Camouflage

Camouflage is an important defensive strategy utilised by many organisms in nature. It is perhaps most often associated with examples such as lions blending in with the dry grass of the East African plains or the remarkable leaf-mimicking katydids of the tropical rainforests, but it is also common, and often equally spectacular, in temperate ecosystems such as the Caledonian Forest.

In biological terms, camouflage is often referred to as cryptic colouration, which means 'concealed or disguised in appearance'. Typically, an animal, bird or insect will have a colour or pattern of colouration which blends in well with the visual appearance of its habitat, thereby making it hard to be seen by predators.

Camouflage in mammals

A simple, but very effective, example of this is provided by the mountain hare (Lepus timidus). For most of the year, the hare is brown in colour, which enables it to blend in well with the heather moorlands where it lives, but in winter its fur turns white, so that it is well-camouflaged in the snow. This is vital to provide protection from its predators, which include the fox (Vulpes vulpes) and the golden eagle (Aquila chrysaetos).

Other mammals which exhibit camouflage include the red squirrel (Sciurus vulgaris), whose reddish colour is a good match for the reddish-orange colour of the young branches of Scots pines (Pinus sylvestris), where the squirrel often forages for pine cones. The reddish-brown coat of red deer (Cervus elaphus) changes to a darker brown or grey in the winter, to blend in with the drab colour of its surroundings, while a red deer calf has white spots on its coat for the first two months of its life. These help the calf to be less visible in the dappled light of spring, when sunlight filters through the canopies of trees to the forest floor, where the calf will rest motionless while its mother is away feeding.

Cryptic colouration in birds

A number of bird species utilise camouflage effectively, including the Scottish crossbill (Loxia scotica). The males and females of this species endemic to the pinewoods of the Caledonian Forest differ in their colouration, with the female's dull green-yellow colour providing good camouflage when she is sitting on her nest. In contrast, the male has a bright orange-red, brick-coloured plumage, which provides good cover against the reddish-orange of Scots pines branches, where, like the red squirrel, the crossbill feeds on seeds from pine cones.

The ground-nesting capercaillie (Tetrao urogallus) relies on blending in with the forest floor vegetation to successfully raise chicks. The female's colouration consists of barred shades of dark and rufous brown, with a chestnut breast flecked with white, and when she is sitting still she is very hard to distinguish from the surrounding heather.

The ptarmigan (Lagopus mutus) lives above the treeline (600 metres) and adopts a similar strategy to the mountain hare, of colour change in winter, to render it less visible in its exposed habitat. Its summer plumage of greyish-brown with some white flecks changes to all white in winter, so that it is well camouflaged against snow.

Insects - the masters of camouflage

It is insects, however, which have perfected the art of cryptic colouration, and have taken camouflage to extreme lengths. Because of their brief lifespans, insect generations are much shorter than those of birds and mammals and typically the time between generations is a year or less for most species. As a result, evolutionary pressures have a greater effect on insects in any given time period, and this may have led to selection which resulted in their excellent cryptic colouration.

In Scotland, various species in a number of insect groups utilise camouflage. For example, the larvae of the pine sawfly (Neodiprion sertifer) are green in colour, and similar in size to the needles of the Scots pine which they feed upon. This renders them less visible to the insectivorous birds which prey upon them.

However, it is the moths which exhibit the greatest diversity and specialisation in camouflage, with many species having patterns of colour on their wings which render them virtually invisible against tree trunks, leaves or lichens. In some species, it is the larvae which are cryptically coloured, whilst in others both the larval and adult forms are well-camouflaged.

Other moths utilise mimicry, in which their appearance closely resembles that of other insects, and the clearwing moths in particular are noted for their resemblance to wasps, which are much less attractive to predators. One relatively rare species, the Welsh clearwing (Synanthedon scoliaeformis), occurs in Glen Affric.

People utilise camouflage too!

The tweed jackets and hats worn by deer stalkers and gamekeepers are a good example of the adoption by humans of the principles of camouflage. The subtle, varied colours of green and brown which make up the patterns of the tweed blend in well with the heather and grasses where stalkers take up position for their shots. The hides used by birdwatchers and photographers to get close to wildlife also utilise camouflage and thereby represent a very real way in which people mimic, and learn from, the natural processes of evolution.

Alan Watson Featherstone