The male fallow deer is known as a buck, the female is a doe, and the young a fawn. Adult bucks are 140–160 cm (55–63 in) long, 85–95 cm (33–37 in) in shoulder height, and typically 60–100 kg (130–220 lb) in weight; does are 130–150 cm (51–59 in) long, 75–85 cm (30–33 in) in shoulder height, and 30–50 kg (66–110 lb) in weight. The largest bucks may measure 190 cm (75 in) long and weigh 150 kg (330 lb). Fawns are born in spring around 30 cm (12 in) and weigh around 4.5 kg (9.9 lb). Their lifespan is around 12–16 years.
Much variation occurs in the coat colour of the species, with four main variants: common, menil, melanistic, and leucistic – a genuine colour variety, not albinistic. The white is the lightest coloured, almost white; common and menil are darker, and melanistic is very dark, sometimes even black (easily confused with the sika deer).
- Common: Chestnut coat with white mottles, it is most pronounced in summer with a much darker, unspotted coat in the winter. The light-coloured area around the tail is edged with black. The tail is light with a black stripe.
- Menil: Spots are more distinct than common in summer and no black is seen around the rump patch or on the tail. In winter, spots are still clear on a darker brown coat.
- Melanistic (black): All-year the coat is black shading to greyish brown. No light-coloured tail patch or spots are seen.
- Leucistic (white, but not albino): Fawns are cream-coloured; adults become pure white, especially in winter. Dark eyes and nose are seen, with no spots.
Most herds consist of the common coat variation, yet animals of the menil coat variation are not rare. The melanistic variation is generally rarer, and white is very much rarer still, although wild New Zealand herds often have a high melanistic percentage.
Only bucks have antlers, which are broad and shovel-shaped (palmate) from three years. In the first two years, the antler is a single spike. They are grazing animals; their preferred habitat is mixed woodland and open grassland. During the rut, bucks spread out and females move between them; at this time of year, fallow deer are relatively ungrouped compared to the rest of the year, when they try to stay together in groups of up to 150.
Agile and fast in case of danger, fallow deer can run at a maximum speed of 30 mph (48 km/h) over short distances (being naturally less muscular than other cervids such as roe deer, they are not as fast). Fallow deer can also make jumps up to 1.75 m (5.8 ft) high and up to 5 m (17 ft) in length.