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Cranes have a reputation as romantics. The birds live in loyal pairs, dance and defend their territory together. When the intruders approach, the birds raise their beaks and sing a single loud song.
In India, the red-headed sarus crane, which is as tall as an adult human, is famous for its monogamy. “When one of the birds dies, the local mythology is that the other bird flies away in grief,” said KS Gopi Sundar, a scientist at the Nature Conservancy in India. “The truth, of course, is a little different.”
Dr. Sundar discovered that pairs of sarus cranes occasionally allow a third bird to join them. He described the behavior last month in the journal Ecology. Living as a trio – unfortunately, not quite a trio – can help birds raise offspring in poor conditions, with one perhaps acting a bit like a bird au pair. The Birds even turn their signature duet into a three-person song.
Dr. Sundar first noticed a trio of sarus cranes in 1999. “When I told the experts in the US about this, they smiled and patted my head,” he said. But he wasn’t ready to give up on the idea. He followed this trio for the next 16 years.
From 2011 it also trained field assistants (usually local farmers) to monitor sarus cranes. After collecting data through 2020, a colleague at the foundation, Dr. Sundar and Swati Kittur accessed this database to search for triads.
Observers had identified 193 triplets among more than 11,500 crane observations. Dr. “So triplets are definitely rare,” Sundar said. Some were one man and two women; some were just the opposite.
Suhridam Roy, a graduate student at the Foundation, visited four of the trio and played recordings of other crane pairs singing regional duets. In response, each trio performed their own synchronized call. Scientists called it triet.
The data doesn’t reveal how many chicks the trio raised or how long they stayed together. But observing this original trio for 16 years gave some clues about their family dynamics.
Dr. These cranes live in a low-quality habitat and the lack of wetland would likely make it harder for a typical duo to raise offspring, Sundar said.
However, in a group of three, the result was better. Each year, one adult in this trio – a female – disappears, while the other two nest and lay eggs. “It wasn’t a band,” said Dr. sundar Only two of the three animals mated each season.
But when the resulting chick or chicks were about a month old, or soon after the nest failed, the missing female reappeared. If there were chicks, he helped to feed them. And working together, the three cranes raised a chick almost every two years.
“It’s very interesting to find such a novel behavior in a system that we all thought was monogamous for a long time,” said Sahas Barve, an evolutionary ecologist at the Smithsonian Institution’s National Museum of Natural History in Washington DC.
And the study raises many questions, he said. Most importantly: “Who is this third bird?”
Dr. In some bird species, including Florida bush jays and Seychelles warblers, bred broods often stay with their parents to form a trio and help raise siblings, Barve said.
However, Dr. Based on other research he’s done, Sundar thinks it’s unlikely that the sarus crane trio would include an adult chick. However, she noted that the third adult may be related in another way. Sharing some genes with the chicken may help explain how this system evolved.
If the third adult is not related – and is not allowed to mate – what good is living in a trio?
Dr. “The only benefit we can think of for the third bird is that it becomes practical,” Sundar said. The helper can learn how to protect his home and feed the chicks. At least one trio that the researchers observed included a very young male.
The scientists also found that triads were more common in undesirable habitats. Dr. Sundar thinks team building can adapt to bad conditions.
Team parenting occurs in the animal kingdom. Monkeys, mongooses, spiders, insects, birds and fish species engage in cooperative reproduction. So are people. But until now, no cranes were known to parent in teams.
“The hard assumptions we have about this bird family,” said Anne Lacy, senior manager of North America programs at the International Crane Foundation.
Ms. Lacy said she and her colleagues had never observed a trio among North American cranes, but added, “Could it be when we’re just not looking? Exactly.”
Dr. Sundar plans to use genetics to find out if sarus crane helpers are related. One question he doesn’t plan to ask, though, is whether the helper is a chick’s actual parent. In other words, is sarus crane really monogamous?
“These birds have been preserved for the mythology that they were always with each other and were loyal,” he said.
Learning that some of the cranes are moving away from their partners, Dr. Sundar said it risks damaging the relationship between human and bird. “Why should we destroy this mythology for a statistical and scientific paper?” said.
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