Thousands of crows were seen hovering above a city in northwest China.

The video, shot in the city of Xining in Qinghai Province on February 6, shows a large murder of crows hovering in the sky.

In another video, the crows later rested on the power lines in a line and the top of trees.

According to the local Urban Administration Bureau, due to the urban heat island phenomenon, the urban area is significantly warmer than its surrounding rural areas, causing birds to fly to towns in the winter.

The video was provided by local media with permission.

2月6日，青海西宁闹市区乌鸦成群，铺天盖地在上空盘旋，遮天蔽日黑压压一片，场面有些瘆人。目击市民介绍，每年冬天，西宁海湖新区成千上万的乌鸦齐聚一堂，晚上乌烟瘴气，第二天地上白茫茫鸟粪，辛苦了环卫工人。
市城市管理局工作人员介绍，由于受“热岛”效应影响，近年来，我市部分区域特别是海湖新区，冬季出现大量乌鸦飞掠和停息的现象。乌鸦属于群集且喜欢食腐的鸟类，冬季野外寒冷，城市所产生的“热岛”效应对其极具吸引力，乌鸦又喜欢集群停在树上睡觉，因此在冬季会看到大量的乌鸦飞掠过城市上空，并在树上、电线上栖息。但这种现象本身没有什么异常，乌鸦集群是正常的自然现象，很多大城市都存在类似现象，市民们不必恐慌，也不必过度解读、传播，在外出时应做好个人和车辆的避让防护。（视频由青海台提供）