As the seasons change, marked shifts occur in the distribution and abundance of North American birds, including here on the Llano Estacado. When a bird is migratory, its range is customarily divided into breeding range and winter range. Summer residents are those birds that travel from their southern wintering grounds in Mexico, Central America, and South America northward in the spring to nest and spend the summer, and then migrate southward again in the fall. Winter residents arrive in the United States in the fall from farther north (Canada, Alaska, Siberia) after their nesting season is over to spend the winter, then return northward again in the spring. Transient are those species that just pass through a region during their northward and southward migrations in the spring and fall. Not all birds migrate, though, but remain in the same general region year-round as permanent residents.
Birds are highly mobile and not bound by range distribution maps. Irregular accidental, vagrant, and irruptive species can sometimes occur far out of their normal ranges. Established range maps are based on actual sightings by knowledgeable and active birders in any area. The ranges of birds is seldom static; ranges constantly change, so they should be considered as fluid. A map should therefore be used just a tool and not as a rule. Birds have an inherent tendency to disperse from their place of birth and invade new areas. If the new areas harbor favorable conditions, the new arrivals can soon establish themselves and thereby expand their ranges.
Raptors are the birds of prey which include eagles, hawks, falcons, vultures, and owls. They are characterized by excellent vision, powerful talons and sharp beaks. Raptors feed on smaller animals---usually vertebrates, but some of the smaller raptors will also take insects as a part of the diet. Most will also feed on carrion.
| Permanent Resident | Summer Resident |
| Red-tailed Hawk | Turkey Vulture |
| American Kestrel | Mississippi Kite |
| Harris’s Hawk (southern Llano) | Swainson’s Hawk |
| Barn Owl | |
| Great Horned Owl | Irregulars and Transients |
| Eastern Screech Owl | Northern Goshawk |
| Burrowing Owl | Zone-tailed Hawk |
| Red-shouldered Hawk | |
| Winter Resident | Rough-legged Hawk |
| Northern Harrier | Broad-winged Hawk |
| Golden Eagle | Osprey |
| Bald Eagle | Peregrine Falcon |
| Sharp-shinned Hawk | Western Screech Owl |
| Cooper’s Hawk | Long-eared Owl |
| Ferruginous Hawk | |
| Merlin | |
| Prairie Falcon | |
| Short-eared Owl |
Only raptors that are permanent residents and summer residents nest on the Llano Estacado. And of these, the species that are most likely to use the nesting platforms at Sibley Nature Center are red-tailed hawk, Harris’s hawk, Swainson’s hawk, turkey vulture, and great horned owl. Their nesting requirements are more generalized and adaptable than the more specific requirements of the other species.