Outside of rodents, the most important prey for North American red-tailed hawks is rabbits and hares, of which at least 13 species are included in their prey spectrum. By biomass and reproductive success within populations, these are certain to be the most significant food source to the species (at least in North America). Adult Sylvilagus rabbits known to be hunted by red-tails can range from the brush rabbit (Sylvilagus bachmani) to the Tres Marias rabbit (Sylvilagus graysoni) at while all leporids hunted may range the pygmy rabbit (Brachylagus idahoensis) to hares and jackrabbits potentially up twice the hawk's own weight. While primarily crepuscular in peak activity, rabbits and hares often foraging both during day and night and so face almost constant predatory pressure from a diverse range of predators. Male red-tailed hawks or pairs which are talented rabbit hunters are likely have higher than average productivity due to the size and nutrition of the meal ensuring healthy, fast-growing offspring. Most widely reported are the cottontails, which the three most common North America varieties softly grading into mostly allopatric ranges, being largely segregated by habitat preferences where they overlap in distribution. Namely, in descending order of reportage were: the eastern cottontail (Sylvilagus floridanus), the second most widely reported prey species overall in North America and with maximum percentage known in a given study was 26.4% in Oklahoma (out of 958 prey items), the mountain cottontail (Sylvilagus nuttallii), maximum representation being 17.6% out of a sample of 478 in Kaibab Plateau, Arizona and the desert cottontail (Sylvilagus audubonii), maximum representation being 22.4% out of a sample of 326 in west-central Arizona. Black-tailed jackrabbits (Lepus californicus) are even more intensely focused upon as a food source by the hawks found in the west, particularly the Great Basin. This species is likely the largest prey routinely hunted by red-tails and the mean prey size where jackrabbits are primarily hunted is indeed the highest known overall in the species. When jackrabbit numbers crash, red-tailed hawk productivity tends to decline synchronically. In northern Utah, black-tailed jackrabbits made up 55.3% by number of a sample of 329. Elsewhere, they are usually somewhat secondary by number. Mean sizes of jackrabbits taken can range up to approximately , but probably quantitatively mostly juvenile and yearling jackrabbits are caught. Prime adult jackrabbits, with weights at times exceeding , are difficult and taken infrequently, short of by particularly large and aggressive female red-tails. Other even larger species are sometimes taken as prey such as the white-tailed jackrabbit (Lepus townsendii), but whether this includes healthy adults, as they average over , is unclear.