Originally published in the Journal of the American Animal Hospital Association Nov/Dec 1979, Vol. 15, page 775.
Reprinted with the permission of the AAHA.
By: Susan M. Landry, BS and H.J. Van Kruiningen, DVM, PhD
A good deal of disagreement exists within the veterinary profession about the proper diet for dogs, some nutritionists advocating meat and fat rations and questioning the need for carbohydrates, and others describing a necessity for carbohydrates and suggesting deleterious effects from high meat protein diets. The proliferation of commercial dog food products and the hyperbolic television advertising associated with them have compounded the dilemma for the veterinarian and the dog-owning public.
The authors became concerned about canine rations because recent studies suggest that canine acute gastric dilation may be related to diet. The disease occurs with greatest frequency in the best-cared-for animals, in dogs fed exclusively soybean-cereal grain-expanded dog food products. Acute gastric dilation occurs shortly after a meal and has been shown to be fermentative in origin.
We conducted a review of the available wildlife literature, with the intent that the information gathered concerning food selection among feral carnivores might influence future considerations regarding the feeding of domestic carnivores.
Review of the Literature
Food habits of feral carnivores have long been of interest to wildlife specialists, who have attempted to elucidate predator-prey relationships and their fluctuations. Three methods have been used to determine the foods of feral carnivores: (1) examination of stomach contents; (2) scat analysis; and (3) direct observation.
In the examination of stomach contents, samples are floated in water and then dried in ovens. This is a common method. A partial identification is accomplished by inspection of undigested fur, bones, feathers, plant material, teeth, scales, and other such tissue. Identification is completed by microscopic study, comparing these materials with reference collections. Stomach contents are relatively easy to identify, and this method allows for distinction between carrion and freshly killed material.
In the scat analysis, fresh feces are collected, floated in water, and dried in ovens. Identification is based on comparisons with reference collections. This method provides a larger sample size than stomach contents, but identification is more difficult.
Direct observation of animals’ feeding is the third method used. Ear tagging devices and radio telemetry permit precise tracking of an animal’s movements, thus allowing first hand observation. This method of monitoring is especially valuable for studying endangered species or animals on game preserves.
We chose to review stomach content analyses because they offer more information than scat analysis and greater numbers than have been studied by direct observation.
Table 1: Food Habits of Coyotes, as Determined by Examination of Stomach Contents
Economic losses to farmers resulted in extensive studies of the coyote’s predatory behavior. Sportsmen and trappers have made a large number of specimens available for research. Thus, the food habits of this canid are well delineated [Table 1]. Sperry, in a 5-year study encompassing 17 states and all seasons, ranked rabbits as the primary food of coyotes. Carrion and rodents were next in importance. Similar findings have been reported for various regions.
Table 2: Comparison of Food Habits of Coyotes from Four Regional Areas in California
Geographic influences on selection by the coyote are exemplified in a study of 2222 stomachs from California. Regional differences among four areas of the state are documented [Table 2]. The intake of rabbits in the eastern region is twice that of other regions, while the deer intake is almost one-half, suggesting a proportional relationship. This type of relationship is also seen in the coastal region where coyotes appear to prey predominantly on the rodent population, resulting in a decreased intake of rabbits, sheep, and birds. Other examples of regional influence can be seen. Stomachs of coyotes from Texas contain fruits of native plants; poultry remnants are a common finding in stomachs of coyotes from such states as Arkansas, Nebraska, and Missouri, where broiler production is a prominent industry. These findings suggest that the coyote is an opportunistic scavenger.
Table 3: Seasonal Variations in Food Habits of Coyotes
In an analysis of 770 stomachs of coyotes in northwestern Missouri, rabbits were the staple food. The percent occurrence, however, varied seasonally and annually, the changes reflecting the population densities of rabbits. The greatest consumption of rabbits occurred in the winter – 58.1% by volume compared to 35.2% in the summer [Table 3]. Mice and rats were found more frequently and in greater quantity in fall and winter months. This report is at variance with other studies, which report highest consumption of rodents during the summer and fall. It may be more difficult for coyotes to find and capture smaller animals in the snow. A slight increase in the amount of carrion consumed in the winter months has been reported.
Unusual foods and/or quantities of food merit mention. Items such as leather, paper, and tinfoil have been found in coyote stomachs. Dirt, sticks, pebbles, and bark are often found in coyotes that have been trapped. Stomachs filled with insects have been reported. Farmers cultivating watermelons have experienced heavy losses from coyotes. Persimmons are frequently found in stomachs and, in areas where they are plentiful, comprise a significant part of the coyote’s diet.
The fox, like the coyote, has been the subject of much research. Foxes have also been considered extensive predators of domestic livestock. Analysis of food habits of the fox indicate that this canid is an opportunistic carnivore, consuming items that are easily obtained.
Table 4: Food Habits of Foxes, as Determined by Examination of Stomach Contents
The major foods of foxes are small mammals such as rabbits and rodents. Although these foods are similar to coyote foods, there are differences. Some reports indicate that rodents are more important to foxes as a staple food, though this is not borne out by available data [Table 4]. In addition, the red fox eats less rabbit and more of other game than the coyote.
The importance of game birds in the fox diet in debatable. Instances can be found where game birds are a major food item. This choice of prey probably occurs when there are large populations of birds or when populations of rabbits and rodents are low. Inspection of fox stomachs often reveals that this animal is not strictly carnivorous. Apples, grasses, persimmons, plums, and miscellaneous vegetation are often found. A comparison of red and gray fox stomach contents shows different preferences. Plants appear more frequently and in greater volume in gray foxes. This difference is especially noticeable in winter months.
Table 5: Food Habits of Wolves, as Determined by Examination of Stomach Contents
The food habits of wolves are modulated by their social behavior. Food is often obtained by a cooperative effort of the pack. As a result of the animal’s size and pack society, the wolf can successfully prey on a variety of animals [Table 5]. Historically, the food of wolves appeared to have been buffalo, antelope, elk, deer, caribou, and moose. Today, when populations are adequate, these animals still comprise the major part of the diet of wolves. Caribou and moose remnants predominate in wolf stomachs in northern regions. In areas where man has settled and substituted domestic livestock for food, the wolf has done likewise. Tissues from livestock occurred 456 times in an analysis of 3346 wolf stomachs. Stomachs were obtained from states west of the 100th meridian and reflect the agriculture of that region. Wolves select animals requiring the least amount of energy to hunt and kill. Domestic livestock is unable to defend themselves effectively and are easily captured. Flesh, hair, and bones of deer are found in the stomachs of wolves from all regions. Deer are also eaten in greater numbers than is represented by their populations. This suggests that deer are the preferred food.
Beaver tissue and carrion are common findings in wolf stomachs. Carrion is utilized as food, particularly by animals that have been handicapped by injuries from traps or by worn teeth and in areas of low prey populations. Minor food items eaten by wolves are rabbits, hares, birds, and fish. Insects, invertebrates, and fruits, such as plums, watermelons, and berries also are seen in wolf stomachs. Infrequently, snowshoe hares are reported as a major food source. The size and social behavior of wolves would suggest that the hare probably does not contribute significantly to the wolf diet.
Table 6: Food Habits of Felidae, as Determined by Examination of Stomach Contents
Bobcats eat mice, hares, rabbits, squirrels, and porcupines [Table 6]. Deer are also considered an important food item, but there is some controversy as to how this animal is obtained. Bobcats have been observed consuming carcasses of deer with gunshot wounds. Eyewitness accounts have also documented instances of bobcats preying on live deer. The actual preference of the bobcat, whether for freshly killed meat or for carrion, cannot be determined from the information available.
The frequency of porcupines in the bobcat diet is significant. Bobcats do not seem to be adversely affected by quills. Porcupines are frequently found in bobcat stomachs even in areas where porcupine population densities are low and where other bobcat food is plentiful. This suggests that porcupines are the preferred food.
Minor food items are birds, skunks, and fish. Leaves, twigs, soil, and other such debris also are commonly found. Since bobcats are ground feeders, the presence of these items is probably the result of accidental ingestion. Green grass is also found frequently enough to be considered a food item. The nutritional value of grass in the bobcat’s diet, however, has not been determined.
Little is known of the food habits of cougars. Deer supply the major portion of the diet – outnumbering the total of all other prey [Table 6]. Other important foods are porcupines and lagomorphs. Tissues from horses, cows, coyotes, bobcats, skunks, and beavers also have been recovered from cougar stomachs. This data indicates that this felid prefers to eat large animals. The intake of lagomorphs may be an indicator of availability rather than preference. Low population densities of larger animals may force the utilization of rabbits and hares for food. The cougar will also consume grasses in both winter and summer. Brown, coarse, giant ryegrass has been found in the stomachs of cougars. This type of grass is avoided by livestock even in winter. Nutritional benefits of this grass for the cougar are unknown.
Knowledge of the food habits of the lynx is also sparse. The major food supply of this felid is the snowshoe hare [Table 6]. Microtines and birds are next in importance. Lynx will also utilize red squirrels, fish, grass, and birds, particularly ducks.
The importance of the snowshoe hare is emphasized by the frequency of occurrence and/or percentage biomass. In Central Alberta, snowshoe hares represented 75.7% biomass, carrion second at 9.8%, and ruffed grouse at 9.2%. In Alberta and MacKenzie districts, snowshoe hares occurred with a 52% frequency, while the second-ranked food item, Microtus, occurred with a 22% frequency. The absolute dependence of the lynx on the snowshoe hare has been attributed to what is termed "feline specialization". Felines choose their foods with respect to their own size. The lynx is a medium-sized feline and thus is limited to capturing small animals.
From these many studies into the food habits of feral carnivores, it can be concluded that the staple diet of carnivores living in a natural setting includes other animals, carrion, and occasionally other fruits and other grasses. The larger the predator, the larger the prey. Wolves and cougars possess the capability to bring down large species of prey and thus eat less frequently than other carnivores and tend to engorge when they do. While the domestic dog is regarded as a descendant of the wolf, out-crossings with other canid species appear to have been responsible for many of our domestic breeds. Most of our domestic breeds possess the conformation, size, ferocity, and hunting capability similar to that of the coyote and the fox, carnivores that hunt individually, catch and kill small animals, eat carrion, and occasionally car fruits or grasses. The data suggested that medium- and small-sized carnivores are sometimes hunters, sometimes scavengers, eating what they can get their claws on. Anatomically, our domestic breeds of dogs possess gastrointestinal systems similar to those of the feral carnivores studied. They share in common strong carnassial teeth, simple stomachs of great digestive capability, thickly muscled esophagus, stomach, and intestine, residual cecae, and simple non-sacculated colons.
Recognizing the limitations inherent in stomach analyses as traditionally performed, it nevertheless appears reasonable to surmise from these reports that carnivores in their natural environment consume diets high in animal protein, bulk, and roughage (not plant fiber, but indigestible or poorly digestible parts of animal carcasses, such as bone, cartilage, scales, fin, fur, feather, tendon, and teeth), and low in carbohydrates and caloric density (the fat content of the flesh of wild rabbits equals 5%).
The medium and small feral carnivores undoubtedly eat several times daily (nightly really) catching as catch can, with periods of rest or fruitless scavenging or hunting in between. From stomach analyses it can also be recognized that carnivores masticate their prey minimally and prefer to swallow large bollets, ie – portions of carcasses with indigestible portions included.
An understanding of the food habits of feral carnivores should influence the diets and feeding practices we impose upon domestic carnivores.