Factsheets

(back to index of Mammals in Ireland)


(2) Land Mammals:
The rodents make up the greatest number of species of mammals throughout the world. In Ireland, the Order Rodentia includes the Red and Grey Squirrel, the Wood and House Mouse, the Brown and Black Rat and the Bank Vole. The rodents lack canine teeth, but like the rabbits and hares, have specialised incisor teeth. Indeed, the teeth are the most characteristic feature of the Rodentia. The incisor teeth continue to grow throughout the life of the animal. For this reason, it is necessary to supply pet rodents, (mice, guinea pigs etc.) with a supply of wood etc. in their cage to enable them to gnaw continuously.

The Red Squirrel:
The Red Squirrel is found throughout the country. It is smaller than the Grey Squirrel and found in a wide variety of habitats, ranging from coniferous forests to parklands. They feed mostly on seeds and berries. Although it is believed that the squirrel can use its fore-limbs for a variety of activities, recent research shows that the squirrel must first pick up a food item (e.g. nut) with its teeth and then transfer it to its paws while in a hunched position. This is clearly an ingrained action. Red Squirrels are known to hoard food items from times of plenty to be used at a later date. Red squirrels are more difficult to observe than Grey Squirrels. One reason for this is their tendency to spend a greater amount of time high up in coniferous trees. One of the few places left to see red squirrels in Dublin is the National Botanic Gardens in Glasnevin. The Red Squirrel is a protected species under the Wildlife Act, 1976.

The Grey Squirrel:
The Grey Squirrel is an introduced species. Although confined mostly to the north and east of the country, the Grey Squirrel is becoming the squirrel most commonly seen in our woodlands and parks. Much has been written about the effect the Grey Squirrel is having on our native Red Squirrels. It is true that they are larger and aggressive and many people believe that the decrease in population of our Red Squirrels is due to the Grey Squirrel. However, the situation is much more complex. Red Squirrels prefer large coniferous woodlands while Grey Squirrels prefer mixed and broadleafed woods. Contrary to most beliefs, the Red Squirrel is not dependent on acorns. In fact, they find them somewhat toxic. As large tracts of coniferous woodlands disappear, this breaks up the habitat of Red Squirrels making it more difficult for them to hold territories. Grey Squirrels feed on acorns and are more omnivorous and in areas where both co-exist, appear to be more successful. Grey Squirrels have filled the vacuum left by the latest Red Squirrel decline.

Both Red and Grey Squirrels are active by day, sleeping by night in their nest or "drey". Both have two litters per year, with an average of three or four per litter. The young leave the nest about 7 or 8 weeks after they are born. Red and Grey Squirrels do not interbreed.

Squirrels, both Red and Grey, are responsible for removing the bark from the growing tips of branches on trees (particularly beech and sycamore) to enable them feed on the sugar rich sap beneath. This damage can be quite severe, making them the enemy of foresters and gamekeepers suspect the Grey Squirrel of taking the eggs of pheasants.

The Wood Mouse:
The Wood Mouse (also known as the Field Mouse) is extremely common and widely distributed in Ireland. It has large eyes and a long tail. Apart from woodlands, it is also found in hedgerows and gardens. In fact, as it is a burrowing animal, it tends to be found whereever suitable soil is present. The Wood Mouse is a nocturnal animal, only occasionally to be seen in daylight hours. It feeds almost entirely on seeds. Insects and snails may be taken. Like other animals, the Wood Mouse will store food in late autumn. The breeding season is from March to October. Pregnancy lasts 20 days and they have two or three litters per year generally with an average of five young per litter. Mice born early in the breeding season are ready to breed before the end of the same season. The lifespan of a Wood Mouse is short, seldom reaching two years. The Wood Mouse forms an important part of the diet of owls and Kestrels as well as Foxes and Stoats. In cold winters, the Wood Mouse will regularly come into houses and out buildings. Its bright golden coat will help distinguish it from the more familiar House Mouse.

The House Mouse:
The House Mouse is found throughout Ireland. They are nocturnal animals, although they do adapt to the activities of the human occupants. Although originally a seed eater, they have learned to exploit man and are now opportunistic omnivores, feeding on whatever is available (cereals, chocolate etc.) and have even been known to chew through electrical insulation. In general they will breed all year round, producing anything up to fourteen litters per year with anything up to twelve young per litter. Populations can therefore build up rapidly and they need to be controlled. They are Ireland's most successful mammal apart from the Pygmy Shrew. By far their greatest predator is man followed by the domestic cat. House Mice are social animals and communicate with each other by scents and vocalisations. Territorial aggression between males can become intense, especially in over-crowded conditions. The damage caused by House Mice is not as great as that done by rats. However, like rats, they are carriers of leptospirosis, a bacterial infection, that can be fatal to humans.

The Brown Rat:
The Brown or Common Rat is a late arrival to Ireland, arriving here aboard ships less than 300 years ago. They have rapidly established themselves as a major pest. The key to this success is its versatility. The Brown Rat thrives wherever man grows or stores food. Their senses of smell and hearing are very sharp, but they have poor eyesight. Brown Rats are excellent diggers and excavate extensive burrow systems. These can be seen at the base of hedges and in fields, particularly those of germinating corn where they leave a series of tell-tale "scrapes" behind. They are omnivorous, feeding on whatever food is available, but preferring food rich in starch or protein. The Brown Rat builds a rather bulky nest of any available material and the litter can be as large as fifteen. They can have up to five litters per year. Control of the Brown Rat is necessary, especially as they can transmit a number of potentially fatal diseases (e.g. Salmonella and Leptospirosis). Up to 50% of rats in some populations may carry Leptospira, which is excreted in their urine. In the 1950's an anticoagulant called Warfarin was developed. This prevented the blood from clotting and caused the poisoned rats to die from haemorrhages. A drop in the numbers of their natural predators (Stoats and birds of prey) may also be responsible for increases, especially locally, in their numbers.

The Black Rat:
The Black Rat is now rare in Ireland. It first arrived here in the Middle Ages aboard sailing ships. Lambay Island, off the coast if Dublin, is one of the few areas in the country where they still reside. The Black Rat is smaller than the Brown Rat It is mainly omnivorous, but prefers fruit, grain and seeds.

The Bank Vole:
The Bank Vole is the only vole found in Ireland. It is an introduced species and found in the south and west of the country. It was discovered in Co. Kerry in 1964. Its habitat is that of dense undergrowth. It generally avoids areas where ground cover is scarce. They are good climbers and jumpers and they excavate burrows and construct underground nests. It is mainly nocturnal, but may occasionally forage for food, during the day. They are omnivorous, feeding mainly on berries, seeds and fruits although they are known to be cannibalistic! The breeding season is between April and September and Bank Voles can produce litters as quickly as every four weeks with an average litter size of four. The Bank Vole population is increasing in Ireland and it is possible that they may become an increasingly important element in the diet of foxes and owls. Bank Voles can cause damage in gardens and forestry plantations and may therefore need to be controlled.

Within the Order Insectivora, (the insect eaters) are two Irish mammals, the Hedgehog and the Pygmy Shrew.

The Hedgehog:
The Hedgehog is possibly the most easily recognised mammal in Ireland. It possesses a coat of protective spines and its overall colour is greyish brown. The Hedgehog is known as the gardener's friend for the good work he does in the garden by eating slugs and snails. Hedgehogs can be noisy animals and will often attract your attention to them in the garden. They will emit a wild scream, like a squealing pig, when they are severely frightened. They are extremely agile animals and are good climbers of walls and fences. If they fall off, they curl into a ball, as they fall, to land unhurt, cushioned by the thick layer of spines. Hedgehogs can also swim. However, many have been found drowned in shallow plastic lined garden ponds due to the steep smooth sides from which they can't escape. Hedgehogs are also thought to collect apples in autumn by deliberately rolling on them so that the apples become impaled on their spines. These can then be carried off to be eaten or stored. Hedgehogs are also known to produce a mass of saliva, which they spread over their spines, a process called "anointing". The purpose of this is still not understood. It has been reported that hedgehogs suck milk from cows. It is true that hedgehogs like milk and they do frequent cow fields but they are far too small to reach the teats of cows, unless they are lying down. However, the teats are very large and the hedgehog has a small mouth (and also sharp teeth!). What is most likely, is when the cow lies down, milk tends to flow from an overfull udder and could be lapped up by a foraging hedgehog. Hedgehogs do build their nests in garden rubbish and gardeners should be careful when burning such rubbish.

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