Swallows eat flying insects. These insects are both abundant and moving constantly. Since the insects are abundant, it is not necessary for the swallow to defend a feeding territory. Nor would defending a territory be worth the effort, since there is more than enough food for all swallows. 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.