If a birder notes variations in the pink, yellow, or orange shades of the bill among different White-crowned Sparrows, what factor primarily dictates this color variation?

Answer

A function of geography

The variation in bill color among adult birds is largely dependent on the geographical location or subspecies, rather than being determined by the bird's sex.

If a birder notes variations in the pink, yellow, or orange shades of the bill among different White-crowned Sparrows, what factor primarily dictates this color variation?
birdappearancefemaleWhite-Crowned Sparrowmale