FOOD HABITS OF WILDEBEEST, ZEBRA, HARTEBEEST AND CATTLE IN KENYA MASAILAND

A study was conducted of grass selectivity shown by four herbivores on open range lands of Kenya Masailand. At four seasons over one year, wildebeest, zebra and kongoni (Coke's hartebeest) were taken. Stomach materials and faeces were sampled from each animal. Faecal samples were collected from cattle that had been grazing in the same area. Simultaneously, vegetation availability assessments were made. A comparison of techniques for determining the food selectivity indicates that faecal and stomach-content analyses provide similar results when the diets are almost entirely grass. The selectivity exhibited by the four herbivores was determined by faecal analyses. Three grass species were preponderant in all diets as well as in the available menu. In comparing the selectivity shown for the three dominant grasses there is a high degree of similarity even though statistical differences are demonstrated. All animals favoured Themeda triandra over Pennisetum mezianum and Digitaria macroblephara. Kongoni displayed the highest degree of selectivity and cattle and zebra had the greatest similarity in diets. Each animal species had a wide spectrum of grasses in their diets: these contained a greater number of species during the drier seasons than during the rainy seasons. Wild animals had a greater diet variation between seasons than did cattle, the diet of the latter remaining much more consistent than the combination of available grasses.     

Resource partitioning between sympatric wild and domestic herbivores in the Tarangire region of Tanzania

The effect of the introduction of an exotic species (cattle) into a native African herbivore assemblage was investigated by studying resource partitioning between zebu cattle, wildebeest and zebra. Resource partitioning was investigated by analysing grass sward characteristics (such as sward height and percentage nitrogen in leaves) of feeding sites selected by the different herbivore species. Linear discriminant analysis was used to determine whether a distinction could be made between feeding sites selected by the different animal species or whether the animal species showed overlap in resource use by selecting similar feeding sites. Wildebeest and zebra did not show overlap in resource use except in the wet season when resources were ample. Cattle showed overlap in resource use with zebra in the early wet season and with wildebeest in the early dry season, seasons when food limitation is likely. In the wet season, cattle showed overlap in resource use with both zebra and wildebeest. Implications of these results for competitive relationships between livestock and wildlife are discussed. We suggest that interpretation of overlap in resource use may be different for an assemblage of long-term coexisting native species as compared to an assemblage of native and exotic species. Among native herbivores, overlap in resource use is not expected based on evolutionary segregation. In a native assemblage to which an exotic species has been introduced, however, overlap in resource use can occur under food-limited conditions and consequently implies competition. Received: 1 September 1998 / Accepted: 20 April 1999     

Grass greenness and grass height promote the resource partitioning among reintroduced Burchell's zebra and blue wildebeest in southern Mozambique

Differences in the selection of habitat and specific dietary items support resource partitioning and coexistence of sympatric African grazing herbivores, such as zebra and wildebeest. In Maputo Special Reserve (MSR), southern Mozambique, these two species were extirpated during the civil war (1977–1992); since 2010, they have been reintroduced into the Reserve. Identifying the resource selection by reintroduced species and how these species coexist, while utilising the same resources, is both of ecological interest and important for the management of wildlife communities and parks. This is a key application of our research. Therefore, the present study investigated resource partitioning between Burchell's zebra (Equus burchelli, Smuts 1832) and blue wildebeest (Connochaetes taurinus, Burchell 1823) in the MSR. We conducted the study from July 2016 to June 2017. The data were collected by direct observation, driving the vehicle along the reserve's roads that covered the vegetation communities where zebras and wildebeest are known to commonly occur. The composition of the diet and specific features of the grass grazed by the two species, including greenness, height, and the number of stems, were assessed. The widely available grass, Aristida barbicollis, contributed most to the diet of both herbivores. The dietary overlap between the two herbivores was higher during the dry season (95%) than wet season (86%). Resources partitioning appears to be determined, principally, by the height and greenness of the grass, with the zebra grazing taller grass, which may facilitate the access of the wildebeest to the greener, lower proportion of the forage. That results follow the expectation that, among native herbivores, overlap in resource use is not expected based on evolutionary segregation.     

Modelling ungulate dependence on higher quality forage under large trees in African savannahs

In African savannahs, large trees improve grass quality, particularly in dry and nutrient poor areas. Enhanced below-canopy grass nutrients, such as nitrogen and phosphorus contents should therefore attract and benefit grazers. To predict whether ungulates really need these forage quality islands we focused on four grazer species, i.e., zebra, buffalo, wildebeest, and warthog, differing in body size and digestive system. We confronted literature estimations of their feeding requirements with forage availability and quality, observed in three South African savannah systems, through linear modelling. The model predicted the proportion of below-canopy grass that grazers should include in their diet to meet their nutritional requirements.During the wet season, the model predicted that all animals could satisfy their daily nutrient requirements when feeding on a combination of below- and outside-canopy grasses. However, wildebeest, having relatively high nutrient demands, could meet their nutrient requirements only by feeding almost exclusively below canopies.During the dry season, all animals could gain almost twice as much digestible protein when feeding on below – compared to outside-canopy forage. Nonetheless, only warthogs could satisfy their nutrient requirements – when feeding almost exclusively on below-canopy grasses. The other ungulate species could not meet their phosphorus demands by feeding at either site without exceeding their maximum fibre intake, indicating the unfavourable conditions during the dry season.We conclude that grazing ungulates, particularly warthog, zebra, and buffalo, actually depend on the available below-canopy grass resources. Our model therefore helps to quantify the importance of higher quality forage patches beneath savannah trees. The composition of grazer communities depending on below-canopy grasses can be anticipated if grazer food requirements and the abundance of large trees in savannahs are known. The model suggests that the conservation of large single-standing trees in savannahs is crucial for maintenance of locally grazing herbivores.     

The relationships between soil factors,grass nutrients and the foraging behaviour of wildebeest and zebra

Summary We examined the relationships between soil factors, nutrients in grasses and foraging behaviour of wildebeest (Connochaetes taurinus) and zebra (Equus burchelli) in a semi-arid nature reserve in South Africa. We tested the hypotheses that: (1) Soil nutrient levels determine the abundance and distribution of grass species; (2) nutrient levels within grass species are correlated with soil nutrient levels; (3) the spatial distribution and diet composition of ungulates is influenced by the nutrient availability in grasses. The distribution of soil factors in upper ground levels did explain the differential abundance of grass species in the reserve. Ordination of nutrient levels in grass species showed high levels of particular nutrients in certain species, but no one species showed uniformly high levels of all nutrients. Moreover, grasses on fertile soils did not necessarily accumulate higher nutrient levels than grasses on poor soils. Thus, nutrient levels in grasses were not correlated with soil nutrient levels. Wildebeest and zebra responded to monthly variations in the levels of N and P in grasses by moving seasonally to habitat types characterized by grass communities containing a high proportion of nutritional species, rather than by selecting particularly nutritious species within communities. We suggest that within semiarid savannas, areas with a higher diversity of grass communities will be more likely to have some of these communities containing high nutrient levels at any given season, than a lower diversity area. Therefore, the higher-diversity area would be likely to support more herbivores, and thus diversity would control carrying capacity.     

The pattern of lion predation in Nairobi Park

The feeding habits of lions in Nairobi National Park have been observed between 1968 and 1972. Nairobi Park is briefly described and the herbivore and predator populations are discussed. The relationship between the changing status of the prey population for the period 1968-72 and the feeding habits of the lions is examined and compared with data from earlier years. Selection ratio (preference ratio) for three of the most important prey species is more closely adjusted to the abundance of these species in the total ungulate population than was the case prior to 1968. Only warthog and eland form an exception. Predation on wildebeest shows the most marked decrease although this species has been increasing during the last 5 years. Wildebeest, kongoni, zebra and warthog have provided 80% of total kills throughout the study on the basis of numbers killed. On this basis, warthog has the highest preference rating. However, the largest contribution to the lions' diet expressed in kg is by kongoni, followed by zebra, wildebeest, eland and warthog, in that order. Kongoni and wildebeest contribute most during the first half of the year and zebra and eland during the last 6 months. Selection for males is significant in zebra and eland and highly significant in kongoni, whilst only in zebra is selection for juveniles evident.     

Dietary composition of wildebeest (Connochaetes taurinus) kongoni (Alcephalus buselaphus) and cattle (Bos indicus), grazing on a common ranch in south-central Kenya

This paper gives the results of a study conducted at Game Ranching Ltd, situated at the Athi Kapiti Plains, Kenya, to determine the dietary composition of cattle (Bos indicus L), kongoni (Alcephalus buselaphus Pallas) and wildebeest (Connochaetes taurinus Burchell), through two forage growing seasons (wet and dry). The dietary preferences and overlaps between the species were also determined. The diet preference of the three herbivores was determined using a microhistological analysis technique. The three dominant grasses in the ranch: Themeda triandra Fork, Digitaria macroblephara (Hack.) Stapf and Penisetum mezianum Leeke, formed the major diets of the animals. The browse component of the diets increased during the dry season by about 100% for all the animal species, with cattle always having twice as much browse as the wild herbivores. However, the animals selected similar diets in terms of plant species during both seasons but were more selective during the wet season. Dietary overlaps were always above 75%, but more than this during the dry season. The dietary overlaps were lower between cattle and wild herbivores than between the wild herbivores. The diet preference index for the animals differed from season to season, and from plant to plant.     

Prey selection and prey preferences of spotted hyenas <Emphasis Type="Italic">Crocuta crocuta</Emphasis> in the Etosha National Park,Namibia

The feeding ecology of the spotted hyena Crocuta crocuta was studied in the central and eastern part of the Etosha National Park, Namibia. Hyenas mainly hunted migratory ungulates such as springbok Antidorcas marsupialis, zebra Equus burchelli, and blue wildebeest Connochaetes taurinus, but also resident species such as the greater kudu Tragelaphus strepsiceros and gemsbok Oryx gazella. There were, however, major differences in the species most frequently killed by hyenas in central and eastern Etosha. The preferred prey species of spotted hyenas in central Etosha was springbok, whereas regarding the abundance of zebra and wildebeest, these two species were rather avoided. In contrast, the prey species preferred by hyenas in eastern Etosha was kudu. Zebra and gemsbok were taken in proportion to their abundance, whereas wildebeest and springbok seemed to be rather avoided. Differences in prey selection and preferences were also reflected in differences in hunting group sizes. In eastern Etosha, where spotted hyenas frequently hunted larger prey, hunting group sizes were significantly larger compared to those in the center of the park.     

You are what you eat: describing the foraging ecology of southern elephant seals (Mirounga leonina) using blubber fatty acids

Understanding the trophodynamics of marine ecosystems requires data on the temporal and spatial variation in predator diet but, particularly for wide-ranging species, these data are often unavailable. The southern elephant seal (Mirounga leonina) consumes large quantities of fish and squid prey in the Southern Ocean relative to other marine mammals; however, how diet varies relative to seasonal and spatial foraging behaviour is unknown. We used fatty acid (FA) signature analysis of 63 blubber cores from adult female M. leonina over three seasons (winter 1999, summer 2000 and winter 2001) to determine diet structure. We detected significant differences between seasons and between the main foraging regions (Antarctic continental shelf versus pelagic). We used the FA profiles from 53 fish, squid and krill species to construct a discriminant function that would classify each seal, from its blubber sample as having a fish- or squid-FA profile. We determined that a higher proportion of M. leonina had fish-dominated diets during the winter and when foraging around the Antarctic continental shelf, and the majority had more squid-dominated diets during the summer when foraging pelagically. Thus, we were able to measure the coarse-scale diet structure of a major marine predator using FA profiles, and estimate its associated seasonal and temporal variation.     

Resource partitioning along multiple niche dimensions in differently sized African savanna grazers

Resource partitioning among mammalian savanna herbivores is thought to be predominantly driven by differences in body size. In general, large herbivore species utilize abundant low quality forage while small herbivores focus on scarcer high quality food items. However, in a natural system other factors such as digestive strategy, season and the presence of megaherbivores (body size > 1000 kg) are likely to complicate allometric predictions. Non‐ruminants are probably better able to cope with abundant low quality food than ruminants of the same size causing a non‐ruminant to act ‘larger’ than allometrically predicted. Also, the effect of alternating seasons with high and low food availability on diet choice and hence the competitive interactions between co‐occurring herbivores is still poorly understood. Lastly, how megaherbivores deviate from allometric predictions (based on smaller species) is still not well quantified. In this study we examine resource partitioning among three ruminant and three non‐ruminant grazers: impala, wildebeest, buffalo, warthog, zebra and white rhinoceros (megaherbivore) in the savanna of Hluhluwe iMfolozi Park, South Africa. We analysed habitat and diet overlap, specifically grass species (something not commonly investigated) and grass height eaten, in both the wet and the dry seasons. We found that habitat utilization differences among the species were generally small and did not vary between seasons. Diets within feeding patches overlapped during the wet season but highly diverged during the dry season. Body mass differences among species explained their dry season resource partitioning for all species except for comparisons with the megaherbivore (white rhino), while differences in digestive strategy were not related to niche overlap in either season. We conclude that savanna herbivores in this system coexist mostly through body size‐driven resource partitioning in the dry‐season, with the exception of the white rhino (megaherbivore).     

Selection for nutrients by red deer hinds feeding on a mixed forest edge

We studied the nutritional behaviour of hinds foraging on a mixed-forest edge by direct observation of their choices at each season and by measuring nutrient concentration in the plants. We compared nutrient concentrations in the observed diets with those in the total available vegetation, and with those of 1,000 randomly simulated diets in which we included only those plants that were actually eaten by the animal. Whether the available or the consumed feeds were used as the basis for comparisons had important consequences due to the presence of conifers and ferns, which were high in soluble sugars but were never eaten by the animals (potentially due to their toxicity). The selected diets were lower in sugars than the total available vegetation in summer, but were actually higher in sugars than the random diets generated from consumed forage species only. Hind diets contained more soluble sugars but not more protein than simulated diets in all seasons. Contrary to our prediction, anti-nutritional compounds (ADL and tannins) were avoided only in winter. Compared to simulated diets, hinds consumed more tannins in spring and summer and more ADL in summer and autumn. We suggest that this was a consequence of selection for soluble sugars, because the preferred plant species, which had high soluble sugar concentrations, also contained a large proportion of the anti-nutritional compounds eaten. In winter, the grass-dominated diets contained more fibre (NDF) and less ADL than the simulated diets, indicating that hinds orient their feeding towards digestible fibres. The switch from a browser to a grazer diet was related to a change in the availability of the nutrients, mainly soluble sugars. In our study, grasses contained more soluble sugars and proteins than deciduous browse during winter. This calls into question the dichotomy usually assumed in the literature between grass and browse in terms of nutrient content. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Current state of forage resources and feeding of reindeer (<Emphasis Type="Italic">Rangifer tarandus</Emphasis>) and musk oxen (<Emphasis Type="Italic">Ovibos moschatus</Emphasis>) in the arctic tundras of Wrangel Island

The species composition and aboveground biomass of plant and lichens and the composition of reindeer and musk ox diet in the arctic tundra of Wrangel Island were studied in 2004 to 2007. The above-ground phytomass in different areas of the island varied from 1105 to 2100 kg/ha. The composition of plants consumed by reindeer and musk oxen and their proportions in the diet were determined by standard micro-histological analysis of plant remains in their feces. The results showed that, either in winter or in summer, both species obviously preferred feeding on willows (Salicaceae), which comprised almost half of their diet. Moreover, their feeding was highly selective, especially with respect to sedges and rushes (Cyperaceae + Juncaceae) and legumes (Fabaceae). Although the contributions of these plant groups to the total aboveground phytomass were very small (less than 4 and 8%), their proportions in the diet reached 27 and 24%, respectively. Mosses were not a preferred forage: their proportion in the aboveground phytomass reached 40%, but that in the diets of both species was below 10% in summer and increased to 20% only in the winter diet of reindeer. At a high abundance of lichens (up to 20% of the aboveground phytomass), neither of the animals consumed them during the study period.     

Rumen function in red deer, hill sheep and reindeer in the scottish highlands.

Red deer, sheep and reindeer grazing on their normal hill ranges were examined at intervals over a period of four years. Samples from the digestive tract were taken at different seasons and processed in the field. The Red deer and reindeer were killed before samples were taken; rumen samples from the sheep were taken by stomach tube, but a number of animals were also killed at different seasons to correlate stomach tube and whole rumen samples. The animals sampled were representative of the general condition of the herds. Examinations were made for parasites and any pathological conditions. In most instances parasitic infections were slight. Apparent seasonal changes were found in the compositions of the diets. The Red deer and sheep ate principally heather and grass, the proportion of heather increasing in the winter. The reindeer ate mainly grass in the summer, with lichens and grass forming the winter diet, and these animals seemed to have a higher nutritional status in the winter than did the other two species. The weights of the animals and of their rumen contents, the concentrations of rumen ammonia and volatile fatty acid, and the rates at which different dietary components were fermented are recorded. Rumen fermentation was low in winter and the diets were generally inadequate for the animals. A lack of nitrogen seemed to be a major factor. Some data on caecal contents are also given.     

The diet of blue whiting, hake, horse mackerel and mackerel off Portugal

This paper deals with the diets of blue whiting Micromesistius poutassou (Risso 1810), hake Merluccius merluccius (L. 1758), horse mackerel Trachurus trachurus (L. 1758), and mackerel Scomber scombrus (L. 1758) off Portugal and explores variations in fish length, water depth, latitude and season. All four species feed on fish; however, hake and mackerel are the first and second most important predators, respectively, blue whiting being the most important fish prey for both species. The diets of blue whiting and horse mackerel are composed mainly of crustaceans. Diet variations according to predator fish size are more important than either latitude or depth. In the diets of blue whiting, hake and horse mackerel, prey importance increases with predator size. For blue whiting and horse mackerel, diet variations with fish length and water depth are correlated: small fish are closely associated with coastal areas where they feed on copepods and decapod larvae. Seasonality in the diet is apparent for blue whiting, hake and mackerel. For blue whiting, the decapod Pasiphaea sivado is the most important prey in summer and autumn, being replaced by the euphausid Meganyctiphanes norvegica in winter. In the diet of hake, seasonality was characterised by the major importance of Macroramphosus scolopax in autumn, whereas the diet of mackerel consisted of zooplankton in summer, fish and decapods in autumn and decapod larvae in winter. Seasonal changes in the diet of horse mackerel correspond to a higher diversity of prey in autumn compared to other seasons (although euphausids are the main prey in all seasons). Seasonality in feeding activity is not as marked for the other species as it is for horse mackerel; the percentage of empty stomachs of horse mackerel is greatest in winter, when spawning takes place at the Portuguese coast.     

Seasonal variation in the diet of South African Galagos

The feeding behavior and diet of two species of bushbaby, Galago senegalensisand Galago crassicaudatus,in South Africa were examined in relation to seasonal changes in climate. The populations studied were allopatric, but both fed predominantly on Acaciagum and invertebrates. Data on their diet were collected by direct observation of a radiocollared female of each species and by analysis of fecal samples. Differences in diet were found between the species within seasons and within species between the seasons. Both spent more time gum-feeding in winter than in summer. Prey size and type differed between the species in summer but converged in winter. The quantity of insects taken was fairly similar between seasons for G. senegalensisbut dropped considerably for G. crassicaudatusin winter. These observations are interpreted in terms of interspecific differences in feeding strategies, which are considered to be a function of the difference in body size of the two galago species.     

Cape mountain zebra in the Baviaanskloof Nature Reserve,South Africa: resource use reveals limitations to zebra performance in a dystrophic mountainous ecosystem

Resource use of Cape mountain zebra was studied in the Baviaanskloof Nature Reserve (BNR) over concerns of the poor performance in population growth. We assessed the seasonal diet, habitat suitability and forage quality of the Bergplaas area in BNR for mountain zebra. Grasses contributed 95.2% to the annual diet of mountain zebra, Tristachya leucothrix contributing the most (39.4%), followed by Themeda triandra (27.6%). Seasonally, T. triandra contributed most to the diet in winter, while T. leucothrix became more important in the summer and also was the only species preferred in all seasons. Mountain zebra concentrated their feeding in Kouga Grassy Fynbos and from our assessment this was the only habitat suitable for mountain zebra. Our analysis of mountain zebra dung indicated that the seasonal nitrogen and phosphorus content was below the threshold values prescribed for grazers, and our study suggests that mountain zebra at Bergplaas are severely resource limited. We emphasize the importance of fire and access to nutrient‐rich lowlands in influencing the nutritional ecology of mountain zebra and provide conservation management recommendations.     

The diet of the Sea Eagle Haliaeetus albicilla and Golden Eagle Aquila chrysaetos in western Scotland

The diets of Sea Eagles Haliaeetus albicilla and Golden Eagles Aquila chrysaetos living sympatrically in western Scotland were studied using pellets and prey remains collected at roosts and nest sites throughout the year. Both species showed changes in diet between winter and summer, and there were differences between species in both seasons. As a rule, Sea Eagles took proportionately more seabirds, waterfowl (ducks and waders) and fish, whilst Golden Eagles took proportionately more rabbits and hares. Sea Eagles had a broader diet than Golden Eagles but a measure of dietary overlap based on taxonomic composition indicated an overlap of more than 90% between the two species.     

Effects of grass and browse consumption on the winter mass dynamics of elk

Much of the research into herbivore ecology and evolution has focused on patterns and mechanisms of niche partitioning in the diets of specialized grazers and browsers, but the significance of the balance of grazing and browsing within intermediate feeders present unique questions that have received less attention. We explored the nutritional effects of varying the balance of grass and browse in the winter diets of elk (Cervus elaphus). We compiled published data from three similar studies that monitored the mass dynamics of captive elk fed diets of pure grass, pure browse or 1 of 14 mixed diets in winter feeding trials. Elk lost mass (up to 22% of initial body weight) in 29 of 33 feeding trials, similar to wild elk in winter. We used regression models of mass dynamics, considering the linear, quadratic or logarithmic effects of the proportion of the diet that was grass (≈1 − proportion of the diet that was browse) and the additive and interactive effects of nitrogen intake. Diet composition had strong effects on mass dynamics, and all models explained ≥73% of the variation (adjusted r ²) in mass dynamics. Nitrogen intake had uniformly positive effects on mass balance, and increasing grass intake caused improved maintenance of body mass up to a point, but further increases in the proportion of grass in the diet had neutral or negative effects on body mass. Overall, the data suggest that elk are adapted to consuming mixed diets. Nonetheless, data on the foraging behavior and diet selection of wild elk in many populations show that elk often consume grass-dominated diets and sometimes consume browse-dominated diets, but rarely consume mixed diets. Physiological adaptations to mixed diets may place unique spatio-temporal constraints on diet selection in intermediate feeders and impose large penalties for a sub-optimal balance of grazing and browsing.     

Fish assemblages across a vegetation gradient in a restoring tidal freshwater wetland: diets and potential for resource competition

Marsh habitats have been the focus of recent worldwide restoration efforts due to their degradation and destruction as a result of human development. We assessed fish resource use at a naturally restoring marsh (Liberty Island, California, USA) by comparing diet composition, stomach fullness, normalized stomach weight, and diet overlap across a vegetation gradient. Fish were collected using gill nets and fyke nets at six sites during spring 2010, summer 2011 and winter 2012. We analyzed 392 stomachs from the eleven most abundant species collected. Prey composition and biomass varied seasonally for all fish species, but there were no notable differences across sites or seasons for stomach fullness or normalized stomach weight for most fish species. Results from non-metric multidimensional scaling (NMDS) and two-way analysis of similarities (ANOSIM) indicated minimal diet overlap between species (R?=?0.633, p?=?0.001) and seasons (R?=?0.413, p?=?0.001). Seasonal habitat and resource use across the vegetation gradient was species-specific. Small but significant spatial diet differences were detected for inland silverside, striped bass and bigscale logperch. Delta smelt exhibited seasonal diet differences by shifting from chironomids and zooplankton during spring, to amphipods and zooplankton during winter. More generally, fish maintained stomach fullness across all sites and seasons while maintaining minimal dietary overlap. Our study emphasizes the importance of tidal marshes as feeding habitat for several fish species, including the endangered delta smelt.     

Winter ecology of Arctic charr (<Emphasis Type="Italic">Salvelinus alpinus</Emphasis>) and brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis>) in a subarctic lake,Norway

We studied habitat choice, diet, food consumption and somatic growth of Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) during the ice-covered winter period of a subarctic lake in northern Norway. Both Arctic charr and brown trout predominantly used the littoral zone during winter time. Despite very cold winter conditions (water temperature <1°C) and poor light conditions, both fish species fed continuously during the ice-covered period, although at a much lower rate than during the summer season. No somatic growth could be detected during the ice-covered winter period and the condition factor of both species significantly declined, suggesting that the winter feeding rates were similar to or below the maintenance requirements. Also, the species richness and diversity of ingested prey largely decreased from summer to winter for both fish species. The winter diet of Arctic charr <20 cm was dominated by benthic insect larvae, chironomids in particular, and Gammarus lacustris, but zooplankton was also important in December. G. lacustris was the dominant prey of charr >20 cm. The winter diet of brown trout <20 cm was dominated by insect larvae, whereas large-sized trout mainly was piscivorous, feeding on juvenile Arctic charr. Piscivorous feeding behaviour of trout was in contrast rarely seen during the summer months when their encounter with potential fish prey was rare as the small-sized charr mainly inhabited the profundal. The study demonstrated large differences in the ecology and interactions of Arctic charr and brown trout between the winter and summer seasons.