The stimulus for spawning is believed to be day length.

Therefore, the flowering will take place under decreasing day length.

As day length increases the size of the clutch also increase.

Females are generally more sensitive to changes in day length.

This is most likely triggered by longer day length.

The timing of migration is controlled primarily by changes in day length.

The primary physiological cue for migration are the changes in the day length.

Experiments have indicated that these changes are induced by day length.

The change to the winter coat can be triggered in the summer by the short day lengths.

This continued for several days, providing the same day length of 9 hours, 15 minutes.