Our summer birds have settled in, and for many, the first brood is hatched and fledged.
I eagerly waited for the arrival of these birds from their home in the tropics way back in late February. Even during those cold and snowy days, I would watch open fields for common grackles and the first red-winged blackbirds.
In March, the first sight of a turkey vulture, like overgrown swallows returning to San Juan Capistrano, was cause for celebration.
In April, even though wildflowers were pulling my attention to the forest floor, I was keeping my eyes on the tree tops for more and more arriving spring migrants. A particular highlight of the month was the first of the chimney swifts. They signaled that the season was changing from icebound to vernal, because to feed those birds, insects had to be on the wing in warmer air.
By May, the return rush of migrants quickened, and the colorful array of warblers ornamented slowly greening trees. Although warbler migration sends a beatific tremor through the birding world, for me, the bird that really signals that winter has passed is the hummingbird. Warblers are looking for a lunch on insects, but hummingbirds dine on flower nectar.
I guess my love of plants and the close connection between hummingbirds and blossoms makes this bird special.
Hummingbirds are fascinating. First, they are the smallest birds. Indeed, they contend for the smallest warm-blooded vertebrate on the planet.
The bee hummingbird (Mellisuga helenae) is, as the name suggests, tiny. It is found only in Cuba, and, unfortunately, is restricted to a few areas of wetland habitat. Several years ago, I unsuccessfully attempted to see this 2-inch-long bird in the Zapata Swamp near the Bay of Pigs.
Just before my trip, a hurricane swept across the eastern end of Cuba. Roads and infrastructure were heavily damaged, so our birding group couldn't get to the best locations.
At the time, there was a fear that the hurricane might have killed off at least one of the populations of this endangered hummingbird. However, friends on subsequent trips reported finding the bird in the places we were scheduled to visit.
To get an idea how small this bird is, look at your index finger. From the end of the fingernail to the second joint is about 2 inches on most adults. The bee hummingbird's body is about that long. The weight of an adult is 1.8 grams -- lighter than a dime.
That's a tiny bird.
It's also small for a warm-blooded creature -- about as small as one can be. Keeping a body warm takes a lot of energy. For large, warm-blooded vertebrates, like elephants, the mass of the interior body is large compared to the surface of the skin. Such a high ratio of inner flesh to outer surface is good for retaining heat. Animals that are smaller have less internal mass compared to external surface, where heat is lost; thus, they have to generate more heat to stay warm.
The bee hummingbird, the tiny Etruscan pygmy shrew (living in southern Asia and weighing 2 grams) and the bumblebee bat of western Thailand (about 2 grams) have to generate a lot of energy to keep those little bodies warm.
In addition, the bee hummingbird beats its wings at about 80 times each second, and as many as 200 times per second during courtship flights, so it has a need for even more energy.
Hummingbirds require so much energy that they eat constantly. Long nights are a problem. They adjust to periods of darkness -- when they can't feed -- by lowering their body temperatures. During the day, their body temperature is about 105 degrees. …