The reasons why turtle doves keep nodding may be:

1. During courtship, the male will make short, intense and coherent "gu-gu" and "gu-gu" sounds to attract mates. The female, while nodding her head repeatedly.

2. Turtle doves will also keep nodding when frightened.

3. If the turtle dove keeps nodding, it may be that it is showing off its feathers, indicating that it is in a good mood.

In addition to nodding, turtle doves also have many other movements, such as:

1. In spring, male birds are sometimes so excited that they flap their wings frequently and nod constantly.

2. When in estrus in autumn, the male bird will make a "coo-coo" sound and nod constantly.

3. When in the trees in winter, the male bird sometimes stands on a branch and makes a "coo-coo" sound and nods constantly.

4. After successful courtship, the male bird will nod continuously and make a series of "kokoko" sounds.

5. When the female bird is frightened or discovers danger, she will suddenly fly out of the nest and make a rapid "coo" sound. This may also be a habit of turtle doves.

6. When the turtle dove is incubating its eggs, when it finds something abnormal outside the nest, it will also knock the eggs in the nest with its mouth and make a rapid "kokoko" sound.

7. When a turtle dove is threatened by territory invasion, it will first extend its neck and make a long and loud "coo" sound, then spread its wings and droop its tail slightly downward.

8. When two turtle doves are at odds with each other or fight, they will stand and half squat and make a rough "hututututu" call, which is relatively fast.

9. When a turtle dove is injured or sick, it will make a low and weak sound of "Uh-huh-huh".

The above is the meaning expressed by the turtle dove’s calls and movements, but the specifics need to be analyzed and judged based on the actual situation.