bird migration period; migration season
Refers to the time of year when birds migrate. Often used in contexts like birdwatching or ecology.
渡りの時期には、たくさんの鳥がこの湖に集まる。
During the migration period, many birds gather at this lake.
渡りの時期はいつですか？
When is the migration season?
Compound of 渡り (migration) + の (possessive particle) + 時期 (time, season). The meaning is transparent from its components.