Methods of Investigating Predation of Livestock

1. What they did

Ranchers in Alberta can receive government help and, under some conditions, compensation when predators kill livestock. That makes it important to know whether a predator really killed an animal, and which one. Many dead animals are scavenged, and finding predator tracks or hair in droppings near a carcass does not prove that predation happened.

This booklet is a practical guide for anyone investigating a predation complaint. The authors set out:

• How to decide the cause of death. Separating predation of healthy animals from pseudo-predation (attacks on animals that were already sick, weak or unlikely to survive) and from other causes such as disease, bloat, starvation, poisonous plants, lightning, cold, theft and injuries on fences.
• How to judge the animal’s health. Coat, hydration, body fat, stomach contents, lungs and circulation.
• How to identify the predator. For bears, wolves, coyotes, domestic dogs, red foxes, cougars, lynx and bobcats, weasels, mink, skunks, badgers, raccoons, eagles, hawks, owls and scavenging birds, they describe range in Alberta, preferred livestock prey, season, how each one attacks and feeds, and the tracks and signs left at the site.
• A summary checklist of what to record at the kill site and on the carcass.

Tracks and scats are not covered in detail; the authors refer readers to the tracking field guides by Halfpenny and Biesiot (1986) and Murie (1954).

2. What they found

Reading the site

• Signs of a struggle (broken and trampled vegetation, tufts of wool or hair, a drag trail of blood) are good evidence of predation, but their absence does not rule it out, especially with small or newborn animals.
• Animals that died of sickness often lie upright or on their side with legs tucked under; animals killed by predators usually lie on their side with legs extended, in or near cover or rough terrain.
• Predator tracks, scat and hair near a carcass show a predator is in the area, not that it killed. If none are found at the carcass, the authors suggest searching nearby fence rows, trails and water-holes.
• Evidence disappears fast: carcasses rot in warm weather, scavengers eat them, and livestock or weather wipe out other signs. If an investigator cannot come at once, the producer can cover the carcass with a tarp.

Reading the carcass

• Bleeding and bruising under the skin are the most important signs that an animal was alive when attacked. Skinning the wounded areas is needed, because blood may not soak through hair or wool.
• Decomposition can look like bruising: the sunny side rots faster, and blood pools on the lower side. These areas are much larger and more even than the local damage from bites.
• A newborn that lived will have spongy, pink lungs that float in water, worn hoof membranes from walking, and milk in the stomach. The authors warn that magpies and crows can pick off hoof membranes, and that rotting lungs can float.
• A knife cut leaves a clean edge with cut hairs; a predator’s tear is uneven. Barbed wire leaves sideways cuts on the chest and sides, while predator claw marks are usually on the upper neck, shoulders or back.

Each predator’s pattern (some examples)

• Grizzly bears bite the top of the neck or back near the withers, often drag kills into cover, usually cover the remains with debris, eat meat before viscera and leave the skeleton intact. Tracks over 13 cm wide are most likely from a grizzly.
• Black bears leave more claw marks, rarely cover their kills, and leave many signs (tracks, scat, trampled grass and trails). Tracks under 13 cm wide are usually from black bears. Of 466 cattle killed by black bears in Alberta from 1974 to 1978, 71% were calves.
• Wolves attack the hindquarters, tail and flanks of cattle, chew and break bones, and may eat the hide of small prey. Calves were about 70% of 1581 cattle killed by wolves in Alberta from 1980 to 1987, with most losses from July to September. Wolf stride is about 100 cm and footprints about 12 cm long by 10 cm wide; in deep snow, pack members often step in the leader’s footprints. Scats 2.5 cm or more across are probably from wolves.
• Coyotes kill over 70% of sheep with a throat bite, often readjusting their grip and leaving many tooth punctures. About one-third of calves killed by coyotes in Alberta are one day old, and about 80% are under a month. They cannot break the larger bones of older prey, and may rub their muzzles on the ground near a kill.
• Domestic dogs cause prolonged chases with many dead and wounded animals, mutilation and little feeding. Different sizes of canid tracks at one site help show that several dogs were involved.
• Foxes and coyotes can be told apart by the gap between canine tooth punctures (1.9 to 2.5 cm for fox, 2.9 to 3.5 cm for coyote); mink and weasel punctures differ in the same way.
• Cougars stalk from cover, kill with a bite to the neck, feed first on internal organs through an opening behind the ribs, leave clean-cut edges, and cover kills by reaching out about 1 m. Lynx and bobcats reach just over 0.3 m when covering a kill, which helps tell their kills from a cougar’s.
• Badgers leave large dig holes and often cache prey in them; raccoons leave hand-like tracks with five bulbous toes; great horned owls typically bite off the heads of poultry; golden eagles leave talon punctures and turn the hide inside out.
• Magpies, ravens and crows rarely kill healthy livestock; most of their attacks are on animals already in trouble, so they are usually pseudo-predation.

3. What they concluded

• Predation is seldom witnessed, so investigators have to reconstruct what happened from the evidence.
• The predator can usually be identified from a combination of signs: tracks, scats, and the way the animal was killed and eaten. Individual predators sometimes behave differently from their species’ usual pattern.
• Predation losses of large animals must come from a major injury (fractured skull, broken neck or back, or massive tissue damage and bleeding), because cattle, sheep and pigs rarely die of fright.
• Pseudo-predation is often hard to tell from predation. The authors suggest that the producer should probably be given the benefit of the doubt, and that pseudo-predation be assigned only to animals that were clearly ill, badly injured or weak when attacked.
• When disease or poisoning is suspected, a veterinarian or regional veterinary laboratory can confirm the cause of death.

4. How tracking was or was not used

This booklet is itself a guide to reading tracks and signs at livestock kill sites. Investigators are told to look for and record tracks, scat, hair, blood trails, drag marks, trampled vegetation, claw marks, tooth punctures, scratch marks near scent posts, scrapes and scratch hills, dig holes and covered kills, and to read the wounds and feeding pattern on the carcass. Track size, stride, toe and claw marks, and gait pattern (for example the bounding pattern of mink and weasels in snow) are given for the main predators. The authors note that wolf and large dog tracks may not be separable by tracks alone, so all the evidence at the site should be used.

6. Other technologies, skills or innovations

• Basic carcass examination (necropsy) skills: skinning wound sites, opening the chest and abdomen, breaking leg bones to check marrow fat, and floating lung tissue in water.
• A magnifying glass to check whether hide was cut by a knife.
• Good clear photographs to document the investigation.
• Rumen and stomach samples sent to a regional veterinary laboratory.

7. Implications for conservation (from the paper)

• Accurate identification of the predator is needed to choose the right control and prevention methods, to recommend changes in livestock management, and to pay compensation fairly.
• Some losses reflect management: young animals left unguarded, overgrazing, missing salt and minerals, and poor water supply can all leave livestock open to predation or poisoning. Closely watching expectant mothers and newborns less than a week old, and keeping head counts, are suggested.
• Higher berry crops can mean fewer black bear problems, and wolves take fewer livestock in Minnesota after severe winters, when weak young moose and deer are easier to catch.