Philantomba monticola
blue duiker

Philantomba monticola, commonly known as the blue duiker, is found throughout Central and Southern Africa. Its range includes Nigeria to Gabon and Kenya to South Africa. (Ronald and Kranz, 2006; Waltert, et al., 2006)

Blue duikers can be found in a variety of forested areas, including rain forests, riverine forests, dense thickets, and montane forests. They are often found near human dwellings, and may use plantations as corridors in their habitat. Piles of dead trees or lumber are sometimes used as resting sites. However, the majority of their time is spent resting in the open or at the base of a tree; this allows them to keep their line of vision clear. ("Philantomba monticola", 1999; Estes, 1991)

Blue duikers are the smallest of the duiker species, weighing no more than 4 to 6 kg. They are typically 55 to 72 cm long, with a 7 to 12.5 cm tail that is black with a white underside. Coat color varies, depending on where the animal lives but the coat is typically brown, often with a blue tint. All males have a pair of grooved horns that are about 5 cm in height. Females may have horns as well, however, horns are frequently not present in females. Blue duikers are very similar in appearance to Maxwell's duikers (Philantomba maxwellii). However, the two can be distinguished by several key features, most notably blue duikers have a smaller skull, with a narrower nasal passage. (Estes, 1991; Ralls, 1973; Ronald and Kranz, 2006)

Blue duikers become sexually mature at 9 to 12 months for females and 12 to 18 months for males. Once sexually mature, they find a mate and remain paired for life. Although blue duikers are considered monogamous, males occasionally breed with other females. (Boehner, et al., 1984; "Philantomba monticola", 1999; Estes, 1991)

Blue duikers are social animals and display a variety of social behaviors, but they do not form large groups, instead associating as mated pairs. An important aspect of behavior is their use of preorbital scent glands, which both genders use to mark their mate. Licking behavior is also displayed and is believed to indicate social acceptance.

Blue duiker pair members remain together throughout the year, spending much of their time in close proximity. Seasonality does not appear to influence their reproduction, as they continue to produce offspring without regard to time of year. After the female calves, the male leaves the territory for approximately one month, during which time other males may enter the territory. The return of the female's mate drives other males away.

Blue duikers have a gestation period lasting anywhere from 196 to 216 days and typically produce only one calf per reproductive event. Newborn calves weigh about 10% of the mother's body weight. After calving, the female conceals her offspring, and for the first several weeks after birth, the majority of contact between the calf and female takes place during nursing. Eventually, when the calf is more mature, it spends more time with its mother. The calf is weaned between 2.5 and 3 months of age, and eventually leaves the territory on its own accord. Female calves typically leave when they are sexually mature, which is between 1 and 1.5 years of age, and males when they are fully grown, at about 2 years of age. Usually, only one offspring associates with the parents at any one time, but occasionally a monogamous pair will share its territory with two offspring of different ages. (Boehner, et al., 1984; "Philantomba monticola", 1999; Estes, 1991)

Blue duiker calves are extremely precocial and are able to run within 20 minutes of birth. The mother typically allows the calf to nurse approximately 3 times a day for the first month, after which the mother reduces nursing events until the calf is weaned at 2.5 to 3 months. Initially, the male is absent, taking leave shortly after the calf is born, and returning approximately one month later. However, he does not travel far, and does occasionally come back and spend time with his mate. It is believed that the male leaves his territory to aid in the protection of his offspring. (Boehner, et al., 1984; Estes, 1991)

In captivity, blue duikers typically live for 10 to 15 years, but the oldest recorded captive individual survived until it was nearly 16 years of age. In the wild, lifespan is shorter, with the oldest known individual surviving to age 12. Captive duikers are commonly afflicted with several illness, most notable of those is 'sloshing syndrome' or rumen hypomotility syndrome. This illness is characterized by a build-up within the rumen caused by limited activity. ("Blue Duiker", 2008; Willette, et al., 2002; de Magalhaes, et al., 2002)

Blue duikers live in dense patches of forest in monogamous pairs. Adults spend the day moving around the territory foraging for food, in the form of leaves and fallen fruit. These animals are diurnal, but have been known to display nocturnal behavior when the female is in estrus. The adult male and female will often forage in different parts of their range during the day, but periodically come back together. Likewise, they may spend all or part of the night in different parts of their territory, or together. Pair members will defend their territory from other duikers by assuming a posture known as 'low-horn presentation'. Usually, the intruding individual will flee once confronted, but occasionally a battle ensues. Battles between blue duikers involve ramming one another repeatedly with the horns. These fights typically end without injury, although occasionally an individual will suffer stab wounds. (Bowman and Plowman, 2002; Estes, 1991; Kranz, 1991)

Blue duikers are among the most widespread of duiker species. This can be attributed in part to their minimal requirements for patches of continuous habitat and ability to survive in disturbed areas. Blue duikers have a minimum critical patch area of 0.7 ha, but typically maintain a home range of 2.5 to 4 ha. They can be found near human inhabited areas, and do not appear to be averse to commercial plantations, which they sometimes use as corridors between patches of appropriate habitat. The largest problem for blue duikers caused by humans appears to be the disassembling of firewood piles, as these duikers use hallows in woodpiles as areas for roosting. (Estes, 1991; Lawes, et al., 2000)

Blue duikers use auditory, visual, olfactory, and tactile senses for communication. They have several methods of displaying alarm to a mate or offspring, including vocalizing and flicking the tail. Auditory signals include snorting, whistling, hitting an object with the horns, and stamping the feet. Each of these displays conveys different messages and may communicate alarm or sexual excitement. Their primary visual display is tail flicking; flicking the black tail reveals a white underside, which is believed to communicate imminent danger. Blue duikers have several scent glands, the most notable of which are the preorbital glands. Preorbital glands are thought to be important in communicating social acceptance and territory ownership. Pair members may scent mark each other, their offspring, or trees in their home range. Individuals often lick one another, a behavior that is thought to indicate social acceptance. Licking is especially evident when a male is courting a female. (Estes, 1991)

Blue duikers are frugivores and primarily feed on fallen ripe and unripe fruit, seeds, flowers, and fungi. They are ruminants, but have a relatively small rumen, which results in a rapid rate of food turnover. In association with rapid turnover, they prefer foods that are low in cellulose and starch with moderate fiber and protein content. They are, however, capable of digesting foods that are relatively high in tannins. Blue duikers spend up to 67 to 76% of their waking hours foraging for food within their territory. (Dierenfeld, et al., 2002; Estes, 1991; Molloy and Hart, 2002)

The diminutive size of blue duikers leaves them vulnerable to many species, including but not limited to hyenas, wild dogs, African golden cats, leopards, crocodiles, baboons, python, civets, crowned eagles, monitors, and humans. They primarily use their visual and auditory senses in detecting predators. Once a predator is spotted, blue duikers will typically communicate alarm, which may include snorting, stamping, whistling, or flicking the tail, depending on the degree of danger. Once this message of danger has been received, a duiker's response is typically flight. Their long hind limbs make them excellent jumpers, able to quickly dive into dense vegetation and disappear. It is this ability that gave duikers their name, for the Afrikaans word meaning 'divers'. ("Philantomba monticola", 1999; Estes, 1991; "Blue Duiker", 2008; "The Living Africa", 1998)

Blue duikers live in forested areas and feed primarily on fallen fruit. The fruit that they find on the forest floor is often dislodged by monkeys that inhabit the same areas. In addition to fruit, blue duikers feed on seeds, however, they apparently do not aid in seed dispersal, because they fully masticate their food. Blue duikers may play host to several parasites. Externally, they are often afflicted with ticks. Internal parasites include several species of Nematoda, Coccidia, Strongyles, Trichuridae, and Moniezia. (Dierenfeld, et al., 1995; Feer, 1995; "Blue Duiker", 2008)

Blue duikers are among the most common duikers hunted for bushmeat. Many human groups living near the Congo basin rely heavily on the meat obtained from duikers for food and income. (Newing, 2001; Yasuoka, 2006)

Although this species sometimes occupies plantation fields, it is not known to be harmful to crops or humans. (Lawes, et al., 2000)

Currently, blue duikers are listed as 'Least Concern' on the IUCN Red List of Threatened Species.