Summer World_ A Season of Bounty - Bernd Heinrich [65]
I come down from my perch and then climb up the birch to inspect the licks. As expected, they are indeed dry now although the woods are still lush and green. But what a difference from what they were like a few weeks earlier! There is no more birdsong. Even the sapsuckers, who were noisily drumming all around this lick when they first came in mid-April, and who continued vigorously into late June and July when their young fledged, have now ceased. The summer is ending and life is clearly on a much more leisurely schedule. The birds may already be fattening, preparing to leave the summer world behind them.
LIFE FEEDS ON OTHER LIFE, AND IT’S NOT ALL ABOUT FLIES sucking blood. Indeed, most of the interesting and—to us—uplifting nature stories emerge from other feeding relationships. Even as I write on 2 July 2007, the Amelanchier (Juneberry) tree in front of my office is being visited by robins, cedar waxwings, purple finches, rose-breasted grosbeaks, a catbird, and a veery. They are feeding on the now ripening (but not yet ripe) berries, and will be spreading seeds in all directions to potentially “plant” more trees. Whether or not we approve of any feeding relationship generally depends on whether we are on the giving or the receiving end. The ruby-throated hummingbird that brightens our summer days is at both the giving and the receiving end of feeding relationships: the receiving end is from us and sapsuckers, and the giving end is the pollination of plants in Central America.
There are at least eighty-six species of hummingbirds in Brazil alone, of 343 species documented so far. America is the hummingbirds’ home, and the South American tropics are the heartland of these jewels of the bird world. Here, in New England, we are graced by only one species, the ruby-throated hummingbird, Archilochus colubris. It is a suburban favorite that is easily attracted to a bottle of plain sugar water marked with a red artificial flower.
Like all hummingbirds, the ruby-throat belongs to a family exquisitely adapted to feed on the nectar of flowers, and many flowers have coadapted to be pollinated by them; one depends on the other. “Hummingbird flowers” have a long tubular neck (corolla) that excludes “nectar thieves”—those animals that feed from these flowers but do not pollinate them. Hummingbird flowers are commonly red. In contrast, the flowers pollinated by sphinx moths—the nocturnal analogues of hummingbirds—are white and strongly scented, to be more easily located by prospective pollinators.
Many hummingbird species are, in turn, adapted to specific kinds of flowers. Even the length and curvature of their bills fit specific flowers (and exclude others). But the ruby-throated hummingbird is, in many ways, one of a kind. It is the only hummingbird that has extended its range into the coniferous forests of northern Maine and Canada, in areas where all summer long there are only small white nectarless flowers on the mossy ground, and no red flowers at all. Farther south I had been astounded to see ruby-throats when there was still snow on the ground, long before any flowers opened, and before there were any leaves on the trees. Once in April when there was still snow on the ground, a hummingbird appeared as if out of nowhere and hovered briefly in front of my face. A friend told me of seeing another one hovering around the head of a pileated woodpecker. I had been wearing a red hat. The woodpecker has bright red feathers on its head. I suspect that these hummingbirds had recently come back from their tropical wintering grounds, where they had been feeding at red flowers. On coming north they were still responding to the same signal that had meant food. But why and how did and could they have risked leaving their tropical paradise with red flowers, to come so far north at a time when there is no red and there