As always during the dry season, animals are free to move since there are no crops to destroy. At this time there is less hay for these animals to feed on. This is why they are free to feed on mangoes and other fruit available to them.
According to Wikipedia, "Serrekunda (or Serekunda) is the largest city in The Gambia, lying southwest of Banjul. Its population as of 2006, was 335,733 people. Although Banjul is The Gambia's capital, it is on an island and cannot grow further, making much of the growth in Serrekunda."