MANILA -- The local government of Batangas City and scientists are now studying why thousands of swallows are migrating to the city. In December last year, residents said they began to notice that the birds are coming in larger groups compared to their number when they started arriving in the city as early as 2010. The city's business district, particularly P. Burgos Street and Rizal Avenue, have to be cleaned everyday because of the droppings of the birds. Scientists from the University of the Philippines Los Baños have yet to determine the particularly species of the migratory swallows.