Birds are members of the class Aves, one of the classes of vertebrates or animals with backbones. They are specialized for flight with forelimbs developed as wings; feathers which insulate and function as lift surfaces and rudders; hollow bones and lack of teeth to reduce weight; brains with well-developed centres for coordination of visual information, balance and muscle activity; an extremely efficient lung with no dead air space; and the levator of the wing attached to the sternum rather than the vertebral column, which lowers the centre of gravity. Like mammals, birds have a high body temperature, which maintains their brains and muscles at a high activity level but requires a considerable amount of food. Birds can reduce their food requirements by migrating to a warmer climate after the breeding season is completed, when they have fed themselves and their growing young on the abundant insects and rodents of the northern summer. A few birds such as nightjars are able to lower their body temperatures, which reduces their food requirements; but this condition is not as well developed or as common as the hibernation of mammals. All birds are oviparous, usually laying their eggs in a nest. They have complex behavioural patterns, particularly associated with the breeding cycle. Their behaviours are based on the senses of sight and audition. Birds evolved from small feathered reptiles, perhaps dinosaurs, during the Jurassic approximately 150 million years ago. They are considered by many to be a group of reptiles specialized for flight, rather than a separate class.
Birds are found on all continents; they inhabit a variety of habitats, from the richest rain forests to the sparsely vegetated tundra and deserts. Their diversity is highest in the rain forests. They can be generalist feeders, such as the widely distributed herring gulls and crows, or highly specialized nectar feeders whose bills may allow them to feed on only a few species of plants.
Saskatchewan has records for 364 of the more than 10,000 modern species of birds. Of these, 300 species occur regularly and are ecologically important. There are representatives of 17 of the 28 living orders: Gaviiformes (loons), Podicipediformes (grebes), Pelecaniformes (pelicans, cormorants), Ciconiiformes (ibis, vultures), Anseriformes (ducks), Falconiformes (falcons, hawks), Galliformes (grouse), Gruiformes (cranes, rails), Charadriiformes (shorebirds, gulls), Columbiformes (pigeons), Cuculiformes (cuckoos), Strigiformes (owls), Caprimulgiformes (nightjars), Apodiformes (swift, hummingbirds), Coraciiformes (kingfisher), Piciformes (woodpeckers), and Passeriformes (all others). The affinities of the avifauna are cosmopolitan (peregrine, osprey), with Eurasia (thrushes, crows, owls), or with the rest of the New World (vulture, warblers, tyrant flycatchers, warblers); there are no species unique to Saskatchewan.
There are a number of species which have been introduced to North America for purposes of sport or to bring in familiar garden birds. Successful introductions which have spread into Saskatchewan are: gray partridge, ring-necked pheasant, wild turkey, rock dove/pigeon, Eurasian collared dove, European starling, house finch, and house sparrow. The turkey and finch are native to North America. Some of these introductions, particularly the sparrow and starling, have had a considerable negative impact on the native avifauna owing to competition for nesting sites and food.
Species have also been lost. Passenger pigeons were found in the eastern woodlands until the late 19th century. Lost by a combination of overhunting and destruction of the extensive woodlands that the species needed for nesting, it exemplifies the effects of human action on the biota of North America. A number of species have been reduced in numbers since the major settlement period. The trumpeter swan, whooping crane and Canada goose were hunted in great numbers for market, sport and feathers until by the early part of the 20th century their numbers were greatly reduced - in the case of the swan and crane, to near extinction. With agriculture, prairie sparrows and ground-nesting songbirds lost their nesting and feeding habitat. By the middle of the 20th century, concern about these and other species led to a variety of programs to conserve our natural heritage (see biodiversity, conservation, conservation agencies).
There are also species which have benefited from the changes brought about by human action, such as the increased vegetation of town sites. Besides the introduced species, some of which have become very numerous, some native species, especially those of the forest edge such as American robins, have taken full advantage of the fruit trees and hedges of the towns. If the apparent warming trends continue, we can expect to see more birds which before never came as far north as Saskatchewan.
The provincial bird symbol is the sharp-tailed grouse, a prairie inhabitant. The largest bird is the trumpeter swan; the smallest is the ruby-throated hummingbird.