Mammalian Prey Digestibility by Bobcats

1. What they did

Bones, teeth, claws and hair are usually thought of as the parts of prey that pass through a predator undigested, and they are what researchers use to work out a carnivore’s diet from their droppings. An earlier study by Meriwether and Johnson (1980) showed that coyotes dissolve a good part of these remains, and that small prey are digested more fully than large prey. The authors ran the same kind of feeding trials with bobcats to compare the two predators.

• Measuring the prey. They dissected 10 gray squirrels and 10 eastern cottontails to find the average proportions of skeletal parts (bones, teeth and claws) and hair in each prey.
• Feeding trials. After weighing, 10 of each prey were fed to each of 3 bobcats in separate trials, so 30 squirrels and 30 cottontails were used in all.
• Recovering the remains. All droppings from one feeding trial were put together in a nylon bag and washed in an automatic clothes washer until the rinse water was fairly clear. The bags were tumbled dry in a clothes dryer, and the hair and skeletal remains were separated by hand and weighed.
• Comparing. They compared the share of bone and hair dissolved by the bobcats with the coyote results from the earlier study, which used identical methods.

2. What they found

Prey

Bone dissolved, bobcat

Bone dissolved, coyote

Hair dissolved, bobcat

Hair dissolved, coyote

Gray squirrel

99% (± 1)

91% (± 4)

93% (± 1)

80% (± 9)

Eastern cottontail

99% (± 1)

93% (± 2)

88% (± 5)

43% (± 12)

Values are means with standard errors. Coyote data are from Meriwether and Johnson (1980).

• Whatever the prey, bobcats dissolved 99% of the bones, teeth and claws they ate.
• Bobcats dissolved 93% of the hair of gray squirrels and 88% of the hair of eastern cottontails.
• The authors report these values as significantly higher than those for coyotes.

3. What they concluded

• When a predator eats larger prey, the larger mass of food in the gut probably shields bones and hair from digestive acids for longer than with smaller prey. So remains of smaller prey might be missing from coyote droppings more often than remains of larger prey, and the authors say this problem is even greater for bobcat droppings.
• They suggest caution when estimating the proportions of different foods in bobcat diets from scat analysis, because the importance of some food items is likely to be overestimated.

6. Other technologies, skills or innovations

• Droppings were cleaned in nylon bags in an automatic clothes washer and dried in a clothes dryer, then hair and skeletal remains were separated by hand and weighed.

7. Implications for conservation (from the paper)

• Diet estimates for bobcats based on scat analysis may be biased, because bobcats dissolve almost all the bone and much of the hair of the prey they eat.