Animal Info - Malagasy Giant Rat

(Other Names: Madagascan Rat, Malagasy Giant Jumping Rat, Malagasy Rat, Vositse, Votsotsa, Votsotse)

Hypogeomys antimena

Status: Endangered


Contents

1. Profile (Picture)
2. Tidbits
3. Status and Trends (IUCN Status, Countries Where Currently Found, History of Distribution, Threats and Reasons for Decline)
4. Data on Biology and Ecology (Size and Weight, Habitat, Age to Maturity, Gestation Period, Birth Season, Birth Rate, Early Development, Dispersal, Maximum Reproductive Age, Diet, Behavior, Social Organization, Age and Gender Distribution, Mortality and Survival, Density and Range)
5. References


Profile

Pictures: Malagasy Giant Rat #1 (47 Kb JPEG) (Anim. Div. Web)Malagasy Giant Rat #2 (138 Kb JPEG) 

The Malagasy giant rat is a large, rotund, rabbit-like rodent with conspicuous large ears. It holds its food in its forepaws and manipulates it in its mouth while it sits semi-upright. It is about 33 cm (13") long (not including the tail) and weighs about 1.3 kg (2.8 lb). The Malagasy giant rat only occurs in a specific habitat - coastal dry deciduous forest mixed with baobab trees resting on sandy and lateritic soils, permanently covered in dry leaf-litter. This rodent forages, alone or in pairs, on the forest floor for fallen fruit, seeds and leaves. It is strictly nocturnal. A mated pair and their offspring spend the day in underground burrows. This complex of tunnels may be up to 5 m (16') across and have 1 - 6 entrance holes. The Malagasy giant rat lives in a family group including one adult male, one adult female and their offspring of the past 2 - 3 years. The two adults constitute an obligate monogamous pair. They stay together until one mate dies. Both sexes are territorial.

The Malagasy giant rat is now confined to an area of 200 sq km (77 sq mi) of fragmented but relatively undisturbed forest remnants near the west coast of Madagascar, northeast of Morondava. Between 1985 and 2000, the suitable habitat declined by about 52%.  The Malagasy giant rat is threatened by habitat loss and competition from introduced black rats. Its habitat is decreasing due to illegal and commercial logging, slash and burn agriculture, charcoal production and burning for creation of cattle pasture. 


Tidbits

*** A recent estimate indicated that by 1990, deciduous forest cover of Madagascar had been reduced to about 3% of its original extent, with few fragments larger than 8 sq km (3 sq mi). (Sommer et al. 2002)

*** The Malagasy giant rat is the largest rodent in Madagascar.

*** Rodents such as the Malagasy giant rat are important seed predators which can play a significant role in the ecology of the fragmented dry deciduous forest of western Madagascar. In forest fragments where these species are missing, seed predation rates are much lower than in the large primary forests. (Ganzhorn et al. 1999)

*** Monogamy such as displayed by the Malagasy giant rat exists in less than 5% of all mammal species and is especially rare within the 1700 described rodent species. (Sommer & Hommen 2000)

*** Female Malagasy giant rats have only 1 - 2 offspring/year. Therefore, this species does not have the potential of rapid population growth characteristic of many other rodents. (Sommer et al. 2002).


Status and Trends

IUCN Status:

Countries Where the Malagasy Giant Rat Is Currently Found:

2004: The Malagasy giant rat is endemic to Madagascar (IUCN 2004).

Population Estimates:

[Note: Figures given are for wild populations only.]

History of Distribution:

The Malagasy giant rat is now confined to an area of 200 sq km (77 sq mi) of fragmented but relatively undisturbed forest remnants near the west coast of Madagascar, northeast of Morondava between the Tomitsy and Tsiribihina Rivers. Its overall population is divided into two subpopulations separated by the Mandroatra River. Between 1985 and 2000, the suitable habitat declined by about 52% (1985: 420 sq km (160 sq mi); 2000: 200 sq km (77 sq mi)). The annual rate of habitat decline increased from 3.9% between 1985 and 1995 to 4.4% between 1995 and 2000.  (Sommer & Hommen 2000, Sommer et al. 2002) 

Threats and Reasons for Decline:

The Malagasy giant rat is threatened by habitat loss and competition from introduced black rats. Its habitat is decreasing due to illegal and commercial logging, slash and burn agriculture, charcoal production and burning for creation of cattle pasture. (Burnie & Wilson 2001, Sommer et al. 2002)

This species is highly sensitive to the activities of man. One study that included surveys of burrow density and investigations of animal presence showed that any signs of human disturbance (e.g. logging and oxcart trails, forest degradation, open forest canopy, temporary camps, cut trees, wood piles, or burned areas) corresponded with a decreased number of active burrows (Sommer et al. 2002).


Data on Biology and Ecology

Size and Weight:

Length (not including the tail): 30 - 35 cm (12 - 14"); Length (including the tail): 54 - 59 cm (21 - 23"); Weight: 1 - 1.5 kg (2.3 - 3.3 lb) 

Habitat:

The Malagasy giant rat is restricted to primary dry deciduous forest. It only occurs in a specific habitat - coastal dry deciduous forest mixed with baobab trees resting on sandy and lateritic soils, permanently covered in dry leaf-litter. It does not occur: in secondary forest formations, where the canopy is open and the undergrowth is very dense, in forest areas near temporary rivers that might be flooded during the rainy season, or in forest areas with stony soils. (Garbutt 1999, Sommer et al. 2002)

 The Malagasy giant rat is one of the species that is found in both the Madagascar & Indian Ocean Islands Biodiversity Hotspot (Cons. Intl. 2005) and the Madagascar Dry Forests Global 200 Ecoregion. (Olson & Dinerstein 1998, Olson & Dinerstein 1999)

Age to Maturity:

Male - 1 year; female - 2 years: A male offspring leaves the parental burrow and territory at the age of around 1 year (before the next reproductive season). If it is able to establish a territory and attract a mate, it can reproduce immediately. Usually, however, it is unable to do this until at least 2 years of age. A female offspring shows delayed dispersal and stays with its parents for two reproductive seasons. Females are probably not sexually mature before the age of 2 years. (Garbutt 1999, Sommer et al. 2002)

Gestation Period:

102 - 138 days (captivity) (Nowak 1999).

Birth Season:

Reproduction occurs during the rainy season (December - March). (Sommer et al. 2002)

Birth Rate:

Females can give birth once or twice to a single offspring during the reproductive season. Therefore, the maximum number of young per year is two. Field data indicate that 60% of females have one offspring per year and 40% have two per year. Almost all females of reproductive age produce a litter every year. The yearly average is at least 1.4 offspring/couple/year (range: 1.1 - 1.7). (Sommer & Hommen 2000, Sommer et al. 2002) 

Generation time: Females - 4.3 years; Males - 3.8 years (Sommer et al. 2002).

Early Development:

Offspring spend the first 4 - 6 weeks in the burrow and begin to leave it regularly during the next 4 weeks. (Sommer et al. 2002)

Dispersal:

Dispersal of matured offspring from their natal burrow and territory to the place of their first reproduction occurs at the age of about 1 year for males (before the next breeding season). However, female offspring show a delayed dispersal (even though they have reached adult body weight) and stay together with their parents for a total of two reproductive seasons. (Sommer & Hommen 2000)

Maximum Reproductive Age:

7 years (Sommer et al. 2002).

Diet:

The Malagasy giant rat forages, alone or in pairs, on the forest floor for fallen fruit, seeds and leaves. It is also known to dig for roots and tubers and to strip bark from saplings. (Sommer et al. 2002)

Behavior:

The Malagasy giant rat is a herbivore and is strictly nocturnal. It moves on all fours or in a 'kangaroo-like' hop on its hind legs.

A mated pair and their offspring spend the day in underground burrows.  Burrows are used for raising offspring and for protection against predation and heat during the day and heavy rain during the night. The family burrow is within their territory, usually on a slightly elevated area of bare soil.  This complex of tunnels may be up to 5 m (16') across and have 1 - 6 entrance holes, although only 1 - 3 of these are in use at any one time, the others being blocked by soil and leaves.  Even the entrances in use are 'plugged' with a barrier of soil at a depth of around 50 cm (20") and must be excavated by the animals to allow passage in and out. (Garbutt 1999, Sommer et al. 2002)

Adult females rarely move after they have settled in a new territory away from their natal burrow. After the death of a male mate, the remaining female always keeps the burrow and the territory, and a new male immigrates to the site. After the death of a female mate, the remaining adult male normally also keeps the burrow and the territory. But occasionally the male moves to live with a widowed female and therefore changes his burrow and territory. Digging of new burrows is rare. After the death of resident animals, burrows are occupied by new immigrants. (Sommer & Hommen 2000, Sommer et al. 2002) 

Both sexes are territorial. Animals from neighboring burrows defend exclusive territories throughout the year, regardless of food abundance or reproductive state.  Only burrow mates have overlapping, similarly sized home ranges. Territory borders are marked with urine, feces and scent gland deposits. (Sommer et al. 2002)

Social Organization:

The Malagasy giant rat lives in a family group including one adult male, one adult female and their offspring of the past 2 - 3 years. The two adults constitute an obligate monogamous pair. They stay together until one mate dies. Dead mates are normally replaced within days or weeks. (Sommer & Hommen 2000, Burnie & Wilson 2001)

Infanticide does not seem to occur among these rats. After the taking over of a burrow by a new mate, formerly sired offspring were tolerated. (Sommer et al. 2002) 

Age and Gender Distribution:

The sex ratio of offspring is approximately 1:1 (Sommer & Hommen 2000).

Mortality and Survival:

Predation by the fossa (Cryptoprocta ferox - Picture (38 Kb JPEG)), the largest carnivore in Madagascar, and a ground boa constrictor is the principal factor responsible for mortality of young and adults.  Infanticide does not seem to occur. (Sommer & Hommen 2000)

Average and range of mortality rates: Young: 0.53 (0.50 - 0.57); Adults: age 1 - 2: 0.13 (0.08 - 0.18); age 2 - 3: 0.21 (0.16 - 0.26); age 3 - 4: 0.40 (0.35 - 0.45); age 4 - 5: 0.68 (0.63 - 0.73); age 5 - 6: 0.71 (0.66 - 0.76); age 6 - 7: 1.0 (.95 - 1.0) (Sommer & Hommen 2000)

Density and Range:

Density: The population density in one study decreased from 1992 to 2000.  Measured population densities were (100 hectares = 250 acres): 1992-1996: 54 animals/100 hectares; 1999: 33 animals/100 hectares; 2000: 22 animals/100 hectares. This is evidence of a population collapse. (Sommer et al. 2002)

Territory: The mean territory size varies between 3.1 and 3.5 hectares (7.8 - 8.8 acres) (Sommer et al. 2002)


References

Anim. Div. Web, Burnie & Wilson 2001, Cons. Intl. 2005, Cook et al. 1991, Ganzhorn et al. 1999, Garbutt 1999, IUCN 1996, IUCN 2000, IUCN 2003a, IUCN 2004, Lidicker 1989, Marwell Zool. Park, Nowak 1999, Olson & Dinerstein 1998, Olson & Dinerstein 1999, Sedgewick Co. Zoo, Sommer & Hommen 2000, Sommer et al. 2002


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Last modified: March 11, 2005;

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