Here, Birds Are Unafraid
Galápagos seabirds tolerate human spectators, and crabs in Panama ignore cars (but hide from trucks)
I recently returned from a Smithsonian tour of the Galápagos Islands. This was my first visit to the Mecca of biologists. Now, I am not easily impressed by wonders of natural history; in the course of nearly 20 years as a tropical biologist, I have seen a lot. In the past, when I was based at the Smithsonian's jewel-in-the-crown Tropical Research Institute, in Panama, I worked in more than 20 different tropical countries, and mainly in rain forests. What was outstanding about the Galápagos was the "tameness" of the animals. On island after island you can walk right up to animals that would, in all other circumstances, be expected to flee.
As a consequence of this tameness, one of the delights of my visit was to stand close to a pair of blue-footed boobies and watch the high-stepping choreography of the pair-bonding process. When a male returns to the nest site, he doesn't just alight. He gives a performance directed at his mate and potentially rival males. He lands flamboyantly: wings outstretched, primaries fanned out to the maximum area, tips curled upward — a toreador's cloak disproportionately magnified. Add to this the almost vertical body, with tail extended in line, and glorious blue legs and feet. These last have their webs fully extended, and whichever one is up is held against the pale belly, maximizing the visual impact. The males may or may not do this while facing females, and may even show such behavior when females are absent. It is the male's way of announcing that this is his territory.
What follows the landing appears comical, almost Chaplinesque, but its message is vital. The male may walk around using exaggerated, deliberate-looking leg movements, displaying his bright-blue legs and feet. Actually his parade is closer to the pick 'em up and put 'em down gait of beflippered scuba divers. Bird guides describe the color of the feet as bright blue, but that is totally inadequate. I remember a once-fashionable color called shocking pink . . . this is shocking blue. The bill is part of the show, too. As the walk-about proceeds, first the bill is held against the chest, pelican-style, then, as if overcome by shyness, the male faces away from the female with bill raised up, and finally may turn toward the female, spread his wings and "sky-point." The head is thrown back, the bill is pointed straight up and the wings are rotated, so that the top sides of the wings are presented to the female.
All of this and more, including whistling and bill-touching, is part of the ritual. The female is not a passive "suitee." She may parade around; jab at the male, dueling style; face away; rattle her wings; and sky-point, too. Eventually, there is symbolic nest building and mating, and then two, sometimes three, eggs are laid. All this can be seen close-up, without a blind, without recourse to binoculars. The birds are not afraid. As one watches the boobies, they in turn regard the human observer from time to time with their beautiful golden eyes.
Boobies' eyes face forward for a simple reason: depth perception. Nonpredators have wide-angle eyes set on the sides of their heads to watch for enemies. We humans have stereo-vision, and a relatively narrow field of view. That's why we need rear- and side-view mirrors in our cars. If we were deer, we'd need front-view mirrors to drive.
Boobies need accurate depth perception because of their fishing technique. They can spot fish from 100 feet and more above the water, and then they fold their wings and drop like stones onto their prey. A squadron — sorry, flock — of boobies may fly in and almost simultaneously drop onto a target area. Another trip highlight was to see feeding frenzies involving fish, birds and whales. These occur when birds find large schools of "bait fish." Predators quickly assemble. I saw feeding frenzies at schools of anchovies, with three species of boobies playing the dive-bomber's role and frigatebirds flying in as low-level attackers, skimming the water and scooping up fish with their hooked bills. Sharks gathered around the melee, while large tuna flashed through the scattering schools. Clouds of anchovy scales slowly fell like confetti around the massacre. As a grand finale a huge Bryde's whale breached nearby, exhaling its breath with a watery sigh. It was netting hundreds of anchovies in its huge whalebone jaw-filters. Great theater!
The Galápagos tameness has — presumably — evolved in the absence of substantial predators. It is found in birds of other oceanic islands. The distance that an animal normally puts between itself and a predator is called flight distance. This equates to the distance a predator can approach before the animal flees.
When I was studying the defensive behavior of crabs in Panama, I found an interesting variation in the flight responses of mangrove crabs. Those that I watched lived close to a major road. They did not flee down into their burrows in response to passenger cars but did retreat when large trucks went by. Trucks were rarer than cars, in a ratio of about 1 to 40. Interestingly, the escape response to trucks persists in the absence of real danger. No crab has ever been attacked by a truck when standing outside its burrow. It is appropriate, however, that escape responses to large moving objects should be difficult to extinguish. But, because hundreds of cars passed by throughout the day, running for shelter every time a car passed wouldn't be energy efficient. In the absence of attacks, many organisms learn to ignore stimuli that are constant or occur frequently. This is a behavioral process called habituation. It occurs widely in the animal kingdom. Scarecrows cease to scare. Plastic owls on buildings finally fail to exclude roosting starlings, and recordings of their alarm calls eventually fail to rid airports of feeding seagulls.
The history of oceanic islands is one of human destruction. Animals and plants have been ravaged by short-sighted exploitation for food, fashion and fancy. The graveyard of vanished species is ominously impressive, with the dodo perhaps the best known. Birds were dominant on many of the islands because flying creatures were most likely to reach islands distant from populating mainlands. Mammals usually came with the human colonists. This happened both intentionally and accidentally. Dogs, pigs and goats were introduced as food sources. Rats made it ashore because they are prime members of the mammalian Explorer's Club and stowaways on vessels of every description.
So what about the future of the Galápagos fauna? The tameness raises some interesting questions. It is not the tameness of habituation, as the earliest visitors noted, since there have been no repeated false alarms from intruding humans. Without contact with major mammalian danger, has fear been bred out? Are humans specifically excluded from the dangerous category? We can't afford to experiment in search of the answers. Neither can we afford any more mistakes in allowing dangerous animals to settle in the enchanted islands. After seeing the glory of it all, I hope we can act in time to save, for future curious naturalists and all who possess a sense of wonder, the essence of the Galápagos magic.
By Michael H. Robinson
Michael H. Robinson, director of the National Zoological Park, is an animal behaviorist.