Nuttall’s cottontail (nuttallii subspecies) COSEWIC assessment and status report: chapter 3

Species information

Name and classification

Sylvilagus nuttallii (Bachman 1837) belongs to the Order Lagomorpha, Family Leporidae. Nelson (1909) assigned S. nuttallii to the Sylvilagus floridanus species group. Results from a phylogenetic analysis of dental traits suggested that S. nuttallii and the Eastern Cottontail (Sylvilagus floridanus) were sister taxa forming an unresolved clade (Ruedas 1998). But, Halanych and Robinson (1997) using mitochondrial DNA (12S rRNA gene) demonstrated that S. nuttallii was most closely related to the Desert Cottontail (Sylvilagus audubonii) with a sequence divergence of only 2.1%. Sequence divergence with S. floridanus was 4.8%.

Traditionally (Nelson 1909; Hall 1981) three subspecies are recognized: S. n. grangeri (Great Plains including Canada and Rocky Mountains), S. n. nuttallii (California to British Columbia), and S. n. pinetis (southern Rocky Mountains) (Figure 1). No genetic studies have been done to assess their validity. Diersing (1978) analyzed geographic variation in pelage and skull morphology among 44 geographic samples from the entire range of S. nuttallii including Canada. His multivariate analysis revealed two discrete groups that differed in cranial and body size. He classified them as S. n. nuttallii and S. n. pinetis/S. n. grangeri. A sample of S. n. nuttallii from British Columbia was strongly divergent from a sample of S. n. grangeri from Saskatchewan and Alberta. Diersing (1978) concluded that S. n. grangeri and S. n. pinetis were morphologically similar and proposed they be synonymized with the name S. n. pinetis taking priority because of its earlier usage. However, because Diersing’s (1978) thesis was not published, this nomenclatural change has no validity under the Code of International Zoological Nomenclature and the Prairie population in Canada should be treated as S. n. grangeri.

In the original COSEWIC report (Carter and Merkens 1994), the two subspecies of S. nuttallii were assigned different COSEWIC rankings. S. n. nuttallii qualifies as a designatable unit because it is a named subspecies and it occupies a different ecozone from the Prairie subspecies, S. n. grangeri.

Another English common name for the species is the Mountain Cottontail. Anderson (1946) applied the English common names Washington cottontail and sagebrush cottontail and the French common name lapin brun de Washington to the subspecies S. n. nuttallii.

Figure 1. Global range of Nuttall’s Cottontail (Sylvilagus nuttallii) and its three subspecies:

  1. S. n. nuttallii
  2. S. n. grangeri
  3. S. n. pinetis

Subspecies boundaries modified from Hall (1981) and Diersing (1978).

1

Morphological description

A small rabbit, S. n. nuttallii has a pale brown dorsal pelage, grey on the sides and rump, and a white ventral pelage (Figure 2). A distinct pale brown nape is present on the back of the head and neck. The ears are tipped with black; the tail is white on the dorsal surface and grey underneath. The skull has a distinct interparietal bone and supraocciptal processes that touch the braincase. Body measurements (range in parentheses) for Canadian S. n. nuttallii are total length 319 mm (263-363) n=9, tail vertebrae 33 mm (24-44) n=9, hind foot 85 mm (75-90) n=9, ear 57 mm (54-58) n=4, and body mass 495 g (342-778) n=4 (Nagorsen 2002).

Figure 2. Nuttall’s Cottontail (Sylvilagus nuttallii). Photo by Dave Nagorsen.

Figure 2.  Nuttall’s Cottontail (Sylvilagus nuttallii). Photo by Dave Nagorsen.

The only other hare or rabbit in the southern interior grasslands of British Columbia is the Snowshoe Hare (Lepus americanus). The White-tailed Jackrabbit (Lepus townsendii) appears to be extirpated. Although L. americanus has a white pelage in winter, animals in brown summer pelage could be confused with S. n. nuttallii. L. americanus lacks the brown nape on the back of the head and the greyish-rump; it is also much larger (hind foot greater than 116 millimetres, ear greater than 63 millimetres) (Nagorsen 2002).

Genetic description

Nothing is known about the population structure of this rabbit in Canada. There are no geographic barriers that would be expected to limit gene flow among S. n. nuttalliiin the Okanagan Basin.

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