The black-eared kite is an ubiquitous sight here in Hong Kong, especially in the winter. However, I had not seen them in such large groups on the ground before I visited Mai Po marshes in December 2018. Here I watched their social behaviour, as they played with objects, presumably dummy prey; a piece of plastic as photographed here.
They also "buzz" each other as seen in the photo, disturbing those on the ground and making them fly and give chase.