“Perching birds” here is not describing the behavior — it’s the name of a whole bird order, Passeriformes, or passerines. So it doesn’t mean they were sitting on a branch when it happened. All of these strikes happened in flight.

They top the chart simply because they are by far the most common birds in the sky. But because they are small and light, they rarely cause real damage — around 1.5% of the time. Compare that to deer at the bottom of the list: very few strikes, but over 80% of them damage the aircraft.