Swan Town or Swallow?

I found out one interesting feature while walking along the Rajang River along the old jetty. There are thousands of swallow flying and the sign of their long presence are theier nest built on buildings. I wonder why there so many swallows in Sibu.

When I was in my hometown Alor Setar, there use to be many swallow and everynight you have to be careful if you walk under the electrical wires overhead because you might me hit by their droppings. And their presence actually create a nuisance. They are noisy and their droppings makes the streets, buildings, cars and everything on the ground looks so dirty. Just don;t know how Alor Setar got rid of the swallows.

However swallow are found in many towns when they come and sleepat night.
The three pictures above was taken at the row of buildings along the Rajang riverfront. Swallow nest were found under roofings and notice how they dirty the building with their droppings.