It's spring (in time of year, if not in temperature), and the local ducks are starting their attempts to make more ducks. We try to discourage them doing so in our garden, as we don't want to watch the effects of nature red in tooth and claw on the resultant ducklings. (Although last year's autumn crop did all survive to adulthood, amazingly enough.)
So, when ducks land on the pond, we chase them off. The last pair I chased did their usual amazing almost vertical take-off, quacking loudly and indignantly. Then, instead of disappearing into the distance, they landed again, on the neighbour's rooftop.
I didn't realise ducks were perching birds.