Landfills are used to hold the waste materials w throw out everyday.  The garbage that arrives at landfills and is added to the pile contains putrescible waste that is also a food source for seagulls and other animals.  Landfill permits require daily cover to be placed on the new waste material to control the presence of vectors which includes seagulls and other animals.  In her June 30, 2017 post titled Large Carnivorous Birds, Janice Kaspersen (Editor of Erosion Control) discusses a research report published by Duke University on the nutrient loads resulting from seagulls in and on landfills and how some companies are using Birds of Prey to control nutrient loading to local waterbodies.