Spotting a Scarlet Tanager in the upper story of an Eastern Forest transports me to the tropics. And it is a tropical forest dweller in our winter months.
Our Northern Cardinal is almost as rosy and House Finches a bit less. Their red plumage is thought to come from carotenoids obtained in the diet (originally beta-carotene, the abundant precursor in plants—think carrots). Since tanagers are mostly insectivorous and insects have a lot of carotenoids, there is an easy explanation for why tanagers are bright red, except for an awkward fact.
While cardinals remain much the same color the year round, male Scarlet Tanagers are much less rouge when they go south, although they still have black wings and a black tail. They look like female tanagers, olive-yellow. Their diet is still based on insects in the tropics, so that is unlikely to account for the change. Since their testosterone levels plummet to female levels after the breeding season, does that suppress gene expression in the liver where carotenoids are converted to pigments (by p450 cytochrome enzymes)? Please enlighten me, readers.
These bluebirds are residents here all year. The first was abandoned but we now have eggs and chicks in two nest boxes. After cool weather, it is now warmer and insects have hatched for parent birds to stuff in the wide beaks of demanding youngsters. They often fly to the ground from a perch for a morsel invisible to us. From a distance, the male plumage looks slate-blue but close-up in the sun they are gorgeous blue and rouge. Evidently, the blue color is created by light scattering (like a prism) whereas pigment is responsible for their sky blue eggshells. Why they are blue to match plumage when many other cavity nesters have white eggs with or without speckles is a question I can’t answer. Recent research confirms that birds tend to be more colorful in the tropics, but our bluebirds are among many exceptions to the rule.
Almost all the Yellow-rumps have left for breeding grounds in the north. They are a pleasure to welcome back in the garden in early fall, quite unmistakable with their yellow rump and side. A large warbler and the only one we expect in winter, often feeding on berries in the middle canopy.
They migrate in large flocks. In the spring of 2001, an estimated 34,000 were seen over Northampton county for two hours. Never here in summer, they are occasionally reported in the west of the state where they rarely stay to breed.