This leads me to believe that this partly accounts for their foraging at night.
Ohio Arbor Day 1913: Arbor and Bird Day Manual|Various
A cow grazed in the woods, which had been partly cleared of under-brush, and had the appearance of a park grove.
Hatchie, the Guardian Slave; or, The Heiress of Bellevue|Warren T. Ashton
Here, on the outer edge of the road, was a gully which the wind of the day previous had partly filled with snow.
The Rover Boys on Snowshoe Island|Edward Stratemeyer
British Dictionary definitions for partly
partly
/ (ˈpɑːtlɪ) /
adverb
to some extent; not completely
usage for partly
Partly and partially are to some extent interchangeable, but partly should be used when referring to a part or parts of something: the building is partly (not partially) of stone, while partially is preferred for the meaning to some extent: his mother is partially (not partly) sighted
slightly, somewhat, partially, at least, bit by bit, by degrees, carelessly, halfway, inadequately, incompletely, insufficiently, notably, piecemeal, relatively, at best, at most, at worst, in part, in some measure, little by little