There are 35 sub-species of Barn Owl. Barn Owls do not build nests themselves, but rely on a variety of nesting sites for laying their eggs. Tree cavities, rock ledges, chimneys & ledges in barns are among the sites that may be used & Barn Owls have sometimes been known to make their own burrows in riverbanks.
Organisms in biology are classified by this system: kingdom, phylum, class, order, genus, species. Kingdoms being the largest groups. Species is the smallest major group before they divide into sub groups. So Genus would be the next group larger if that is what you mean, but all the other groups would be larger as well.
Linnaeus used this as the top rank, dividing the physical world into the plant, animal and mineral kingdoms. As advances in microscopy made classification of microorganisms possible, the number of kingdoms increased, five and six-kingdom systems being the most common. Domains are a relatively new grouping. The three-domain system was first proposed in 1990, but not generally accepted until later.