As I've mentioned before, you won't find sea gulls on the beaches of Copacabana or Ipanema in Rio. However, go further south, down to Santa Catarina and beyond, and they do start to appear. One of the commonest is the Kelp Gull, or Larus dominicus - the "dominicus" part coming from the Dominican order of friars who also had black and white plumage. In Brazil it's known as the "Gaviota dominicana".
In fact, the Kelp gull is not just found in Brazil, but all over the southern hemisphere, from the Falkland Islands to South Africa to New Zealand and Australia. As with many successful species they are ominvores, eating almost anything, which means that like their northern cousins they flock to waste sites and rubbish tips. Also, rather nastily, they seem to have a habit of pecking into whales when they surface. Slightly more admirably, they seem to be intelligent enough to use tools, or at least use stones to smash open mussel shells. They also pick up mussels and drop them from a great height, quite a common sight on the Falklands apparently.
The one thing don't eat is kelp, or seaweed - the name probably comes from seeing them investigating weed washed up on the shore looking for molluscs or insects.