This is a video from India about a nest of rose-ringed parakeets (Psittacula krameri), also known as ring-necked parakeets.
The Vogelwerkgroep Zuid-Kennemerland in the Netherlands reports about their counting of ring-necked parakeets in Haarlem. All these birds sleep in two trees along the Amerikavaart canal.
On Saturday 19 December, around sunset, 783 parakeets were counted. A record number for this species in Haarlem in winter. In January 2014, 638 birds had been counted.
When a sparrowhawk (a bird of prey, roughly the same size as the parakeets) flew near a tree, it did not really upset the ring-necked parakeets. Only five birds started flying to drive the sparrowhawk away.
However, when a goshawk, a bigger bird of prey, appeared, all parakeets started flying, and it took them ten minutes to settle again.