Summer Diet Research Articles

White-tailed Deer (<i>Odocoileus virginianus</i>) Subsidize Gray Wolves (<i>Canis lupus</i>) During a Moose (<i>Alces americanus</i>) Decline: A Case of Apparent Competition?

Moose (Alces americanus) in northeastern Minnesota have declined by 55% since 2006. Although the cause is unresolved, some studies have suggested that Gray Wolves (Canis lupus) contributed to the decline. After the Moose decline, wolves could either decline or switch prey. To determine which occurred in our study area, we compared winter wolf counts and summer diet before and after the Moose decline. While wolf numbers in our study area nearly doubled from 23 in winter 2002 to an average of 41 during winters 2011–2013, calf:cow ratios (the number of calves per cow observed during winter surveys) in the wider Moose range more than halved from 0.93 in 2002 to an average of 0.31 during 2011–2013. Compared to summer 2002, wolves in summers 2011–2013 consumed fewer Moose and more White-tailed Deer (Odocoileus virginianus). While deer densities were similar during each period, average vulnerability, as reflected by winter severity, was greater during 2011–2013 than 2002, probably explaining the wolf increase. During the wolf increase Moose calves remained a summer food item. These findings suggest that in part of the Moose range, deer subsidized wolf numbers while wolves also preyed on Moose calves. This contributed to a Moose decline and is a possible case of apparent competition and inverse-density-dependent predation.

Diet of the Mohave Ground Squirrel (Xerospermophilus mohavensis) in Relation to Season and Rainfall

The Mohave ground squirrel (Xerospermophilus mohavensis) is endemic to the western Mojave Desert of California. It is listed as threatened under the California Endangered Species Act, yet there is little published information on its habitat requirements. We studied the diet of Mohave ground squirrels at 4 sites in desert scrub habitat in Inyo County, California, primarily by microhistological analysis of 754 samples of fecal pellets collected from live-trapped animals. Over all sites and seasons, shrub foliage was the largest component of the diet (39.8% relative density) and mainly derived from several taxa of Chenopodiaceae: winterfat (Krascheninnikovia lanata), spiny hopsage (Grayia spinosa), and saltbushes (Atriplex spp.). Forb leaves were next in importance (34.1% relative density), especially from Fabaceae (Astragalus and Lupinus), Polemoniaceae (Gilia and Linanthus), and Asteraceae. Flowers, pollen, and seeds were also major components (20.3% relative density). Leaves composed nearly all of the diet in spring, whereas pollen, flowers, and seeds made up about a third of the diet in summer. Following dry winters when annual forbs were limited, Mohave ground squirrels depended primarily on foliage from perennial shrubs and forbs. Following wet winters when spring annuals were abundant and most plant species flowered and set seed prolifically, squirrels consumed a high proportion of leaves plus flowers, pollen, and seeds of annual forbs. Mohave ground squirrels reproduced only after winter rainfall >80 mm that resulted in a standing crop of herbaceous annuals ≥100 kg · ha-1. Mohave ground squirrels consumed very little of the nonnative annual plant biomass present on our study sites (Erodium, Salsola, Bromus, and Schismus contributed <3% overall to the diet). Conservation implications include the following: (1) priority should be given to protecting habitats supporting preferred perennial forage plants, including winterfat and spiny hopsage; (2) habitats with an understory dominated by native annual forbs have higher value than those dominated by nonnative plants, especially annual grasses; and (3) if climate change results in lower and less regular winter precipitation, suitable habitat for Mohave ground squirrels may be reduced and fragmented in the drier portions of the geographic range.

Are Bison Intermediate Feeders? Unveiling Summer Diet Selection at the Northern Fringe of Historical Distribution

Bison (Bison bison) were historically distributed throughout North America with the northern edge of the distribution occurring in north-central Manitoba and surrounding provinces. Despite bison occupying the boreal zone of North America, little is known of their forage selection patterns of herbaceous plant material when occupying pastures within a densely forested aspen ecosystem. In 2015 we initiated a study to examine forage selection patterns for bison among and within summer months (June–August). We hypothesized that vegetative composition of bison diets would be consistent with availability, would shift with forage availability, and would predominately consist of grass and sedge species. We opportunistically collected adult female bison fecal samples (N = 99) and identified forage composition using the DNA barcoding method. We estimated availability of forage to the lowest taxonomical level possible using a modified Daubenmire frame. Overall, bison diets were composed of 44.3% grass, 37.7% forb, 16.3% browse, and < 2% sedge and rush. Forage availability comprised 51.2% grass, 28.3% forb, 11.0% sedge, and 7.6% rush. All analyses indicated that use and availability for grass, forb, sedge, and rush differed (P ≤ 0.05) throughout the summer. Grass and forbs were important dietary components for bison, comprising > 80% of bison diets. However, bison selected for these two dietary components independently as the summer progressed. Our results indicate that these bison consume a large portion (~54.0%) of low-cellulose, high cell-soluble forages to meet their dietary needs. This suggests that bison may be or become intermediate foragers and are more like elk (Cervus elapus) than domestic cattle or sheep when inhabiting forested systems at the northern edge of their historical distribution. Herd managers and biologists should be cognizant of the importance of eudicots for bison and adopt a management plan that promotes a spatially heterogenous vegetative schematic.

Straight from the caribou’s (Rangifer tarandus) mouth: detailed observations of tame caribou reveal new insights into summer–autumn diets

High-quality habitats for caribou (Rangifer tarandus (L., 1758)) are associated primarily with lichens, but lichens alone fail to satisfy summer nutritional requirements. To evaluate the summer forage value of plant communities across northeastern British Columbia (BC), where populations of northern and boreal ecotypes of caribou are declining, we observed foraging by tame, female caribou. We compared diet composition with forage abundance to determine forage selection and to quantify forage availability. Deciduous shrubs, not lichens, largely dominated summer diets. Caribou were highly selective foragers, with 28 species comprising 78% of diets. Caribou avoided ≥50% of understory vegetation in all communities, especially conifers, evergreen shrubs, mosses, and two genera of terrestrial lichens. Availability of accepted forage (species not avoided) was strongly heterogeneous across landscapes. Alpine shrub areas and mid-elevation spruce–fir stands in the mountains, as well as treed rich fens and white spruce communities in the boreal forests, provided the greatest quantities of accepted forage for caribou. Dry alpine sites and unproductive black spruce communities provided the least accepted forage. Our work has direct implications to caribou conservation by contributing to a greater understanding of the forage value of summer habitats, with implications to habitat selection, seasonal movements, and distribution ecology.

Trophic position and seasonal changes in the diet of the red wood ant Formica aquilonia as indicated by stable isotope analysis

1. Red wood ants are among the most numerous generalist predators and strongly affect the composition of arthropod communities in forest ecosystems. However, their trophic position remains poorly understood. Stable isotope analysis was applied to study the trophic position of Formica aquilonia and reveal seasonal changes in its trophic links with both myrmecophilous aphids and other invertebrates in a mixed forest of western Siberia.2. The δ15N values of F. aquilonia exceeded those of herbivores and aphids by approximately 3.5‰. Despite obligate trophobiotic relationships with aphids, F. aquilonia occupied the trophic position of first‐order predator. The higher content of 13C in the worker ants, compared with members of grazing food chains, was explained by their consumption of 13C‐enriched aphid honeydew.3. Myrmecophilous tree‐dwelling aphids were enriched in 13C and 15N relative to grass‐inhabiting species, and the honeydew of tree‐dwelling aphids had higher δ13C values than those of the honeydew of grass‐inhabiting aphids.4. The decrease in δ13C values of the worker ants from spring and summer to autumn apparently reflected the transition from the collection of tree sap and feeding on the aphid honeydew from trees with high 13C content in the spring and early summer to a more diverse liquid diet in late summer, which included 13C‐depleted honeydew of aphids from herbs.5. The prevalence of the 15N‐depleted aphid honeydew in the ants' diet in the second half of the summer is discussed as one possible explanation for the seasonal decline in δ15N values of the worker ants.

Using behavioral and stable isotope data to quantify rare dietary plasticity in a temperate bat

Seasonal reliance on plant-based resources is very uncommon in temperate insectivorous bats. The pallid bat (Antrozous pallidus) is an exception and in the Sonoran Desert switches from an arthropod-based diet to one that includes cactus nectar during spring when columnar cacti bloom. Such cactophily is a common strategy among nectar-feeding phyllostomid bats, including migratory Leptonycteris species that consume nectar and fruit from columnar cacti. Spring nectarivory by A. pallidus begs the question of whether they also consume cactus fruit during the summer, despite lacking morphological and physiological adaptations for frugivory. We recorded foraging behavior of bats at 134 fruits of the cardon cactus (Pachycereus pringlei) in Baja California Sur, Mexico, and used stable isotope analysis to quantify incorporation of fruit into the summer diet of A. pallidus. We found that A. pallidus visited cardon fruits just as frequently as the lesser long-nosed bat, Leptonycteris yerbabuenae (51.0% and 49.0% of total observed visits, respectively), and removed the same amount of fruit (t59 = –0.85, P = 0.40). Carbon isotopes in wing tissue (n = 37) and exhaled breath (n = 35) of A. pallidus were consistent with frugivory, although variability in the proportion of cactus-derived δ13C in A. pallidus was higher in summer than in spring. Our results confirm that nectarivory in A. pallidus extends to frugivory, highlighting remarkable dietary plasticity in a temperate bat. Moreover, these data suggest that A. pallidus may be an important mutualist to columnar cacti in parts of the Sonoran Desert.

Saccharomyces cerevisiae boulardii improves performance of pigs fed low and high energy diets in summer

Saccharomyces cerevisiae boulardii improves performance of pigs fed low and high energy diets in summer

Invertebrate Abundance at Northern Bobwhite Brood Locations in the Rolling Plains of Texas

Northern bobwhite (Colinus virginianus), a bird of significant ecological and economic importance throughout the Rolling Plains region of Texas, has experienced significant population declines. Bobwhites have been the focus of extensive research for decades but little is known about foraging ecology of adults and chicks during post-hatch. Invertebrates are a key summer diet component for chicks, and supply the necessary proteins and minerals needed to fuel rapid body development. We examined brood-foraging sites to investigate invertebrate abundance. We radiomarked 121 bobwhite hens during winter-spring 2008 and 2009 and subsequently monitored 14 broods post-hatch. We collected invertebrate samples from 34 brood points and random paired-locations using sweep nets. Samples were sorted by Order to ascertain abundance and diversity. There was no difference in total abundance, abundance of Coleoptera, Hemiptera, Orthoptera, and Order diversity between brood and random locations. Northern bobwhite hens do not appear to select foraging sites based upon invertebrate abundance in the Rolling Plains of Texas.

Weekly Summer Diet of Gray Wolves (Canis lupus) in Northeastern Minnesota

Abstract Wolves (Canis lupus) are opportunistic predators and will capitalize on available abundant food sources. However, wolf diet has primarily been examined at monthly, seasonal, or annual scales, which can obscure short-term responses to available food. We examined weekly wolf diet from late June to early October by collecting scats from a single wolf pack in northeastern Minnesota. During our 15 wk study, nonungulate food types constituted 58% of diet biomass. Deer (Odocoileus virginianus) fawns were a major food item until mid-July after which berries (primarily Vaccinium and Rubus spp.) composed 56–83% of weekly diet biomass until mid-August. After mid-August, snowshoe hares (Lepus americanus) and adult deer were the primary prey. Weekly diet diversity approximately doubled from June to October as wolves began using several food types in similar proportions as the summer transitioned into fall. Recreational hunting of black bears (Ursus americanus) contributed to weekly wolf diet in the fall as wo...

Variation in the diet of Arctic Cod (Boreogadus saida) in the Pacific Arctic and Bering Sea

Arctic cod, Boreogadus saida (Lepechin, 1774), is a nodal species in Arctic marine foodwebs as an important prey of many birds, marine mammals, and other fishes, as well as an abundant predator of zooplankton and epibenthic fauna. We examined the summer diet of Arctic cod across a latitudinal gradient extending from the southern limit of their distribution in the eastern Bering Sea to the northern margins of the eastern Chukchi Sea (ECS) continental shelf. Specimens were collected from demersal and pelagic trawls conducted between 1999 and 2012, and across a range of predator sizes (3–26 cm). Arctic cod diets vary with body size and between regions within the study area, and appear to vary between years in the eastern Bering Sea, indicating opportunistic feeding habits. Constrained Analysis of Principal Coordinates was conducted on ECS demersal samples and revealed consumption of fish and decapod crustacea were positively correlated with Arctic cod length while consumption of euphausiids and copepods had the opposite relationship. The demersal Arctic cod diet in the northern latitudes of the ECS was dominated by copepod consumption (47% by weight, %W), but copepods were less important (12–26%W) in the central and southern latitudes of the ECS and in the northern and eastern Bering Sea—areas where diets were more varied in their composition. High levels of variation in the diet of Arctic cod highlights the need to monitor Arctic cod diets to identify consistently dominant prey types and potential future changes to trophic relationships related to climate change or increasing anthropogenic activity.

Seasonal Variation in the Food Habits of the Eurasian Harvest Mouse (Micromys minutus) from Western Tokyo, Japan.

A previous quantitative analysis of the food composition of the Eurasian harvest mouse (Micromys minutus) in Japan showed that it is insectivorous and granivorous. This supports the expectation that such a small mammal requires highly nutritious foods. Other studies have analyzed the feces of harvest mice, but these were only collected during winter in order to minimize disturbance of the animals. In the present study, we collected samples from all four seasons in order to understand changes in diet throughout the year. Results showed apparent seasonal differences in the diet of harvest mice. Insects accounted for ca. 30% of the diet in summer and autumn and seeds increased from 27% in winter to 50% in spring, suggesting the insectivorous nature of the harvest mouse in summer and autumn and graminivorous nature in winter and spring. These results strongly suggest that the harvest mouse is an opportunistic feeder. It has previously been thought that the harvest mice capture insects in the stalk zone of tall grassland community, but here, DNA analysis shows that harvest mice feed on ground-dwelling invertebrates, such as pill bugs (Armadillidium sp.) and carrion beetles (Calosilpha sp. or Ptomascopus sp.). This suggests that the harvest mouse goes down to the ground to feed on them.

The Summer Diet of a Juvenile Barbell Steed, Hemibarbus labeo, in the Surf Zone of the Nakdong River Estuary, Korea

The Summer Diet of a Juvenile Barbell Steed, Hemibarbus labeo, in the Surf Zone of the Nakdong River Estuary, Korea

WoodpigeonColumba palumbusDiet Composition in Mediterranean Southern Spain

Knowledge of the feeding habits of a bird species is necessary to evaluate how food availability can affect its population status. The Woodpigeon Columba palumbus is a granivorousfrugivorous species that is widely distributed throughout Europe. However, there is little information about its feeding habits both in Spain and Mediterranean region. The diet of Woodpigeons in a mountain area of southern Spain was quantitatively assessed on a monthly basis during 2011 and 2012. The birds were sampled on their way to roost sites after they had finished feeding and the contents of their crops were subsequently analysed. Twenty plant species and five snail species were identified in the diet. The consumed items varied significantly between seasons. Thus, acorns of Quercus sp. were the most consumed item during winter, cereals dominated the summer diet and tree fruits predominated in spring and autumn. The Woodpigeons showed a preference for cereals and acorns rather than tree fruits and pasture vegetation. Woodpigeons showed considerable plasticity in their feeding habits, since they were able to change the main food item consumed over a short period of time and fed on most of the typical Mediterranean tree fruits.

Recent summer diet of hooded Cystophora cristata and harp Pagophilus groenlandicus seals in the drift ice of the Greenland Sea

Harp Pagophilus groenlandicus and hooded Cystophora cristata seals are important predators in drift ice areas of the Greenland Sea (the West Ice) during spring and summer. Their summer (June–July) diet was studied in the West Ice in 2008 and 2010, based on analysis of the gastrointestinal contents of 179 and 20 hooded and harp seals, respectively, in addition to 70 harp seal faeces samples. The diet compositions of harp and hooded seals deviated significantly from each other, implying that the degree of food competition was relatively low. Polar cod Boreogadus saida dominated the hooded seal diet and amphipods (mostly Themisto sp.) dominated the harp seal diet. Krill and the squid Gonatus fabricii were eaten by both species. The importance of G. fabricii for hooded seals was lower in this study compared with previous studies, and krill only occurred sparsely. The occurrence of polar cod, Themisto sp. and krill in the diets of the two seal species coincides well with the geographical and vertical distribution of these three prey items and the previously recorded dive depths of the seals. The inclusion of demersal fishes such as sculpins and snailfish in the diet of some hooded seals was more likely a result of increased availability rather than changes in prey preference, as these seals were collected above shallower waters. Both species showed a rather narrow niche breadth.

Feeding ecology of the scops owl, Otus scops (Aves: Strigiformes), in the island of Pianosa (Tuscan Archipelago, Central Italy) outside the breeding period

ABSTRACTAll of the published studies but one about the diet of the Eurasian scops owl Otus scops, a nocturnal raptor of conservation concern, were carried out during the breeding period, just before or immediately after the chicks fledged. The species is a trans-Saharian migrant with few resident populations in Europe. Orthoptera make up the staple of its diet in summer. In this study, we investigated the diet of scops owls on the island of Pianosa after the breeding period through the analysis of pellets. A total of 327 fragments belonging to at least 14 taxa were identified from 56 pellets collected after the breeding period, between late August and March. By frequency, invertebrates constituted 80.00% of the diet, with Coleoptera being the most represented order (62.35% of the total diet) and Orthoptera poorly represented (8.24%). Vertebrates included two bird species, three small mammals and the Moorish gecko. Although the meal-to-pellet interval for scops owls is unknown, we suggest that the bank vole, which is not recorded on any Italian island, and possibly the wild mice, may have been preyed upon in nearby areas, before a migratory movement towards a warm area (e.g. Pianosa) occurred.

The Importance of Cultivated Plants in the Diet of Red and Roe Deer and Mouflon

The botanical composition of red and roe deer and mouflon diet was studied in the mosaic landscape in Drahanská vrchovina highlands, Czech Republic. We focused on the proportion and quality of agricultural crops and natural forest plants and estimated quality of the herbivore diet. Diet quality was monitored by the near infrared reflectance spectroscopy on the basis of nutritional quality of diet items. Red deer, roe deer and mouflon ingested all cultivated plants growing close to forest. However, the proportion of cultivated plants varied between seasons and herbivore species. The peak of crops consumption occurred in summer – when cereals spikes were ripe. The average proportion of corn for red deer was 40%. Cultivated plants were well accessible for herbivores in the study area and during vegetation period formed an important part of their diet, but the importance of cultivated plants for herbivores was lower compared with natural food resources present in forests during vegetation period. Although the main natural food sources had lower nutritional value, they formed the main part of herbivore diet in the study area. The availability of cultivated plants increases the quality of food supply during the growing season, but for herbivores the natural food sources are crucial, forming the main part of their diet both in summer and in winter. Wildlife management should reckon with feeding preferences of herbivores.

Seasonal Variation of Harbor Seal's Diet from the Wadden Sea in Relation to Prey Availability.

The Wadden Sea has an important role for marine mammals in terms of resting, nursing and foraging. Harbor seal is the most abundant marine mammal species in this area. The use of the food resources of the Wadden Sea by seals is not clear, and previous studies showed that this species can travel kilometers away from their haul-outs to forage in the North Sea. In this study, we analyzed the stable isotopes of vibrissae from 23 dead harbor seals found on the island of Sylt to investigate their diet. The predator´s carbon and nitrogen isotope compositions were compared to the compositions of different potential prey items from the Sylt-Rømø Bight and from the North Sea in order to study seasonal pattern in the diet and in the foraging location. In parallel, seasonal variation of abundance and biomass of the potential prey items from the Sylt-Rømø Bight were studied and compare to their contribution to the seal´s diet. The results revealed a change in the seal´s diet from pelagic sources in spring to a benthic based diet in summer, and an increasing use of the North Sea resources in fall and winter in accordance with the seasonal variation of the availability of prey in the Sylt-Rømø Bight.

Show Me Your Rump Hair and I Will Tell You What You Ate - The Dietary History of Muskoxen (Ovibos moschatus) Revealed by Sequential Stable Isotope Analysis of Guard Hairs.

The nutritional state of animals is tightly linked to the ambient environment, and for northern ungulates the state strongly influences vital population demographics, such as pregnancy rates. Continuously growing tissues, such as hair, can be viewed as dietary records of animals over longer temporal scales. Using sequential data on nitrogen stable isotopes (δ15N) in muskox guard hairs from ten individuals in high arctic Northeast Greenland, we were able to reconstruct the dietary history of muskoxen over approximately 2.5 years with a high temporal resolution of app. 9 days. The dietary chronology included almost three full summer and winter periods. The diet showed strong intra- and inter-annual seasonality, and was significantly linked to changes in local environmental conditions (temperature and snow depth). The summer diets were highly similar across years, reflecting a graminoid-dominated diet. In contrast, winter diets were markedly different between years, a pattern apparently linked to snow conditions. Snow-rich winters had markedly higher δ15N values than snow-poor winters, indicating that muskoxen had limited access to forage, and relied more heavily on their body stores. Due to the close link between body stores and calf production in northern ungulates, the dietary winter signals could eventually serve as an indicator of calf production the following spring. Our study opens the field for further studies and longer chronologies to test such links. The method of sequential stable isotope analysis of guard hairs thus constitutes a promising candidate for population-level monitoring of animals in remote, arctic areas.

Estimation of a Killer Whale (Orcinus orca) Population's Diet Using Sequencing Analysis of DNA from Feces.

Estimating diet composition is important for understanding interactions between predators and prey and thus illuminating ecosystem function. The diet of many species, however, is difficult to observe directly. Genetic analysis of fecal material collected in the field is therefore a useful tool for gaining insight into wild animal diets. In this study, we used high-throughput DNA sequencing to quantitatively estimate the diet composition of an endangered population of wild killer whales (Orcinus orca) in their summer range in the Salish Sea. We combined 175 fecal samples collected between May and September from five years between 2006 and 2011 into 13 sample groups. Two known DNA composition control groups were also created. Each group was sequenced at a ~330bp segment of the 16s gene in the mitochondrial genome using an Illumina MiSeq sequencing system. After several quality controls steps, 4,987,107 individual sequences were aligned to a custom sequence database containing 19 potential fish prey species and the most likely species of each fecal-derived sequence was determined. Based on these alignments, salmonids made up >98.6% of the total sequences and thus of the inferred diet. Of the six salmonid species, Chinook salmon made up 79.5% of the sequences, followed by coho salmon (15%). Over all years, a clear pattern emerged with Chinook salmon dominating the estimated diet early in the summer, and coho salmon contributing an average of >40% of the diet in late summer. Sockeye salmon appeared to be occasionally important, at >18% in some sample groups. Non-salmonids were rarely observed. Our results are consistent with earlier results based on surface prey remains, and confirm the importance of Chinook salmon in this population’s summer diet.

Summer diet composition of walleye pollock and predator–prey relationships with copepods and euphausiids in the eastern Bering Sea, 1987–2011

The composition of walleye pollock diets from the eastern Bering Sea continental shelf was determined from 25 years of sampling during summer surveys from 1987 through 2011. Substantial differences in the stomach contents of walleye pollock were found among the sizes and geographic strata that correspond to geographic distribution of the prey. With increasing pollock size, copepods decreased in importance in middle and outer shelf areas while mysids decreased in importance in the inner shelf. Euphausiids increased in importance with increasing pollock size in southeastern areas of the shelf, and fishes and shrimp increased in importance with increasing pollock size in northeastern areas of the middle and outer shelf. The biomass-weighted average diet composition of eastern Bering Sea pollock in each year׳s survey indicated perennial but variable importance of euphausiids and copepods as prey. An index of partial fullness indicated an interannual pattern of below-average consumption of copepods by the surveyed pollock from 1993 to 2004, but during this period the amount of euphausiids consumed continued to fluctuate about a mean that was similar to years surveyed before and after that period. The summer feeding success, as indicated by average stomach fullness, of intermediate sizes of pollock appears to be closely related to the consumption of copepods (especially for pollock 30–39cm fork length (FL)) and prey other than euphausiids (especially for pollock 40–49cmFL). Length-specific predator–prey relationships with copepods and euphausiids correspond to patterns in pollock feeding migrations. Interannual trends in the biomass of copepods in the EBS are reflected most closely in the diet of 20–29cmFL pollock, and trends in the biomass of euphausiids in the EBS are reflected most closely in the diet of the largest pollock (60+cmFL). Climate-mediated changes in the zooplankton community will likely have differential impacts across the demographic spectrum of pollock in the EBS.