Wallowing
Wallowing in animals is comfort behaviour during which an animal rolls about or lies in mud, water or snow. Some definitions include rolling about in dust, however, in ethology this is usually referred to as dust bathing. Wallowing is often combined with other behaviours to fulfil its purpose; for example, elephants will often blow dirt over themselves after wallowing to create a thicker "coating", or pigs will allow the mud to dry before rubbing themselves on a tree or rock to remove ectoparasites stuck in the mud.
Functions
Many functions of wallowing have been proposed although not all have been tested by rigorous scientific investigation. Proposed functions include:- Thermoregulation – domestic pigs, great Indian rhinoceros, warthogs, elephants
- Providing a sunscreen – pigs, warthogs, elephants
- Male-male conflict social behaviour – elk, European bison, deer
- Removal of ectoparasites – white rhinoceros, American bison, warthog
- Social cohesion – American bison
- Relief from moulting – European bison, elephant seals
- Relief from biting insects – tamaraw, American bison, tapirs, warthog, elephants
- Play in young animals – American bison
- Skin maintenance – hippopotamus
- Camouflage – warthog
- Scent-marking – Some animals urinate in a wallow before entering and rolling in it, presumably as a form of scent-marking behaviour
- Skin microbiome 'selection' – Horses
Domestic pigs
Pigs lack functional sweat glands and are almost incapable of panting. To thermoregulate, they rely on wallowing in water or mud to cool the body. Adult pigs under natural or free-range conditions can often be seen to wallow when air temperature exceeds 20 °C. Mud is the preferred substrate; after wallowing, the wet mud provides a cooling, and probably protecting, layer on the body. When pigs enter a wallow, they normally dig and root in the mud before entering with the fore-body first. They then wriggle the body back and forth, and rub their faces in the mud so all of the body surface is covered. Before they leave the wallow, they often shake their heads and body, often finishing with rubbing against a tree or a stone next to the wallow. When indoors and hot, domestic pigs often attempt to wallow on wet floor surfaces and in the dunging areas.Although temperature regulation seems to be the main motivation for wallowing in pigs, they will still wallow in colder weather. While many have suggested that pigs wallow in mud because of a lack of sweat glands, pigs and other wallowing animals may have not evolved functional sweat glands because wallowing was a part of their behavioural repertoire.
Pigs are genetically related to animals such as hippopotamus and whales. It has been argued that wallowing behaviour and the desire to be in shallow, murky water could have been a step to the evolution of whales and other marine mammals from land-dwelling mammals.