These birds form a trio, but perhaps not a throttle

Cranes have a reputation for romance. The birds live in loyal pairs, dance and defend their territory together. When intruders approach, the birds raise their beaks and emit a loud song with one voice.

In India, the Saros crane – with a scarlet head and as tall as an adult human – is celebrated for its monogamy. “When one bird dies, local legends are that the other birds turn away in grief,” said KS Gopi Sundar, a scientist at the Nature Conservation Foundation in India. “The truth, of course, is a little different.”

Dr. Sundar discovered that Saros bird pairs sometimes allow a third bird to join them. The behavior was described last month in the journal Environment. Living as a trio of—unfortunately, not entrained—may help the birds raise their young in poor conditions, and one may act like a pair of icy birds. The birds even turned their signature duet into a song for three.

Dr. Sundar first discovered the SARS Crane trio in 1999. “When I mentioned it to experts in the US, they smiled and patted my head,” he said. But he wasn’t ready to give up on the idea. He followed this trio for 16 years.

Beginning in 2011, he also trained field assistants (usually local farmers) to monitor Saros cranes. After collecting data up to 2020, Dr.

Observers spotted 193 trios out of more than 11,500 sightings of the crane. “So triples are definitely rare,” said Dr. Sundar. Including a male and two women. Some were in the opposite direction.

Suhridam Roy, a graduate student at the institution, visited four of these three and played recordings of other crane pairs singing their regional duets. In response, each trio made its own simultaneous call. Scientists called it triple.

The data does not reveal how many chicks these trios raised or how long they lived together. But 16 years of observing this original trio has given some hints about their family dynamics.

Dr. Sundar said these cranes lived in a low-quality habitat, where a lack of wetlands likely made it difficult for a typical duo to raise young.

But 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 thorn,” said Dr. Sundar. Only two of the three animals mate each season.

But when the resulting chick or chicks were about a month old, or just after the nest failed, the absent female reappeared. If there were chicks, I helped feed them. Working together, the three cranes reared a chick approximately every two years.

“Finding new behavior like this in a system that we all thought had been monogamous for so long is very interesting,” said Sahas Barf, an evolutionary ecologist at the Smithsonian Institution’s National Museum of Natural History in Washington, D.C.

He said the study raises many questions. Most important: “Who is this third bird?”

Dr. Barfi said that in some bird species, including Florida scrubbirds and Seychelles fowl, the budding offspring often stays to form triplets with their parents and helps them raise their siblings.

But Dr. Sundar thinks it’s unlikely that Saros Crane’s triads include a mature chick, based on other research he’s done. However, he noted, the third adult could be related in another way. Sharing some genes with the chick could help explain how this system evolved.

If the third adult is unrelated – and not allowed to mate – what benefit does he gain from living in a trio?

“The only benefit we can think of for the third bird is that it is training,” said Dr. Sundar. The helper can learn how to defend his home and feed the chicks. At least one trio that the researchers observed included a very young male.

Scientists also saw that triads were more common in undesirable habitats. Dr. Sundar believes that working as a team may be an adaptation to poor conditions.

Team parenting appears throughout the animal kingdom. Species of monkeys, mongoose, spiders, insects, birds and fish participate in cooperative breeding. So do humans. But so far, no parent is known about the cranes in teams.

“It’s difficult assumptions we make about this family of birds,” said Ann Lacey, senior director of North American programs for Crane International.

Ms. Lacey said she and her colleagues had never noticed a triplet among North American cranes, but added, “Could it happen when we’re not just looking? Absolutely.”

Dr. Sundar plans to use genetics to find out whether or not the crane assistants are related. However, one of the questions he does not plan to ask is whether the helper is the real parent of the chicks. In other words, is the frank lever really monogamous?

“These birds are preserved for the myth that they are with each other all the time, and that they are loyal,” he said.

Knowing that a percentage of cranes stray from their partners may damage the human-bird relationship, Dr. Sundar said. “Why destroy this mythology for the sake of a census and a scientific paper?” He said.

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