Nest-building; the act of animals (birds, insects, etc.) constructing nests, hives, dens, or similar structures.
春になると庭の木で小鳥が巣作りを始めた。
When spring came, a small bird in the garden began building a nest in the tree.
ミツバチの巣作りは六角形の巣房を作る点が特徴だ。
Honeybees' nest-building is characterized by making hexagonal cells.
子供たちは公園で枝や葉を集めて小さな巣作りをして遊んだ。
The children gathered twigs and leaves in the park and played at building little nests.