RSPB Spotlight: Hares

From birth as tiny leverets to adulthood, hares are at particular risk from predators and infectious diseases, and their main task is to survive. They spend a lot of time hidden away in individual forms, though in the first few weeks of life they are cared for by their mothers. They have evolved to keep warm and safe, and to grow fast: within a few months, they reach adult size.

Adult hares are tempting prey for many predators and leverets are even better. They are perfect bite-sized morsels for animals such as Foxes, and the probability of a leveret ending up as Fox food (killed, or scavenged once dead) is high. They may also be attacked by Stoats, cats, Buzzards, Magpies and other predators, die of disease, or be killed by farm machines, cars or other vehicles.

A newborn Brown Hare leveret has about a 50 per cent chance of surviving to the end of the suckling period, and about a 30 per cent chance of surviving for the first year of its life; thereafter, if it is lucky, it has a 50 per cent chance of survival each year. It’s not a great prognosis, and life for a leveret is mainly about avoiding predators. Without the protection of burrows, hares are particularly vulnerable but they have evolved ways to maximise their chances of survival to adulthood.

At birth, Brown Hare leverets weigh only 100g (3½oz), – about the same as an apple. Mountain Hares in Scotland weigh about 90g (3⅛oz), and Irish Hares are believed to weigh 170–180g (6–6⅓oz), though few have been weighed. The weight depends on the number of leverets in the litter – bigger litters consist of smaller leverets, just as human twins typically each weigh less than a single baby would. Close observation of the behaviour of mother hares and leverets has only been carried out for the Brown Hare, however a similar pattern of vital but apparently minimal maternal care also occurs in Mountain Hares. Hares do not receive any care from their fathers.

Leverets are born in what seems a randomly chosen place, though no doubt the mother has her reasons for its selection; she spends a lot of time there in the few weeks before giving birth. The leverets are fully furred at birth and their eyes are open. They quickly move away from each other and find shelter. Some leverets are born with white spots on their heads, which may help to camouflage the leverets. It is unknown why only some leverets have them, and why they are not seen in adults. Leverets with white spots are – incorrectly – said to be males, or leverets from litters of a certain size.

Leverets have little odour and keep very still, each remaining separate in its own tiny form during the day. About 45 minutes after sunset each evening leveret littermates come together at their place of birth, where they play and run around for a few minutes. Eventually they sit still, perhaps grooming themselves and each other, and await their mother. She turns up about 15 minutes after they do, having spent the day a few hundred metres away. The leverets approach their mother; they will sometimes approach other passing adult hares, so the mother sniffs her leverets to check their identity. Then she may lick them to remove any urine or dirt on their fur that might make their scent stronger and give them away to predators.

In the first week after birth, the mother allows the leverets to drink her milk for up to five minutes each evening. Mother hares have six nipples, so with litters of more than six, leverets would have to take turns to feed. Each leveret feeds for only a few minutes and that is it for the whole day – their one quick feed has to give them enough energy to last 24 hours. After providing milk, the mother jumps away, leaving her leverets to their own devices until they meet again at the same time the next evening. If you ever come across a leveret in its own form, don’t assume it has been abandoned and is in need of help from humans. It is probably experiencing the normal solitude of a leveret, and will meet its mother at dusk.

It seems a lonely existence, but this is how leverets avoid being eaten by Foxes and other predators. If the littermates spent all their time together and the group was discovered by a predator, they would all be eaten and the entire litter would perish. By spreading themselves out, the littermates make it more likely that at least one of them will survive to adulthood.

When they are a few days old, the leverets move further away from each other, and each end up about 100m (328ft) from their birthplace during the day. The time the mother allows them to feed for decreases, from five minutes in the first week to only one to two minutes as they get older, and suckling still takes place only once every 24 hours.

If the birthplace changes in character (perhaps through flooding or farming operations) and is no longer deemed suitable, the mother and her leverets search for each other and meet up somewhere else. If she is disturbed during suckling, the female leads the leverets away with her tail held up, the white tail-patch acting as a signal for her leverets to follow. Researchers noticed that when a Barn Owl came to a litter of leverets’ birthplace at around the time they were due to suckle, the mother and leverets took cover until it had left, before suckling as usual later on. Mountain Hare mothers are very loyal to their chosen birthplace and they will return to it even after being disturbed.

Brown Hare mothers give their leverets milk for at least 17–23 days. They carry on for longer – often for 30 days, or occasionally for over 67 days – with big litters and their last litter of the season. Scottish Mountain Hare mothers provide milk for around 28 days, and will also continue for a little longer, up to 42 days or even more, for their last litter of the year. At the end of the breeding season, when she is no longer pregnant, the mother may feed her final litter of leverets for longer because it will help them to make it through the harsh winter, when food is less readily available.

How can the tiny leverets grow so fast when they are fed so infrequently? At 30 days of age, Brown Hare leverets weigh on average 8½ times their birth weight. This growth rate is phenomenal. Imagine the same growth rate for a human baby. The average birth weight for humans is 3.5kg (7¾lb); 8½ times that is 30kg (66lb) – the weight of a nine-year-old child! Scottish Mountain Hares also grow fast – 14g (½oz) per day in the wild, or 30g (1oz) per day in captivity.

Leverets do start to feed on grass and other vegetation from about day 15 of their life, so they are not totally dependent on milk. Leverets from large litters eat more solid food than those from smaller litters. But there must be something very special about hares’ milk to allow the leverets to grow so fast while spending so little time drinking it. Scientists at the Research Institute of Wildlife Ecology in Vienna devised a hare-milking machine in order to collect milk from captive hares for analysis. They found that the milk consisted of 20–26 per cent fat. How does this compare to the fat content in other mammals’ milk? Well, fat content is quite variable, from as low as 0.2 per cent in Black Rhinoceroses’ milk up to 60 per cent in the milk of some seals that have to suckle their young for only a few days on constantly changing ice floes. Animals that suckle their young little and often, such as cows and primates, produce milk that is lower in fat than those that suckle rarely, such as hares. Cows’ milk is 3–5 per cent fat and human milk is about 4.5 per cent.

The fat in hares’ milk comes mainly from the mothers’ food, and captive hares fed a high-calorie diet eat less but produce fattier milk than those fed on standard hare food. This explains why hares are such selective feeders: they need a high-energy diet to aid their escape from predators, which would be more difficult if they had to run with a bulky stomach full of low-energy food. But they also need to provide high-quality milk for their young, so they can feed them only briefly, once every 24 hours. Like so many of the hare’s features, its parental behaviour has evolved to help it and its young avoid predation.

Tony Holley – hare-watcher

Making close observations of the private lives of secretive, well-hidden hares without disturbing them is a huge challenge, and few people have ever attempted it systematically. On the Somerset Levels in south-west England, Tony Holley became fascinated by the Brown Hares he could see from his house. He bought a small piece of grassland and managed it specifically for hares, allowing some cattle grazing to create the perfect mixture of grasses, reeds and clumpy thistles. Hares liked the conditions there and used it for feeding, breeding and resting.

Between 1977 and 1987, Tony spent thousands of hours observing hares with high-powered binoculars and telescopes. He was able to identify individual hares from natural markings on their bodies, such as small scars, ear nicks and fur patches. By occasionally glimpsing male genitals and female teats, he was also able to sex the hares. He was the first person to realise that male hares have a hierarchy relating not only to food but also to mates, and that dominant males are able to mate with more females than subordinate ones. He named the hares he observed and watched their most intimate moments, recording and photographing boxing, mating, feeding, mothers with leverets, and many other aspects of hares’ lives. He studied interactions between hares and predators, including Foxes and crows, and he wrote about the timing of their activity, their use of forms, and about aspects of grooming, stretching and play in leverets.

Tony wrote his PhD thesis on hares and published papers that are still used by biologists. His observations were second to none, and much of what we know about Brown Hare behaviour comes from Tony.

Leverets spend time exploring their surroundings in their first few days of life. They need to know their way around in case of attack by a predator, or in case they are flushed from their form and need to get back to it. They also play. Brown Hare leverets often run conspicuously up and down a familiar path (called ‘streaking’ on the ‘race track’ by researcher Tony Holley). They sometimes hold their tails up while doing this, and occasionally jump around. Each leveret in a litter has its own separate ‘race track’, and they converge at the site where the littermates meet to feed each evening (their birthplace).

As well as avoiding detection and surviving attacks by Foxes and other predators, leverets have to keep themselves warm and dry. Imagine how cold you could get as a tiny leveret born in the open in February. Researchers in Austria found that, during the long breeding season there, Brown Hare leverets may be exposed to extremes of temperature (−26°C to +38°C/−15°F to +100°F), and monthly rainfall can be up to 244mm (9⅔in). They tested the ability of leverets in their first week of life to cope with low temperatures and found that, at least down to −8°C (18°F), leverets are able to cope with the cold by increasing the heat they produce via energy from food. Though leverets are furred at birth, their fur is mainly for camouflage and does not provide much insulation. It is likely that, when it’s cold, leverets restrict the blood flow to their skin to minimise heat loss; they feel cold to the touch, but their internal body temperature remains stable.

Despite their adaptations to harsh weather conditions, leverets do need more energy when it is cold, and there is a price to pay for spending energy on keeping warm: slower body growth and higher likelihood of death from illness. Leverets exposed to lots of rain are less likely to survive than those experiencing drier conditions. Captive young Brown Hares in dry, sheltered cages grow faster than wild ones do, which shows that wild hares need to spend lots of energy just on keeping warm. For wild leverets, shelter and food quality are important, which is perhaps why habitat management can significantly benefit populations of hares.

Wild hares can become infected by a range of viruses, bacteria, yeasts, internal parasites such as worms, and external parasites such as fleas and ticks. Some of these cause sickness and death, others probably make infected hares more likely to be shot, killed by a predator or run over by a car, while some seem to have no adverse effect on the hares.

Most illnesses affecting hares, as far as we know, are shared by Brown Hares and Mountain Hares. However, European Brown Hare Syndrome, caused by a type of virus, expressing itself as a form of viral hepatitis, affects mainly adult Brown Hares in autumn. It can cause death 5–24 hours after the first symptoms appear. The disease was identified in 14 per cent of a large sample of Brown Hares from Sweden and is also common in other European countries. In Croatia in 1986, 30,000 hares were estimated to have died of European Brown Hare Syndrome. The virus is transmitted via direct contact between hares, or when hares come into contact with infected droppings.

Pseudotuberculosis (caused by the bacterium Yersinia pseudotuberculosis) is found in up to 20 per cent of hares found dead. Mountain Hares can also be infected with the bacteria Pasteurella, Leptospira interrogans and Francisella tularensis, and 60 per cent of Brown Hares sampled in the Netherlands were infected with the bacterium that causes syphilis.

Coccidiosis (caused by Eimeria, a protozoan or single-celled animal-like organism) affects mainly young hares in autumn, and is perhaps the most common natural cause of death in hares in the British Isles. It is an infectious disease, probably transmitted when hares come into contact with other infected hares or with their droppings.

Helminth worm parasites are found in the livers, stomachs, lungs and intestines of the majority of wild hares. The stomach worm Graphidium strigosum is mainly found in Rabbits, but infects hares where Rabbits and hares live close together. External parasites found on hares include many species of fleas, lice, mites and ticks.

Hares occasionally suffer from grass sickness, a disease of the central nervous system that is associated with lush grazing and also occurs in horses. The cause of grass sickness is unknown.

Young hares can be born at any time during the long breeding season but, regardless of their age and size, in order to have any offspring they eventually have to be ready to mate in the mating season. The age at which hares reach puberty depends on when they were born, and their growth depends on the habitat and weather conditions.

In England, male Brown Hares born before May reach puberty at three months of age, so, if they get access to any females, they can breed in their year of birth. They are still quite small when they become fertile (2–2.5kg/4⅓–5½lb) and whether they actually father any young is unknown, but they are physically able to. Males born from May onwards don’t become fertile until the beginning of the next breeding season, in December, by which time they may be seven months old. In warmer southern Europe, hares are more likely to be able to breed in the year of their birth. In Australia, female Brown Hares can breed at three months of age; in England, they can breed from around five months old, but this is rare and most first-time mothers are older.

As well as being able to breed, adults are defined as being of adult size and weight. Brown Hares reach their adult weight at about six months of age. Mountain Hare leverets are smaller than adults until they are about four months old, and, as far as we know, they don’t breed in their year of birth.