CHAPTER 2: AFFECTEO ENVIRONMr.NT 



200 



H ' 1 1 1 ' H 



182 



1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 



YEAR 



Figure 4. Minimum fall number of wolves in the State of Montana, 1979-2002, and the first known 



dispersal events leading to a new pack in the Montana population (USFWS unpubl. data). The 

 arrows show the years of the first known dispersals of radio-collared animals into the State of 

 Montana to start a new pack or join an existing pack. 



Reproduction. Wolves normally do not breed until at least 22 months of age (Mech 1970). Breeding 

 usually occurs only between the dominant male and female in a pack. In the northern Rockies, the 

 breeding season peaks in mid- to late February (Boyd et al. 1993). Wolves localize their movements 

 around a den site and whelp in late April, following a 63-day gestation period. After the pups are about 

 eight weeks old, they are moved to a series of rendezvous sites. In northwestern Montana, maximum 

 litter size averaged 5.3 (range 1-9) from 1982 to the mid 1990s. By December, average litter size 

 declined to 4.5 (Pletscher et al.l997). 



Pup survival is highly variable and influenced by several factors, including disease, predation, and 

 nutrition (Mech and Goyal 1993, Johnson et al. 1994). In northwestern Montana from 1982-1995, 85% 

 of pups survived until December, though survival varied year to year (Pletscher et al. 1997). Pup 

 mortality in the first eight months of life was attributed to human causes (8 of 20 mortalities, 40%), 

 unknown causes (2 of 20, 15%), and disappearance (9 of 20, 45%). In YNP, during the first four years, 

 133 pups were bom in 29 litters and 71% were believed to still be alive in 1998 (Bangs et al. 1998). Pup 

 survival varied between 73-81% from 1996-1998. However, canine parvovirus was strongly suspected as 

 a contributing factor in the low pup survival (45%) in 1999. In 2000, pup survival rebounded to 77% 

 (Smith et al. 2000). 



Occasionally, more than one female in a pack may breed, resulting in more than one litter per pack 

 (Ballard et al. 1987). This phenomenon has been documented in YNP (Smith et al. 2000, USFWS et al. 

 2000, USFWS etal. 2001). 



17 



