Wolves have a highly variable diet, showing how very adaptable they are and have had to be while surviving in different environments. They are opportunists with hardened digestive systems allowing them to survive on a highly variable range of food, including garbage where forced to. They also have great ability to locate prey and food in general. The 1963 book Never Cry Wolf by Farley Mowat insinuated that wolves mainly have to live off mice – this is, however, incorrect.
Diet in Eurasia
The natural habitat of the wolf and its prey throughout Eurasia has been fragmented, altered and destroyed by human activities. Many native prey species have been completely destroyed. In human-inhabited areas wolves are forced to feed on domestic animals and garbage. Of course, it is the wolf’s diet that causes massive conflict with humans. Prior to the restoration of wild prey in many areas of Eurasia in the 1980s and 1990s wolves preyed on livestock. Native wild Eurasian ungulates wolves are able to prey on today include moose, red deer and wild boar. Wild reindeer are the primary prey species in the tundra regions of Siberia. In times of extreme prey scarcity wolves may again turn to easily accessible livestock, however they prefer to feed on wild prey as opposed to enclosed domestic livestock – even feeding on carcasses (used for bait by people so wolves can be shot) before turning to livestock.
Wolves also feed on fruit to compensate for lack of prey. They have been known to travel through vineyards and orchards in times of prey scarcity and eat grapes, watermelon, apples, pears, figs, plums and other fruits. Grass isn’t uncommonly found in wolf faeces – as with pets, wolves will sometimes eat grass – perhaps to induce vomiting to rid the intestines of parasites.
In areas where wolves are left with garbage to scavenge from, they not only eat meat scraps and fruit but have also been known to consume non-edible rubbish such as plastic, tinfoil, cigarettes and even long shards of glass.
Diet in North America
In winter the diet of North American wolves is dominated by ungulates. In the late nineteenth century, native bison were nearly completely eliminated on the North American continent. Millions of bison may have existed on the grasslands and plains of North America before this point, which could have supported 200,000 wolves. Nowhere else on earth could there have been such a concentration of prey and wolves. However, the arrival of Europeans brought a huge cull of bison and their eventual replacement with livestock. Wolves were generally eliminated by private and government control efforts. Even so, wolves currently existing in North America do not typically subsist on domestic animals and garbage except in small local areas. In eastern provinces of Canada wolf populations are mainly supported by moose and white-tailed deer, while Western provinces provide multi-prey systems with up to four of five ungulate species available. North of continuous forest on mainland Canada wolves rely on migratory caribou. On arctic islands muskoxen are the primary ungulate prey.
And, of course, wolves absolutely cannot exist without some form of water. Water is the universal solvent for an array of chemical reactions in the body, it is required for temperature regulation, digestion, and helps eliminate toxins from the liver. Wolves can lose water via urine, expired air, faeces and lactation. While desert wolves are not as well adapted to conserving water as other desert mammals, they have a greater ability to travel and seek out distant sources of water that may be inaccessible to other animals. Wolves’ kidneys in general are also able to concentrate urine to a high degree.
In midwinter at northern latitudes, however, wolves can survive with drinking little or no water. They can obtain water from prey tissue and from water produced by digestion (metabolic water). Lactating females do need to drink water frequently though, which is why den sites are often limited to areas within reach of a water source. A nursing female needs to produce about 1.2 litres of milk each day.
Wolves are very mobile animals, well equipped for minimizing food scarcity. They can locate prey over large areas even when it is scarce. They spend up to half their time traveling in order to locate prey for hunts. They rely on tracking, scenting, sight and chance encounters. When moving in a particular direction they generally file one behind the other, but in areas of hill or heavy forest/scrub cover they tend to fan out, increasing the pack’s line of sight.
Once wolves locate prey they attempt to get as close as possible – thus begins the stalk. Stalking wolves tend to behave excitedly, quickening their pace and wagging their tails, but they also hold a tight restraint over themselves. Most prey species are potentially dangerous to wolves (for example, many old wolves possess broken ribs from being swung around into trees when grasping the nose of a moose) – a wolf must be careful enough when approaching another animal to avoid harm to itself, yet be bold enough to attack. Experience and learning helps wolves fine-tune their judgement for this balance.
When the wolf and its prey first see and confront each other (usually at a distance), several different scenarios can occur. The most optimal for the wolf is that the prey animal flees – which spurs a rush or chase. However, prey also often remain in place or even approach the stalking wolf. This complicates the situation for the wolf – because many prey species can pose a danger to wolves, they generally wait until the prey animal turns to run rather than confronting them head-on. If a large prey approaches a wolf or stands its ground the wolf will attempt to threaten it face-to-face. If this does not work, however, the wolf will eventually leave (but this can take up to several hours). Wolves have been known to remain near prey herds for up to a week, occasionally testing certain animals and waiting for a flee response. When an individual does flee, wolves will immediately pursue – even if they are already feeding on a kill.
This ‘rush’ phase differs in each individual hunt. With small single prey such as hares, deer or caribou calves wolves will attempt to catch up to them as soon as possible and they are easily killed or fatally wounded with a few bites. With herds of prey wolves may run with them for a while, watching for the most vulnerable individuals. The next part of the hunt is the chase, which is a continuation of the rush. Wolves will continue to test herds, trying to rush in and attack any calves that are protecting on the inside of the group. They watch for slow or lame animals that tend to fall behind the rest of the herd. Wolves can run at 56-64 km/hour and may continue running for 20 minutes or longer. Wolves most often give up chases within 1–2 kilometres although they have been known to follow prey for up to 21 kilometres. The chase is either ended with a kill or with wolves giving up.
Single wolves are known to be able to kill even the largest prey such as moose, but it is generally more efficient to have at least one other wolf involved in a hunt. However, packs hunting together often contain young and inexperienced animals that may not add a lot of benefit to a hunting group – packs kill less food per wolf than pairs do. Hunting pairs have the most efficiency per wolf. Multiple wolves in a hunting party are able to make use of different techniques, such as ambushing, taking turns chasing an animals (‘relay running’) or heading off fleeing prey.
Canids differ to felids with their killing techniques where felids generally aim to kill prey with a single crushing bite but canids (including wolves) usually have to kill animals with several shallower bites delivered more opportunistically. Felids are able to more readily grasp prey with sharp claws – wolves, however, have duller claws that are worn by travel which is why they are especially reliant on their bite ability.
While wolves have adapted to survive on a range of available food, their teeth are adapted for an all-meat diet. They lack the bone-crushing teeth found in felids, however they have one movable joint in their skull that helps prevent dislocation when the mandible (jaw) is stressed during prey capture and consumption. Jaws are as long as possible given their width, allowing for maximal gape (jaw-opening) dimensions. The front teeth – the incisors and canines – are the primary tools wolves use to subdue their prey. Canine teeth stab and hold, and the incisors help keep this hold. These teeth must hold the entire weight of the wolf’s strength and the prey’s as they struggle – keeping in mind a moose can swing a wolf full around in the air while the wolf is attached to its face or nose. Wolves have been known to lock on to a rear leg of a moose as it runs for dozens of metres, dragging the wolf along. More broken canines are seen in skulls of wolves where moose serve as the predominant prey as opposed to smaller mammals.
Canine teeth are also used to slash at the hides and muscle of prey, producing lacerations and extensive bleeding; slashing then holding (unlike felids that stab and hold). Incisors also nip or pull at live prey, remove tissue from dead prey, and ingest small non-struggling food items such as berries or small mammals.
Carnassials (the teeth directly behind the canines) are used for slicing through hide and meat. Species such as wolves have enlarged carnassials helping them to feed on large prey. They also crush and grind. Each carnassial tooth has two shearing edges separated by a V-shaped notch on each edge of the cutting blade. As the jaw closes, the upper and lower blades shear past each other, trapping and cutting food between the notches. This also keeps the edges sharpened.
Wolves consume entire carcasses of prey so as not to suffer specific nutrient deficiencies. Muscle tissue alone is not enough; it does not contain a correct balance of required nutrients. They tend to tear into the body cavity of large prey and pull out the largest internal organs (e.g. lungs, heart and liver) for primary consumption. The rumen (the first division of a ruminant’s stomach) – which can weigh up to 60kg in a moose – is usually punctured and the contents spilled out. The vegetation in the intestinal tract is of no interest to wolves, but the stomach lining and intestinal wall are consumed and their contents further strewn around the kill site. Smaller internal organs, such as the kidneys and spleen, are then exposed and eaten immediately. After these choice organs are consumed, the large muscle masses associated with each leg of a prey animal provide the bulk of food eaten by wolves.
Elements of wolf-killed prey and their nutritional components:
Liver – B vitamins, vitamin A, copper, zinc, manganese, essential fatty acids
Brain – essential fatty acids
Heart – essential fatty acids, protein
Kidney – essential fatty acids, protein
Muscle – protein, source of energy, fat (small amounts)
Bone – calcium, phosphorus
Blood – protein, water
Digestive tract – fatty acids, microflora (for biotin)
Hair – minerals (possibly), helps speed passage of food through intestinal tract.
Bones are a surprisingly well-balanced source of nutrients for canids. They can maintain themselves on a diet of bones alone for weeks during times without fresh kills. The fatty marrow in fresh bone is a good source of protein and fat. Wild wolves tend to have depleted bone marrow fat levels themselves – this is the last stored source of energy used before muscle catabolism is required to sustain life. In the absence of food they lose weight daily. However, wolves are adapted to a feast-or-famine diet, and can quickly recover weight lost during periods of fasting. Captive wolves often have problems with weak bones due to being fed a meat-only diet – commercial foods that do not contain nutrients from, for example, vital organs, are not enough to support the potential a wolf’s body has.
After a kill wolves will gorge themselves on prey and eat up to 25% of their body weight, packing their stomachs and causing their sides to become distended. They may then travel for a distance and rest or sleep for several hours, which probably aids digestion after these gorging periods. A wolf may also cache food when it is sated. They cache anything from an intact caribou calf to several regurgitated food chunks. Caching, more commonly practiced in summer as opposed to winter, helps secure excess food left from large prey, reducing loss to scavengers and maggots. When prey is difficult to find or catch a wolf can utilise its cached food. In cold regions cached food lasts longer because the ground sometimes freezes over. Caches are commonly raided by other carnivores even though wolves try to distance their caches from obvious kill sites.
At the White Wolf Sanctuary we provided animals with road-kill (elk, deer etc.) where possible – either whole carcasses or parts. With whole carcasses the wolves would tear instantly into the belly, pulling organs out for consumption and ridding the carcass of stomach contents. Even captive-bred animals keep this innate behaviour and evolved subconscious knowledge to consume organs first. From time-to-time they would catch ravens that would come to scavenge from carcasses, but generally they would be so full they would lumber off to sleep, leaving the carcasses undefended. We never starved the wolves; they were provided food about once a day but the amount would vary. Carcasses, however, were definitely the most enjoyed meals – they would roll in them, carry and throw limbs around. I never saw an individual cache food – obviously there was never any need to – although they would regularly go back to old bones.
For this and more information see:
Behavior, Ecology and Conservation
Edited by L. David Mech and Luigi Boitani