Ý ß LIFE STAGES with literature reports for the Sun bear - Helarctos malayanus: Use sub-contents list below, or simply scroll down the page to view findings.

LIFE STAGES  - Editorial Comment

Editorial Comment

BREEDING SEASON: Data from bears in zoos indicate breeding at any time of the year. Fecal steroid (oestradiol and progesterone) data from female bears in a wildlife rehabilitation centre in Sarawak, Malaysia, indicate seasonal breeding (oestradiol peak August to September, progesterone peak November to January, in unmated females) and a female wild sun bear in Sabah, Malaysia was accompanied by a male in late October.

OESTRUS/OVULATION: Sun bears are polyoestrous. Behavioural oestrus usually lasts just one or two days but may extend to as long as five to seven days. Spontaneous ovulation may occur in unmated bears. Females may return to oestrus within days after the death of a newborn cub.

GESTATION/PREGNANCY:  Gestation length is variable; gestations of just three months (95-96 days) have been recorded in captivity, but also pregnancies of 174 to 240 days, suggesting delayed implantation sometimes occurs.

PARTURITION/BIRTH: Sun bears appear to be non-seasonal breeders. Births in zoos have occurred at all times of the year. In Tenasserim, Burma, cubs are born at the start of the hot weather.

NEONATAL/DEVELOPMENT: Cubs are born blind, deaf, helpless and hairless. The eyes open at 20-30 days, the first teeth appear at 35 - 45 days, hearing develops and improves over the first 50 days, cubs start trying to walk from 25-35 days. External stimulation is required for urination and defecation in the first two months. Cubs first accompany their dam from about 55-65 days and start eating solid food at 65-85 days. The deciduous canines are shed in the seventh month and adult dentition is present by about 18 months.

LITTER SIZE: Sun bears produce one or two cubs per litter.

TIME BETWEEN LITTERS / LITTERS PER YEAR:  The normal inter-litter interval is not known. In one zoo, following loss of a cub at seven weeks, a second litter was born less than five months after the first.

LACTATION / MILK PRODUCTION: Little information is available. A single milk sample taken at 90 days of lactation contained 10.8 % fat, 8.4 % protein, 3.2 % lactose, and had a calculated gross energy content of 6.7 kJ/g.

SEXUAL MATURITY: These bears reach sexual maturity at two to three years old.

MALE SEASONAL VARIATION: No clear seasonal variation, but individual males may show sustained increases in testosterone at intervals of four to six months. Increases in testosterone in male bears in zoos were noted in April-May, June-July and September-October.

LONGEVITY / MORTALITY: Sun bears in zoos have lived as long as 33 years.

(References are available in detailed literature reports below)

Breeding Season

Source Information

• Mating may occur at any time of the year. (B285.w4)
• Females may enter oestrus and mate at any time of the year. (D246)
• Breeding may occur at any time of the year. (B424)
• Any time of the year (based on captive data). (B336.51.w51)
• Data for captive sun bears in Sarawak, Malaysia, indicate a progesterone peak early November to January. This was measured by faecal analysis; progesterone concentration varied from a low of 32.2 ng/g faeces to a peak of 152.1 ng/g (in a 5-year-old female in November,) 102.7 ng/g in an 11-year-old female in November and 157.3 ng/g in a seven-year-old female in January. The photoperiod in this area shows little variation over the year; the rainy period lasts November to February, while June to August is a dry period. (J27.63.w2)
• Data for captive sun bears in Sarawak, Malaysia, indicate a peak in fecal oestradiol 17β concentrations in August to September, and  a higher number of superficial vaginal anuclear cells in August than in March. (J27.64.w2)
• In Sabah, Malaysia, a female was accompanied by a male in late October. (J345.15.w1)
• Sun bears are non-seasonal breeders. (J296.62.w1)

Oestrus / Ovulation

Source Information

• Behavioural oestrus may last as long as five to seven days but just one to two days is more common. (D246)
• Spontaneous ovulation may occur, followed by pseudopregnancy (as indicated by lactation in unmated bears: milk could be expressed by squeezing the nipples of anaesthetised bears). (J27.63.w2)
• Sun bears are polyoestrous. The intra-oestrus interval in non-pregnant females has been measures varying from 140 to 216 days. Oestrus behaviour has been described including sluggishness and rubbing of the genitalia on logs; the external genitalia were swollen and pink during oestrus. (J296.62.w1)
• Return to oestrus may occur shortly after early loss of a cub; data from European zoos indicate interbirth intervals of 126 +/- 9 days following death of the cub shortly after birth. (P6.2.w5)

Mating / Gestation / Pregnancy

Source Information

• At the East Berlin Zoo, gestation period was 95 to 96 days (for six births). (B147, J23.10.w1)
• At Fort Worth Zoo, pregnancies of 174, 228 and 240 days were recorded, indicating delayed implantation. (B147, J23.14.w1)
• Gestation length shows considerable variation: three to eight months. (B285.w4)
• Gestation of three months seen at the East Berlin Zoo (one cub born 1st April, rejected at seven weeks and another born 30th August the same year. (J23.3.w1)
• Successive gestations of 95 and 96 days reported. (B423)
• Gestation of 95-96 days. (B424)
• Both 95-97 days and 174 - 240 days reported. (B336.51.w51)
• 97 days. (B144)
• There is some variation in length of pregnancy in sun bears; it is not clear whether delayed implantation occurs. (J296.62.w1)
• In zoos in Europe, the length of gestation was 95 to 107 days. (P6.2.w5)
• Gestation is a little over three months. (B448)

Parturition / Birth

Source Information

Parturition:

• Hollow logs are used as maternity dens, as indicated by the finding of newly born cubs in such logs. (J296.62.w1)
• A female was observed using a video camera at Wellington Zoo. Contractions were observed from about six hours prior to the cubs being born, and were seen at greater frequency and with shorter intervals closer to the birth. (N18.47.w1)

Seasonality:

• Births may occur any time of the year. (B147, B285.w4)
• At the East Berlin Zoo, births in late April and late August. (J23.3.w1) Further births in June, January, September, February and November. (J23.10.w1)
• In Tenasserim, Burma, cubs are born at the start of the hot weather. (B426.8.w8)
• Any time of the year. (B336.51.w51)
• Births in zoos have been reported in April, August and September. (B288.w11)
• In Sabah, Malaysia, a radiocollared female which had been accompanied by a male in October 1999 was absent from the main study area for most of February and March 2000 (did not visit the oil palm plantation adjacent to the forest and was only occasionally detectable near the forest margin) but did use the oil palm plantation in March 2001. It was speculated that her absence February to March 200 may have represented the female's denning period due to cubbing. (J345.15.w1)
• From 18 birth dates determined over a period of 25 months for wild bears in East Kalimatan (Indonesian Borneo), births occurred in 15 months, with no seasonal (wet versus dry) differences in occurrence of births. (J296.62.w1)
• Data from bears in European zoos, both from observation of mating and birth dates, and from faecal steroid analysis, indicate non-seasonal breeding. (P6.2.w5)
• In South-East Asia, at the start of the hot weather. (B448)

Neonatal Development

Source Information

• Cubs are born blind, deaf, helpless and hairless. The eyes open at 20-30 days, the first teeth appear at 35 - 45 days, hearing develops and improves over the first 50 days, cubs start trying to walk from 25-35 days. External stimulation is required for urination and defecation in the first two months. Cubs first accompany their dam from about 55-65 days and start eating solid food at 65-85 days. The deciduous canines are shed in the seventh month and adult dentition is present by about 18 months.

Birth: 

• Blind and hairless. (B424)
• At birth, cubs are deaf and have closed eyes. Hearing develops and becomes sharper over the first 50 days. (D246)
• For the first two months, cubs require external stimulation for urination and defecation. (D246)
• Dentition is complete by 18 months. (B424)
• Blind, deaf and hairless at birth. (J23.9.w5)

Eyes and ears:

• Cubs are blind at birth. (B424)
• The eyes are closed at birth. (D246)
• Hearing develops and becomes sharper over the first 50 days. (D246)
• Zoo data: eyes open: 20 - 30 days. (D247.6.w6)
• in one hand-reared cub, the eyes first opened at 13 days but appeared cloudy until about five weeks. The cub was noted to be able to hear at six weeks old. (J23.9.w5)
• Observations on seven cubs found that the eyes opened at about 25 days but the cubs did not appear to have sight until 50 days; hearing was poor at 30 days but sharper from 50 days. (J368.11.w1)

Thermoregulation:

• --

Growth rate/weight gain:

• --

Tooth development:

• Zoo data: first tooth: days. 35 - 45 (D247.6.w6)
• One hand-reared cub started teething, canines first, at six weeks. (J23.9.w5)
• For two captive born cubs, the deciduous canines were shed during the seventh month and the bears had complete adult dentition by about 18 months of age. (B423)
• Adult dentition is present by about 18 months (based on captive data). (D246)
• Observation of seven cubs noted that the upper incisors and canines started to appear at 40 days and the complete adult dentition was in place at 18 months. (J368.11.w1)
• All teeth present by 15 months. (B448)

Feeding, exploration and dispersal:

• Zoo data:
  • Attempt to walk from: 25 - 35 days. (D247.6.w6)
  • First accompany dam: 55 - 65 days. (D247.6.w6)
  • First intake of solid food: 65 - 85 days. (D247.6.w6)

Litter Size

Source Information

• One or two. (B147)
• One cub in each litter at the East Berlin Zoo. (J23.3.w1, J23.10.w1)
• One or two cubs. (B423)
• 1-3 (B144)
• In European zoos, nearly all litters have contained a single cub, although twins have occurred. (P6.2.w5)
• Two cubs per litter. (B448)

Time between Litters/ Litters per year

Source Information

• At the East Berlin Zoo, one cub was born 1st April, rejected at seven weeks and another born 30th August the same year. (J23.3.w1)

Lactation / Milk Production

Source Information

• A milk sample taken at 90 days of lactation from a zoo bear contained 27 % dry matter (total solids), including 10.8 % fat, 3.2 % lactose, 4.6 % casein, 3.8 % whey protein, 1.5% ash, 0.37% calcium and 0.24% phosphorus. It had a calculated energy content of 6.7 kJ/g gross energy. (J332.53.w1)

Sexual Maturity

Source Information

• Two to three years. (D246)
• A captive female showed first oestrus at 3.5 years but did not conceive until three years later. (J23.10.w1)
• Two or three years. (J368.11.w1)

Male Seasonal Variation

Source Information

• A study of male sun bears in zoos in North America and New Zealand, based on fecal testosterone levels, found that testosterone levels were often elevated during periods of breeding behaviour. There was no obvious seasonal pattern to testosterone excretion, but in general levels were low early in the year and showed increases in April-May, June-July and September-October, with brief troughs in mid-May and July. Older males had higher testosterone levels than did young males. Sustained increases generally occurred at intervals of four to six months. (J54.24.w1)

Longevity / Mortality

Source Information

• About 31 years recorded in captive bears. (B147)
• To 33 years in captivity. (B285.w4)
• Lifespan: Up to 20 years six months, and 24 years nine months, have been recorded for individuals in captivity. (D246)
• In captivity, a life span of 20 years six months has been recorded. (B423)
• A life span of about 20 years in captivity. (B424)
• Sun bears may die from starvation when the mast (fruiting season) fails. (J17.119.w1, Th9.IV.w4)
• 24 years nine months in captivity. (B39.w8)
• Up to 20 years in captivity. (B448)

Age Estimation Techniques: 

• --