In September mating season begins. Males of most species use special calls to attract females, which can include purrs, clicks, and buzzing. Bats also concentrate on building up fat stores for the coming months
In October, more mating is taking place, and building up fat reserves is becoming crucial to survive the winter season. Bats are seeking suitable hibernation sites, and beginning periods of torpor.
Bat Conservation Trust page, containing lovely artwork depicting the Bat Calendar.