Avian manus claws

["Norton, Patrick" <Patrick.Norton@state.me.us>]

I spent part of the week-end reading C. William Beebe's 1906 book _The   
Bird; Its Form and Function_ (Henry Holt and Company.)  The book includes   
a photograph taken by the author of the forearm of an Ostrich (feathers   
removed) which clearly shows two curved claws protruding from the skin,   
presumably from the end of digits I and II. The author claims this is the   
typical condition of adult Ostrich as well as adult "swan, Osprey, Turkey   
Vulture and the various Ostrich-like birds."  Unfortunately, the book   
does not include any references.

Can anyone on the list confirm Beebe's claim? Up until now, I was under   
the impression that, among the living birds, only young Hoatzin exhibited   
manus claws.