Figure 14.— Muskrat litter a few hours 

 old. 



a mate and invades another's terri- 

 tory. This is particularly in evi- 

 dence in spring during the active 

 mating period when muskrats fre- 

 quently show bites and slash marks. 

 Mating takes place during the 

 latter part of March. The gesta- 

 tion period is rather short, 28 or 29 

 days. The first, or early-spring, 

 litters are usually born between 

 April 27 and May 5— the period 

 that is most productive in the total 

 number of young born and that has 

 the highest rate of survival of 

 young. In northern areas, two lit- 

 ters, and occasionally a third, are 

 produced a year. In Maryland, 

 three litters a season are common, 

 the third being born in August or 

 September; on rare occasions a 

 fourth litter may be produced very 

 late in the year. 



Spring and fall litters are usually 

 born in small nests that are hol- 

 lowed out inside the house, or bed, 

 and lined with fresh shoots of very 

 fine grass. In northern regions the 

 nests are lined with finely shredded 

 pieces of cattail. In summer, birth 

 of the young may take place in more 

 open situations or on rafts made of 



cattails, rushes, or grass ; in brush 

 piles; or in flimsily constructed 

 nests thrown up just above the reach 

 of high tide. 



The size of the muskrat litter has 

 been recorded as ranging from 1 to 

 13 young but evidently it varies 

 with the race concerned. The com- 

 mon eastern muskrat {Ondatra z. 

 zibetUcus) averages 6 young 

 throughout most of its range; the 

 Virginia or coastal muskrat {0. z. 

 macrodon) averages 4.4 young ; and 

 the Louisiana muskrat {O.z. rivali- 

 cius) averages but 3.85, seemingly 

 compensating for this low number 

 by producing as many as four or 

 five litters a year. 



Muskrats weigh less than an 

 ounce at birth and are blind, almost 

 naked, and helpless (fig. 14). Dur- 

 ing the lactation period the mam- 

 mae, or teats, of the muskrat are 

 retractile and the tips are some- 

 what recurved. When a nursing 

 mother is disturbed she plunges un- 

 der water, the young clinging to 

 her; if some are torn loose the 

 mother usually manages to retrieve 

 them. 



The young muskrats develop rap- 

 idly and their eyes open in 14 to 16 

 days after birth (fig. 15). Known 

 as mice, they often begin to nibble 

 on green, succulent vegetation be- 



FiGURE 15.— At l.'i days young muskrats 

 have well-developed fur, and the eyes 

 are just beginning to open. 



10 



