Yellow-rumped Warbler (Setophaga coronata)
What is this bird? We don’t have snow here in Florida, which would allow this bird to be more camouflaged. On the contrary, it would stand out against all the tropical green. Being white makes it much more visible and thus vulnerable to predators, and perhaps not as attractive to mates. However, this small warbler appears healthy.
There are
two primary pigments that color feathers: melanines (transferred to feathers
and tissues by the enzyme tyrosinase) and carotenoids (obtained through diet by
some species). Depending upon concentration and distribution, there are two
melanin pigments: eumelanin (black, gray) and pheaomelanin (red dark brown and
in less concentrations, yellow).
Albinism is a rare, genetically determined result where there is an absence of
the tyrosinase enzyme that is essential in producing melanin. This
total absence of pigment from even eyes usually exhibits white feathers, but
red beak, eyes, and legs as the blood underneath is the only color seen.
Without color the eyes are more sensitive to light and have less depth
perception so albino birds are vulnerable to predators and seldom reach
adulthuood. Yet through diet certain species of albinos can still have
yellow/pink caratanoid coloring through their diet.
This is not an albino warbler, since this warbler has some color – dark eye color, yet similar to abinos, no coloring in its beak and legs, allowing its blood circulation underneath to give their red coloring. This bird is called leucistic (pronounced lu-sis-tic), an uncommon genetic phenomenon showing some but not full color, when pigment cells are unable to develop.
The normal eye color and yellow side patch and rump, are just like the Yellow-rumped Warbler! However, it shows lighter brown streaks on its sides, back, head, and wings where darker brownish-black concentration is usual for this species. The light brown is there but not the black pigment, indicating lack of the eumelanin pigment. So this is called partial leucism and appears that the eumelanin pigment did not differentiate, but the pheaomelanin pigment did.
Very uncommon to see these odd genetic phenomena, and rarer still to catch a photo of it, as such birds likely do not survive long. Makes identifying the bird a challenge, doesn’t it?
Juanita Baker, Coordinator
Florida Bird Photo of the Month
Pelican Island Audubon Society