Breaking up of swan families in winter disrupts spring migration
Young Bewick's swans only survive their first spring migration if they stay with their parents long enough. If they lose their parents in winter, they leave later and are unable to keep up with the rest of the population. As a result, there is a greater chance that they will die in their first year of life.
Bewick's swans, a species of swan native to the Arctic tundra of European Russia, undertake a long journey to the Netherlands and surrounding countries in the fall for the winter months. In a recent study published in Behavioral Ecology and Sociobiology, biologists from the UvA, NIOO-KNAW, and other institutions analyzed 55 swans, including adults and juveniles from 12 families.
The researchers found that young swans only survive their first spring migration if they stay with their parents for a significant portion of the journey. If they lose their parents during the winter, they depart for the spring migration later and have a much lower chance of survival. The study revealed that 10 of the 24 juveniles in the study lost their parents due to disturbances at roosting and feeding sites, primarily caused by hunters.
These orphans departed for the spring migration nearly a month later than other juveniles and had a survival rate of only 40%, compared to 86% among those who stayed with their parents. One orphaned swan, named 036T, managed to reunite with its biological father in the Russian Arctic and successfully completed the spring migration.
The findings highlight the critical importance of family cohesion and a disturbance-free environment during the vulnerable periods of early migration for the survival of young Bewick's swans and the overall population.
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