Females direct mate choice, using three strategies:
Sampling: females visit several harem-holding males, staying with each a few days before switching, usually returning to a male they visited within a week of estrus for mating
Inciting: use sampling behavior until estrus, then run away from the male, inciting chasing and aggressive displays and fights among competing males. Female watches competition and mates with the winner
Quiet: a month before estrus, female moves to an isolated, peripheral location occupied by a single male and stays with him throughout estrus and mating
Male approaches female with a high-pitched whine
Receptive female raises her tail and stands
Male approaches waving his head from side to side in a pronounced gesture, making low sucking sounds, then mounts
Copulation is brief, one forceful pelvic thrust
Females may be harassed by bachelor males, with increasing aggression as estrus approaches; they often seek refuge with a territorial male, which chases off the bachelor
Male pronghorn utilize different breeding systems within the same population, influenced by resources, population density, and sex ratio. (Maher, 2000)
Territorial: When resources vary in quality or are clumped in defined locations, breeding males compete for the best territories (containing water and succulent vegetation) then defend a band of females within that territory
Dominance: When resources are more uniform, bands with females and multiple males form; the males maintain a dominance hierarchy among them and the most dominant male conducts most of the breeding
Harems: When resources are widely dispersed, population levels are low, or the sex ratio is skewed (1 male to 10 or more females), individual males defend a harem without regard to a defined territory
Sexual maturity: females – 16 to 17 months; males – 1 year, although most will not breed until they are 3 to 4 years old and can compete to defend a territory or harem
Northern populations: mid to late September, three-week rut is typical
Southern populations: September to October, although breeding behavior is seen as early as July
Synchronous birthing, most fawns born within a 10-day period
Gestation and Birth
245 to 255 days
After fertilization, ova can develop for nearly a month before implantation.
Northern populations: typically May to June
Southern populations: typically June to July
Birthing season is influenced by habitat and environmental conditions
Litter size: Usually twins; subordinate females sometimes have one fawn
Size at birth: 7 to 9 pounds, 20 to 29 inches
Fawns are large; combined weight of twins at birth is about 18% of maternal weight
Infant (< 1 year old)
Age at weaning: 4 to 5 months
Reach full weight by 4.5 years, females reach this faster than males
Sexual maturity for males by one year, but at this age they don't usually have an opportunity to breed.
Females are sexually mature around 16 months, but have been known to conceive at 5 months.
7 to 10 years
Female pronghorn usually give birth to twins, but subordinate females sometimes have one fawn.
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