AMERICAN WEASELS

Coloration of head and foreparts in tensubspecies of long-tailed weasel, Mustela frenata. All figuresare of males, approximately × 1/2.

In regions of heavy rainfall (see figs. 2 and 3) there is an increasein pigmentation and extent of blackish color backward over the neck anda decrease in extent of the white facial markings. In regionsprogressively more arid (see figs. 3 to 7) there is a decrease inpigmentation and extent of blackish color and an increase in extent ofthe white facial markings.

As shown by rearing mammals from humid regions in arid regions, andvice versa, the color is not visibly altered in one or a fewgenerations; the color is an hereditary character. Beginning with thesouthernmost subspecies (fig. 1) and continuing northward to thenorthern subspecies (fig. 10) there is a darkening, next a lightening,and finally a darkening closely conforming to amounts of precipitationin the geographic regions concerned. A fuller discussion of thiscorrelation is given on page 51.

Fig. 1. Map showing localities of capture ofspecimens depicted in plate 1.