City ecologist Anneke Blokker talked about Amsterdam's greenery and biodiversity and took a closer look at the city's 'hardest night worker': the bat. Without bats, we would be as many as 19,000 insects a year richer per resident of Amsterdam. Eight different bat species are found in the city, and bats also live in the Oude Kerk. The idea was to try to spot bats from the roof this evening, around dusk. For this, 'bat detectors' were used; a compact electronic device that converts ultrasonic sounds of bats to a sound that humans can also hear.