There is a reputation for cranes to be romantic. The birds dance and defend their territory together. Birds lift their beaks and emit a loud song when an invader approaches.
In India, the sarus crane is celebrated for its monogamy when one of the birds dies.
The sarus crane couples occasionally let a third bird join them. He described the behavior in a journal. Living as a trio, not quite a throuple, may help the birds raise young in poor conditions. The birds make a song for three.
The sarus crane trio was first spotted by Dr. Sundar in 1999. He was not going to let go of the idea. He followed them for 16 years.
He trained field assistants to watch sarus cranes. After gathering data through 2020, Dr. Sundar and Swati Kittur dug into the database to look for trios.
More than 11,500 crane Sightings were spotted by Observers. Some included a male and two females.
A graduate student at the foundation played recordings of other crane pairs singing territorial duets after visiting four of these trios. Each trio performed a call. It was called a triet by the scientists.
The data doesn't show how long these trios stayed together. 16 years of observing the original trio gave hints about their family dynamics.
A lack of wetlands would most likely make it hard for a couple to raise a young crane.
The outcome was better in a group of three. Each year, one adult in that trio vanished while the other two nested and laid eggs. Two of the three animals have sex.
The female reappeared when the chick or chicks were about a month old or after the nest failed. She helped feed the birds. The three cranes worked together to raise a chick.
It is interesting that this behavior was found in a system where we all thought that they were monogamous for a long time.
The study raises a lot of questions. Who is that third bird?
In some bird species, grown offspring stay to form a trio with their parents and help raise their siblings.
Dr. Sundar thinks that sarus crane trios may not include a grown chick. He noted that the third adult could be related in another way. Sharing genes with a chick could help explain how the system evolved.
If the third adult is unrelated, and it is not allowed to mate, what benefit does it receive from living in a trio?
The only benefit that we could think of for the third bird is that it is getting practice. The helpers can learn how to defend their home. A very young male was in at least one of the trio.
The trios were more common in undesirable habitats. Dr. Sundar thinks teaming up may be an adaptation to bad circumstances.
There is team parenting in the animal kingdom. Cooperative breeding of species of monkeys, mongooses, spiders, insects, birds and fish. Humans do the same. No cranes have been known to parent in teams.
Anne Lacy is senior manager of North America programs for the International Crane Foundation.
She said that she and her colleagues had never seen trios among North American cranes. Absolutely.
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 helpers is a true parent. Is the sarus crane monogamous?
He said that the birds are preserved for the mythology that they are with each other all the time.
The relationship between human and bird is at risk if it is learned that some cranes stray from their partners.
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