Researchers have discovered that some pairs of Sarus Cranes accept a third bird to help care for their chicks during challenging foraging conditions.
A trio of Sarus Cranes singing together. (Photo: Suhridam Roy).
In India, the Sarus Crane, a species that stands as tall as an adult human, is well-known for its pair-bonding behavior. However, K. S. Gopi Sundar, a scientist at the Nature Conservation Foundation in India, has found that sometimes these pairs allow a third individual to join them. He described this behavior in the March issue of the journal Ecology. According to the study, this arrangement may help the cranes raise their chicks under difficult conditions. The third bird can serve as an auxiliary helper in the family.
Sundar first observed a trio of Sarus Cranes in 1999 and continued to monitor them for 16 years. Starting in 2011, he also trained local farmers as field assistants to track the Sarus Cranes. After gathering information throughout 2020, Sundar and his colleague Swati Kittur explored the database to identify these trios. Observers documented 193 groups in over 11,500 observations. Sundar concluded that this behavior is quite rare, with some groups consisting of one male and two females or vice versa.
Suhridam Roy, a researcher at the foundation, approached four of the crane trios and recorded their calls. Each group has its unique song. The data does not reveal how many chicks the trios have raised or how long they stay together. However, 16 years of observing the first trio provided some clues. These cranes live in harsh environments, and the scarcity of wetlands likely makes chick-rearing difficult for a typical pair.
In contrast, the trio shows better outcomes. Each year, one adult in the trio (usually the female) disappears while the other two nest and lay eggs. According to Sundar, only two of the three individuals mate each season. When the chicks are about a month old, the absent female reappears to help feed the chicks. The three cranes cooperate to raise a chick nearly every year.
The research team believes that the behavior of living in a group of three is an adaptation to challenging conditions. Cooperative breeding is relatively common in the animal kingdom. Species such as monkeys, meerkats, spiders, insects, birds, and fish also engage in cooperative breeding. Sundar plans to use genetics to investigate whether the helper bird is related to the other two birds in the group.
