。
A bird is singing in the cage.
Literal
Cage [possessive-の] inside [locative-で] bird [subject-が] singing-[state-ている] [confirmation-ね].
A contrasting use of 籠 — here referring to a cage (with a bird inside). 鳴く ('to cry, chirp, sing' for animals) is the standard verb for bird sounds, animal cries, insect chirps. Note that ね at the end suggests the speaker is drawing the listener's attention to share the observation.