Migratory birds fly at the Huswah Nature Reserve in the southern port city of Aden, Yemen, Dec. 9, 2019. During the past years, the Huswah Nature Reserve received large swarms of migratory birds with around 150 different species but recently the number of migratory birds dwindled until 50 species, according to local officials. (Photo by Murad Abdo/Xinhua)