August 14, 2014
Springer Science+Business Media
Preen gland secretion causes hoopoes’ eggs to change color, possibly giving signals about the robustness of the mother bird, researchers have found. Hoopoe females use cosmetics on their eggs - and the eggs gradually change color when they are incubated, from bluish-grey to a more saturated greenish-brown. This happens because secretion from the uropygial or preen gland – a substance birds use to preen and protect their feathers – is transfered from the female hoopoe’s gland to her eggs directly with the bill and by means of belly feathers.