Discover all you need to know about pipistrelle bats.
In early summer, large maternity colonies of pipistrelles in houses provide great watching opportunities.
Bats need to emerge as early as possible because insects are less abundant after dusk, but they also need to avoid any birds of prey active in daylight.
Pipistrelles mostly come out about 30 minutes after sunset. Faster fliers, such as noctules, emerge earlier, and slower species later.
Emergence from the roost is risky, and you often hear the bats squeaking as they wait for the right light levels.
They burst out in clusters, probably to confuse any predators waiting to ambush them. They fly off fast, keeping close to walls or hedgerows for cover.
Just before leaving their roost, pipistrelles squeeze together at the entrance. © Federico Gemma
Safety in numbers
They sometimes bunch into small groups, again for defence or to follow a bat that found a good foraging area the previous night.
Large colonies tend to emerge earlier: there is safety in numbers.
In early summer, heavily pregnant females have to leave later, because they are easier for predators to catch. The same applies to youngsters that are still learning their flight skills.
Bats swarm as they return to their roost. With fewer predators around, they may be seizing the chance to communicate. © Federico Gemma
Get out and watch bats an hour before dawn.
There are far fewer predators around, so returning individuals are more relaxed and ‘swarm’ around the entrance.
They flutter excitedly in circles, often for half an hour, before going in.
It’s possible that they’re transferring information about feeding sites.
Find out more about the work of illustrator Federico Gemma.