# Local feeding specialization of the red fox (Vulpes vulpes) in response to eastern cottontail (Sylvilagus floridanus) introduction (NW Italy)

> What does a generalist eat when a new prey moves in? After American eastern cottontails spread into a nature reserve on Italy’s River Po, scats showed that red foxes there became cottontail specialists: lagomorphs rose from about a quarter of fox scats to three quarters, and the foxes’ diet narrowed by half. As a bonus, foxes and badgers now overlap far less in what they eat.

Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/2005-balestrieri-remonti-local-feeding-specialization-red/

## Citation and access

- **Authors:** Alessandro Balestrieri, Luigi Remonti and Claudio Prigioni
- **Year published:** 2005
- **Journal or source:** Hystrix, the Italian Journal of Mammalogy
- **Full citation:** Balestrieri, A., Remonti, L. and Prigioni, C. 2005. Local feeding specialization of the red fox (Vulpes vulpes) in response to eastern cottontail (Sylvilagus floridanus) introduction (NW Italy). Hystrix, the Italian Journal of Mammalogy (n.s.) 16(2): 113–126.
- **DOI:** 10.4404/hystrix-16.2-4349
- **Access status:** Hosted (freely available elsewhere)
- **PDF:** https://www.originalwisdom.com/wp-content/uploads/2026/11/2005_Balestrieri_and_Remonti_etal_local-feeding-specialization-of-the-red-fox-in-response-to-eastern-cottontail-introduction.pdf

## Tags

- **Species:** Mammals > Red fox
- **Region:** Europe > Italy
- **Tracking:** Scat; Sign surveys; Tracking
- **Behaviour and ecology:** Behaviour; Feeding; Interspecific competition; Predation
- **Methods and technology:** Chi-square test; Descriptive statistics
- **Data type:** Existing data; New field data
- **Observer qualification:** Not reported
- **Discipline:** Behaviour and ecology
- **Year published:** 2005

## Detailed keywords

- **Species:** Studied: red fox (Vulpes vulpes). Compared with existing data: Eurasian badger (Meles meles), a possible competitor for food. Main prey: eastern cottontail (Sylvilagus floridanus), an introduced North American rabbit. Other food remains in fox scats: common dormouse (Muscardinus avellanarius), water vole (Arvicola terrestris), fat dormouse (Myoxus glis), bank vole (Clethrionomys glareolus), Microtus voles, rats (Rattus sp.), wood mice (Apodemus sp.), house mouse (Mus domesticus), insectivores, small songbirds (Passeriformes), ducks and their relatives (Anseriformes), beetles (Coleoptera), grasshoppers and crickets (Orthoptera), Hymenoptera, carrion of a stone marten (Martes foina), and fruits including American pokeweed (Phytolacca americana) and wayfaring tree (Viburnum lantana). Also in or near the study area: European hare (Lepus europaeus); wild rabbit (Oryctolagus cuniculus), which died out there in the early 1990s after disease outbreaks. Other introduced mammals of NW Italy named: coypu (Myocastor coypus), grey squirrel (Sciurus carolinensis) and Finlayson’s squirrel (Callosciurus finlaysoni).
- **Location and habitat:** Garzaia di Valenza Natural Reserve, province of Alessandria, south-east Piedmont, north-western Italy, on the left bank of the River Po. About 250 ha of flat land: poplar plantations (25.3%), rice fields (17.0%), woods of willow, poplar and alder along an abandoned river meander (17.1%), cereal crops (13.4%), dry gravelly ground with tall herbs and black locust shrubs (9.5%), three naturalized artificial lakes (9.4%) and flood drift near the riverbed (8.1%). Trees and shrubs with edible fruits are rare.
- **Topics:** diet analysis; scat analysis; alien (introduced) prey species; predation on introduced species; prey switching; local (realized) feeding specialization of a generalist predator; optimal foraging theory; trophic niche breadth; niche overlap and competition for food between red fox and badger; the specialist-generalist continuum; seasonal diet; foxes as a possible limiting factor for an introduced species.
- **Statistics or models:** Frequency of occurrence (F%), relative frequency of occurrence (RF%), percent volume (V%) and mean percent volume (Vm%); Levins’ B index of niche breadth; Pianka’s O index of niche overlap; chi-square tests with the sequential Bonferroni correction; Spearman’s rank correlation; multiple regression with backward elimination (on four seasonal values, N = 4). Inconsistencies in the paper: (1) the results for the cottontail breeding period are labelled “1988/89” and “1999/00”, although both should be from this study (1998 to 2000), so “1988/89” is probably a typo for 1998/99; (2) the Results give a lagomorph frequency of 27.3% in fox scats before cottontails arrived, while the Discussion says lagomorphs made up only 23% of the overall diet then (possibly a different measure); (3) Fedriani et al. is cited as 1998 in the text but listed as 1988 in the references.
- **Data type:** New field data: 115 fox scats collected monthly, June 1998 to February 2000 (winter 30, spring 24, summer 39, autumn 22). Existing data: fox and badger diet in the same area in 1988 to 1989 (Canova and Rosa 1994) and badger diet in 1998 to 2000 (Balestrieri et al. 2004). Volume 16 is dated 2005; the journal’s online record gives 2006.

## Synopsis

### 1. What they did

Red foxes are the classic generalist, eating whatever food is plentiful in each place and season. The authors asked what happens when a new, abundant prey arrives. The eastern cottontail, a rabbit native to the Americas, was introduced to Piedmont in north-western Italy in the mid-1960s and reached their study area, a 250 ha nature reserve on the River Po, in the mid-1990s. By the end of 2000 there were more than 15 cottontails per km² there. The native wild rabbit had died out in the area in the early 1990s, and hares were always scarce.

- Collecting scats. Each month from June 1998 to February 2000 they walked a 4.1 km transect through the main habitats and collected 115 fox scats.

- Analysing them. In the laboratory the scats were washed through sieves, and food remains were identified: mammal hairs under the microscope with reference keys, feathers, reptile and amphibian remains, insect parts, fruit seeds, and earthworm bristles.

- Comparing. They compared their results with fox and badger diets recorded in the same area in 1988 to 1989, before the cottontails came, and with badger diet in 1998 to 2000. They measured how wide each diet was (niche breadth) and how much the fox and badger diets overlapped.

### 2. What they found

Fox diet, 1998 to 2000

- Foxes ate mostly meat. Mammals were in 93.9% of scats and made up 87.7% of the diet by volume.

- Lagomorphs (rabbits and hares), which the authors attribute almost entirely to cottontails, were by far the main food: in 75.6% of scats and 68% of the diet by volume.

- Rodents made up 17.2%, mainly common dormice and water voles. Birds, mostly small songbirds, made up 6.6%. Everything else was under 5%; fruit was eaten only occasionally (1%).

- Lagomorphs were the main food in every season. Only insect eating changed with the season, peaking in summer.

- How often foxes ate lagomorphs did not change between the cottontail breeding season (February to September) and the rest of the year.

- The more lagomorphs foxes ate in a season, the narrower their diet. Diet was narrowest in winter and widest in spring. Birds were eaten more when rodents were eaten less.

Before and after cottontails

- Before cottontails arrived (1988 to 1989), lagomorphs were in only 27.3% of fox scats, against 75.6% afterwards, even though wild rabbits were plentiful then. Foxes also used to eat maize (in 24.2% of scats); after the cottontails arrived, none was found.

- Fox niche breadth halved, from 0.64 to 0.31.

- Badger niche breadth hardly changed (0.54 to 0.49). Badgers did eat more earthworms and frogs and less Prunus fruit in 1998 to 2000.

- Diet overlap between foxes and badgers fell from 0.59 to 0.13.

### 3. What they concluded

- In this area foxes act as local specialists on cottontails. Their diet is dominated by one food, and that food is used steadily through the year. This is a “realized” specialization of a typical generalist, which the authors explain with optimal foraging theory: predators should favour the most profitable prey.

- Cottontails are very profitable prey. They offer about 35 times the body mass of most voles and mice, breed quickly, and, unlike wild rabbits, do not dig burrows, so they (especially the young) may be more exposed to foxes.

- The few other foods foxes ate (dormice, water voles, songbirds) live in the same dense, bushy field margins and hedgerows that cottontails favour, so foxes may simply come across them while hunting cottontails.

- Because foxes now focus on cottontails while badgers eat mainly earthworms and maize, the two species compete less for food, especially in summer, when drought makes earthworms scarce and badgers look for other protein.

- Foxes may limit this introduced species, whose effect on native hares is still unknown. More research is needed on how fox specialization affects competition with other local predators, such as stone martens.

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

Fox scats were collected monthly along a fixed 4.1 km transect, and the food remains in them were identified in the laboratory. The paper does not say how the scats were recognized as fox scats in the field (for example by size, shape, smell or location), and no other check of identity, such as DNA, is reported.

### 5. Tracker or observer certification

Not reported. The paper does not say who collected the scats or how they were identified as fox scats, although all the diet results depend on that identification. Laura Gola and Barbara Zappia are thanked for help with the field research.

### 6. Other technologies, skills or innovations

- Scat analysis following Kruuk and Parish (1981) and Prigioni (1991): scats washed through sieves of 1.5, 0.3 and 0.1 mm mesh, with the finest sediment checked under a microscope for earthworm bristles.

- Mammal hairs identified at 20x and 40x magnification with a hair atlas; feathers, reptile and amphibian remains with published keys; insects and fruit seeds with reference collections.

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

- Introduced species can change native ecosystems in many ways, and serving as prey for native predators is probably the most overlooked.

- Cottontails were introduced for hunting but are rarely shot, because hunters prefer hares. Foxes may act as a limiting factor for this introduced species, whose impact on native lagomorph populations is still unknown.

- By specializing on cottontails, foxes may reduce competition for food with badgers.

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

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

- The whole study rests on scats gathered along a transect and correctly assigned to fox, but how that identification was made is not described. Where red fox scats could be confused with those of other carnivores in the area (the paper mentions badgers and stone martens), reporting how scats were identified would help readers judge the results.

## Cite this summary

Lawrence, K. 2026. Summary of: Local feeding specialization of the red fox (Vulpes vulpes) in response to eastern cottontail (Sylvilagus floridanus) introduction (NW Italy) (Balestrieri and Remonti et al., 2005). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/2005-balestrieri-remonti-local-feeding-specialization-red/