That pattern of morphological convergence includes larger bills, reduced rust coloration in plumage, and increased melanism or dark coloration.
The work of Burtt and colleagues provides a nice complement to recent work on the genetic basis of melanism in birds.
Adaptations to short, cool summers include activity at low temperatures, selection of warm habitats and microhabitats, melanism and hairiness coupled with basking behaviour, and prolonged or abbreviated life cycles.
Albinism does occur in some populations, but there are no published records of melanism (black fur) in lions.
However, melanism and amelanism are known to occur in many species of natricine snakes.
Oh yes, one coyote and one melanistic squirrel also made the list!
By the time the George Reserve was revisited in 1994 and 1995, the percentage of melanic specimens had dropped to 18.3%.
Its gorgeous spotted coat is distinctive, but jaguars with uncommon melanistic coloration are pure black.
Such is the case with melanistic (black pigmentation) variation in some anenomefish species.
There may still be very good mechanistic reasons why melanic plumage color reveals individual quality in European barn swallows, but they should have nothing to do with carotenoid signaling.