A change of diet from rodents to rabbits (Oryctolagus cuniculus). Is the wildcat (Felis silvestris) a specialist predator?

1. What they did

Most studies of the wildcat’s diet have found that rodents are their staple food, which suggests they are rodent specialists. But some studies have found rabbits to be the main prey where rabbits live. The authors asked whether wildcats are true rodent specialists, or “facultative specialists” that switch to another rewarding prey, such as rabbits, when it is available.

They worked in central Spain, where wildcats are found throughout but rabbits occur only in patches:

• Choosing the areas. They searched trails for wildcat scats to find 29 areas with wildcats: 21 in Mediterranean vegetation (holm oak forest, scrub and pasture) and 8 in higher Pyrenean oak forest.
• Checking for rabbits. They searched each area for rabbit burrows and latrines. Rabbits were present in 15 of the Mediterranean areas and in none of the oak forests, giving 15 areas with rabbits and 14 without.
• Collecting scats (1997 to 1999). They walked at least 1 km of trail per area every season and collected 239 wildcat scats, holding 558 prey items. Prey were identified from bones and teeth.
• Comparing diets. They compared how often each prey type appeared (frequency of occurrence), the estimated weight of food eaten (consumed biomass) and diet diversity between areas with and without rabbits, between seasons, and between the two habitats.

2. What they found

Rabbits replace rodents

• Where rabbits were present, they were the main prey: found in 61% of scats and about 90% of the biomass eaten.
• Where rabbits were absent, rodents were found in 82% of scats, compared with 41% where rabbits were present.
• The same shift held when only Mediterranean areas were compared, so it was due to rabbits, not habitat. The rodents that rose most where rabbits were absent were the common vole and the wood mouse.
• Insectivores and reptiles were also eaten less where rabbits were present; birds and arthropods did not differ.

Seasons

• Where rabbits were present, rabbit remains peaked in summer (84% of scats) and were lowest in winter (17%). Rodents followed the opposite pattern: 89% in winter and 11% in summer.
• Where rabbits were absent, rodents stayed steady at about 82% all year, while insectivores, reptiles, birds and arthropods rose in spring or summer.
• Diet diversity was highest in summer and lowest in winter (more than twice as high), and slightly lower where rabbits were present.

Habitat

• In the absence of rabbits, wildcats ate more rodents in Mediterranean areas (97% of scats) than in Pyrenean oak forests (77%).
• In the oak forests they ate more reptiles, insectivores (especially white-toothed shrews and Iberian blind moles) and arthropods.
• Oak forest scats also held remains of two Iberian hares, an unidentified ungulate and a cat’s claw.

3. What they concluded

• Wildcats are not rodent specialists. They are opportunistic predators of small animals that eat according to what is available, with a strong tendency to specialize in rabbits where rabbits are present in their home range, and in rodents where there are none.
• Where prey is scarce, as in the Pyrenean oak forests, they behave like typical generalists.
• Rabbits are a highly rewarding prey: two to three adult rabbits or four young ones could meet a wildcat’s daily needs, compared with about 30 small rodents. Rabbits weakened by myxomatosis or rabbit haemorrhagic disease may also be easier to catch.
• The summer peak in rabbits fits the season when inexperienced young rabbits and sick adults are most available; wildcats turn to rodents in winter, when rabbits are harder to catch.
• The authors did not measure rabbit abundance, only presence or absence.
• The cat’s claw is, to their knowledge, the first reported case of a wildcat eating another cat: superpredation if it was a domestic cat, or cannibalism if it was a wildcat.

4. How tracking was or was not used

The study rests on signs. Trails were surveyed for scats both to confirm that wildcats were present in each area and to collect the scats for diet analysis. Wildcat scats were recognized using the methods of an earlier study (Lozano et al. 2003), which are not described in this paper. Rabbit presence or absence was judged by searching for rabbit burrows and latrines. No trailing was reported.

5. Tracker or observer certification

Not reported. The paper does not say who searched for and identified the scats, or how accurate scat identification was. This matters because the whole diet analysis depends on the scats being from wildcats rather than other carnivores.

6. Other technologies, skills or innovations

• Prey identified from bones and teeth in scats, using published identification keys.
• Prey biomass estimated from mean prey weights, with a seasonal formula for rabbits based on the share of young and adult rabbits taken.