Monogamy Over Migration

Lovebird sandhill cranes along the Old Plank Road Trail weather winter together

|  STORY BY CINDY CAIN  |

A female sandhill crane appears to have chosen monogamy over migration this winter as she sticks by her mate through brutally cold weather.

As a result, the sandhill crane couple will be spending Valentine’s Day together nibbling on a romantic meal of bugs and seeds at the Will County wetland they now call home.

The coosome twosome, nicknamed Abel and Mabel by observers, should have headed south by now, as most cranes do in the winter. But it appears that Abel cannot fly higher than a few feet off the ground. And while  Mabel can fly, she hasn’t budged for warmer climes. Even when the weather turns nasty and coyotes come sniffing around the pair hoping for easy pickings, Mabel won’t migrate without Abel.

“If it is a mated pair, and one, in fact, has impaired flight and/or doesn’t know to migrate, then the flight-capable one may be sticking around purely out of monogamy,” said Chris Gutmann, facility supervisor at Isle a la Cache Museum. “Sandhill cranes are what’s known as perennially monogamous, which means mates may be pair-bonded throughout their lives. This is not as common as you might think in birds, so sandhill crane monogamy has been the subject of multiple studies by ornithologists.”

Death and divorce

The bond can be broken by death, and failure to reproduce can cause “divorce” in sandhills, Gutmann added. “One study showed that sandhill pairs that did not successfully reproduce were five times more likely to divorce," he said. "They usually start breeding between 2-7 years old."

But Mabel seems to be loyal to her mate, even though the two haven't appeared to produce offspring and Abel appears to have limited flight capabilities, possibly due to an injury.

“If that’s what is going on with these two cranes, then that must be a really strong pair bond for the flight-capable crane to ignore all of the internal and external triggers to migrate,” Gutmann said. “Those are strong triggers.”

(Photo by Chad Merda)

While most cranes migrate south and southeast from this area to avoid winter, some do not and they are able to survive because sandhill cranes are a very cold tolerant species, said Andrew Gossens, Sandhill Crane Project Manager at the International Crane Foundation in Baraboo, Wis. So there is hope for Abel and Mabel.

"If they survived the polar vortex, they are doing something right and there is a good chance they will make it to spring," Gossens said in an email.

And even if Mabel takes off at some point, she could return. Gossens said he received an email from a Wisconsin resident who reported that a crane with a wing injury was left behind by its mate in the fall, but the migrating crane returned to the injured crane in the spring.

"And they successfully produced a chick the past year," he said.

(Photo by Chad Merda)

Complex behavior

If creatures exhibit monogamous behavior, Smithsonian.com says it might be due to genetics. But DNA alone can’t always explain these traits because “ … monogamy is a complex behavior that is propelled by a variety of factors – like the need to protect offspring from rival males, or the need for male-female pairs to work together to defend limited habitat space.”

Sandhill cranes are not the only perennially monogamous birds. The National Wildlife Federation reports that eagles also stick with one mate. “Bald eagles are solitary, but monogamous animals. Although they spend winters and migrations alone, bald eagles maintain the same breeding pair year after year. A mated eagle pair finds a nesting site and produces offspring each year. If one of the pair dies, the surviving bald eagle will look for a new mate in the next breeding season.”

(Photo via Shutterstock)

The National Audubon Society lists eight additional bird species that mate for life: black vulture, Laysan albatross, mute swan, scarlet macaw, whooping crane, California condor and Atlantic puffin.

Some mammals also are monogamous, but it is not the majority, according to a Live Science’s “Life’s Little Mysteries” feature. “Only 3 to 5 percent of the 5,000 species of mammals bond for life, including otters, beavers and wolves. When only primate species are considered, the rate is slightly higher. Six percent of the 300 primate species in the world, including gibbons, are considered monogamists.”

Cheatin’ hearts?

House wren (Photo via Shutterstock)

While some bird species are monogamous for life, others are seasonally so or just appear to be monogamous.

“A pair bond may last for just one nesting, such as with house wrens; one breeding season, common with most songbird species; several seasons, or life,” an article in Bird Watcher's Digest explained.

What is more common for songbirds, the article states, is social monogamy. A male bird will defend his nest and territory and feed his family and sometimes help incubate eggs.

“But genetic testing of songbird nestlings, even in socially monogamous species, shows that the father who sired them isn’t necessarily the one who is helping to rear them,” Bird Watcher’s Digest explained. “In other words, a socially monogamous female songbird sometimes ‘cheats’ on the male with whom she has a bond. And her socially monogamous mate may have fathered eggs in other nests.”

(Lead image by Chad Merda)

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