JERUSALEM, Sept. 11 (UPI) -- Migrating Eurasian blackcaps lower their internal temperature at night to retain fat and save energy, Israeli scientists have learned.

The blackcaps were studied in Midreshet ben-Gurion, Israel, where they stop to fatten up before setting off again on their journey, researchers Micha Wojciechowski and Bery Pinshow said Friday in the Journal of Experimental Biology.

Wojciechowski and Pinshow captured birds, weighed them and monitored their body temperatures and metabolic rate as the birds stocked up on fruit and meal worms.

During the day, the birds' body temperatures averaged 108.5 degrees Fahrenheit and fell as dusk approached, averaging about 101 degrees during the night, the researchers said.

The metabolic rates of the lighter birds dropped the most, with some birds conserving as much as 30 percent of their energy by becoming hypothermic, Wojciechowski and Pinshow said.

Huddling together for warmth and dropping their temperatures at night shortened the birds' refueling stopovers, Wojciechowski and Pinshow said.