This image of a small colony of herring gulls illustrates what had been a mystery to me until recently. These birds were sleeping and resting at Naskeag Point during a snow flurry on chilly Tuesday.
Note that most of them are sleeping with their beaks tucked under their shoulder blade (scapula) feathers. This is a very vulnerable, sensory-dulling position, especially for a large bird that can’t take off like a rocket when a predator comes by. Why would they take that increased risk?
It turns out that head-tucking significantly lowers birds’ respiratory and metabolic rates as compared to untucked sleeping, according to thermal imaging research. This means that tucking creates significantly less heat loss.
Now look at the image again. Note that not all of the birds are tucked in. One advantage of sleeping and resting in a group is that there is a likelihood that a few in the group will be awake at any given time and will be readier to give a warning.
(Image taken in Brooklin, Maine, on March 7, 2023. Brooklin Weather today at 7 a.m.: partly cloudy; temperature 34°F; north-northwesterly wind at 11 mph with gusts of 20.)