# Effects of prey size, meal size, meal composition, and daily frequency of feeding on the recovery of rodent remains from carnivore scats

> How many mice does a coyote scat really hold? In feeding trials with captive coyotes, the share of mouse teeth that came through ranged from 1% to 24%, depending on how much and what else the coyote ate, and how often. Hair passed through undigested, so the authors suggest using teeth and bones to identify rodents in scats, and hair to judge how much of each was eaten.

Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/1997-kelly-garton-effects-prey-size-meal/

## Citation and access

- **Authors:** Brian T. Kelly and Edward O. Garton
- **Year published:** 1997
- **Journal or source:** Canadian Journal of Zoology
- **Full citation:** Kelly, B. T. and Garton, E. O. 1997. Effects of prey size, meal size, meal composition, and daily frequency of feeding on the recovery of rodent remains from carnivore scats. Canadian Journal of Zoology 75(11): 1811–1817.
- **DOI:** 10.1139/z97-810
- **Access status:** Publisher link only
- **Where to find it:** https://doi.org/10.1139/z97-810

## Tags

- **Species:** Mammals > Coyote
- **Region:** North America > United States
- **Tracking:** Bones; Hair; Scat; Tracking
- **Behaviour and ecology:** Behaviour; Feeding
- **Methods and technology:** Analysis of variance (ANOVA); Linear regression
- **Data type:** New field data
- **Observer qualification:** Not needed
- **Discipline:** Behaviour and ecology; Wildlife tracking
- **Year published:** 1997

## Detailed keywords

- **Species:** Studied: coyote (Canis latrans), captive. Prey fed: mice (Mus musculus) and rats (Rattus norvegicus and Neotoma micropus; the paper gives only scientific names for the rats). Filler: ground sheep meat. Other species discussed from earlier studies: domestic dog (Canis lupus), bobcat (Felis rufus) and ermine (Mustela erminea).
- **Location and habitat:** Feeding trials in outdoor covered kennels at the Logan, Utah, field station of the United States Department of Agriculture (USDA) Denver Wildlife Research Center, United States. Comparison scats from free-ranging coyotes in Curlew Valley, Utah.
- **Topics:** scat analysis; diet analysis; prey digestibility; recovery of hair, bone and teeth from scats; correction factors for scat analysis; feeding trials with captive animals; gastric retention time; meal size; meal composition and energy content; feeding frequency; bone to hair mass ratio (B:H) as an index of digestion; identifying small rodents from teeth and bones; apportioning scats to prey by hair. Inconsistencies in the paper: the sheep-meat filler in the 4-rat meals is 19% in Table 1 but 29% in the Results and Discussion; the 10-mouse filler is 78% in Table 1 but 79% in the Discussion; and the 2-rat filler is 63% in Table 1 and the Results but 66% in the Discussion. The Results say rat bone recovery showed “the same pattern” as mice, although the test was not significant (P = 0.0684) by the paper’s own 0.05 level.
- **Statistics or models:** two-factor and single-factor analysis of variance (ANOVA); Fisher’s least significant difference post-hoc tests; least-squares linear regression of the percentage of teeth recovered on B:H; square root, natural logarithm and arcsine transformations; significance level P < 0.05.
- **Data type:** New data from feeding trials with captive coyotes: first set of trials (T1) June to September 1986, second set (T2) April to May 1988. Field scats collected in Curlew Valley, Utah, in 1986.

## Synopsis

### 1. What they did

Researchers often work out what carnivores eat by picking apart their scats and identifying the hair, bones and teeth of prey. This assumes that a steady share of those remains comes out the other end. The authors tested that assumption with feeding trials on captive coyotes, asking how prey size, the number of prey, meal size and meal make-up affect how much of a mouse or rat survives digestion.

- The coyotes. In the first set of trials (June to September 1986), 20 coyotes (11 females, 9 males) aged 1.3 to 9.4 years; in the second (April to May 1988), 22 coyotes (8 females, 14 males) aged 1 to 9 years. Each trial fed a known number and mass of dead prey to one coyote.

- The prey. Mice (average 23.1 g) and rats (average 209.5 g and 253.4 g for the two rat species).

- Three approaches. (i) Varying the number of prey while keeping each meal at 600 g by adding a filler of ground sheep meat (higher in energy) or the other prey (rats with mice, mice with rats); (ii) varying the number of prey with no filler, so meal size changed; (iii) feeding the same prey over time (one rat every 4 hours or five mice every 2 hours) instead of as one meal a day.

- Collecting the scats. Food mixed with an undigestible red dye marked the start and end of each trial, so every scat from the trial meals could be collected. Scats were gathered every 2 hours, dried, washed and sieved, and the hair, bone and teeth were weighed and the teeth counted.

- Field comparison. They compared the ratio of bone mass to hair mass (B:H) in the trial scats with scats from free-ranging coyotes in Curlew Valley, Utah.

### 2. What they found

Teeth

- The share of teeth recovered depended on how prey were fed. For mice it ranged from 1% to 24.4%, and for rats from 13.8% to 52.5%.

- The fewest teeth were recovered when meals contained sheep meat. The most mouse teeth were recovered when mice were fed over time.

Bone and hair

- More mouse bone was recovered when mice were fed over time than when they were fed with sheep meat.

- Hair recovery did not differ by how prey were fed, so the authors treated hair as undigestible. Bone is digested.

- With sheep meat in the meal, bone and teeth recovery did not rise even when the mass of mice fed was four times greater or the mass of rats doubled. Only when the sheep meat was removed (the 50-mouse and 6-rat meals) did significantly more bone and teeth come through.

Bone to hair ratio (B:H)

- Because hair is not digested and bone is, B:H works as an index of digestion: the higher the value, the less the prey were digested.

- For mice, B:H fell as the share of sheep meat rose, and rose with meal size (large meals were digested less). Neither relationship was significant for rats.

- For both mice and rats, the percentage of teeth recovered rose with B:H.

- Scats from wild coyotes in Curlew Valley (25 scats, mouse-size prey only) had higher B:H values than any of the trial scats. However, 96% of scats contained bone when 40 mice were fed over time, close to the wild scats (all contained bone), compared with only 65% when 25 mice were fed at once.

### 3. What they concluded

- How much bone and teeth coyotes digest varies with prey size, meal size, meal make-up and how often prey are eaten. Hair digestion does not seem to be affected.

- The likely explanation is how long prey stay in the stomach’s acids. Higher-energy food (sheep meat) keeps prey in the stomach longer, so more is digested. Prey eaten one after another over time spend less time there and are digested less.

- By changing how and with what prey were eaten, they raised the share of mouse and rat teeth recovered by more than 2400% and almost 400%.

- Feeding prey over time gave results closer to wild scats, so feeding trials used to derive correction factors should take feeding frequency into account.

- They recommend using teeth or bones to identify the small rodents in a scat, and then a visual estimate or sample of hair to divide the scat among the prey present. They caution against using counts of teeth or diagnostic bones to work out how many prey, or how much prey, a scat represents without allowing for how variable their recovery is.

- B:H from all the scats of one meal explained much of the variation in tooth digestion, but applying it to field samples, where not all scats from a meal are collected, is untested and should be considered unreliable.

### 6. Other technologies, skills or innovations

- Ferric oxide, an undigestible red dye mixed into food, to mark the start and end of each trial so every scat from the trial meals was collected.

- Scats washed in nylon bags in a clothes washer, then separated through a 2.5 mm sieve.

- An interactive computer program (PROGRAM SCAT), from the senior author’s thesis, combines correction factors and gives variance and sample-size estimates.

### 8. Implications for tracking (Original Wisdom's observations)

_These are Original Wisdom's observations, not the authors'._

- For anyone reading prey remains in carnivore scats, the number of small rodent teeth or bones in a scat is a poor guide to how many prey were eaten: depending on the meal, as little as 1% of mouse teeth came through. Hair gave a steadier picture.

## Cite this summary

Lawrence, K. 2026. Summary of: Effects of prey size, meal size, meal composition, and daily frequency of feeding on the recovery of rodent remains from carnivore scats (Kelly and Garton, 1997). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/1997-kelly-garton-effects-prey-size-meal/