Blue duiker

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 colouration. The coat can be a shade of blue, grey or brown, and even black. The grey-legged northern subspecies show a grey to brown colouration, 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 colouration; 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. The southern subspecies, on the other hand, have reddish tan legs and reddish coats. P. m. hecki is a light fawn to greyish black with light red flanks and a white underbelly; a change in tone can be observed as the rump is a darker reddish fawn. The paler P. m. defriensi is grey in the middle portion of the back, with red to fawn sides, and dark rump and tail. P. m. monticola, light grey to fawn with a reddish rump, is darker than P. m. bicolor, that has reddish orange flanks. P. m. anchietae is a pale grey or brown on the back with white underparts and a black tail; there is a clear transition from the grey sides and anterior parts to the reddish rump. P. m. simpsoni is distinguished by a facial stripe with white ventral parts; the rump is redder than the flanks. The blue duiker bears a significant resemblance to Maxwell's duiker. However, the latter is nearly twice as large and heavier as the former, with a larger skull. While colouration is more uniform in Maxwell's duiker, the blue duiker shows two different colourations. Another point of difference is the pedal gland (in the hooves), which has a simpler opening in the blue duiker. Walter's duiker is notably lighter in colour; the flanks are brown instead of grey.