For most plants and animals, just listing the family, genus or species is enough to let biologists know what the other levels should be. The most common way to list the taxonomic name of an organism is to list the genus and species; this is known as binomial nomenclature, meaning a two-name system.
The grey jay is a relatively large songbird, though smaller than other jays. A typical adult grey jay is between 25 to 33 cm (9.8 to 13.0 in) long. Its wingspan is around 45 cm (18 in). It weighs about 65 to 70 g (2.3 to 2.5 oz). Adults have medium grey back feathers with a lighter grey underside.
Buteo jamaicensis. Red-tailed hawks average 48 to 65 centimeters in length. Their wingspan is approximately 4 feet, or 122 centimeters. There is sexual dimorphism in size: females are 25% larger than males. This kind of sexual dimorphism, where females are larger than males, is common in birds of prey.