Anomalurus derbianus (Gray, 1842)

Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Anomaluridae, Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona: Lynx Edicions, pp. 270-279 : 277-278

2.

Lord Derby’s Anomalure

Anomalurus derbianus

French: Anomalure de Derby / German: Lord-Derby-Dornschwanzhérnchen / Spanish: Anomaluro de Lord Derby

Other common names: Derby's Flying Squirrel, Lord Derby's Flying Squirrel, Lord Derby's Scaly-tailed Flying Squirrel, Lord Derby's Scaly-tailed Squirrel

Taxonomy. Pteromys derbianus Gray, 1842 ,

“W. Africa, Sierra Leone.”

Although numerous forms have been attributed to A. derbianus , they are junior synonyms, and no subspecies are recognized. Monotypic.

Distribution. W, C & E Africa, from Sierra Leone E to Uganda and SW Kenya, and S to Tanzania, N Mozambique, N Malawi, Zambia, and N Angola, also on Bioko I.

Not yet recorded in Benin where may occur and possibly on Zanzibar I.

Descriptive notes. Head-body 260-400 mm, tail 220-330 mm; weight 0-45—1-1 kg. Lord Derby’s Anomalure shows the highest variability in color in the family; it varies geographically and within populations. Lord Derby’s Anomalures range in color from more or less uniformly brownish to those with reddish backs, dark gray patagia, black ears, and silverfish stripes on nose. Head typically has a black-to-brown mask around eyes, muzzle, and surrounding the ears. Gliding membranes, which stretch between limbs and onto base of tail, are similarly colored above but black bristles reinforce edge of membrane behind elbow strut. Ventral surface is much less variable and patagium is generally white, but sometimes underside of membrane between hindlegs is brownish to blackish. Base oftail has 12-14 scales. Primary variation among Lord Derby’s Anomaluresis in gray or russet tints on back and shoulders. Face is relatively short and round; naked pinkish ears are set in a surrounding bed of dense velvet-black fur. Bristles covering hind claws are black.

Habitat. Variety of forest types from moist rainforests to relatively dry savanna woodlands from sea level up to elevations of ¢.2400 m. In the south-eastern part of its wide distribution, Lord Derby’s Anomalure is known to occur in savanna woodland. Although they can be common in undisturbed forest, they may also nest within dead trees in areas that have been cleared and burned for agriculture, as long as trees are within gliding distance to nearby forest.

Food and Feeding. Bark of trunk and main branches of several genera of trees appear to be the dietary staple of Lord Derby’s Anomalure. Feeding individuals appear to focus on bark wounds caused by falling branches, elephanttusks, and growth splits. As a consequence of this feeding behavior, some trees such as beli ( Julbernardia pellegriniana, Fabaceae ) may lose all their bark on their trunks and main branches over a number of years. Loss of bark appears to be tolerated by the tree because they are able rapidly to regrow their cambium layer, suggesting that these rodents and trees have coevolved. Lord Derby’s Anomalures eat fruits of Carapa (Meliaceae) and Syzygium (Myrtaceae) , leaves of Cynometra (Fabaceae) and Myrianthus (Moraceae) , and bark of various trees, including those of the genera Neoboutonia (Euphorbiaceae) Cynometra , Pentaclethra (Fabaceae) , Klainedoxa (Irvingiaceae) , Carapa , Syzygium , and Strombosia ( Olacaceae ) and Strombosia ( Olacaceae ). Elsewhere, they eat fruits, flowers, leaves, nuts, and occasional insects such as ants and termites.

Breeding. Breeding of Lord Derby’s Anomalures appears to be seasonal in drier areas but not in the main forest block. In some areas, females are known to segregate to give birth and rear young. Pregnant females have been taken in Cameroon in June-July when rains begin, so young are probably born toward the end of rains in September— November. Other observations in Tanzania found well-grown young in May-June during the early dry season. In Equatorial Guinea, lactating females have been collected in February-May, and in Uganda and Kenya, four births were recorded in January, two pregnancies in March, and a lactating female in May. Vaginas of pregnant females are firmly sealed with hard plugs after mating. Generally only one young is born at a time, although there are records of 2-3 young. Offspring remain on a ledge high up in a hollow tree until almost fully grown. Both parents bring offspring well-masticated food, carried in their mouth and cheeks—swollen by a wad as large as a tangerine.

Activity patterns. Lord Derby’s Anomalure is nocturnal, with individuals resting in hollow trees during the day, preferably in virgin forest. These hollows can be up to 40 m above the ground (in some woodlands they occupy empty beehives). One radiocollared individual in Gabon had one primary nesting tree hollow and five secondary hollows. They tend to nest alone or in pairs of one female and a young. Other observations suggest that up to eight individuals may share a denning tree, but little is known about their social behavior. Lord Derby’s Anomalures also appear to be sedentary, living in the same hole all year, except when fruit is ripe in another area. Individuals retain use of their dens over very long periods, but seasonal shifts have been recorded. Along with a threatening or defensive hiss and growl, Lord Derby’s Anomalures also purr and twitter. They like to sunbathe in early morning and more rarely in the evening. Pruning in closed-canopy forest is often less frequent or conspicuous than in more open or sunlit areas. Where light breaks through close to a food tree, intense pruning of young trees may help maintain access to a ready food supply by killing or maiming competing trees and keeping flight-paths open. Night is spent moving in lower branches oftall trees and smaller growth, often not more than 9 m above the ground. While resting, a Lord Derby’s Anomalure orientatesitself with head upward and body parallel with the bole of the tree.

Movements, Home range and Social organization. When leaping from one tree to another, membranes of Lord Derby's Anomalures are curved such that an individual assumes shape of a small umbrella. They prefer to land on trunks rather than branches of trees. Immediately before reaching a tree trunk, head is actually at a lower level than tail, but at the last second, forelegs are thrown back over shoulders, head comes up, and tail sweeps up to meet it over the back. An individual instantly assumes a vertical position in midair. Momentum carries it to an upright trunk, to which it instantly adheres, and it invariably commences an ascent using its front two feet together and then pulling up the two hindfeet and arching its back like a giant loop-caterpillar. Backward-directed scales at base of the tail and forwardly directed claws on hindfeet dig into the three bark, thus forming a rigid tripod to support the individual while forefeet are released and moved upward. Glides of more than 40 m by Lord Derby’s Anomalures have been recorded at an estimated glide angle of 24° from horizontal. Species of Anomalurus can gallop up the smooth bark of a giant forest tree with great speed. Distance traveled per night averages 540 m; home range averages 3-4 ha for females and 3-3 ha for males. A radio-collared female had a home range of 3-4 ha; 50% of locations in a small central area comprised 11:3% of her home range. Densities of Lord Derby’s Anomalures are 27-54 ind/km?. Blue Monkeys (Cercopithecus mitis) prey on Lord Derby’s Anomalures in Budongo Forest Reserve, Uganda.

Anomalure ( Zenkerella insignis ).

Status and Conservation. Classified as Least Concern on The IUCN Red List. Although localized populations of Lord Derby’s Anomalures may be at risk from logging and forest clearance,it is common and widespread. It is also used in traditional medicine.

Bibliography. Allen (1922), Delany (1975), Dorst & Dandelot (1970), Fairgrieve (1997), Grubb et al. (1998), Haltenorth & Diller (1977), Jackson (2012), Jackson & Thorington (2012), Jones (1971), Julliot et al. (1998), Kingdon (1974, 1997), Rahm (1969), Sanderson (1940), Schunke (2005).

Figures

1. Beecroft’s Anomalure (Anomalurus beecrofty), 2. Lord Derby’s Anomalure (Anomalurus derbianus), 3. Pel’s Anomalure (Anomalurus pelii), 4. Lesser Anomalure (Anomalurus pusillus), 5. Long-eared Pygmy Anomalure (Idiurus macrotis), 6. Zenker’s Pygmy Anomalure (Idiurus zenker), 7. Cameroon Anomalure (Zenkerella insignis)

Distribution. W, C & E Africa, from Sierra Leone E to Uganda and SW Kenya, and S to Tanzania, N Mozambique, N Malawi, Zambia, and N Angola, also on Bioko I. Not yet recorded in Benin where may occur and possibly on Zanzibar I.