Range use by large herbivores is determined by a number of factors including:

• feeding value of different vegetation patches
• shelter from wind or rain
• social behaviour
• human disturbance or management.

In general, large herbivores spend most time on vegetation types that have the highest feeding value. In practice, the other factors influencing herbivore movements generally cause them to be distributed over all vegetation types but with a bias towards those that give the highest nutritional return.

The differences in the grazing attributes of each large herbivore, together with differences in the other factors determining movement, lead to each using its range in a different way.

Sheep

Sheep typically group together in flocks of about one hundred animals. The flock stays largely within its home range, which is often bounded by topographic features such as streams or mountain ridges.

Within the flock, there are sub-groups of ewes frequently made up of related animals. Each of these sub-groups occupies a smaller home range, or heft, typically where they were born and reared. The heft will normally include a range of vegetation types. The individuals that occupy a heft will tend to spread out while foraging. The combined hefts will cover most, or all, of the home range of the flock so the flock will normally be spread out over its whole home range.

Super-imposed on the behaviours described above is a range of others. During the day, sheep will tend to graze on favoured vegetation types, often at the foot of the hill.  At night-time they have a tendency to move uphill. This is thought to be an evolutionary response to the threat of predation.

In summer, sheep may move uphill to avoid flies, to cool down or to exploit later growth of grasses at higher altitudes. In winter they will use walls or woods to shelter from high winds. Shepherding is rarely carried out these days but, when it is, sheep are normally herded up the hill daily to encourage the sheep to spread their grazing pressure more evenly. Sheep congregate around winter feeding sites, where these are provided.

Cattle

Cattle cannot graze short grassland efficiently but, because of their larger gut size, have a greater ability than sheep or red deer to digest poor quality forage. As a result they are more likely to move onto mat-grass or purple moor-grass in summer. Most breeds of cattle grazed in the hills currently have to be taken off in winter. Hardy breeds can be left on all year but will normally need supplementary feeding in winter.  Cattle need to have a water supply and will often concentrate around it on hot days.

Cattle tend to move around their range as a herd. Although they are usually not found on very steep slopes, or above about 600 m, they will move off the more nutritious vegetation and use their range as fully as do sheep if they are on the site for enough of the year to become familiar with all of it.

Goats

Domestic goats are usually confined to lower, enclosed pastures but there are several local populations of feral goats in the Scottish hills. When wet, goats lose heat rapidly. They are therefore restricted to areas with rocky outcrops or caves where they can shelter from rain. Survival of kids is low in Scotland. This, together with the limited availability of shelter, means that most populations are not increasing.

Goats, like sheep, live in family groups of females each with its own territory. Males operate singly or in peer groups. The forage preferences of goats are similar to those of red deer but goats have a slightly greater ability to eat low quality forage. Due to their greater agility, they are also able to exploit vegetation on cliff ledges and in boulder fields to a greater extent than can red deer or sheep.

Horses and ponies

Horses and ponies are found only rarely in the uplands. They tend to graze in mixed sex groups. Unlike ruminants, which have a four-chambered stomach, they have only one stomach. This means that food stays in the digestive tract for less time and digestion is less efficient. Ruminants also ruminate, or chew the cud, thereby breaking down food into smaller particles that are easier to digest.

The process of rumination makes digestion more effective but reduces the time available for feeding. The digestive system of horses and ponies therefore allows them to process food quickly, and in large quantities, but does not extract as much of the nutrients from their food as does that of ruminants. However, with their upper as well as lower incisors they can crop grass swards shorter than can most ruminants.

Horses and ponies can therefore consume large amounts of food quickly and can more effectively graze very short swards. As a result, horses and ponies have a greater tendency to concentrate on high quality grasslands than would be expected from their body size. If only poor quality forage is available, they require large quantities.

Red deer

Red deer show similar foraging preferences to sheep, however, they have a higher propensity to browse dwarf shrub, shrub and tree species. This is partly because of competition between sheep and red deer when they share the same range (see below) and partly because their larger guts allow them to digest rough vegetation better.

Red deer range over much larger areas than sheep and are often segregated into hind and stag groups. Stags tend to wander over a wider area than hinds. Stags taking part in the autumn rut spend very little time feeding.

Red deer will often congregate at high density in sheltered wintering areas. This is exacerbated by the common practice of providing supplementary feed to stags in winter. Red deer are woodland animals by preference and will make use of any available woodland for shelter and forage. As well as browsing on trees, red deer will sometimes also strip their bark. This usually happens in winter.

Roe deer

Roe deer are more likely to browse trees than are sheep or red deer. They will generally only be found where there is some woodland to provide forage and cover. Roe deer will not generally bark strip trees but they will fray them with their antlers.

Adult female roe deer are largely solitary or occur in small family groups. Each of these will have its own home range that will overlap with those of other roe deer.

Adult males hold territories between April and August. At other times of the year they are less likely to defend a territory. Each territory overlaps those of several females. Some males will not be able to compete successfully for a territory. During severe weather all deer may share communal feeding grounds.

Mountain hares

Mountain hares feed largely at night and rest during the day uphill in long heather.  They feed mostly in heather-dominated vegetation, preferring stands of younger, pioneer heather. They select strongly for grasses growing amongst the heather, resulting in a diet of less than half heather in summer and almost totally heather in winter when these grasses are largely dead or have been removed by grazing. They are generally found higher up the hill than brown hares, which feed largely on grassland.

Rabbits

Rabbits can occur in large numbers anywhere (except at high altitudes) where there is abundant good grassland and either scrub cover or sandy soils for burrowing in. They have small mouths, can be very selective and have a distinct preference for short, high quality grasslands. They will eat heather if there is little grass available. The grazing pressure of rabbits is at its highest close to warrens and adjacent to areas of scrub used for cover.

Interactions between grazing species

Interactions between grazing species can be positive or negative. All species compete for the available vegetation. Smaller herbivores, with smaller mouths, are able, however, to graze grass swards to a shorter sward height and still gain the daily intake of digestible material that they need.

The larger mouth sizes of larger herbivores restrict the efficiency with which they can graze short swards. Large herbivores also have a higher daily intake requirement that they are unable to satisfy from short swards.

In theory, larger herbivores will move off grasslands before smaller ones as the grass sward becomes shorter. In that sense, small herbivores can ‘outcompete’ larger ones. Thus, in theory, stags move off good grasslands before hinds, deer before sheep and sheep before rabbits. Large herbivores are, however, better at digesting rougher vegetation and can survive where vegetation quality is too low to support smaller herbivores.

Cattle can graze mat-grass or purple moor-grass to a level that allows more nutritious grass species to increase in abundance, thus increasing the overall livestock productivity of upland areas. There is increasing anecdotal evidence that red deer tend to avoid areas grazed by sheep or cattle and will move back into the area if stock are removed. This avoidance may be partly due to competition for food but may also be due to avoidance of the increased human presence that usually comes with stock grazing.

Horses and ponies go against this trend in that, despite their large size, they can graze short swards effectively because they have both upper and lower incisors. They are thus able to ‘outcompete’ cattle, goats, sheep and red deer on good quality grasslands.

Sheep are also thought to disturb the feeding of mountain hares. They compete directly with hares for food and may cause a reduction in hare numbers.