Lord Derby's Scaly-tailed Squirrel

Lord Derby's Scaly-tailed Squirrel is the largest member of the family Anomaluridae, an ancient lineage of arboreal, gliding rodents endemic to African tropical forests. Despite its common name, it is not a true squirrel (Sciuridae) but belongs to a distinct evolutionary lineage more closely related to springhares (Pedetidae). It possesses a large patagium (gliding membrane) supported by a unique cartilaginous spur projecting from the elbow, allowing it to glide considerable distances between trees. Its common name derives from rows of overlapping keratinous scales on the underside of the tail base, which grip tree bark like crampons during landing.

Sub-Saharan Africa, from Sierra Leone, Guinea, Liberia, Ivory Coast, and Ghana in the west, through Cameroon, Gabon, Republic of Congo, and the DRC in Central Africa, to Uganda, Kenya, Tanzania in the east, and south to Zambia, Zimbabwe, Malawi, and Mozambique.

Wide range across sub-Saharan Africa: West Africa (Sierra Leone, Guinea, Liberia, Ivory Coast, Ghana, Nigeria), Central Africa (Cameroon, Equatorial Guinea, Gabon, Republic of Congo, Central African Republic, DRC, Rwanda, Burundi), East Africa (Uganda, Kenya, Tanzania), and southern Africa (Zambia, Malawi, Zimbabwe, Mozambique).

Altitude and depth

Mainly a lowland species, found from sea level up to approximately 2,000 m, though most common below 1,500 m in continuous forested zones.

Seasonal movements

No significant seasonal migrations recorded. The species is largely resident year-round in its forest habitat. Foraging intensity may shift with local fruit and flower availability across seasons.

Primarily inhabits lowland tropical rainforests, including primary and mature secondary forests. Also found in forest-savanna mosaics and gallery forests flanking rivers. Strictly arboreal, it depends heavily on large, old trees with hollow trunks for roosting and shelter.

Adaptations to its environment

The cartilaginous elbow spur supporting the patagium is unique among all gliding mammals globally, providing precise control of the gliding membrane during flight. Oversized dark eyes are highly adapted for nocturnal vision in forest interiors. The overlapping keratinous tail scales provide a ratchet-like grip on smooth bark surfaces upon landing. Strong, curved claws allow secure clinging to vertical trunks.

Listed as Least Concern (LC) by the IUCN Red List. The species has a broad distribution and no documented population decline meeting threatened thresholds. However, local populations in heavily deforested areas are under increasing pressure.

Estimated population

No precise global population estimate is available. Overall population trend is considered stable, though locally declining in regions experiencing rapid deforestation and heavy hunting pressure.

Primary threats include deforestation and forest degradation driven by logging, agricultural expansion, charcoal production, and human settlement. The selective removal of large old trees eliminates essential hollow-trunk roosting sites. Hunting for bushmeat is a localized but significant threat across Central and West Africa.

Diseases and parasites

No diseases of conservation concern have been specifically documented. As an arboreal forest rodent, it likely hosts typical ectoparasites (fleas, lice, ticks, mites) and endoparasites (nematodes, protozoa) common to African forest mammals.

Protected within numerous national parks and forest reserves across its range, including Taï National Park (Ivory Coast), Lopé National Park (Gabon), Kibale National Park and Bwindi Impenetrable Forest (Uganda), and various DRC reserves. National wildlife protection laws in most range countries apply to this species.

Recommended actions

Priority actions include preserving old-growth forests with abundant large hollow trees, strengthening anti-logging enforcement in key habitat areas, monitoring bushmeat markets, conducting systematic population surveys to establish baseline estimates, and raising local community awareness about the species' ecological value.

Dorsal fur is grey to dark grey-brown, often with a faint yellowish or rufous tinge, while the ventral surface is pale grey to whitish. The large patagium is dark-fringed. Eyes are large, rounded, and dark brown. The tail is moderately bushy, and rows of rigid, overlapping keratinous scales are clearly visible on the underside of its base.

Size

Head-body length: 27–44 cm; tail length: 22–35 cm, giving a total length of up to approximately 79 cm. Wingspan of extended patagium can approach 60–70 cm.

Weight

Approximately 450–1,200 g; one of the largest anomalurids. No strong sexual dimorphism in body mass has been documented.

Distinctive features

Distinguished from other Anomalurus species by its considerably larger body size and broader, grey-brown dorsal coloration. The cartilaginous elbow spur is shared with congeners but is most robust in this species. Compared to A. pusillus (Beecroft's Scaly-tail), A. derbianus is two to three times heavier; compared to Idiurus species, it is dramatically larger.

Differences between males and females

Sexual dimorphism is minimal; males and females are similar in body size and coloration. Females possess two pairs of mammary glands on the ventral surface.

Largely solitary when foraging at night. During the day, individuals roost communally in hollow tree trunks, with groups of 2–8 animals recorded sharing the same roost cavity, possibly family-related individuals.

When it is active

Strictly nocturnal. Animals emerge from hollow-tree roosts at or after dusk, conduct nocturnal foraging and gliding activity, and return to roost before dawn. They are rarely active during daylight hours.

Diet

Predominantly herbivorous. Diet consists of bark (particularly the inner cambium layer of specific tree species), leaves, flowers, fruit pulp, and seeds. Bark-gnawing is a highly characteristic and frequent feeding behavior. Insects and other invertebrates may be consumed opportunistically.

How it feeds and hunts

Primarily a forager rather than an active predator. Uses sharp, continuously growing incisors to scrape and strip bark from tree trunks and branches. Glides between foraging trees to minimize terrestrial exposure. Fruit and seeds are collected directly from branches or captured mid-glide.

Communication

Generally quiet; known to produce soft clicks, low chatters, and occasional alarm calls when threatened. Scent marking via glandular secretions likely plays a role in territory delineation and mate assessment. Body postures during gliding and landing may convey information between individuals.

Interactions with other species

Natural predators include large forest owls (e.g., Bubo species), genets, African civets, and arboreal snakes. It competes with other cavity-roosting species (hornbills, other anomalurids) for hollow trees. By consuming fruit and dispersing seeds, it functions as a minor seed disperser for certain forest tree species.

Role in its ecosystem

Contributes to forest ecosystem dynamics as a seed disperser and, through intensive bark feeding, may locally influence tree physiology and nutrient cycling. Its strict dependence on mature forest with large hollow trees makes it a valuable indicator species for old-growth forest integrity.

Breeding appears to occur year-round in equatorial zones, possibly with peaks tied to local food availability. Gestation duration is estimated at approximately 120–150 days, notably long for a rodent of this body mass. Litter size is typically 1–2 young (rarely 3), born in a relatively precocial state.

Raising the young

The female is the sole caregiver. Young are born with eyes open and a coat of fine fur, and are nursed in the roost cavity for several weeks. Juveniles begin accompanying the female on nocturnal excursions before gradually becoming independent.

Maturity and lifespan

Age at sexual maturity is estimated at approximately 1–2 years. Wild lifespan is poorly documented but estimated at 6–10 years. Captive individuals have reportedly lived beyond 10 years under optimal conditions.

Classification

Mammalia > Rodentia > Anomaluridae > Anomalurus > Anomalurus derbianus (Gray, 1842).

Subspecies

Several subspecies are recognized: A. d. derbianus (West Africa: Sierra Leone to Ghana), A. d. jacksoni (de Winton, 1898; East Africa: Uganda, Kenya, Tanzania), A. d. chrysophaeus (Ryley, 1913; Cameroon/Central Africa region), and A. d. laticaudatus (parts of southern Africa). Subspecies boundaries remain under ongoing taxonomic revision.

Scientific synonyms

Originally described as Pteromys derbianus Gray, 1842; also encountered in older literature as Anomalurus derbii. The genus Anomalurus was established by Waterhouse, 1843.

Recent studies

Recent molecular phylogenetic studies (e.g., Fabre et al., 2012; Blanga-Kanfi et al., 2009) have confirmed the placement of Anomaluridae in Anomaluromorpha, clarifying their deep evolutionary divergence from other rodent groups. Taxonomic studies using genetic and morphological data have helped refine subspecies boundaries within A. derbianus, though a comprehensive revision remains lacking.

Genome and DNA

Cytogenetic studies have suggested a diploid chromosome number (2n) in the range of 52–54 for Anomalurus species, though precise data for A. derbianus specifically remain limited. Molecular phylogenetic analyses consistently place Anomaluridae within the clade Anomaluromorpha, as sister to Pedetidae (springhares), representing an ancient divergence within Rodentia.

Compared with similar species

Among anomalurids, A. derbianus is the most widespread and one of the largest species. A. pelii (Pel's Scaly-tailed Squirrel) rivals it in size but has a restricted West African distribution. Idiurus macrotis and I. zenkeri (pygmy scaly-tails) are dramatically smaller, weighing only 14–25 g. Zenkerella insignis (cameroon scaly-tail) uniquely lacks a functional patagium entirely. Compared to true flying squirrels (Pteromyini), anomalurids are not closely related and represent a remarkable case of convergent evolution in gliding.

1) The cartilaginous elbow spur supporting its gliding membrane is unique among all gliding vertebrates on Earth — no other gliding mammal, bird, or reptile uses this structure. 2) Despite sharing the name 'squirrel,' it is phylogenetically closer to the African springhare than to any squirrel species. 3) A single glide from a tall forest tree can exceed 100 meters, and upon landing, the tail scales lock into the bark like a ratchet, preventing backward slip on vertical surfaces.

Where and how to see it

Best observed at night in mature primary rainforest. Recommended sites include Kibale National Park and Bwindi Impenetrable Forest in Uganda, Lopé National Park in Gabon, and Taï National Park in Ivory Coast. Arriving at dusk to watch animals emerge from hollow-tree roosts is the most reliable technique. A dim red-filtered headlamp minimizes disturbance while allowing the large reflective eyes to be spotted.

Risks to humans

No notable risk to humans. Like any wild rodent, it may bite defensively if handled. There are no documented cases of venom, significant disease transmission, or attacks on humans.

Human uses

Hunted for bushmeat in parts of West and Central Africa, where it is consumed locally. Occasionally represented in zoological collections worldwide. No significant use in traditional medicine has been widely documented in scientific literature.

Myths and legends

In some forest-dwelling communities of Central and West Africa, silent nocturnal gliders emerging from the canopy are associated with ancestral spirits or supernatural forest beings. However, detailed myths or legends centered specifically on A. derbianus are not well documented in the ethnozoological literature, and its cultural significance remains largely unstudied.