Giant root-rat

The giant root-rat (Tachyoryctes macrocephalus), also known as the Ethiopian African mole rat or giant mole rat, is a species of rodent in the genus Tachyoryctes. It is endemic to Ethiopia's Bale Mountains. Its natural habitat is subtropical or tropical high-altitude grassland, where it can reach densities of up to 2,600 individuals per square kilometre. The giant root-rat has thick fur and large teeth. It creates large networks of tunnels whilst foraging for food before making holes to the surface to feed on nearby vegetation. There are many species that predate on Tachyoryctes macrocephalus, especially the Ethiopian wolf. It is threatened by habitat loss.

Tachyoryctes macrocephalus typically have small eyes and thick russet fur. They have large upper teeth called incisors that are especially prominent.^[2] The eyes are placed near the top of the forehead, and are sometimes called "periscopes" due to their ability to scan for predators.^[3] Individuals usually lack a part of the ear called a pinna.^[4] The limbs are typically short with claws, and individuals have short tails.^[5] Their weight can range between 160 grams to 930 grams. The length of their body ranges from 160 millimeters to 313 millimeters. Their molars are hypsodont (having a high crown and a short root), and the interparietal bone is very short.^[6]

The hair is usually gray at its base, and the head is significantly larger than the rest of the body.^[7] The rodents typically eats grasses nearby their burrows and spend the majority of their time underground. The typical body mass is around 1 kilogram.^[8] In the skeleton, the occipital shield is small and horizontal, the zygomatic plate is very broad and vertical, the mesopterygoid fossa is V-shaped and the back of the glenoid fossa is open.^[9] Male individuals are often larger in size compared to female root-rats.^[10]

Tachyoryctes macrocephalus breeds year-round and gestation lasts for 37 to 49 days. Some females are polyestrous (conceiving a second young whilst nursing the first) or breed once every 6 months.^[6] Males sometimes deposit a copulatory plug to help assist during mating.^[11] Individuals use rainfall and changing temperatures to help determine the appropriate time for breeding.^[12] Females in the genus Tachyoryctes are induced ovulators, meaning ovulation usually only occurs during mating.^[13]

Tachyoryctes macrocephalus is endemic to the grasslands in Ethiopia's Bale Mountains.^[14] It is a member of the genus Tachyoryctes, which is a sister genus to Rhizomys.^[15] Fossil records have suggested the species previously lived in South Asia up to northern India.^[9] The species likely originated from a split with Tachyoryctes splendens (the African root-rat) around 1.3 million ago.^[15]

The giant root-rat is unique compared to other mole rats as these individuals mostly forage above ground, and other species mostly forage underground. Tachyoryctes macrocephalus obtains food by digging a tunnel to a patch of herbage.^[5] It forages for about 20 minutes, until it has exhausted the supply of herbs about its tunnel, after which it blocks the tunnel it has built from the inside. It mostly eats grasses and herbs, with some individuals feeding mostly on roots.^[5] Giant root-rats collect their food without leaving the tunnel they have built, opting to leave the lower half of their body inside whilst quickly grabbing the vegetation outside.^[5] The network of tunnels that are built significantly impact the land above them, disturbing the content of the soil and the plants that no longer have sufficient nutrients.^[15] The tunnels they create whilst foraging are long, stretching up to 34 m (112 ft) in length.^[16]

Various species are known to prey Tachyoryctes macrocephalus. The Ethiopian wolf (Canis simensis) uses the giant root-rat as primary source of food, accounting for 96% of the prey they choose to eat alongside similar rodents.^[17] Early humans known as hunter-gatherers (around 47,000 years ago) that lived in the Ethiopian region frequently preyed on the giant root-rat as well.^[15] Other predators of this species include Servals (Leptailurus serval), African striped weasels (Poecilogale albinucha), Abyssinian owls (Asio abyssinicus), among others.^[6] When being attacked by predators the giant root-rat will try to escape by running back into the holes it had created in the past, and bite the predator if none are available nearby.^[6]

The IUCN Red List has labelled the giant root-rat as endangered (facing a high risk of extinction).^[18] Humans settling in areas the rodent lives in has made an impact on how Tachyoryctes macrocephalus tends to burrow. They are only found in a relatively small area of less than 1,000 km² (390 sq mi) in the Bale Mountains at a high altitude.^[16] Nearby livestock also has an effect on the availability of food for the giant root-rat. The livestock tends to consume the same vegetation as the rodent, thus hindering the availability of its food.^[16] Other factors resulting from the nearby livestock hurt the foods the rodents eat; the feces result in a condition called nutrient overloading that can lead to an increase in invasive plant species and the movement of the animals can trample the rodent's potential food.^[16] The deteriorating habitat and limited space that the rodent lives in have resulted in a significant decrease in the population, leading to its endangered status.^[15] In 2010 there were determined to be around 2000 to 4,800 animals per square kilometre residing in the Bale Mountain area.^[1]