Aerial photo taken on April 4, 2020 shows Yue Jianqiang, staff member of the Ulan Suhai Lake Nature Reserve, observeing migrant birds on a tower at the wetland of Ulan Suhai Lake in Bayannur, North China's Inner Mongolia autonomous region. The wetland of Ulan Suhai Lake is an important breeding location for migrant birds like mute swans. As their spawning period started from late March, staff of the nature reserve have strengthened patrol and protection effort to monitor birds' living and breeding condition. [Photo/Xinhua]

Yue Jianqiang, staff member of the Ulan Suhai Lake Nature Reserve, observes migrant birds at the wetland of Ulan Suhai Lake in Bayannur, North China's Inner Mongolia autonomous region, on April 4, 2020. [Photo/Xinhua]

Yue Jianqiang, staff member of the Ulan Suhai Lake Nature Reserve, patrols the wetland of Ulan Suhai Lake by speedboat in Bayannur, North China's Inner Mongolia autonomous region, on April 4, 2020. [Photo/Xinhua]

Aerial photo taken on April 4, 2020 shows Yue Jianqiang, staff member of the Ulan Suhai Lake Nature Reserve, patrolling the wetland of Ulan Suhai Lake by speedboat in Bayannur, North China's Inner Mongolia autonomous region. [Photo/Xinhua]

Aerial photo taken on April 4, 2020 shows Yue Jianqiang, staff member of the Ulan Suhai Lake Nature Reserve, patrolling the wetland of Ulan Suhai Lake by speedboat in Bayannur, North China's Inner Mongolia autonomous region. [Photo/Xinhua]

Photo taken on April 4, 2020 shows mute swans swimming at the wetland of Ulan Suhai Lake in Bayannur, North China's Inner Mongolia autonomous region. [Photo/Xinhua]