Young Barn Owls Invade Neighboring Nests, Reducing Local Owlets' Survival Rates

A new study conducted by the University of Haifa and the Shamir Research Institute reveals that young barn owls, which have left their natal nests but are not yet fully independent hunters, often enter active nests of other owls to steal food. This behavior, documented during two breeding seasons in the Hula Valley, negatively impacts the survival rates of the resident owlets.

Researchers tagged 464 owlets and 108 adult barn owls with tiny electronic identification devices and installed RFID systems in 50 active nest boxes to monitor owl movements continuously. They recorded over 1.2 million detections, enabling them to identify short and nocturnal visits that traditional periodic checks would miss. Approximately 13 percent of the tagged owlets were later identified as young barn owls visiting other nests, with over half of the monitored nest boxes experiencing at least one visit from a foreign young owl.

The study found that such visits were more frequent when multiple active nests were within 500 meters and when the local owlets were younger. While the total number of owlets leaving the nest did not significantly change with the frequency of visits, the survival rate of local owlets decreased as the number of visits by foreign young owls increased. Video evidence showed young intruders taking prey brought by the resident parents and sometimes displaying aggression toward local owlets, including one recorded fatal attack.

The researchers suggest that the older, more developed visiting owls may outcompete the younger local owlets for food, indirectly reducing their survival chances. They caution that increasing nest box density to promote barn owl populations for rodent control might inadvertently raise competition and reduce offspring survival. The study was funded by the Ministry of Innovation, Science and Technology and the Jewish National Fund.