Argentina. The world's largest swallow was found in Argentina. This kind of swallow is called "black-necked swallow" and is the largest swallow in the swallow family. Their body length is about 20 cm, their wingspan can reach more than 50 cm and their weight is about 50 grams. Black-necked swallows are mainly distributed in the Andes and southern regions of South America. They like to nest at high altitude, and usually choose cliffs, rocks or the top of buildings as nesting sites. Black-necked swallows have black and white feathers, and the feathers on their heads and necks are black, hence the name "Black-necked Swallows".