Symbol of fidelity hides little secret

The black-necked crane mainly summers in the Qinghai-Tibet Plateau. The breeding areas are alpine meadows, lakesides and riverine marshes and river valleys. Their wintering areas extend to parts of Yunnan and Guizhou province in China, Bhutan and the northern plains of India. According to the article, the crane is recognized as a unique representative of high-altitude cranes. It has maintained its status as one of the least-studied cranes.

Li and his research partners from Sichuan University, Nanjing University and Zoige nature reserve focused their study on cranes during breeding season, when the birds establish sparsely spaced colonies, suggesting the potential for high mate fidelity due to low breeding density, according to the article.

From 2017 to 2020, the researchers conducted annual fieldwork in Flower Marsh from March to October, rigorously monitoring the cranes. "The cranes we studied in Zoige are considered to be part of the bird's eastern population," Li told China Daily. "They usually winter in Guizhou and Yunnan provinces."

They identified and tagged each breeding pair, located their nests and recorded satellite navigation coordinates. Over these four breeding seasons, they documented nine nests in Flower Marsh. In addition to the nest-area samples from Flower Marsh, they expanded their dataset to include tissue samples, egg membrane samples and nine blood samples from both Nalecho Marsh and Flower Marsh.

In total, 48 egg membrane samples from offspring, nine blood samples, four tissue samples and 65 adult feather samples were collected in Zoige for DNA extraction.

The researchers identified 58 individual birds over the four-year period — seven female and eight male adults, and 25 male and 18 female offspring.

"Black-necked cranes are large birds under State first-class protection," said Professor Li Zhongqiu from Nanjing University's School of Life Science in Jiangsu province, who is one of the article's co-authors. "In the past, if we wanted to study their tendency for extra-pair copulation, we had to try to catch the breeding pairs and put satellite tracking devices on them, and wait to see whether the same pairs would return to the same nest the next year. The method is actually hard to carry out and is unreliable."

Documenting nine nests and collecting samples for analysis posed a different challenge, the professor said.