Birds that feed on flocks commonly retire together into roosts. The reasons for roosting commune are not always obvious, but there are some likely benefits. In winter especially, it is important for birds to keep warmth at night and conserve precious food reserves. One way to do this is to find the sheltered roost. Solitary roosters shelter in dense vegetation and enter a cavity- horned larks dig holes in the ground and ptarmigan burrow into snow banks- but the effect of shelter is magnified by several birds huddling together in the roosts, as wrens, swifts, brown creepers, bluebirds, and anis can. Body contact reduces the surface area exposed to the cold air, so the birds keep each other warm. Two kinglets huddling together were found to reduce their heat losses by a quarter and three together saved a third of their heat.

GIẢI THÍCH:

1. Nếu để are thì benefit phải thêm "s"

2. Dấu "," và Brown phải có khoảng cách

3.Khi bạn kết hợp một động từ với dạng to be, bạn thường cần dạng -ed hoặc -ing

4.Two kinglets hudding together là số nhiều nên phải dùng Were

5. Losses giới từ là by.