Gray Wolf (Canis lupus) Fact Sheet: Reproduction & Development

Mating system

• Monogamous in low-density populations, with some exceptions (Packard 2003)

Female receptivity

• Once per year (monestrus) unlike domestic dogs (McNay et al. 2006; Hayssen et al. 1993)
• 1-2 weeks during estrus (Packard 2003)

Courtship and mating

• Reproductive status of both sexes responsive to changes in day length (Hayssen et al. 1993; Kreeger 2003)
• Mating behaviors highly correlated with rising and falling concentrations of testosterone, estrogen, and other steroid hormones (Packard 2003)
  • Courtship and bonding behaviors precede mating and may begin c. 2 months prior to estrus (Packard 2003)
    • Bonding characterized by close sleeping, following, nuzzling, parallel-walking, wrestling, sniffing, and increased marking (increased urination)
    • Immediately prior to estrus, females prance, body-rub, paw, nuzzle, and cuddle (placing her chin on her mate's back) to indicate receptivity to mating advances
  • Copulation coincides with estrus; a period lasting c.one week (Packard 2003)
    • Female averts tail; male mounts female (Hayssen et al. 1993; Packard 2003)
    • 1-11 copulations may occur per estrus period, typically c. 5-6 (Packard 2003)
• Near birth, females may "localize" near the den site where birth occurs (Packard 2003)

Mating season

• Dec. to early Apr. (Mech 2002)
  • Southern populations earlier, Oct. to Feb.
• Latitude highly predictive of onset of mating
  • Timed to ensure birth is likely after the most severe winter storms and allow sufficient time and resources for successful growth and development of pups (Packard 2003)

Gestation

• 60-65 days (Kreeger 2003)

Birth

• Litter size: 5-7 pups typically; average 6 (MacNulty et al. 2009; McNay et al. 2006; Mech 1970)
• Born blind and deaf at den sites (Kreeger 2003)
  • Weight at birth: 300-500 g (Kreeger 2003)
  • Darkly furred, some with white star on the chest (Packard 2003)
  • Ears small; nose blunt or pugged (Kreeger 2003)

Den sites

• Located commonly near water and away from territorial edges (Mech et al. 1998; Packard 2003)
  • Ideally in well drained soils (Mech et al. 1998)
  • Either hidden away under foliage or in the open with extensive views of the surrounding area (Mech et al. 1998)
• Structure often dictated by the terrain (Packard 2003)
  • Crevice, rock cave, or shallow scrape in the frozen tundra above the Arctic Circle (Packard 2003)
  • Burrows in sandy bluffs, under tree roots (Packard 2003)
  • Taking over dens of coyotes or foxes (Mech et al. 1996; Mech et al. 1998; Packard 2003)
• Constructed and provisioned prior to birth, sometimes many months prior
  • Several pack members may participate; adults and yearling pups (Packard 2003)
• Repeated use of dens is common (Mech and Packard 1990; Packard 2003)
  • Multi-decade use observed, one den site in Denali National Park used intermittently between 1940 and 1989 (Mech and Packard 1990)
  • Multi-century use possible, c. 700 years based on presence of fossil remnants at a den on Canada's Ellesmere Island, Northwest Territories (Mech and Packard 1990)
• Several dens may be used within a territory (Mech and Packard 1990; Packard 2003)
  • Mothers carry pups using the mouth c. 5 weeks, until sufficient motor skills are developed (Packard 2003)
• Used for c. 8 weeks, to raise pups (Mech 1970)

Pup (< 1 yr)

• Three stages of pup development (summarized from Packard 2003 unless otherwise noted)
  • Birth to 12 or 14 weeks
    • Rapid growth occurs
    • Develop sensory systems, muscle coordination, and social skills (Kreeger 2003; Packard 2003)
• Neonatal/infancy period (summarized from Packard 2003 unless otherwise noted)
  • Birth to opening of eyes, 0-2 weeks
  • Confined to den c.3 weeks after birth (Mech 1970; Packard 2003)
    • Mother remains at den much of this time; food is provided to her by the father and other pack members (Mech 2000b; Mech and Boitani 2003; Packard 2003)
  • Suckle reflexively, c.every 5 hours
    • Milk similar to domestic dog's but higher in protein and lower in fat (Kreeger 2003)
      • Sufficient arginine (an amino acid) important for proper eye health (Kreeger 2003)
• Transition period (summarized from Packard 2003 unless otherwise noted)
  • Opening of eyes to emergence from den, 1.5-3 weeks
    • 10-14 days, eyes open and often bluish in color (Kreeger 2003; Packard 2003)
  • Olfactory and tactile senses well developed
    • Exploring their environment by scent
  • Visual and auditory senses limited, develop with age
    • Fully developed by 5 weeks
• Socialization period (summarized from Packard 2003 unless otherwise noted)
  • Pups emerge from den at c.4 months of age; develop social skills and learn how to be wolves
    • Elicit care from parents and other pack members (Packard 2003)
    • Follow pack members, learning to seek shelter and hunt (Packard 2003)
    • Play with litter mates (Packard 2003)
  • Explore near den site, usually within 0.5 km (0.3 mi); 3-5 weeks
  • Ingest first solid food and begin weaning at about 5-9 weeks
    • Fed regurgitated meat (Mech and Boitani 2003; Packard 2003)
      • Nursing may continue for several more weeks (Kreeger 2003)
    • Pups initiate feeding by licking and poking at muzzle of parent or pack mate (Packard 2003)
    • Pups cache food; surplus meat is stored near the homesite for later consumption (Packard 2003)
  • Accompany adults to carcasses once weaned (Packard 2003)
  • Howl by 1-2.5 months (Fentress 1967; Harrington and Mech 1978; Mech 1970; Schonberner 1965)

Juvenile/Subadult (12 weeks - maturity)

• Join in hunts at 4-10 months of age (Packard 2003)
• Fully grown by 12-14 months; growing points of skeletal regions close (Fuller et al. 2003; Kreeger 2003; MacNulty et al 200)
  • Older juveniles distinguished from adults by reproductive activity (Medjo and Mech 1976)
  • Reproductive activity observed as early as 9-10 months of age (Medjo and Mech 1976)
• Disperse from natal pack 9-36 months (Packard 2003)
  • Population specific

Adult

• Reach maturity at 5-6 years for both sexes, one study in northern Minnesota, U.S. (Mech 2008)
• Peak hunting proficiency c.2-3 years of age, one study of wolves in Yellowstone National Park, U.S. (calculated by MacNulty et al. 2009)
  • Decline in overall predatory performance by c. 3 years of age, projected age (MacNulty et al. 2009)
  • Declines in attack, killing, and selection reported as early as 1-2 years of age (MacNulty et al. 2009)
• Males
  • Capable of reproducing by 10 months (in managed care), but rarely so young in the wild (Kreeger 2003)
• Females
  • First estrus at 22 months or older (Kreeger 2003)
  • First reproduce at 2-4 years of age (MacNulty et al. 2009)
  • Regularly reproduce at 4-9 years of age (Mech 2008)
  • Reproductive until 10-11 years of age (Mech 1988)

Managed care

• Canis lupus baileyi
  • Median life expectancy
    • 11 years (AZA 2023)

Wolves killed by humans

• Impacts on mortality rates are extremely variable across their range
  • Historically hunted to near extinction in the U.S. (for more refer to the Management Actions section under Population & Conservation Status)
  • Current rates minimal, around 4%, for Denali wolves (Mech et al. 1998)

Intra-specific fighting: wolves killed by wolves

• Major source of mortality among wolves, multi-year study of Denali wolves (Mech et al. 1998)
  • 39% (22 of 57) of radio-collared individuals
  • To 65% possible, including deaths due to unknown causes
• Freshly killed wolf remains often show signs of conflict with other wolves (Mech et al. 1998)

Parasitic infection and disease

• Typically play minor roles in wolf mortality in the wild (Mech et al. 1998)
• Parasitic infection (Kreeger 2003)
  • Protozoans: Isopora, Toxoplasma, Sarcocystis, Babesia
    • Mostly benign; exacerbate other health conditions
  • Helminths (flukes, tapeworms, and nematodes): Trematodes, Cestodes, Alaria, Metorchis conjunctus, Ancylostoma caninum, Toxocara canis, Dioctophyma renale, Dirofilaria immitis(heartworm), and others...
    • Some more benign than others
    • Infect organs such as the liver, gall bladder, heart, intestines, kidney
  • Ectoparasites: Sarcoptes mites (mange mites), Trichodectes canis (lice), Ixodes (ticks)
• Disease (see Kreeger 2003; Mech et al. 2008)
  • Viral infections: rabies, canine distemper, parvovirus, hepatitis, and coronavirus
  • Mange, dermatomycosis/ringworm
  • Lyme disease

Accidents (Mech et al. 1998)

• Burial in snow due to avalanche
• Drowning

Reproduction

• Litter size
• 5-6 pups/litter (McBride 1980)
• Born April-May (McBride 1980)

Den Characteristics

• Dug-out spaces under rock ledges on slopes of canyon walls or hills (McBride 1980)

Mexican wolf pup (C. l. baileyi).

Pups emerge from the den when c. 3 weeks old, though they will leave and re-enter the site until c. 8 weeks of age. Howling starts within 1-2.5 months of age.

Image credit: © U.S. Fish and Wildlife Service. Some rights reserved.

Fentress (1967)
Fuller et al. (2003)
Harrington and Mech (1978)
Hayssen et al. (1993)
Kreeger (2003)
MacNulty et al. (2009)
McBride (1980)
McNay et al. (2006)
Mech (1970,1988, 2000b, 2002, 2008)
Mech and Boitani (2003)
Mech and Packard (1990)
Mech et al. (1996, 1998, 2008)
Medjo and Mech (1976)
Packard (2003)
Schonberner (1965)