Darren Naish has a new blog post on bird anatomy, Clubs, spurs spikes and claws on the hands of birds (part I). The focus is mainly on the pointy bits that don’t originate directly from the digits, but it’s the “normal” bits—claws—that fascinate me.
Anyone into birds knows about the well-developed wing claws on digits I and II of young Hoatzins, but as Darren points out there are a lot of birds with wing claws, even chickens. Most people never notice them, though, because they’re so tiny. In chickens, the claw on digit I (the alula, homologous to our thumb) is reduced to an inconspicuous nubbin that’s easier to feel than to see (if you’re a carnivore, check for it the next time you cook a chicken).
The first bird that I ever noticed a wing claw on was the Crested Wood-Partridge or Roul-roul. I had the privilege of getting to know these exquisite little birds back in the late 1970s when I worked as a zookeeper. A pair that lived in the rainforest exhibit of the bird house occasionally produced eggs, and with artificial incubation one of these produced a chick.
The normal procedure for precocial chicks was to place them in a plywood brooder box with a heat lamp, some gamebird starter mash with chopped lettuce garnish, and a drown-proof waterer and just leave them alone. This works fine with your average gallinaceous bird, but Roul-rouls are not your average gallinaceous bird. “Roulettes” are fed by their parents for the first few days of life, and since the parents in this case weren’t involved, this job fell to me.
Several times a day I would get the chick out of its box, place it on the bird house’s kitchen counter, and present it with succulent morsels of greens, fruit, boiled egg, and chopped mealworm. It was on the first of these close encounters that I noticed something hard and shiny protruding from the leading edge of the roulette’s wing: a long, curved black claw. I was stunned. It could have been a kitten’s claw, except that it was sticking out of a bird’s wing.
Up to that moment in my young life, the evolution of birds had been an abstract concept, based on evidence with which I had a basic familiarity but no personal experience. Seeing the wing claw on the Roul-roul chick was like being smacked upside the head with evolution.
Roul-rouls spend their days on the ground but roost in trees. I wonder if, like the young Hoatzin, the Roulette’s wing claws help it navigate the third dimension of its rapidly vanishing tropical forest home?