The park’s twelve drummers drumming are great spotted woodpeckers. They begin drumming at the end of winter as part of a courtship ritual in which the male marks out his territory and advertises his presence by drumming his beak against hollow wood 10 to 20 times in just 2 seconds, and the females replies briefly as she enters his territory.
Here is a video:
Video recorded in March 2019 by George Ewart
Southwick Country Park Nature Reserve 