# Feeding habits and overlap among red fox (Vulpes vulpes) and stone marten (Martes foina) in two Mediterranean mountain habitats

> Do red foxes and stone martens compete for the same food? By sorting through 856 scats collected along mountain routes in Spain’s Sierra Nevada, researchers found their diets almost identical in a moist oak valley, but quite different in a dry pine and juniper valley, where martens climbed for berries that foxes largely ignored.

Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/2002-padial-avila-feeding-habits-overlap-among/

## Citation and access

- **Authors:** José M. Padial, Enrique Ávila and José M. Gil-Sánchez
- **Year published:** 2002
- **Journal or source:** Mammalian Biology (Zeitschrift für Säugetierkunde)
- **Full citation:** Padial, J. M., Ávila, E. and Gil-Sánchez, J. M. 2002. Feeding habits and overlap among red fox (Vulpes vulpes) and stone marten (Martes foina) in two Mediterranean mountain habitats. Mammalian Biology 67(3): 137-146.
- **DOI:** 10.1078/1616-5047-00021
- **Access status:** Publisher link only
- **Where to find it:** https://doi.org/10.1078/1616-5047-00021

## Tags

- **Species:** Mammals > Red fox; Mammals > Stone marten
- **Region:** Europe > Spain
- **Tracking:** Scat; Sign surveys; Tracking; Tracks and signs identification
- **Behaviour and ecology:** Behaviour; Carnivore coexistence; Feeding; Interspecific competition; Intraguild interactions; Predation
- **Methods and technology:** Chi-square test
- **Data type:** New field data
- **Observer qualification:** Not reported
- **Discipline:** Behaviour and ecology
- **Year published:** 2002

## Detailed keywords

- **Species:** Studied: red fox (Vulpes vulpes) and stone marten (Martes foina). Food remains found in scats (78 items in 14 categories; the paper gives most items by scientific name only): small mammals (Arvicola sapidus, Microtus duodecimcostatus, Apodemus sylvaticus, Eliomys quercinus, Mus spretus, Rattus rattus, Crocidura russula, Suncus etruscus, Talpa occidentalis); lagomorphs (Lepus granatensis, Oryctolagus cunniculus [sic]); carrion (Capra aegagrus f. hircus, Capra pyrenaica, Ovis ammon f. aries, Sus scrofa, Sus scrofa f. domestica); birds (Alectoris rufa, Columba sp., Otus scops, Turdus merula, Turdus sp., Pyrrhocorax phyrrocorax [sic]); reptiles (Elaphe scalaris, Malpolon monspessulanus, Natrix maura, Timon lepida, Psamodrummus algirus [sic]); arthropods (including Melolonta melolonta, Apis melifera, Mantis religiosa, Buthus occitanus, Scalopendra sp., beetles, grasshoppers, wasps); wild fruit (juniper Juniperus phoenicea, serviceberry Amelanchier ovalis, blackberries Rubus sp., fig Ficus carica, Celtis australis, Prunus sylvestris, Sorbus aria, Crataegus monogyna, Juniperus oxycedrus, Rosa sp., Rubia peregrina); cultivated fruit (Malus domestica, Pyrus communis, Vitis vinifera, plum, cherry, medlar); and others: stone marten (Martes foina) remains in both fox and marten scats, Mustela nivalis, eggs, honey, grass and rubbish.
- **Location and habitat:** Sierra Nevada National Park, south-eastern Spain (Iberian Peninsula), two river valleys in the Guadalquivir basin, 16 km apart. Mesic habitat: Genil river valley, 1200 to 1400 m above sea level, semi-humid supramediterranean, acid soils, dominant trees Quercus pyrenaica, Sorbus aria, S. torminalis, Castanea sativa, Cotoneaster granatensis, Quercus rotundifolia and Pistacea terebinthus, remains of humid forests from glacial periods, mean 11 °C and 800 mm rain a year, cattle grazing, game activities forbidden. Xeric habitat: Dilar river valley, 1000 to 1400 m, dry supramediterranean, calcareous soil, woodland of Pinus pinaster, P. halepensis and P. silvestris nevadensis with Juniperus phoenicea and Amelanchier ovalis, mean 14 °C and 600 mm rain, burned some years earlier, affecting its replanted P. pinaster forest. Note: the coordinates given for the xeric site (N41° 03’, E4° 53’) cannot be right for a valley 16 km from the mesic site (37° 08’ N, 3° 23’ E).
- **Topics:** diet, scat analysis, trophic niche breadth, trophic niche overlap, interspecific competition, coexistence of sympatric carnivores, frugivory (fruit eating), seasonal diet variation, food availability, intraguild predation (fox eating marten), habitat differences.
- **Statistics or models:** Frequency of occurrence (%F) and percentage of volume (%V) of food items; chi-square tests on contingency tables; Levins’ index B (niche breadth); Pianka’s index (niche overlap), based on %V. Inconsistencies: the abstract says the fox’s niche breadth was higher in the mesic habitat, but Table 1 gives 3.80 (mesic) and 5.76 (xeric); the abstract names Morus ulmifolius fruit as a main marten food in the xeric habitat, but no such item is in Table 2 (blackberries, Rubus sp., are); in Table 2 some values look misprinted (marten reptiles in the xeric habitat %F 0.0 but %V 0.9; Hiulus sp. %F “10”; Mus spretus in mesic fox scats %F 0.2 but %V 4.5).
- **Data type:** New field data: scats collected monthly from April 1997 to March 1998 along one route in each habitat (cleared of old scats in March 1997). 856 scats in total: 178 mesic (104 marten, 74 fox) and 678 xeric (546 marten, 132 fox).

## Synopsis

### 1. What they did

Red foxes and stone martens are both opportunists that eat a bit of everything, and they live side by side in the Sierra Nevada mountains of southern Spain. The authors wanted to know how much their diets overlap, and whether that changes between habitats and seasons.

They chose two river valleys 16 km apart in Sierra Nevada National Park: a moister (“mesic”) valley with oak and chestnut woods, and a drier (“xeric”) valley with pine, juniper and serviceberry. In each valley they picked one route, cleared it of droppings in March 1997, and then two or three people collected all fox and marten scats along it in the first week of every month, from April 1997 to March 1998.

They collected 856 scats, washed and sieved them, and identified 78 food items, which they grouped into 14 categories. For each species, habitat and season they worked out how often each food appeared and what share of the scat volume it made up, how varied the diet was (diet breadth), and how much the two diets overlapped.

### 2. What they found

Moist (mesic) valley

- The two diets were very similar, and overlap was high all year (overall Pianka index 0.92, where 1 means identical diets). It peaked in winter (0.99), when snow and frost would make food scarce.

- Both species ate mostly small mammals (including voles and mice), carrion (mainly domestic goat and Iberian ibex, Capra pyrenaica), insects, cultivated fruit and berries.

- Martens’ share of carrion was much higher here than in the dry valley (25% of scats against 3%).

Dry (xeric) valley

- The diets were clearly different. Overlap was moderate over the year (0.47), highest in spring (0.54) and lowest in autumn (0.25).

- Martens ate mainly small mammals and the fruit of juniper (Juniperus phoenicea) and serviceberry (Amelanchier ovalis). Serviceberry mattered most in summer and juniper in winter; juniper appeared in 28% of marten scats.

- Foxes ate mainly carrion, small mammals and rabbits (rabbit in 23.5% of fox scats), with some cultivated fruit.

Other findings

- Foxes relied on small mammals, carrion and cultivated fruit in both valleys.

- Marten diets differed significantly between the two valleys; marten diet breadth was higher in the dry valley.

- Marten remains turned up in fox scats six times (two in the moist and four in the dry valley), all in spring or summer.

### 3. What they concluded

- Habitat strongly shaped how much the two diets overlapped, mainly through how much small fruit (mostly berries) was available. Fruit was more worthwhile for martens than for foxes.

- Martens seemed more adaptable than foxes, probably because they are smaller and climb, so they can reach small berries in trees and bushes.

- Competition between the two may be possible in the moist valley, but it did not appear strong enough to decide where each species lives.

- The marten remains in fox scats could be cases of intraguild predation, where one predator kills another, as foxes are known to limit small mustelid and pine marten populations.

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

The whole study rests on scats: finding them along set routes each month and assigning each one to fox or marten. The paper does not say how the scats were identified to species (for example by size, shape, smell, placement or accompanying tracks), and no checks such as DNA were reported. With 678 scats from the dry valley and 546 of them assigned to marten, the accuracy of that sorting matters to every result.

### 5. Tracker or observer certification

Not reported. The scats were collected by “two or three people”, and the acknowledgements thank naturalists of the Signatus group and others for field help, but nothing is said about who identified the scats or how their skill was checked.

### 6. Other technologies, skills or innovations

- Standard scat analysis: drying, washing and sieving.

- Levins’ index for diet breadth and Pianka’s index for diet overlap.

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

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

- Diet studies built on scat collection depend on telling one species’ scat from another’s, here fox from stone marten, yet the method is not described. Readers cannot judge how many scats may have been misassigned, which could affect the overlap results.

- Clearing a route of old scats and then collecting at a fixed time each month is a simple way to make sure each sample covers a known period.

## Cite this summary

Lawrence, K. 2026. Summary of: Feeding habits and overlap among red fox (Vulpes vulpes) and stone marten (Martes foina) in two Mediterranean mountain habitats (Padial and Ávila et al., 2002). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/2002-padial-avila-feeding-habits-overlap-among/