Norway or Brown Rat- Rattus norvegicus

Introduced and breeding. Prolific breeders, with the right conditions females can produce five litters a year. Head and body is 17.5-25cm (7-10 inches) tail long and scaly 12.5-20cm (5inches) small ears (acute hearing), tiny eyes and a blunt nose. Fur is coarse, dark browny grey with a lighter underbelly.

These rats are comfortable in any situation, settlements or tussac being popular. They are omnivorous and opportunistic, eating whatever is available, tussac roots, insect life, marine invertebrates, ground nesting birds (eg petrels) and eggs. They nocturnal, like to be on the ground and generally nest in burrows beneath buildings or in tussac. Rats led to the expiration of some petrels and passerines on some islands in the Falklands. The endemic Cobb's Wren and Tussac bird, Falklands Thrush, Black-throated Finch, Falkland Diving Petrel, Grey-backed Storm Petrel, White-chinned Petrel, Fairy Prion, Wilson's Storm Petrel and Thin-billed Prion are particularly affected by rodents. Falklands Conservation has cleared Norway rats from 19 small islands in the Falklands group and it is hoped birds will return to breed on them. On South Georgia rats were wreaking havoc with birdlife but a massive rat eradication programme, a £10m campaign led by the South Georgia Heritage Trust involving helicopters dropping poison pellets, was launched during 2010/11.Teams checking after two years seem confident that the rats have gone. Numbers of the South Georgia Pipit Anthus antarcticus, the world's most southerly songbird and found no where else, have already increased.

Black rat (Ship rat)- Rattus rattus

Introduced and breeding
Black rats are currently thought to only exist on New Island in the Falkland Islands, where they have probably been for over 100 years. Studies (Quillfeldt etal. 2008) conducted during summer months when birds are breeding showed that although their diet varied with age and habitat, vegetation was the most important followed by animal matter, insects and larvae. Their impact on the population of thin-billed prion appeared minimal apart from to the population that nested in the tussac grass. Black rats are smaller, (18-20cm) 7-8 inches than brown rats, have no scales on their long tails which is longer (21.5-25.5cm, 8.5-10 inches) than the head and body together, a pointed nose, large ears and dark brown fur. The body is more slender than brown rats. It grows to 150-200g in weight. They prefer to be around settled areas, living in tops of buildings and drier areas rather than burrowing.

Mouse- Mus musculus

Introduced and breeding. Small animal, 7.5-8.5 cm (3-3.5 inches) with a 7-9.5cm 2.75 -3.75) inch tail, and medium ears. Short grey-brown fur. Mice very likely arrived in the early 1700s with the first settlers. They were recorded on Saunders Island at the first British settlement in 1774 and Port Louis in 1842. Common in settlements, camp houses, shanties and the camp. In the days when shepherds used sheepskins for blankets in shanties they often had to shake mice droppings out before using them. Mice eat berries and seeds and tend to be more prevalant in settlements in winter.

Sources include: Falkland Islands State of the Environment Report 2008 Otley H, Munro G, Clausen A, Ingham B. A Field Guide to the Wildlife of The Falkland Islands and South Georgia - Ian J Strange, Wikipedia

Photographic credits: Szasz-Fabian Jozsef/Shutterstock.com, Holger Kirk/Shutterstock.com, Black rat -Maslov Dimitry/ Shutterstock.com, Irinak/Shutterstock.com