The Northern Jacana In Costa Rica
Its Mating System Is Close to That of Arctic Migrants
Northern jacanas (Jacana spinosa) are found in almost every pond in Costa Rica. These birds walk across pond vegetation as they glean insects. Having long, thin toes, jacanas spread their weight evenly across the vegetation keeping it from tipping. They pick up one foot then slowly and deliberately place it in front of the other, spreading their toes widely as it steps down. With each step, the plant sinks a little into the water, but because the bird's weight is so evenly distributed, even the tallest of water hyacinths sways only slightly.
Polygamy: Having More Than One Mate
The jacana's polygamous mating behavior is even more unusual. Polygamy is practiced by many bird and mammal species, but the jacana's form of polygamy is rare. Jacanas are polyandrous: One female establishes a territory, attracts and mates with several males, then lays several eggs in a separate nest for each male. She drives away rival females from her mates, but the job of raising the kids belongs to the males.
Arctic Conditions Facilitate Polyandrous Mating
Polyandry is also practiced by spotted and solitary sandpipers and phalaropes that migrate between southern South America and the high arctic, but is very rarely seen in tropical birds. Arctic birds sometimes arrive before the ice and snow are completely gone. As soon as the ice melts, pools and muskegs produce the highest concentrations of mosquitoes and other insects on Earth.
The breeding season in the arctic is so short that if a female's nest fails once she has started to incubate, she will probably not have enough time to re-nest and loses her chance to produce offspring for an entire year. Thus, females attempt to provide several males with eggs, before laying a final clutch that they incubate themselves.
The abundance of arctic insects allows incubating birds to leave the nest for very short periods to forage, and twenty four hours of summertime daylight allows them to feed at any time. Thus, nest attendants do not require a partner to provision them while incubating. The chicks rapidly become self sufficient and migrate south shortly before temperatures drop radically and their insect prey dies.
Tropical Conditions
Jacanas live in a climate that fluctuates only slightly in temperature through the year, but their food availability cycle is only slighty different from the arctic cycle. Although active all year, insect abundance explodes at the onset of the rainy season, and jacana chicks hatch at or just after the rains begin. To take fullest advantage of this short period of abundance, female jacanas entice several males into their territories, mate with and provide each male with eggs, then guard the incubating males closely.
Infanticide
Unmated females sneak into other females' territories and destroy the eggs or kill the chicks in a male's nest. If the resident female is no longer able to produce more eggs, she becomes uninterested in a male without chicks. This allows the unmated female to lure the male onto her territory, build a nest, mate, and have him raise her chicks. If the male jacana refused to mate with the female that killed his chicks, he would probably not father any offspring that year as most late season females have finished laying eggs.
Infanticide And Mate Switching Are Common
The practice of infanticide by territory invaders is widespread in animals.
- When male lions evict or kill the resident males in a pride, or a male langur (a type of monkey) chases out the resident harem master, the males kill every youngster they can find. The females rapidly become reproductively ready and the new male(s) sire the next group of offspring.
- If a new male mouse enters a colony, all pregnant females that smell his urine undergo spontaneous abortions and become sexually receptive, the Bruce effect. They then reject suitors until they can mate with this new male.
- Female baboons often sneak away from the dominant male to mate with a lower ranked male. If they are caught, the females (but not the males) will be subject to intense physical punishment from their original consorts. But they are willing to repeatedly take this risk.
All of these: jacanas, lions, monkeys, rodents, and baboons, attempt to mate with individuals other than their original partner if the opportunity arises – even though the new individual might have killed their children.
Most Monogamists Are Also Not Faithful
That members of monogamous pairs have extra pair copulations with others has only recently come to light as researchers compare the DNA of offspring with that of their putative parents. When the opportunity arises, both males and females of most species use this strategy to increase genetic variability in their offspring. Though practiced by some humans and a few animal species, faithful monogamy is an extremely unusual mating strategy.
Jacana's Open-wing Display
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Jacana Walking
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Jacana Habitat
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