Ontogenetic and seasonal variation in diet was examined for 11 species of insectivorous forest-floor frogs and lizards from a lowland wet forest in north-eastern Costa Rica. Specimens were collected systematically over an entire seasonal cycle and represented individuals of all sizes. Individual prey items were removed from stomachs of preserved specimens, measured and identified. Ontogenetic shifts in prey size were pervasive. Ontogenetic shifts in prey composition were limited to four species; these were not the species with greatest range in body size, nor the species with the broadest diets. Small prey types (ants, mites, collembolans) decreased in representation and large prey types (roaches, orthopterans, millipedes) increased in importance over ontogeny; this could be because prey selection is based primarily on prey size or because of different prey preferences among age classes. There is little evidence for size-structure in this assemblage. There is no evidence that total availability of arthropod prey varies among seasons, but some evidence that preferred prey are less common in the wet season. Diet was similar between lizards and frogs. Lizards were more likely to have empty stomachs, but also greater stomach volume, than frogs; this indicates a difference in food-gathering strategies. Our study indicates strong similarity between frogs and lizards in diet despite enormous differences in physiology and behaviour.

The diet and pattern of food resource use by the pygmy skunk Spilogale pygmaea, an endemic and threatened species of western Mexico, was evaluated in the tropical dry forest of Chamela, Jalisco. Analysis of scats (n = 104) and stomach contents (n = 5) obtained during 1997, 1998 and 2000 showed that pygmy skunks fed mainly on invertebrates. Insect larvae constituted the most represented food item in samples. During 2000, food resource use was quantified by comparing occurrence of available prey with occurrence of items found in scats. Even though pygmy skunks seem to be opportunistic foragers, some invertebrates were positively selected, such as insect larvae and Myriapoda, thus suggesting that pygmy skunks may target prey of high nutritional value. The diet varied considerably between consecutive dry and rainy seasons of the studied years, with little overlap in food items. Pygmy skunks may adjust food resource use in response to temporal variations in prey abundance, by incorporating other food items in their diet during the dry season, when food is scarce. Dietary switching between seasons indicates that pygmy skunks may exhibit strategies similar to those of other tropical carnivores to deal with a highly seasonal environment.

This study describes the diet composition of 42 rainbow trout, Oncorhynchus mykiss (Walbaum, 1792) (90-480 mm TL), capturedin May 1995 in the Urederra River (North of Spain). Rainbow trout of all sizes fed mainly on midge (adults, larvae andpupae), but there were some differences in the feeding habits of small and large fish. We found that as the trout grew larger terrestrialprey became the most important food item. Rainbow trout avoided Leuctridae and showed some preference forEphemeroptera, Diptera larvae and Nemouridae larvae. Native fish predation and exploitation of the same trophic resources inthe Urederra River, could negatively affect native fishes, such as European minnow,Phoxinus phoxinus L., 1758 or brown trout, Salmo trutta L., 1758.

Predation by wolves Canis lupus on roe deer Capreolus capreolus was studied by scat analysis in five areas of the Province of Arezzo, north-eastern Tuscany, Italy. In the intensive study area (ISA) roe deer represented 19.1% of mean per cent volume (MPV) while in the other areas its use ranged between 10.9% and 53.4% of MPV. A low degree of variation was found in both annual and seasonal use of roe deer, although seasonal differences were more marked in those areas where roe deer use was lower. In ISA, roe deer was negatively selected among species: the Ivlev's electivity index ranged between −0.41 and −0.89. Analysing intra-specific selection, in ISA <1-year-old individuals were preferred by wolves, mainly during the fawns' first months of life. This trend was confirmed in the other areas, where fawns represented more than 50% of the relative number of roe deer prey. In ISA, the use of roe deer (as MPV) was not correlated with its density or with that of the main prey, wild boar, and in almost all the other areas no relation between use and density of roe deer was founded. However, in the one area where both roe deer density and use were the highest, these two variables seemed to exhibit a comparable trend. The use of roe deer was negatively correlated with the percentage of forest cover among all the study areas.

The diets of larvae and juveniles (cut-off size: 20 mm) of Limnothrissa miodon (Boulenger) were studied at 2-h intervals during four 24-h cycles (two during the rainy and two during the dry season) in the Bukavu Basin, Lake Kivu. Larvae and juveniles are both diurnal feeders, and they both feed essentially on copepods, which are the most abundant prey in littoral areas, but they show a marked preference for larger organisms (cladocerans), when available. This indicates a rather intense resource sharing, and probable competition between life stages, which is partly solved through spatial behaviour and segregation. During the dry season, when food resources are scarcer, larvae and juveniles make slightly offset inshore migrations during the day, so that they feed at different places, on copepods of different sizes. Because diel migrations are size-structured, it is suggested that cannibalistic pressure (by adults over juveniles, and by juveniles over larvae) may also be a driving factor for these migrations. Plankton samples revealed that there were few cladocerans, while copepods were abundant and their size was similar to that prior to the introduction of L. miodon in Lake Kivu, thereby suggesting that some form of dynamic equilibrium has been reached in the food web.

Food habits of tigers Panthera tigris in terms of prey abundance were studied in the semi-arid deciduous forests of Ranthambhore National Park, western India, between November 2000 and April 2001. Wild prey availability was assessed by line transects (n=8) and prey selection by the tigers was determined from analysis of scats (n=109). Compared to some other parts of the country, prey abundance was found to be high at 96.65 animals km−2. Chital Axis axis was the most abundant wild prey in the study area, followed by common langur Presbytis entellus, sambar Cervus unicolor, nilgai Boselaphus tragocamelus, wild pig Sus scrofa and chinkara Gazella bennetti. Chital (c. 31%) and sambar (c. 47%) constituted the bulk of the tigers' diet and were preferred prey. Nilgai and chinkara contributed minimally to the tigers' diet (c. 5–7% and <1%, respectively) and were used less than their availability. Domestic livestock made up 10–12% of the tigers' diet. The average weight of an animal consumed was between 107 and 114 kg reflecting a preference for large prey. The analysis reveals that parts of Ranthambhore have high prey abundance, thus making it important for long-term tiger conservation. Despite the high prey abundance, tigers were still considerably dependent on domestic livestock, posing challenges for the park management to resolve potential areas of conflict.

Factors influencing prey selection by insectivorous bats are poorly understood but may be related to interspecific differences in echolocation call structure. The diet of Eptesicus fuscus was compared with prey abundance across a foraging season to examine prey selection by a bat species which has an echolocation call dominated by a frequency-modulated (FM) component. Guano samples were collected on 18 occasions from a single colony between May and September 2000. Abundance of aerial insects was measured using a black-light trap on nights when guano was collected. Regression analysis was used to test the hypotheses that E. fuscus: (1) does not take prey in proportion to their relative abundance; (2) forages preferentially for beetles in a manner predicted by foraging theory. Relative abundance (= proportion in relation to other prey types) of prey in trap samples was not a good predictor of prey in the diet across periods or within periods, which suggests selective foraging. Beetles (42–96% of the diet by per cent volume) were consistently eaten in higher proportions than their relative abundance. The absolute abundance of beetles (= abundance irrespective of the abundance of other prey types) explained 60% of the variation in beetle use with more beetles eaten when they were abundant. Absolute beetle abundance explained 66%, 53% and 47% of the variation in the use of three other prey types, with more of these prey eaten when beetle abundance was low. Finally, absolute beetle abundance explained 60% of the variation in diet breadth, which increased when beetle abundance was low. Our results agree with predictions derived from foraging theory and support the hypothesis that E. fuscus forages selectively for beetles, consuming a wider variety of prey when beetle abundance is low. These results are similar to those found for the greater horseshoe bat Rhinolophus ferrumequinum which has an echolocation call dominated by a constant-frequency (CF) component, and suggest that some FM bats may discriminate among prey taxa, at least at the ordinal level.

In this study the predation and fish prey selection of otters Lutra lutra L. living by eutrophic fish ponds on agricultural land and in a protected area of temperate climate in Hungary were investigated. The correlations between fish in the diet of the otters (by spraint analysis involved 1942 and 1280 samples for the two habitats) and the fish stock available (by harvest and sample fishing) were generally close. Prey selection was significantly related to selected species of a particular size range (P<0.01). The preference calculations were performed with Ivlev's index of preference (Ei, minimum −1, maximum +1). Regardless of species, the otters avoided (Ei=−0.51) fish heavier than 1000 g, with a preference for individuals weighing between 500 and 1000 g (Ei=0.79). No substantial or clear preference was observed in the weight range below 500 g (Ei=−0.02–0.38). The preference for fish in accordance with their characteristic sites of occurrence within the body of water was also significant (P<0.01). They avoided fish living primarily in open water (Ei=−0.64) and to a lesser degree those occurring near the pond bed (Ei=−0.22). They favoured fish inhabiting the area with a covering of aquatic plants (Ei=0.46), and showed a preference to a lesser degree for fish living in the shallow littoral regions (Ei=0.14). With the cessation of fish farming and the effect of the drastic changes which occurred in the vegetation, the otters fed substantially on the stock of alternative sources of prey such as amphibians and water insects as well as terrestrial animals, and at such times, depending on season, fish became a secondary source of prey.

The diet of the short-toed eagle (Circaetus gallicus) was studied during the breeding season by analysing pellets and remains generated by adults and nestlings. The raptor proved to be a specialist feeder, as snake prey comprised almost 95% of the diet, in both frequency and biomass. We gathered information on prey availability and prey size availability (1499 specimens of nine different species) by searching for snakes in the study area. Regressions of vertebra centrum length and dorsal-scale length on snout–vent length (SVL) of the snakes were used to calculate prey size. The taxonomic diet composition differed depending on the sample analysed – remains or pellets – but we failed to find between-year diet differences. Most of the snakes identified (140 out of 141) belonged to only three species, Malpolon monspessulanus, Elaphe scalaris, and Coluber hippocrepis. Other prey included Lacerta lepida, Natrix maura, Bufo bufo, and Alectoris rufa, and many secondary prey (prey from stomach of the prey) were also detected in the pellets. The three main prey species were consumed according to their availability in the study area, but the eagles selected on the basis of prey size. Large snakes within 700–1000 mm SVL were positively selected, whereas snakes under 600 mm SVL were negatively selected. Adult eagles consumed the same prey species as those carried to the nest to feed their single nestling, although prey given to nestlings proved larger in size and biomass, suggesting that adults consumed the smallest prey, reserving the largest for nestlings.

The feeding habits of the neotropical river otter Lontra longicaudis were studied in a headwater stream of the Atlantic Forest, south-eastern Brazil, for 17 months. The otters fed mainly on fish (93% of the scats), but invertebrates were also frequent items in the diet (78.9% of the scats), as observed for the same species in lentic habitats and for other species of Lontra as well. It is suggested that the high proportion of invertebrates in the diet in comparison to Lutra is related to differences in the dentition of the two genera. The observed seasonal variation in the diet of L. longicaudis was probably a result of fluctuations in the abundance of a main prey item, a megalopteran larva (Corydalus sp.). Prey selection, regarded as differences between rates of predation and relative abundance of food items, was demonstrated for the two most important groups of otter prey: fish and crustaceans. Although they are able to capture mobile prey, otters seem to prefer feeding on prey showing lower escape ability – among fish they select armoured catfish, and among crustaceans they select crabs.

Analysis of 904 small carnivore scats collected over a two-year period in a seasonal forest in the south-western Central African Republic yielded the remains of 732 shrews, rodents (<1 kg), and bats comprising at least 34 species. Most scats belonged to the long-nosed mongoose, Herpestes naso, the numerically dominant carnivore in the study area. Shrews were the principal small mammal prey with respect to number of individuals and frequency of occurrence. The mean monthly frequency of occurrence of shrews was 21.7% and of small rodents (<100 g) was 20.8%. Both shrews and small rodents occurred significantly more often in scats collected during dry season months, and live-trapping of rodents over a 22-month period revealed similar peaks in availability. In contrast to many mammalian carnivores, shrews did not appear to be used as an alternative prey source: not only did consumption levels of both prey types fluctuate in synchrony, but the availability of rodents apparently had no effect upon the likelihood of including shrews in the diet. Preferential use of small mammals by long-nosed mongooses was tested for the 10 rodent species for which abundance indices were calculated. Mongooses preyed selectively on several rodent species (Praomys spp., Deomys ferrugineus, Stochomys longicaudatus, and Grammomys rutilans), while the most common rodent in the study area, Hylomyscus spp., was found in scats at lower frequencies than expected. In accordance with the habitat specificities of these ‘preferred’ rodent prey, it is suggested that mongooses and perhaps other small carnivores were foraging in micro-habitats characterized by higher-than-average vegetation understorey thickness where the simultaneous rate of encounter with arthropods, their main prey, and shrews was apt to be high.