Evolution's Rainbow. Joan Roughgarden
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biologists are more observant than birds?
In woods near Oslo, Norway, male flycatchers who had set up territories were presented with individual caged birds to see if they could distinguish the sexes.24 A territory-holding male who hadn’t already attracted a female reacted to a female by showing off the entrance to his nest hole and calling enticingly. When the same male was presented with a macho black-and-white male, he was not so hospitable, and jumped on the cage of the visitor, pecking at it, trying to attack, and not bothering with any welcoming calls. When a feminine brown male was presented, the male again showed off his nest hole and called invitingly. Is the territory-holding male making a mistake, believing the feminine brown male is a female?
Later in the season, after these territory-holding males had attracted a female, they were again presented with the feminine male. This time, about half of the territory holders did not court the feminine male visitor, but instead reacted aggressively. The investigators concluded that the territory holders had now acquired enough “experience” with females to tell the difference between a female and a feminine male, so they were no longer deceived.
But some of these very same territory-holding males had bred the preceding year. Didn’t they become “experienced” at that time? The investigators concluded that the territory-holding males forgot over the year how to tell a feminine male from a female, and needed “recent sexual experience for correct sex recognition,” which had to be “refreshed each year.” Could territory-holding male birds be this dumb?
At the beginning of the breeding season, the feminine males tend to arrive late, and they must find space for their territories amid the territories of birds that arrived earlier. The feminine males are allowed to settle closer to the macho males than the macho males can settle next to each other. If you were a macho male, wouldn’t you allow a friendly neighbor to settle closer to you than an aggressive neighbor? Not that the feminine males are necessarily wimps. When forced to compete with a macho male for a nest box in experimental aviaries, the feminine male attacked first and won, provided he fought at all. Twenty percent of the time the feminine male didn’t bother fighting and simply let the macho male have the nest box.25
Males with territories who had not yet attracted a female have been observed in the wild advertising to feminine males. The territorial male shows off his nest hole, gives enticing calls, and the feminine male joins him and they enter the nest cavity together. Does it seem plausible that the feminine male has used deceit to enter the home of a territorial male “to obtain information” about his “nest site quality”? Would the feminine male be that devious?
A simpler explanation is that territorial males who have not yet attracted a female are horny and invite romance with feminine males. Once the territorial males have attracted a female, they are no longer horny and no longer interested in courting a feminine male. A simpler explanation is that no one is deceived, no one forgets from year to year, and no one requires continual updating of his limited memory. A simpler explanation is that the two male birds who retire together into the nest hole are enjoying a romance. These birds may be neighbors building a cooperative relationship based on same-sex sexual attraction.
The problem with deceit theories of animal behavior is that not only must some animals be implausibly dumb, but others must be remarkably devious—there must be great asymmetry in cognitive ability. Imagine a bird sneaking into the nest of another to spy on it. What would a bird do with what it saw? Does a bird keep a file cabinet in its head full of dirty secrets about its neighbors? I don’t think so, and scientists have not shown any such thing.
The European kestrel (Falco tinnunculus), a dramatic bird of prey, offers another instance of cross-dressing. Males two years and older are blue-gray with brick-red on the back and spots on the head. The females are mostly brown, with a barred pattern on the head. One-year-old males resemble females, so much so that observers find it difficult to tell young males from females. Biologists have therefore suggested that year-old males are female mimics who deceive older males into thinking they are females.
About thirty birds were housed in isolation at a field station in central Finland.26 A bird was placed in a box with one-way glass on the sides. Birds were also placed on the sides; these birds couldn’t see the central bird because of the one-way glass, but the central bird could see them. The biologists then noted which side bird the central bird paid most attention to and tried to associate with—called the “preferred bird.”
When the central bird was a macho male and was offered a macho male on one side and a female on the other, he always preferred the female. When he was offered a feminine male on one side and a female on the other, he preferred either in a fifty-fifty ratio. The investigators claim they’ve shown that a macho male bird can’t distinguish a feminine male from a female. Clearly, though, there is another possibility: a macho male may be quite able to tell the difference between a feminine male and a female, but he doesn’t care which he sits next to.
When the central bird was a female and was offered a macho male on one side and a feminine male on the other, she always preferred the macho male. The investigators claim they’ve shown that females are better able to distinguish sexual identity than males are. The experiment doesn’t speak to whether a female can distinguish a feminine male from a female. The female wasn’t presented with a choice between a feminine male and a female; the female was offered only males.
The investigators go on to speculate that “the better sex recognition ability of females compared with males may have evolved because she is the ‘choosy’ sex. Males . . . do not need to be so good at sex recognition as females.” Deceit theory is a trap. Deceit theory forces scientists to take sides on who is smarter—in this case, claiming that females are smarter than males.
A different kind of cross-dressing is found among red-sided garter snakes (Thamnophis sirtalis parietalis).27 One of seven distinct subspecies of the common garter snake, this nonpoisonous snake is predominantly black with yellow stripes and red bars, and eats invertebrates and small rodents. Females are 10 centimeters larger than males, averaging 55 and 45 centimeters, respectively.
The red-sided garter snake has made Manitoba’s interlake region world-famous for snake-watching, and the town of Inwood has even created a monument in recognition of its large population of garter snakes. Snake dens (or hibernacula) can be found in tree roots, shale cliffs, rock piles, sewers, foundations, animal burrows, rock outcrops, and sinkholes. Twenty thousand garter snakes may gather in a single den during the winter. In spring the snakes’ mass emergence creates an awesome natural spectacle. As far back as the 1880s fashionable picnics were held near Stony Mountain just to watch this phenomenon. But the snake gatherings have also provoked fear. In a labor strike, penitentiary construction workers once refused to work at Stony Mountain until the den was destroyed.
After the snakes emerge, they mate and then disperse to their summer homes in marshes and shallow lakes. Males hang around the dens longer than the females, so that the ratio of males to females near the den entrances is ten to one. Courtship takes place in small groups called “mating balls,” in which one animal is courted by several others. These “suitors” align their bodies with the courted individual and vigorously work to position their tails base to base with the tail of the courted individual, resulting in a ball of writhing snakes.
Females have special lipid perfumes in their skin that turn males on. In 1985 some male garter snakes were found with female perfumes in their skin. Of two hundred mating balls, about 15 percent consisted of a male, presumably with female perfumes in his skin, surrounded by courting males. The males with female perfumes were called—you guessed it—female mimics. The feminine males who joined female-centered mating balls in progress were thought to be distracting the males already there, thus giving themselves greater access to the female.
As with the other claims of female mimicry, the story had internal contradictions. In choice experiments, the males preferred a female to a feminine male, showing that males could tell the difference—they were not deceived. Moreover, in 2000 it was found that all male garter snakes have female perfumes when they emerge from the den in the spring and that all males court these perfumed males in addition to females. At this point, the investigators floated four deceit-based theories