Blue Duiker
Activity is diurnal (limited to daytime). Secretive and cautious, the blue duiker confines itself to the forest fringes. Territorial, individuals of opposite sexes form pairs and occupy territories, nearly 0.4–0.8 hectares (0.0015–0.0031 sq mi) large and marked by preorbital gland secretions. The blue duiker feeds on fallen fruits, foliage, flowers and pieces of bark, provided mainly by the forest canopies in their habitat. The age when sexual maturity is gained has been given differently by different studies. The species is monogamous, with pairs remaining together throughout the year. The length of the gestational period has been estimated from as little as four months to as long as seven months. Births occur throughout the year, though the birth rate might fall in the dry season. The calf is mainly kept in hiding and weaning occurs at 2.5 to 3 months.
The habitat consists of a variety of forests, including old-growth, secondary, and gallery forests. Forests are preferred as these provide the animal with shelter through the dense understory and forage through the canopy. Though categorized as Least Concern by the International Union for Conservation of Nature and Natural Resources (IUCN), the blue duiker is under threat from extensive bushmeat hunting across its range.
Taxonomy and etymology
The scientific name of the blue duiker is Philantomba monticola. It is placed in the genus Philantomba, along with Maxwell's duiker (P. maxwelli) and Walter's duiker (P. walteri), and the family Bovidae. The species was first described by Swedish naturalist Carl Peter Thunberg in 1789. It is sometimes treated as a species of Cephalophus, another genus of duikers, although Philantomba has been recognised as a genus by zoologists such as Peter Grubb and Colin Groves. Owing to the remarkable similarities between the two species, some zoologists such as Theodor Haltenorth consider Maxwell's duiker as a race of the blue duiker.
While the generic name Philantomba has no clear origin, the specific name monticola has been derived from the Latin words montis (mountain) and colo (meaning "I cultivate" or "I inhabit"), in reference to its montane habitat. The common name "blue" refers to one of its typical coat colours. The common name of duiker comes from the Afrikaans duik or Dutch duiker – both mean "diver", which refers to the practice of the animals to frequently dive into vegetation for cover.
In 2012, Anne R. Johnston (of the University of Orleans) and colleagues constructed a cladogram of the subfamily Cephalophinae (duiker), that includes the three genera Cephalophus, Philantomba and Sylvicapra, based on mitochondrial analysis. Philantomba was shown to be monophyletic. It is sister to the rest of the subfamily, from which it diverged nearly 8.73 million years ago (in the late Miocene). The blue duiker split from Maxwell's duiker 2.68 to 5.31 million years ago. This cladogram, however, did not include the newly discovered Walter's duiker. Marc Colyn (of the University of Rennes 1) and colleagues, who had discovered this species in 2010, had prepared a similar cladogram (below) that included it.
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Subspecies
As many as 16 subspecies of the blue duiker have been proposed. In 1997, Jonathan Kingdon demarcated seven major populations of the species. In 2001, Groves and Grubb identified the following subspecies, bifurcating them into two groups on the basis of their colouration and geographical occurrence:
The grey-legged or northern subspecies
- P. m. aequatorialis (Matschie, 1892) – The range, bounded by the Congo River on the west, extends from the Democratic Republic of Congo into Uganda, and up to the Nile River. It is also found to the northeast of the Imatong Mountains (South Sudan).
- P. m. congicus (Lönnberg, 1908) – The range extends from the east of the Cross River across the Ubangi River to the Congo River, till Lisala (Democratic Republic of Congo). It is also found north of the mouth of the Congo River and in Cameroon and Gabon.
- P. m. lugens (Thomas, 1898) – The range extends from the Southern Highlands of Tanzania till the Malawi border, though it may occur in the Nyika Plateau in northern Malawi.
- P. m. melanorheus (Gray, 1846) – The type locality is Bioko, Equatorial Guinea.
- P. m. musculoides (Heller, 1913) – Occurs in eastern Ugandan and Kenyan forests. The range extends as far east as the East African Rift.
- P. m. sundevalli (Fitzinger, 1869) – It occurs in the eastern African coast, and on the islands of Mafia, Pemba and Zanzibar.
The red-legged or southern subspecies
- P. m. anchietae (Bocage, 1879) – The type locality is northern Angola.
- P. m. bicolor (Gray, 1863) – The range extends from Zanzibar to the KwaZulu Natal region in South Africa.
- P. m. defriesi (W. Rothschild, 1904) – The type locality is to the west of the steep cliffs in the Muchinga Province (Zambia).
- P. m. hecki (Matschie, 1897) – Occurs in Malawi, east of the valley of the Luangwa River (Zambia) and northern Mozambique.
- P. m. monticola (Thunberg, 1789) – Occurs in the Eastern Cape and Western Cape provinces of South Africa.
- P. m. simpsoni (Thomas, 1910) – Occurs between the lower Congo River and its tributary Kasai River.
Description
The blue duiker is a small antelope; in fact, it is the smallest duiker. The head-and-body length is typically between 55 and 90 centimetres (22 and 35 in). It reaches 32–41 centimetres (13–16 in) at the shoulder and weighs nearly 3.5–9 kilograms (7.7–19.8 lb). P. m. anchietae is the largest subspecies. Sexually dimorphic, the females are slightly larger than the males. The blue duiker is characterised by a flat forehead, large eyes, small ears with a line of white, large nostrils, a broad mouth and agile lips. The dark tail measures slightly above 10 centimetres (3.9 in). A remarkable feature of the tail is the row of white crinkly hairs on either flank that reflect light efficiently, so that when the animal moves its tail up and down, it looks like a luminous signal in the dark habitat. The duiker has short, spiky horns, around 5 centimetres (2.0 in) long and hidden in hair tufts. A row of minute pores surrounded by a few hairs in the preorbital glands (near the eyes) secrete an opaque liquid consisting of 45 volatile compounds. The pedal glands (near the hooves) produce a pungent, whitish fluid.
The subspecies show a great degree of variation in their coloration. The coat can be a shade of blue, grey or brown, and even black. The grey-legged northern subspecies show a grey to brown coloration, with a posterior stripe that marks a transition from the rump to the buttocks. P. m. congicus has a bright grey to black back, with dull grey flanks; a dark brown stripe marks the shift from the black rump to the lighter buttocks. P. m. sundevalli is similar, though the difference between the flanks and the rump is less notable. P. m. aequatorialis is paler and browner than P. m. congicus with a less sharp transition. The stripe is fainter and the back darker in P. m. musculoides. P. m. lugens can be told apart from its darker coloration; the flanks and the dorsal parts are dark grey to brown, the underside grey and a black rump. The diminutive P. m. melanorheus stands apart as well, with black dorsal parts, pinkish grey sides, and long thick fur.