Fennec Foxes

 The fennec fox is the smallest wild canid, measuring 20 cm (8 in) at the shoulder and weighing 1-1.5 kg (2-3 lb). They have the largest ears relative to body size in the dog family, measuring up to 15 cm (6 in) in length. Fennecs have a soft, thick coat. Coloration of upper parts is reddish cream or fawn, the underbody is white, and the tail tip is black. They are fastidiously clean and, unlike other foxes, they have no odor. The heavily furred tail (sometimes referred to as a “sweep”) helps the fox to change direction quickly, and keeps the fox’s nose and feet warm when it curls up to sleep. The caudal (or “violet”) gland is covered in bristles and appears as a black spot proximally on the tail of all vulpine foxes. Its function is unknown. Foxes have three pairs of mammary glands. They have paired anal sacs on either side of the anus. These coat feces with scent and can be evacuated voluntarily. There are also glands located between the toes. Their feet are covered with fur, protecting the soles from heat and enabling the fennec to run in loose sand. Fennecs have exceedingly large tympanic bullae, emphasizing their dependence on hearing for predation. The fennec fox has the same dental formula as the domestic dog (I3/3, C1/1, PM4/4, M2/3). Compared with other vulpines, their canines are reduced and their teeth are sharply cuspidate, which may facilitate insectivory (2). The tapetum lucidum is well developed, and the pupil is eliptical. Fennec foxes exhibit many unique physiological adaptations to desert life. Fennec metabolism functions at only 67% of the rate predicted for an animal its size. Similarly, resting heart rate is only 118 bpm, which is 40% lower than could be expected. Normal body temperature is 38.2˚C (100.8˚F). Fennec foxes will shiver when the ambient temperature drops below 20˚C (68˚F). As air temperature rises, the fennec radiates body heat by dilating blood vessels in its feet and large, vascular ears. The fennec lets its body temperature rise to 40.9˚C (105.6˚F) before beginning to sweat, reducing water loss. When it pants it curls its tongue so that saliva is not wasted. Respiratory rate at rest is 23 breaths/min. Fennec foxes start to pant only when temperature exceeds 35˚C (95˚F), and jaws open to a full pant only at 38˚C (100˚F). Panting rates of up to 690 breaths/min have been observed (1). Although fennec foxes will drink freely when opportunities arise, laboratory studies suggest that fennecs can survive indefinitely without access to free water (2,3).