The northern shrike catches most of its food within its own territory and therefore defends a large area from other northern shrikes. Large birds defend large territories. Red-tailed hawks defend a territory that averages about 130 hectares. Golden eagles and red-tailed hawks both prey on small mammals that are difficult to find. Bald eagles, which are mainly fish-eaters, have smaller territories than do golden eagles.
Fish are more abundant than are small mammals.
This means that the bald eagle needs a territory with sufficient fishable waters, not large land areas. The belted kingfisher requires a stream and the common loon needs a lake. Such bird species have no interest in defending the surrounding land area. Those birds that defend a feeding territory prey on food that is spread evenly throughout the territory. Competition from other pairs of birds would leave too little food for their young.