find an answer to its identity. Sometimes you have to take a step back though, and acknowledge that even with an unknown bird, its general impression can give important clues. While many of the field marks appear to point towards Black-billed Cuckoo, the overall impression of the bird is wrong. The bill is actually a little too small, and its vocalizations are too guttural. Plus the tail is too small.
|A young Yellow-billed Cuckoo. Can't you tell?|
First off, why does the tail look small? It’s missing tail feathers, which is important because that’s a sign of molting, and a heavy molt like this would make it harder for a migrant to continue on its southerly journey. It’s hard to see in most of the photos, but you can just make out a pale area continuing inward from the beak towards the eyes. They aren’t feathers – no, this bird is a fledgling, and the pale area is the gape it retains from its time in the nest. It’s late in the year, and most field guides indicate this plumage doesn’t continue past August, but cuckoos are apparently notoriously late breeders. Plus, I blame global warming.
|You always hear about confusing fall warblers, but never confusing fall cuckoos.|
So why is the bill so thin and black? Turns out, some young Yellow-billed Cuckoos actually have dark bills in the nest, and even fewer retain that past fledging. In addition, young birds don’t have very large bills to begin with, but the real kicker lies in the bird’s feathers. They’re shaggy and fluffy, not sleek like those of most cuckoos. This bird is in juvenal plumage, that awkward stage when a bird is just out of the nest and learning to fly. The fluffy feathers obscure part of the beak, making it look even smaller than it should.
|How a Yellow-billed Cuckoo is supposed to look - sleek, slender, and with a big honkin' yellow bill!|
And what about those weird sounds the bird was making, that call and response with another cuckoo in the woods? It seems this was the call of a juvenile bird, and while it maintained the tempo of a Black-billed Cuckoo, it’s growling, guttural nature is unmistakably Yellow-billed. It’s something I should have noticed in the field, but the call was so strange I pretty much dispelled the idea of Yellow-billed Cuckoo from my mind.
So there you have it. A mistaken ID, but one resulting from a perfect storm of odd and poorly-known circumstances. This could have been identified correctly in the field, but it takes an expertise much greater than mine. You can’t look at this bird and use its field marks to ascertain its identity. You have to know so much more – about its breeding habits, about its growth cycle, about its social behavior. You have to understand the bird’s whole biology to figure out its identity, and until you do, you’re just a guy looking at pictures in a field guide. The whole thing is an experience always remember, and for the rest of my life, I’ll never again mis-identify a fledgling Yellow-billed Cuckoo with a black bill. You could say I… won’t get fooled again.