London:

Herds of red and fallow deer also roam freely within much of Richmond and Bushy Park. A cull takes place each November and February to ensure numbers can be sustained. Epping Forest is also known for its fallow deer, which can frequently be seen in herds to the north of the Forest. A rare population of melanistic, black fallow deer is also maintained at the Deer Sanctuary near Theydon Bois. Muntjac deer, which escaped from deer parks at the turn of the twentieth century, are also found in the forest. While Londoners are accustomed to wildlife such as birds and foxes sharing the city, more recently urban deer have started becoming a regular feature, and whole herds of fallow and white-tailed deer come into residential areas at night to take advantage of the London's green spaces.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". When do culls to ensure sustainability of London's deer population occur?
each November and February