# Diets of desert mule deer in altered habitats in the lower Sonoran Desert

> What does a desert mule deer eat when much of their range has been turned into cattle pasture? By examining plant fragments in deer and cattle dung from four ranches in Sonora, Mexico, the authors found 96 food plants, 69 never recorded for desert mule deer before. The deer lived mainly on shrubs and trees, while the introduced buffelgrass that fed the cattle barely featured in their diet.

Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/2012-alcala-galvan-krausman-diets-desert-mule-deer/

## Citation and access

- **Authors:** Carlos Hugo Alcala-Galvan and Paul R. Krausman
- **Year published:** 2012
- **Journal or source:** California Fish and Game
- **Full citation:** Alcala-Galvan, C. H. and Krausman, P. R. 2012. Diets of desert mule deer in altered habitats in the lower Sonoran Desert. California Fish and Game 98(2): 81–103.
- **Access status:** Hosted (freely available elsewhere)
- **PDF:** https://www.originalwisdom.com/wp-content/uploads/2026/11/2012_Alcala-Galvan_and_Krausman_diets-of-desert-mule-deer-in-altered-habitats.pdf

## Tags

- **Species:** Mammals > Domestic cattle; Mammals > Mule deer
- **Region:** North America > Mexico
- **Tracking:** Scat; Tracking
- **Behaviour and ecology:** Behaviour; Feeding
- **Methods and technology:** Descriptive statistics; Plot searches
- **Data type:** New field data
- **Observer qualification:** Not reported
- **Discipline:** Behaviour and ecology
- **Year published:** 2012

## Detailed keywords

- **Species:** Studied: desert mule deer (Odocoileus hemionus eremicus) and domestic cattle (diets compared at Rancho San Luis only). Present in all four areas but not studied: white-tailed deer (Odocoileus virginianus), collared peccary (Pecari tajacu), mountain lion (Puma concolor), coyote (Canis latrans), antelope jackrabbit (Lepus alleni) and desert cottontail (Sylvilagus audubonii); feral burros (Equus asinus) and black-tailed jackrabbit (Lepus californicus) also at El Americano. Food plants: 96 plant taxa in mule deer diets, including mesquite (Prosopis juliflora), ironwood (Olneya tesota), jojoba (Simmondsia chinensis), bird-of-paradise (Caesalpinia pumila), fairy duster (Calliandra eriophylla), chainfruit cholla (Opuntia fulgida), moradia (Glandularia delticola) and the introduced buffelgrass (Cenchrus ciliaris).
- **Location and habitat:** Four cattle ranches in central and western Sonora, Mexico: Rancho San Luis (54 km north of Hermosillo), Rancho La Jubaivena (14 km west of San Luis), Rancho La Pintada (52 km south of Hermosillo, at the base of Sierra Libre) and Rancho El Americano (25 km north of Puerto Libertad, Pitiquito). Plains of Sonora, Central Gulf Coast and Lower Colorado River Valley subdivisions of the Sonoran Desert: desert scrub with shrubs, small trees and cacti, much of it converted to buffelgrass pasture and grazed by cattle. Average annual rainfall from 320 mm (San Luis) to 180 mm (El Americano).
- **Topics:** diet composition; forage classes (browse, forbs, grasses, succulents); seasonal and regional variation in diet; diet overlap between wild and domestic herbivores; introduced buffelgrass pastures and habitat alteration; overgrazing; diet diversity and rainfall; fecal (dung) analysis; 69 plant species newly recorded as mule deer forage.
- **Statistics or models:** Microhistological analysis of plant fragments in feces (relative density); Morisita’s similarity index as modified by Horn (values over 0.60 counted as biological overlap); Shannon-Wiener diversity index (H’) with t-tests for paired comparisons between areas and seasons. Possible inconsistencies in the paper: in Appendix II the large values (for example 19.1 to 28.9% for mule deer) are printed on the “Mesquite mistletoe” row and small values on the “Mesquite” row, whereas Appendix I gives mesquite 24.0% and mesquite mistletoe under 1% at San Luis, so the two row labels look swapped. Moradia is named Glandularia delticola in the text but Verbena delticola in Appendix I, where Glandularia delticola is listed separately as hillside vervain. The text says “77 of the same plant species” were used by both herbivores at San Luis but also that “only 45” were used by both in at least one season, and the abstract gives 45.
- **Data type:** New field data: dung collected monthly from January 1991 to December 1992 at Rancho San Luis (mule deer and cattle), and in 2002, 2003 and 2004 at La Jubaivena, La Pintada and El Americano (mule deer only).

## Synopsis

### 1. What they did

Large parts of central Sonora, Mexico, have been overgrazed by cattle and turned into pasture of buffelgrass, a grass brought in from elsewhere. By the 1990s it covered 1.2 to 1.6 million hectares of Sonoran rangeland. Nobody knew how this affects wildlife, and the diets of desert mule deer had never been described in the Sonoran Desert of Mexico. The authors set out to describe what desert mule deer eat there, and to compare the diets of mule deer and cattle where buffelgrass pastures occur.

- Study areas. Four ranches in central and western Sonora, from the wetter Plains of Sonora (320 mm of rain a year) to the dry Central Gulf Coast (180 mm). Buffelgrass covered 27% of one area, over 50% of another, and under 2% of the driest area.

- Collecting dung. At Rancho San Luis (1991 and 1992), all old pellets were cleared from 1200 permanent circular plots along 24 transects, and every mule deer pellet group that appeared was collected each month. Cattle dung was collected from plots where cattle gathered (water, resting places, salt licks). In the other three areas (2002 to 2004), at least 18 fresh mule deer pellet groups were collected each month across the area, during a radio-tracking study of the deer.

- Reading the plant fragments. In the laboratory, samples were pooled by season and year, and plant fragments in the dung were identified under a microscope against reference slides. Plants were grouped as browse (shrubs and trees), forbs (herbaceous plants), grasses and succulents (cacti).

- Comparing diets. They measured how much the diets of mule deer and cattle overlapped in each season, and how varied (diverse) the mule deer diet was in each area and season.

### 2. What they found

What mule deer ate

- 96 plant species: 45 browse, 33 forbs, 12 grasses and 6 succulents. 69 of these had never been reported as food for desert mule deer.

- Browse was the main food in every area, 77% to 88% of the yearly diet. Mesquite, ironwood, jojoba, bird-of-paradise and fairy duster each made up 10% or more of the diet somewhere.

- Forbs made up 5% to 10% on average, rising during or after the summer and winter rains, when annual plants appear.

- Grasses were eaten least: under 1% of the yearly diet at La Jubaivena and El Americano, 2% at La Pintada and 9% at San Luis. At San Luis, grasses made up 45% and 19% of the summer diet in 1991 and 1992, mostly native grasses.

- Buffelgrass was not important for mule deer: at most 5% of the summer diet and under 1% of the yearly diet, even though it was plentiful.

- Cacti varied most between areas, from 2% of the diet at El Americano to 12% at La Pintada. Chainfruit cholla was the cactus eaten most, found in the diet in all areas.

What cattle ate (Rancho San Luis)

- 57 plant species. Grasses made up 57% of the diet, browse 30%, forbs 9% and cacti 4.5%.

- Buffelgrass was the cattle’s most important food, 21% of the diet, eaten most in summer and autumn.

- Ironwood and mesquite, the two most important browse plants for the deer, were also the most important browse plants for cattle. Cattle ate the most browse in spring (45%).

Overlap and diversity

- Mule deer and cattle shared 45 food plants, but their diets only overlapped in a meaningful way in spring (Morisita index 0.67). Overall overlap was 0.50, below the 0.60 the authors count as overlap.

- The variety of plants in the deer diet differed only a little. The only significant difference between areas was between the wettest (San Luis) and the driest (El Americano), with the driest area having the most varied diet.

### 3. What they concluded

- As elsewhere in their range, desert mule deer in Sonora live mainly on browse, and their diet changes with area, season and year, following what plants are available.

- The high use of grasses at Rancho San Luis may reflect the good cover of native grasses there, but the authors say this is not conclusive and needs more research.

- Diet diversity followed rainfall: the drier the area, the more varied the diet.

- Buffelgrass, widespread in the Plains of Sonora, is little used by desert mule deer.

- Habitat altered for cattle, with fewer shrubs and trees for cover and browse, is a challenge for managing and conserving desert mule deer in northwest Mexico.

### 4. How tracking was or was not used

Tracking was not a focus of the study. The whole study rests on collecting dung (scat) and attributing it to mule deer or cattle: mule deer pellet groups were gathered from cleared plots and across the study areas. The paper does not say how mule deer pellets were told apart from those of other animals, although white-tailed deer, collared peccary and feral burros were also present.

### 5. Tracker or observer certification

Not reported. The paper does not say who collected or identified the pellet groups in the field, or how. Field assistants are thanked by name. The laboratory technician who identified plant fragments under the microscope is described as experienced and tested for reliability, but that concerns the plant identification, not the dung identification.

### 6. Other technologies, skills or innovations

- Microhistological analysis: identifying plant fragments in dung under a microscope (100 times magnification) against reference slides made from local plants.

- Permanent, pre-cleared pellet plots, so that each month’s collection held only fresh dung.

### 7. Implications for conservation (from the paper)

- Desert mule deer rely on browse, so the loss of shrub and tree cover and browse in habitat altered for cattle is a challenge for their conservation in northwest Mexico.

- Buffelgrass pastures, which now cover large areas, add little food for desert mule deer.

- Knowing the main food plants of desert mule deer, and how they relate to each other, is essential for improving habitat.

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

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

- Dung studies like this depend on correctly identifying each pellet group in the field. Where similar species share the area (here white-tailed deer and mule deer), reporting how scat was identified, and by whom, would help readers judge the results.

## Cite this summary

Lawrence, K. 2026. Summary of: Diets of desert mule deer in altered habitats in the lower Sonoran Desert (Alcala-Galvan and Krausman, 2012). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/2012-alcala-galvan-krausman-diets-desert-mule-deer/