deer ecology

Reproduction

A female deer is being chased by a male deer across a harvested field during the breeding season.
Deer are on the move to find mates during rut. Here a male is chasing a female across a harvested field.
Photo: Chris Young

Breeding season (rut)

October–January

Breeding system

Polygamous—One male mates with several females during the breeding season. Healthy males may mate with 6–8 females.

Litters

One litter per year with 1–3 fawns, but usually 2.

First time mothers usually give birth to just one fawn.

Sex ratio—Number of males to females depends on multiple factors. In deer, the sex ratio can vary from 1:1.

Birth area

Females tend to give birth in grassy areas near woods, usually isolated from other deer. They often use the same fawning areas they used in previous years.

Maturity

Females attain sexual maturity the same year they are born. Males attain maturity the second breeding season after birth or about 18 months.

Gestation period

200–210 days

Time of birth

April–July, but most often May–June

Fawns

This fawn is resting in grass and other green vegetation.
Young fawns spend a lot of time resting.
Photo: Chris Young
  • Fawns weigh 4–7 pounds at birth and can stand and run slowly within a few hours.
  • For the first weeks of life, they avoid predation by remaining motionless in areas of cover.
  • Their spotted coat provides camouflage in the broken patterns of sunlight reaching the woodland floor.
  • Fawns are often left alone. If you find a fawn, leave it where you found it. Many “rescued” fawns that people thought were orphans were not actually orphaned.

Care of young

The female raises the fawn. Female deer will typically flee when a human or predator approaches their fawn. They may or may not make alarm sounds.

Weaning

About 5 weeks of age

More About Fawns

This young fawn is laying on the leaf-covered ground in a woodland. Its white spots help it to blend in with its surroundings.
This fawn’s spots helps it blend into its surroundings.
Photo: Jared Duquette

Fawns in the first week after birth exhibit alarm bradycardia (heart rate decreases quickly to aid in the “freezing” response) to avoid detection by predators. They also are virtually scent-less after birth to help them avoid predators, but they gain scent as they age.

Activity of fawns during the first week of life consists of nursing and moving between bedding sites, which accounts for only 3% of their time. They sleep and rest the remainder of the time. By 9 weeks of age, fawns are active 27% of the day.

The fawn and mother make sounds and use their sense of smell to help locate each other. If the fawn is threatened, the female snorts and stamps her front feet and may charge the predator to drive it away. As the fawn grows and gets stronger, it begins following the female as she forages.

Fawns nurse an average of twice daily. As the fawns age, the time spent nursing increases, but the frequency does not.

Fawns must have microorganisms in their rumen to break down the vegetative matter they consume. For their first month they live exclusively on milk. After a month or so, fawns begin to eat grasses, tender woody vegetation, and even shelled corn. At times, the female will drive a fawn away that still wants to suckle after attaining the age of 5 to 6 months.

Small fawns are unafraid of humans. Until they are 4 or 5 days old, they will not attempt to escape when detected. It is at this stage that most deer fawns are taken alive illegally because they are mistaken for orphans. Sometimes, fawns end up in strange places such as on sunny porch steps. If you find a fawn by itself, do not move it. The female is usually nearby, though not necessarily in sight. She will return to the fawn twice a day so that it can nurse.

In one Illinois study, 121 females produced 221 fawns (102 females, 119 males) that survived to at least one year old. Among these 221 fawns, 35 (29%) birth events produced single fawns, 78 (63%) produced twins, and 10 (8%) produced triplets. It is possible for a pregnant doe to have four or five fawns but it is very uncommon.

While twin fawns are common, deer sometimes have three or even four fawns per litter. Here a female deer is standing with her three fawns.
While twin fawns are common, deer sometimes have three, or even four, fawns per litter.
Photo: Robert J. Reber

For Midwestern states, the percent of fawns that became pregnant ranged from 2% (Minnesota) to 29% (Iowa to Nebraska). For yearlings, the percent range was 55% (Iowa to Nebraska) to 88% (Minnesota). For adults, the pregnancy rates varied from 71% to 96% (multiple states). Contrary to what was once believed, females never reach senescence; they reproduce until they die.

Interestingly, a study of deer in west-central, northern, and east-central Illinois found that dominant females of any age produced more female offspring. Of fawns born to younger dominant females, 72% were female, compared to fawns born to older dominant or subordinate female breeders of any age, only 50% were female.