A Males Work is Never Done
In the topsy-turvy world of wattled jacanas, it´s the females who get their guys
- Tui De Roy - Photographs by Tui De Roy and Mark Jones
- Jan 01, 2000
Dawn comes early on the Isthmus of Panama, and life along the Chagres River is already stirring at 5:30 am when biologist Stephen Emlen points his canoe into a mat of floating plants in the middle of a lagoon. Keel-billed toucans with their preposterous, rainbow-hued mandibles beat overhead while flocks of parrots erupt from communal roosts in the lowland rain forest, dashing off to feeding territories. Howler monkeys rend the tranquil setting with abrasive screams and a pair of masked ducks, the male resplendent in chestnut breeding plumage, flees upriver.
Emlen, a behavioral ecologist at Cornell University in Ithaca, New York, drops an anchor, opens his laptop computer and settles into a reasonably comfortable seat where he’ll spend most of the day. Focusing his binoculars on a dark, rail-like bird with awesome toes, a sunflower yellow bill and a crimson wattle plastered on its forehead, he says, "This place is so beautiful that it gives me goose bumps."
The spreading carpets of water hyacinth and water lettuce along the broad and unhurried Chagres are indeed striking, but they mask a world that is topsy-turvy - at least where the wattled jacana, the object of Emlen´s attention in recent years, is concerned. Female jacanas are the larger, domineering gender, and the strongest of these avian amazons assemble harems of as many as five males, mating promiscuously while fighting off incursions by lesser, unmated females. The smaller male jacanas, on the other hand, have no time for hanky-panky. They’re too busy defending their territories from other males and caring for eggs and chicks - which, Emlen has recently discovered, may not even be their own. Moreover, they get no help from the female unless it´s to chase away a predator.
Says Emlen, "It’s one of the most extreme examples of sex role reversal in the whole animal kingdom. But what really astonished us was to find cuckoldry in a situation where males have evolved to perform all of the parental care."
A circumtropical family of eight species, including two in the New World, jacanas inhabit freshwater swamps, lakes, lagoons and seasonally flooded pastures. For decades, taxonomists couldn’t agree whether to classify jacanas with rails or shorebirds; genetic studies now appear to confirm the latter. They prefer wetlands with calm water and expanses of low-lying aquatic vegetation, giving them an unimpeded view of the neighborhood. The birds´ common name (pronounced JAC-uh-nuh) is a transliteration of a Brazilian Indian word for the wattled jacana, which breeds from Panama to northern Argentina. The other New World species, the northern jacana, nests from Mexico to Panama and is seen on occasion in southern Texas.
Males of both American species are around 9 inches long and weigh about 3 ounces - about the size of the familiar kill deer - while the females weigh half again as much as their mates. Both genders have conspicuous yellow spurs at the bend of their wings that apparently are used in combat. But a jacana´s most striking physical characteristic is the length of its toes and toenails. The feet of a northern jacana, for example, cover an area 4-1/2 inches wide and 5-1/2 inches long. This distributes the bird’s weight so it can walk with ease across buoyant leaves while gleaning insects, snails and the seeds of water lilies. Thus the colloquial names "lily-trotter," "lotus bird" and "Jesus Christ bird," although Emlen affirms that jacanas can’t walk on water.
It´s not news that gender roles are topsy¬turvy in seven of the eight jacana species. (The exception to the rule is the lesser jacana of Africa - a tiny bird about the size of the smallest sandpiper - which has returned to two-parent care in recent evolutionary time.) The surprise, Emlen says, is the male jacana´s tolerance for being cuckolded.
Scientists are discovering that female infidelity is rampant in the bird world. "There´s a lot of hanky-panky going on among species that we believed were socially monogamous," says Emlen, whose work was funded by the National Science Foundation. "It turns out that multiple paternity is very common, even among beloved backyard birds like the cardinal and robin." However, in most bird species where both sexes share incubating the eggs or feeding the young, a cuckolded male can reduce his share of parental care and the female will pick up the slack.
The Cornell team, Emlen says, had assumed that a male jacana would bear full responsibility for incubating eggs and raising the young only if he were certain that they are genetically his own. "Instead," he explains, "the male sits on the nest watching as the mother bird mates promiscuously with other males." Truth is, there’s no way he can overlook her infidelities: Jacana copulations are frequent, flashy and loud. Even though a single encounter would provide all the sperm she needs, the female averages 65 copulations for each clutch of four eggs, zooming from one male to another in rapid succession. Moreover, when a male mounts her, he raises his wings and flashes a billboard of yellow flight feathers accompanied by ecstatic squawking from both birds.
To make sense of the watt led jacana´s mating system - the costs and benefits to both genders - Emlen and Cornell colleague Peter Wrege spent five to six months a year from 1990 to 1995 on the Chagres where the river slips through Soberania National Park on its way to the Panama Canal. Every resident jacana on their 32-acre study site was color -marked with the help of undergraduate students, and on average the researchers kept track of the goings-on of 25 females and 40 male mates. They logged the details of 1,354 copulations, and they drew blood samples from 465 birds so geneticist Michael Webster of the University of Buffalo could determine the male parentage of jacana chicks by their DNA fingerprints.
Emlen and his colleagues discovered that in three out of four cases, the female copulated with multiple mates and, in these cases, most broods included chicks that were not sired by the nest-male. However, the risk of being cuckolded depended on the presence of a "sexually available" co-mate in the harem. Females rarely copulated with males that were incubating eggs or tending chicks less than a month old.
Moreover, there´s a significant difference between jacana breeding behavior and that of phalaropes, shorebirds that are a classic example of avian sex¬role reversal, or polyandry. The female phalarope is usually monogamous - but she´s not strongly bonded to her mate. In the case of the arctic ¬nesting red phalarope, the female deserts her smaller, dull¬ colored mate as soon as the clutch of eggs is complete. She may start a second clutch if there are extra males around for her to court. But the nesting season in the high Arctic, unlike the Tropics, is short and unforgiving, and undeveloped young may be left behind to perish when it comes time for the male caretakers to migrate.
The female jacana, in contrast, bonds with every male in her harem. "Male jacanas have territories of their own upon which she superimposes herself," says Emlen. "She copulates with all those males, provides eggs for all those males and defends all those males." The latter responsibility weighs heavy as the number of males under the female’s wing increases. A bird with a harem of four, for example, has to patrol an area twice the size of a football field. Since a polyandrous mating system creates a large floating population of females without territories and mates, the have-nots cruise the marsh every morning, challenging the resident females.
Knock-down-drag-out fights where a dominant bird loses one of her males or her whole harem are rare but dramatic - and so is the aftermath. The new female on the block either finds her rival’s nests and punctures the eggs or she stalks the chicks and kills them one by one, freeing the nest-male from his responsibility for their care. Within hours of doing the deed, she’ll be soliciting copulation from him; a week later he will be presented with a new clutch of four eggs. And for the next three months he’ll either be tending the eggs, which hatch in 28 days, the longest incubation period of any bird on the marsh, or babysitting the slow- growing chicks.
Jacana nests are little more than an accumulation of leaves and stems tossed atop some floating plants. But the male doesn’t sit on the eggs during incubation. Instead, he slides his wings between the eggs and the sodden platform and cuddles them against brood patches, two to a side. Moreover, the nest itself, however skimpy, floats! "When a tropical downpour causes the river to rise, the nest merely rises with it," Emlen says, adding that in some species such as the comb¬ crested jacana in Australia, the male will actually roll his eggs over the lily pads to safety if severe flooding threatens to carry the nest downstream.
Mere fluff balls with huge toes when they peck their way out of the shells, the young jacanas follow the male to favorite feeding places and climb under his wings when it´s cold or raining. "He´s a very attentive dad," Emlen says, "but a lot of things can go wrong in jacanal and." That’s where the resident female enters the caretaking picture, if only for a few minutes a day.
The male jacana is the first line of defense against predators, and there are a lot of them on this Panama lagoon: purple gallinules, overwintering peregrines, otters, introduced bass, huge turtles, caimans and boa constrictors that hang out on the floating vegetation. ("We´ve caught them in the act of swallowing banded adult jacanas," Emlen remembers. "Oh, the joys of field work!") A warning call from the male will send older chicks scurrying to hiding places while younger ones disappear by sinking underwater, remaining motionless and breathing through their bill tips until the male sounds an all ¬clear call note. But if there’s a threat he can’t handle, a more intense alarm will summon the female to his side.
Even so, wattled jacana nesting success is extremely low. Roughly half the nests are lost before the eggs hatch, and half of the chicks perish before they reach independence. "That has to be the key to the whole mating system," Emlen says. "If you´re going to lose most of your clutches, you specialize in producing a lot of them. So the female jacana, freed of her parental responsibilities, became an egg ¬making machine. And if a large, dominant female can maintain a harem, her reproductive success is further enhanced by having lots of males raising young for her."
The hard¬working males, of course, pay the cost. The female jacana can produce a clutch of eggs in six to ten days, but they’re very small for her body size, and that accounts for an incubation and chick¬ raising period that Emlen describes as "ridiculously long." And while the nest -male is fully aware of being cuckolded, there’s nothing he can do about it, like breaking the eggs or abandoning the chicks, because he can´t tell his own offspring from the progeny of a neighbor. Further, because the females no longer have incubation behavior in their repertoire, "the males are trapped in the care-giving role and their only choice is all or none," Emlen says.
Is there a positive side to the male jacana´s role? Emlen notes that in highly competitive situations where there is limited space for nests, some males never get a chance to reproduce at all. Moreover, all of the nest- males in the Panama jacana study sired some of the young in each brood they tended. Says Emlen: "I guess you could say the males are making the best of a bad situation."
Field Editor Les Line has previously written about Stephen Emlen´s studies of bee¬eaters for International Wildlife. Photographer Natalie J. Demong has documented many of Emlen´s field projects.