Wednesday, September 24, 2014

What We're Reading: New Natural History



The Homing Instinct: Meaning and Mystery in Animal Migration, by Bernd Heinrich

I always look forward to a new Bernd Heinrich book, because I know that his close observations of animal behavior and the new discoveries he reveals about how specific species “work” are going to be unfailingly interesting. So, too, is learning about the ingenious field and laboratory experiments that have been devised to make these discoveries. You get an exhilarating sense of how science works to find the answers to mysteries of behavior, and come to realize that the answers always seem to lead to yet other questions and other experiments. You are reminded, as always in a Heinrich book, how all of life shares certain “problems” that must be solved, and how these problems with their tight margins for error--the unforgiving laws of life’s economy--are solved with an infinite number of biological and evolutionary “inventions.”

Heinrich is an author who always struggles to organize his peripatetic field observations and eclectic natural history interests into a book with a unifying theme. Some chapters of his books are more related to the theme, while others seem to have only a tenuous connection. For those who have read his previous books, it is apparent that they are a miscellany of smaller studies, often made over the course of a long career, and they know that the author might take you just about anywhere. But that’s one of the lessons. Animal behavior is hard to parse, both when it comes to any individual species but also when we attempt to make generalizations. We cannot assume that a particular behavior we observe in any given species arises from the same motivation or purpose as it may in another, or that it becomes manifest through the same biological mechanisms. It is something integrated into the entire survival strategy of the animal, one behavior in a unique and complex system of behaviors that has been developed over a long evolutionary history. We may be able to generalize through a knowledge of physics and physiology about what an animal needs to survive, but the solutions to these “problems” in any given species--how any single species “works”--is something we can know fully only through observation of the species, from the detail of the particular.

Bar-tailed Godwit

In The Homing Instinct, Heinrich gives us a number of variations on the meaning of “home” for animals, including humans, but the shared “meaning” of home, the common denominator, is that it is a place where the food necessary for raising a new generation is abundant, and where the young of a species can be raised to maturity safe from predators and from a sometimes harsh climate. This safety can be achieved by the selection of a place to dwell and by “building” structures that provide sustenance and protection. Often a place called “home” may involve not only protection from predator species, but the staking out and defending of a territory from other members of the same species.

Heinrich uses this framework to look at homing behavior and migration in a variety of species, exploring the amazing journeys made by salmon and eels from freshwater streams to the depths of the great oceans and back, and offering explanations of how they navigate during their astonishing journeys. He also looks at the epic migratory behavior of sea turtles. Some species like monarch butterflies and ladybugs make generational migrations, a migration cycle in which the individuals who left are not the generation that returns from the point of departure. There is a fascinating chapter on how bees find a suitable location and establish a new home and how they find their way back to it from their forays for nectar in the surrounding fields and meadows.

Heinrich’s exploration of migration is fresh in that he ranges beyond just a discussion of the iconic representatives of migratory behavior--birds. But he does discuss here the incredible and poignant flight of the bar-tailed godwit, which flies non-stop from the Arctic tundra to Australia, arriving with just half its beginning body weight. The discussion about how birds navigate is one of the most interesting parts of the book. The author reminds us that homing requires not only a compass but a map, and he examines the latest ideas about how birds are able to navigate. For most species the knowledge seems to be genetic, but some of the behavior may be learned. Birds seem to be able to sense the earth’s magnetic fields, use landmarks and the position of the sun, and make calculations for course corrections based on time and place. A series of ingenious experiments suggest that some birds apparently navigate by the stars.

                                               Salmon


Sea turtle
The Homing Instinct contains engaging details of animal behavior, but there are also some “big” ideas that Heinrich extracts from them for our consideration. What we interpret as a homing instinct may exist in tandem with a dispersal instinct. A home may become overpopulated or resources there may be insufficient. Individuals seeking to prosper and breed may face better odds by leaving their home. He reminds us that we have a tendency to seek not only a single purpose for a specific behavior in an animal but that we frequently attribute such behavior (and its management) as a response to a single sensory stimulus. It now appears that migrating animals may use a variety of senses to navigate. We do not understand how each sense interacts with the others to allow them to do this. Behavior is more complex than we had supposed. We know about the importance of genetic diversity and its role in the survival of a species, but Heinrich suggests here that “imperfections” in migratory behavior are also an important way that nature keeps options open for a species: A few animals do not find their way back to the homing ground on the migration with the rest of their species and miss the mark. Yet they may find themselves in a place that is even more conducive to their successful survival or, perhaps, the traditional home and the population of the species homing there may be lost to a natural catastrophe or a man-made cataclysm.

No doubt the most intriguing and--what will no doubt be the most controversial--idea in The Homing Instinct is what Heinrich has to say about some of the major species extinctions with which we are familiar here in America. He finds in their story something ominous for the future of our own species. He explores the history of the extinct Rocky Mountain grasshopper, the passenger pigeon, the Carolina parakeet, and the Eskimo curlew (and the almost extinct bison), and explains that hunting was not the sole cause of their extinction. They were particularly vulnerable because they were “overly gregarious” species who “homed to the herd,” animals who were not attached to a particular place as a home but rather to each other, to the group. Key and vital behaviors in such groups are triggered by their “conforming” behavior, which is the foundation of their sociability. The large size of these groups actually triggers a narrowed and sequenced range of behavior (including nesting and reproductive practices), and when that is disrupted a destructive cascade can be set in motion that finishes them off in short order. Heinrich is concerned that we may have become such a species. 

The now extinct Passenger Pigeon

The great 19th-century entomologist Jean-Henri Fabre wrote, “Life has unfathomable secrets. Human knowledge will be erased from the world’s archives before we possess the last word that a gnat has to say to us.” We live today in an age when we believe that we can come to know everything there is to know about life and the life of any species on this planet, and also one, ironically, in which we don’t seem to care very much if we come to know it, that such knowledge has little to do with us and how we live. But if you are one of those people who is desirous of knowing that little of the all we cannot know, if you think that little may still be of some vital use to us as a species, or if you simply delight in indulging your sense of intellectual curiosity about the world in which we live, you couldn’t start at a better place than reading a book by Bernd Heinrich.


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