Ord's Kangaroo Rats in North-Central Kansas: Patterns of Body Size and Reproduction

Abstract

Ord's kangaroo rats (Dipodomys ordii) were collected in Russell and Lincoln counties, Kansas during 1977–1986. Most specimens (n = 43 of 45) were collected in the Saline River valley during 1985–1986. All individuals were necropsied to document features of body size and reproductive condition for both females and males. For 43 kangaroo rats captured in the Saline River valley, 35% were males. Sex ratios tended to differ between nights 1–2 (18% males) and nights 3–5 (41% males); a pattern likely caused by delayed capture of males relative to females over the 5-day sampling period. For 45 Ord's kangaroo rats, mean body length was similar for males (109.5 mm) and females (108.2 mm). As expected, body mass increased significantly with increasing body length for males and non-pregnant females. Tail length also increased significantly with increasing body length for males and females; body length explained almost 80% of the variation in tail length for males in contrast to <45% for females. Hind foot and ear lengths also increased significantly with body length for males and females but sex did not have a significant effect on either variable. Three pregnant females were captured during June–July; litter sizes were 2, 2 and 3 (one fetus was resorbing also resulting in a realized litter size of 2). All large males (body mass >58 g) captured during June-July were scrotal, whereas all smaller males were non-scrotal. Three males collected from late autumn through mid-winter were non-scrotal.