Like his previous works, Summer World allows Bernd Heinrich to express his exuberance about nature. A German-born biologist and the son of an entomologist, Heinrich immigrated to the United States with his parents when he was ten and was raised in Maine. After receiving a Ph.D. in biology at the University of California, Los Angeles, in 1970, he began his teaching career at the University of California, Berkeley, where he taught from 1971 until 1980. He then returned to the East Coast to teach at the University of Vermont, where he has spent the remainder of his professional career.
Heinrich has observed closely and recorded diligently the existences of many of the animals and plants that have intrigued him since childhood. Pencil in hand, he has perched in trees and lurked behind bushes, quietly watching the life that unfolds around him and sketching much of it in illustrations that enrich his book greatly. One of the most striking elements of his explorations has been his discovery of many symbiotic relationships among small animals, birds, insects, and the flora and other fauna on which many of them are dependent for their continued existences. Heinrich poses many questions and generally refrains from offering glib answers to them. Posing such questions, however, is an important part of what he is attempting in his book.
Readers will complete Summer World and Heinrich’s earlier companion volume, Winter World: The Ingenuity of Animal Survival (2003), with many unanswered questions but with a great deal to consider and cogitate upon. One of the more beguiling questions Heinrich poses has to do with the migration patterns of the ruby-throated hummingbird. This tiny creature typically weighs about as much as a penny. Heinrich points out that the bird is attracted to specific flowers whose pollen lies so deep inside their bloom that only the tiny hummingbird can access it. Its bill alone has the curvature and length to get deeply enough into the flower to retrieve its pollen. Thus, it is not only the only bird capable of feeding on this pollen but also the only creature capable of pollinating the plant.
Such a unique adaptation may pose the question of whether it is the result of intelligent design. Some readers will subscribe to that theory, while others will consider this remarkable symbiosis an example of evolutionary adaptation and will link it to the survival of the fittest. There is no single answer to Heinrich’s question, but wrestling with such questions as they occur throughout the book provides challenging mental exercises for those to whom such matters are important.
Addressing the migration patterns of the ruby-throated hummingbird, Heinrich considers its annual flight from Mexico to the southern United States as winter wanes, as well as its return flight when summer is nearing its end. The most perilous leg of the hummingbird’s journey involves a flight over 520 miles of open water, as the bird crosses the Gulf of Mexico. This is a daunting expedition for a tiny bird that regularly must consume twice its body weight in food every day in order to survive.
The hummingbird flies at about thirty miles an hour, so to cross the Gulf of Mexico it must fly nonstop for over seventeen hours. On the whole of its two-thousand-mile migratory flight, it fattens up daily on as much food as it can in the early morning, then it takes off and flies until nighttime. On its flight across the Gulf of Mexico, it has no place to land and no way to rest.
Some of the migrating birds avoid the long flight over open water and instead follow a longer route along the Texas coast that gives them opportunities to refuel along the way. Heinrich is at a loss to explain why different birds of the same species adopt different migration patterns, and he wonders whether some of the birds have foreknowledge of the hazards that each route poses. He leaves his readers to think through this puzzle and to work it out in their own minds.
Achieving a level of excitement and curiosity often found in well-crafted mystery stories, Heinrich, in his observations of the wood frog, presents an exciting story of death and resurrection and charges it with an urgency that will keep readers intrigued. As soon as winter appears to have ended, wood frogs emerge, having spent the winter in a state of suspended animation beneath the forest’s carpet of decaying leaves. Many of these frogs have been frozen stiff during the long New England winter. They have no heartbeats. They have no respiration. Their digestive activities have ceased. They have no detectable brain activity....
(The entire section is 1895 words.)