Witte nagels bij Torenvalken Falco tinnunculus

Among almost 2000 nestlings and more than 400 full-grown Kestrels ringed in a study area in the central Netherlands in the 2000s, a nestling male was found with a single white claw (one foot), and a female nestling with three of the four claws (on both feet) white instead of black. These birds were recorded in the same nestbox, respectively in 2009 and 2011. The male was recaptured in October 2009, when its claw was still found to be white.