deer ecology
Reproduction
Breeding season (rut)
October–January
Breeding system
Polygamous—One male mates with several females during the breeding season. Healthy males may mate with 6 to 8 females.
Litters
One litter per year with 1 to 3 fawns, but usually 2.
First-time mothers usually give birth to just one fawn.
Sex ratio—The 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 at about 18 months.
Gestation period
200 to 210 days
Time of birth
April–July, but most often May–June
Fawns
- Fawns weigh 4 to 7 pounds at birth and can stand and run slowly within a few hours.
- For the first weeks of life, fawns avoid predation by remaining motionless in areas of cover.
- A fawn’s 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. A 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
Fawns in the first week after birth exhibit alarm bradycardia (the heart rate decreases quickly to aid in the “freezing” response) to avoid detection by predators. They also are virtually scentless 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 the 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 mother is usually nearby, though not necessarily in sight. She will return to the fawn twice a day so that it can nurse.
n 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.
For midwestern states, the percent of fawns that became pregnant ranged from 2% (Minnesota) to 29% (Iowa to Nebraska). For yearlings, the 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; to fawns born to older dominant or subordinate female breeders of any age, only 50% were female.