128 RODENTS OF IOWA 



and during the absence of the parent the young are covered and 

 completely concealed by the material of the nest. At such times 

 the top of the nest is so like the surrounding surface of the 

 ground, on which lie dead leaves and grasses, that its presence 

 can be detected only by chance. ' ' 30 The young are suckled in the 

 nest for about three weeks and then are left to shift for them- 

 selves. 



The pelage of hares and rabbits varies in length and thickness 

 according to climate. Its color responds readily to climatic in- 

 fluences, also, a fact which accounts in large part for the great 

 number of recognized geographical races. The pelage is thickest 

 on the back, and is made up of three sets of hairs which are best 

 differentiated in this region; a short dense underfur, a longer 

 coarser coat of hairs, and a still longer coarser and thinner set 

 of hairs the tips of which overlie the middle coat. Differences in 

 pelage due to age are to be noted also; the Juvenal pelage is soft 

 and woolly and is carried until the animal is about half grown 

 when it gives place to the postjuvenal pelage which is characterized 

 by the greater development of the middle hairy coat. The post- 

 juvenal pelage is retained until the animal is almost full grown,, 

 when the typical adult pelage takes its place. This pelage has 

 the characteristic coarse hairs of the middle coat accompanying 

 the long black hairs of the back. 



Of our representatives of the family the varying hare and white- 

 tailed jack rabbit have two annual molts, while the great plains 

 jack rabbit and the cottontail molt but once during the year. In 

 the two former the change from the white winter coat to the dark 

 summer coat is brought about only very gradually. In the two 

 latter the single molt usually occurs in the late summer or early 

 fall. 



Among American rabbits, variation due to sex is not marked, 

 though usually very old females are slighth/ larger than males 

 of the same age. However, individual differences in coloration, 

 size, length of ears, hind feet, proportion and size of skull are 

 very marked, thus adding to the difficulty of delimiting closely 

 related forms. Many forms are also subject to much variation 

 due to environmental conditions, while other forms seem to be 

 little affected. 



^Nelson, E. W., N. A. Fauna, No. 29, 21-22, 1909. 



