Relative Abundance Of Prey Research Articles

Prey detection by a stepwise visual template matching mechanism

Predators can improve prey capture using a search image, and recent prey provide a visual template with which subsequent prey are compared. Considering trout feeding responses to mayfly prey of different sizes and phenological availability across years, we tested if changing relative abundances (ratios) of prey of the same species, but different body sizes, shifted trout feeding behaviour. For example, we hypothesized that a feeding switch from larger to smaller prey required continuous exposure to the novel smaller prey. The hypothesis that continuous exposure to novel small prey results in their acceptance was not supported. Rather, we discovered that trout identify novel prey using a dynamic stepwise visual neural template prey matching process, which involves the formation of focal prey template based on size or type, rejection of novel prey that do not match the size or type templates and modification of the existing or development of multiple prey templates that eventually enabled recognition of novel, small prey. We also discovered trout store multiple visual prey templates in memory. These results have implications for predator and prey dynamics, optimal foraging, the persistence of rare prey, prey species coexistence and predator selection on prey phenology.

Human-driven breakdown of predator-prey interactions in the northern Adriatic Sea.

Long-term baseline data that allow tracking how predator-prey interactions have responded to intensifying human impacts are often lacking. Here, we assess temporal changes in benthic community composition and interactions between drilling predatory gastropods and their molluscan prey using the Holocene fossil record of the shallow northern Adriatic Sea, which is characterized by a long history of human transformation. Molluscan assemblages differ between the Isonzo and Po prodelta, but both show consistent temporal trends in the abundance of dominant species. Samples of mollusc prey collected at high stratigraphic resolution indicate that drilling frequencies have drastically declined in the Po prodelta since the mid-twentieth century, while a weaker trend in the more condensed sediments of the Isonzo prodelta is not statistically significant. The decrease in drilling predation intensity and the community turnover are linked to the loss of predatory gastropods and the increased relative abundance of less-preferred prey during the most recent decades. Our results align with data showing the substantial depletion of marine resources at higher trophic levels in the region and indicate that the strong simplification of the food web initiated in the late nineteenth century accelerated further since the mid-twentieth century.

Predator in proximity: how does a large carnivore respond to anthropogenic pressures at fine-scales? Implications for interface area management.

Driven by habitat loss and fragmentation, large carnivores are increasingly navigating human-dominated landscapes, where their activity is restricted and their behaviour altered. This movement, however, raises significant concerns and costs for people living nearby. While intricately linked, studies often isolate human and carnivore impacts, hindering effective management efforts. Hence, in this study, we brought these two into a common framework, focusing on an interface area between the critical tiger habitat and the human-dominated multiple-use buffer area of a central Indian protected area. We employed a fine-scale camera trap survey complemented by GPS-collar movement data to understand spatio-temporal activity patterns and adjustments of tigers in response to anthropogenic pressures. We used an occupancy framework to evaluate space use, Bayesian circular GLMs to model temporal activity, and home range and step length analyses to assess the movement patterns of tigers. Further, we used predation-risk models to understand conflict patterns as a function of tiger presence and other habitat variables. Despite disturbance, a high proportion of the sampled area was occupied by 17 unique tigers (ψ = 0.76; CI [0.73-0.92]). The distance to villages (β ± SE = 0.63 ± 0.21) and the relative abundance of large-bodied wild prey (β ± SE = 0.72 ± 0.37) emerged as key predictors of tiger space use probability, indicating a preference for wild prey by tigers, while human influences constrained their habitat utilisation. Distance to villages was also identified as the most significant predictor of the tigers' temporal activity (μ ± σ = 3.03 ± 0.06 rad) that exhibited higher nocturnality near villages. A total of 11% of tiger home ranges were within village boundaries, accompanied by faster movement in these areas (displacement 40-82% higher). Livestock depredation probability by tigers increased with proximity to villages (P = 0.002) and highway (P = 0.003). Although tiger space use probability (P = 0.056) and wild prey abundance (P = 0.134) were non-significant at the 0.05 threshold, their presence in the best-fit predation-risk model suggests their contextual relevance for understanding conflict risk. The results highlight the importance of appropriately managing livestock near human infrastructures to effectively mitigate conflict. Shared space of carnivores and humans requires dynamic site-specific actions grounded in evidence-based decision-making. This study emphasises the importance of concurrently addressing the intricate interactions between humans and large carnivores, particularly the latter's behavioural adaptations and role in conflict dynamics. Such an integrated approach is essential to unravel cause-effect relationships and promote effective interface management in human-dominated landscapes.

Temperature alters the predator-prey size relationships and size-selectivity of Southern Ocean fish

A primary response of many marine ectotherms to warming is a reduction in body size, to lower the metabolic costs associated with higher temperatures. The impact of such changes on ecosystem dynamics and stability will depend on the resulting changes to community size-structure, but few studies have investigated how temperature affects the relative size of predators and their prey in natural systems. We utilise >3700 prey size measurements from ten Southern Ocean lanternfish species sampled across >10° of latitude to investigate how temperature influences predator-prey size relationships and size-selective feeding. As temperature increased, we show that predators became closer in size to their prey, which was primarily associated with a decline in predator size and an increase in the relative abundance of intermediate-sized prey. The potential implications of these changes include reduced top-down control of prey populations and a reduction in the diversity of predator-prey interactions. Both of these factors could reduce the stability of community dynamics and ecosystem resistance to perturbations under ocean warming.

Diet composition and variation in four commonly landed and threatened shark species in Maharashtra, India

The diets of Carcharhinus limbatus, Scoliodon laticaudus, Chiloscyllium arabicum and Ch. Griesum from the west coast of India were investigated. We compared trophic resource use and overlap across and within benthic and pelagic habitat guilds, between the two sympatric species belonging to family Hemiscyliidae, and between the life stages of S. laticaudus. It was observed that there was a significant difference in the diet composition of benthic and pelagic shark species. There was no difference in the diet of the two sympatric Chiloscyllium species. S. laticaudus showed an ontogenetic dietary niche shift from an invertebrate-rich to an ichthyophagous diet. Specifically, C. limbatus showed an ichthyophagous diet while S. laticaudus showed a diet consisting of both benthic and pelagic prey. C. arabicum, C. griesum, and S. laticaudus were less dependent on teleosts and displayed similar diet composition. The study also found that several of the prey species were commercially important fish species caught in the fisheries of Malvan. Thus a change in the relative abundance of either prey or predators due to fishing pressure could influence coastal food webs, leading to impacts both on ecosystems and fisheries.

Predicting carrying capacity of a large carnivore from prey densities: a new approach.

Large carnivores play a crucial role in maintaining the balance of the ecosystem. Successful conservation initiatives have often led to a huge increase in predators which has often led to negative interactions with humans. Without the knowledge of the carrying capacity of the top predator, such decisions become challenging. Here, we have derived a new equation to estimate the carrying capacity of tigers based on the individual prey species density. We used tiger densities and respective prey densities of different protected areas. Relative prey abundance was used instead of absolute prey density as this could be a better surrogate of the prey preference. We used a regression approach to derive the species-wise equation. We have also scaled these coefficients accordingly to control the variation in the standard error (heteroscedasticity) of the tiger density. Furthermore, we have extended this regression equation for different species to different weight classes for more generalized application of the method. The new equations performed considerably better compared to the earlier existing carrying capacity equations. Incorporating the species-wise approach in the equation also reflected the preference of the prey species for the tiger. This is the first carrying capacity equation where the individual prey densities are used to estimate the carnivore population density. The coefficient estimates of the model with the comparison with prey-predator power laws also reflect the differential effect of tigers on different prey species. The carrying capacity estimates will aid in a better understanding of the predator-prey interaction and will advance better management of the top predator.

Ecological effects of a declining red wolf population

AbstractCarnivores, especially wolves (Canis sp.), have profound impacts on their ecosystems, affecting the abundance and behavior of prey and competitors, but this has not been examined in detail for red wolves (C. rufus). We studied a population of red wolves that was reintroduced to eastern North Carolina in 1987 and initially thrived, peaking at 120 animals. Due to an increase in anthropogenic mortality and a decline in government support, the population experienced a crash starting in 2014. We evaluated changes in the relative abundance of prey and competitor species during the red wolf decline with 25 camera traps run primarily on National Wildlife Refuges from 2015 to 2021. If red wolves were having an ecological effect on the mammal community, we expected this effect would decline as the wolf population waned, resulting in increased prey and competitor populations. Supporting this, we found that relative abundance increased for most prey and competitor species including American black bear (Ursus americanus), bobcat (Lynx rufus), Virginia opossum (Didelphis virginiana) and Northern raccoon (Procyon lotor). For all species, this increase was most notable after spring 2018, the second year with low red wolf reproduction. For some species, the increase was dramatic; the detection rate for raccoon, bear and bobcat doubled from the spring of 2018 to the spring of 2021. White‐tailed deer (Odocoileus virginianus) showed a general increase in relative abundance but remained prevalent even at their lowest detection rates. Our results lend correlational support to the hypothesis that red wolves had a strong effect on their ecosystems by suppressing prey and competitor populations when they were at their peak. This study adds to the growing body of evidence that reintroductions of large predators have ecological impacts, with the caveat that these impacts can decline rapidly if the predators dwindle back to critically low numbers.

Feeding strategy and prey selectivity in common minke whales (Balaenoptera acutorostrata) foraging in the southern Barents Sea during early summer

Stomach content samples from 33 minke whales (Balaenoptera acutorostrata), caught during Norwegian commercial whaling between May-June 1998, were collected in four sub-areas in the southern Barents Sea. Simultaneously, a comprehensive resource survey was conducted in order to identify and estimate the abundance of potential prey items for the whales in the four sub-areas. Krill (Thysanoessa sp. and Meganyctphanes norvegica) dominated the diet in all but one sub-area although pelagic fish such as capelin and herring also contributed significantly. The minke whales displayed monophagus feeding in all sub-areas investigated, including the medium-scale area resulting from pooling of all sub-areas. The small-scale resource surveys revealed significant variations in absolute and relative prey abundance between sub-areas, while the temporal (1-7 days) variations in relative prey biomass within sub-areas appeared to be less significant for all prey items, except herring (Clupea harengus) and perhaps capelin (Mallotus villosus). Krill was by far the most important prey item available in all areas, followed by either herring, cod (Gadus morhua) or saithe (Pollachius virens), depending on sub-area and survey. Although minke whale prey preference appeared to vary greatly in space, some new features of minke whale foraging behaviour were evident. Minke whales showed a strong preference for capelin, whereas gadoids (cod, haddock (Melanogrammus aeglefinus) and saithe) appeared to be avoided by the whales. Krill appeared to have been either avoided, fed upon randomly or were the preferred prey depending on sub-area and analyses level.

Relative abundance and size composition of prey in the common minke whale diet in selected areas of the northeastern Atlantic during 2000-04

A total of 210 common minke whales (Balaenoptera acutorostrata) were sampled in five different areas in the northeastern Atlantic during May-June 2000-04. Analysis of forestomach contents revealed a relatively mixed diet at the population level, whereas on an individual level, each whale had fed upon mainly one species. There were significant differences in diet composition between areas and some differences between years. The importance of krill in the Barents Sea increased with latitude and krill dominated the Spitsbergen diet. Capelin dominated the diet around Bear Island and contributed considerably to the diet along the coast of northern Norway. In the latter area, herring and haddock were also a great part of the diet. The diet in the Norwegian Sea consisted of mainly mature herring, while the diet in the North Sea was dominated by sand eels and mackerel. The minke whales were found to feed on a wide range of prey sizes, apparently determined by the availability of different size classes.

Hunger sweetens the beans: evidence of opportunistic feeding behaviour of the little owl (Athene noctua, Scopoli 1769) from Peloponnese, Greece

Abstract The little owl (Athene noctua) is a common raptor in Mediterranean habitats. To acquire more information on its diet, this study identified cranial and post-cranial skeletal material from 70 owl pellets collected during the 2016 and 2017 breeding seasons. The material was used to quantify the little owl’s relative prey abundance using MNI (minimum number of individuals), a taphonomical unit. This study is the first to examine the diet of the little owl in the Peloponnese (southern Greece). After examining 3,691 isolated skeletal and exoskeletal remains from the processed pellets, a total of 78 and 108 prey items were recorded for the two consecutive years. This study, in congruence with previous research, showed that in both years the little owl favoured primarily small mammals and arthropods, with a clear predominance of Thomas’s pine vole (Microtus thomasi) and arthropods from the class Diplopoda. Finally, a redundancy discriminant analysis (RDA) was applied to our two-year results, along with those from similar studies in the Mediterranean region, to examine the relationship between habitat types and prey taxa, which supported the little owl’s opportunistic feeding behaviour, depending on variation of ecological factors.

Ocelot occupancy in fragmented areas of the Brazilian Cerrado and Atlantic Forest

ABSTRACT Species occurrence in the landscape is influenced by habitat characteristics such as vegetation structure and resource availability. Habitat fragmentation causes a reduction or elimination of required resources, leading to the decline or disappearance of populations and species. Among carnivores, variables such as vegetation characteristics, prey availability, and human infrastructure were strongly associated with species occupancy. However, the relationship between these variables and ocelot (Leopardus pardalis) occupancy in fragmented landscapes remains poorly understood. The aim of this study was to investigate the influence of habitat characteristics, prey availability, and human infrastructure on ocelot occupancy in the protected areas of São Paulo. We sampled 55 sites using unbaited camera traps from October 2012 to August 2017 with a sampling effort of 10.175 trap-nights. We fitted models to determine how vegetation characteristics, prey availability, and human infrastructure affect ocelot occupancy. Ocelots were detected in 40% of sites, with a higher occupancy probability in sites with a greater relative abundance of prey and a farther distance from urban areas; however, there was no significant relationship with native vegetation. Thus, preservation of the ocelot requires the reduction of human impacts on these landscapes.

Delineation of blacktip shark (Carcharhinus limbatus) nursery habitats in the north-western Gulf of Mexico.

Coevolution with predators leads to the use of low-risk habitats by many prey species, which promotes survival during early developmental phases. These nurseries are valued by conservation and management agencies because of their contributions to adult populations. However, the physical and geographic characteristics, like shallow depths and isolation from other marine habitats, that restrict access to predators and thereby reduce risk to juvenile animals can also limit scientific research. Consequently, many nursery habitats are still unidentified and understudied. Here we used gillnet monitoring from 1982 to 2018 to delineate blacktip shark (Carcharhinus limbatus) nurseries in the north-western Gulf of Mexico and elucidated their physical, environmental and biological characteristics. Nursery habitats within estuaries (<2% of spatial area) were proximate to the Gulf of Mexico and exhibited significantly lower variability in salinity than non-nurseries. However, relative abundances of predators and prey were not significant delineators of nursery habitats. As such, food and risk may not influence juvenile blacktip habitat use as expected. Alternatively, reduced osmoregulatory stress attributed to predictable environments likely provides advantageous conditions for blacktips to develop foraging and antipredator tactics, which is vital prior to the winter migration of juvenile sharks into the Gulf of Mexico.

Comparison of the Relative Abundance of Potential Prey to the Diet of the Louisiana Pine Snake (Pituophis ruthveni)

Pituophis ruthveni (Louisiana Pine Snake) occurs in parts of western Louisiana and eastern Texas and was recently listed as a threatened species under the Endangered Species Act. It is considered a diet specialist because it mostly feeds upon Geomys breviceps (Baird's Pocket Gopher), which make up ∼75% of its estimated total prey biomass. Diet specialization is rare among vertebrates. One factor that can influence dietary diversity is the availability and abundance of prey items. To gain more insight on the Louisiana Pine Snake's diet, we sampled terrestrial and subterranean small mammals across 3 study sites within the range of this snake species in Louisiana to determine their relative abundance and availability. We compared these results to diet studies of the Louisiana Pine Snake to determine if any small mammal species were consumed more often than expected. The total of 59 small mammals captured consisted of Baird's Pocket Gopher, Sigmodon hispidus (Hispid Cotton Rat), Peromyscus spp. (deer mice), and Reithrodontomys spp. (harvest mice). Baird's Pocket Gopher had significantly higher relative abundances and biomass than terrestrial small mammals. When compared to proportions of actual consumed prey species, the Louisiana Pine Snake preyed upon Baird's Pocket Gopher significantly more than expected based on their availability in the environment. Finally, Chesson's prey selection index determined that the Louisiana Pine Snake positively selected Baird's Pocket Gopher, while the other species were either randomly or negatively selected. The results of this research provide some insight into the factors affecting the diet choices of the Louisiana Pine Snake.

Jaguars in the matrix: population, prey abundance and land-cover change in a fragmented landscape in western Mexico

AbstractHabitat fragmentation threatens biodiversity worldwide, particularly affecting large-bodied species that require vast territories and move across long distances, including most large felids. The jaguar Panthera onca has lost more than half of its habitat throughout its range and its subpopulations are becoming isolated, making them susceptible to local extinction. Knowledge about the status of its subpopulations in highly fragmented environments is lacking but urgently needed. Using camera traps during 2019–2020, we estimated number of individuals, age classes and sex ratio, occupancy, relative abundance and density of jaguars in Nayarit, western Mexico. We also determined the relative abundance of potential prey and estimated the land-cover change rate during 1999–2019, using GIS. We found that a resident subpopulation of five adult females, two adult males and one cub, at a high density (5.3 individuals/100 km2), is supported by at least 14 wild prey species. Natural habitat in the area is rapidly decreasing because of expanding agriculture and shrimp farming: agricultural areas increased from 39 to 50% and mangroves decreased from 35 to 26% of the study area over 20 years. The high jaguar population density and the diversity and relative abundance of remaining wild prey are remarkable, considering that natural habitat in the area is highly fragmented, shrinking rapidly and embedded in a matrix of human-dominated land-cover types. Effective conservation actions are needed urgently, including the protection of patches with native vegetation, reforestation to maintain connectivity between these patches, and the involvement of local communities.

Assassin snails (Anentome helena) as a biological model for exploring the effects of individual specialisation within generalist predators.

Quantifying feeding behaviour of generalist predators at the population and individual levels is crucial for understanding the structure and functioning of food webs. Individual predator/consumer feeding niches can be significantly narrower than that of the population across animal taxa. In such species, the population of a generalist predator becomes essentially an ensemble of specialist individuals and this often highly affects the dynamics of the prey-predator interactions. Currently, few experimental systems exist that are both easily technically manipulated in a lab and are reliable to accurately assess effects of individual specialisation within generalist predators. Here we argue that a freshwater predaceous snail, Anentome helena (also known as an ‘assassin snail’), is a convenient and reliable experimental system to study feeding of a generalist predator on multiple food types which exhibits well-pronounced specialisation of foraging individuals. Using A. helena we experimentally test: (i) how relative prey abundances in the environment affect the feeding patterns, (ii) whether the feeding patterns are consistent over the duration of the experimental period, and (iii) compare the feeding niche breadth of individuals to that of the laboratory population. By offering four different prey snail species, at a range of relative abundances, we show that there are consistent patterns in feeding. Importantly, the consumption of each prey was independent of the relative abundance at which they were present. Individual predators showed selectivity to a particular prey, i.e. the population of assassin snails seems to be formed of individuals that specialise on different prey. Our findings would contribute to the recent revision and the ongoing debate on the classification of predator species into generalists and specialists.

Trade-offs in prey quantity and quality in gray whale foraging

To forage optimally, predators face complex decisions regarding target prey distribution, quantity, and quality. We paired theodolite tracking of gray whalesEschrichtius robustusin Port Orford, Oregon, USA, with concurrent sampling of their zooplankton prey to examine foraging decisions relative to prey quantity (abundance) and quality (caloric content). We tested the hypotheses that whales (1) feed more than search or transit in areas with high quantity and quality prey and (2) select foraging habitat dominated by the calorically rich mysidNeomysis rayii. Relative prey abundance was assessed through standardized image analysis of camera drops, and zooplankton prey community was determined from net tows. These data were spatially interpolated and modeled to generate daily layers of species-specific prey abundance and calories (20 m grid) for comparison to whale behavior derived from tracking data. Whales fed significantly more in areas with higher prey abundance and calories than where they searched and transited. Whales increased foraging effort as overall prey availability increased, yet foraging probability was significantly correlated with the quantity and quality of the mysidHolmesimysis sculpta, which has significantly lower calories thanN. rayii. However, during the study period, the maximum abundance ofN. rayiiwas 4 times lower than that ofH. sculptaand never reached the quantity threshold determined by a logistic regression needed to support whale foraging behavior. Hence, gray whale prey selection involves trade-offs between prey quantity and quality to maximize energetic gain, and prey quality should be considered alongside abundance in ecological studies investigating predator decision-making.

Optimal Foraging Theory Explains Feeding Preferences in the Western Pacific Crown-of-Thorns Sea Star Acanthaster sp.

AbstractThe selectivity of crown-of-thorns sea stars (Acanthaster sp.) for different coral prey types was quantified in the field and laboratory and compared with a range of nutritional and food quality parameters as well as the growth performance of sea stars fed on different types of coral. Growth rates of small juvenile Acanthaster sp. without previous exposure to coral fed for 6.6 months on 15 individual species of corals showed that the highest rates of growth were achieved on the same types of corals for which adult sea stars show the strongest preference, both in the field and in controlled aquarium conditions. Small Acanthaster sp. (ca. 20 mm, 0.5 g) fed on Acropora formosa, Stylophora pistillata, Seriatopora hystrix, and Pocillopora damicornis increased in size by an average of 9.2-10.7 mm (4.2-5.6 g) per month, compared with 0.1-0.4 mm (0.004-0.028 g) per month on coralline algae fed controls and species such as Porites lutea, Porites lichen, Lobophyllia hemprichii, and Turbinaria mesenterina. Field studies on the same reef where the parents of these juvenile sea stars were collected demonstrated a strong sequential preference for acroporid and then pocilloporid corals, with faviid, merulinid, and poritid corals selected significantly less frequently than other corals when their relative abundance was taken into account. This order of preference by adult field-collected sea stars was confirmed and exhibited even more emphatically in aquarium experiments, where the relative abundance of prey species could be controlled. The growth experiments and measurements of comparative food value between preferred and non-preferred coral prey suggest that feeding preferences in Acanthaster sp. for Acropora and pocilloporids arose consistent with optimal foraging theory and evolved in response to this species being able to feed successfully and efficiently. The high abundance and, therefore, encounter rate of Acropora and pocilloporids is not considered to be an important factor in the evolution of feeding preferences, although relative abundance of alternative prey does affect selectivity. Individual growth and population fitness and reproductive output of Acanthaster sp. will be enhanced by preferential feeding on acroporid and pocilloporid corals, reinforcing the importance of optimal foraging theory in the evolution of feeding preferences.

Negative frequency-dependent prey selection by wolves and its implications on predator–prey dynamics

Many species exhibit selective foraging behaviour, where consumers use a nonrandom subset of available food types. Yet little is known about how selective foraging behaviour varies with environmental conditions and the community level consequences of such selection dynamics. We examined selective foraging by wolves preying primarily on elk in Yellowstone National Park (YNP) over a 12-year period and on moose in Isle Royale National Park (IRNP) over a 47-year period. Specifically, we assessed how selection for calves and senescent adults varied with their frequency in the environment, wolf abundance and winter severity. Selection for senescent adults decreased as the relative abundance of senescent prey increased (i.e. negative frequency-dependent selection) in both study sites. In IRNP, selection for calves was also negatively frequency dependent and declined with increasing wolf abundance. These results are inconsistent with the pattern of positive frequency-dependent selection expected under the prey-switching hypothesis. These results suggest that selection is primarily driven by intraspecific differences in prey vulnerability and wolves’ interest in minimizing their risk of injury, as opposed to maximizing intake rates. Lastly, we ran simulations to evaluate how predator–prey dynamics were influenced by dynamic patterns of selection, like those observed in YNP and IRNP. The simulations indicated that predators are more efficient (i.e. steeper slope of the numerical response) when selection for calves is negatively frequency dependent, which results in a lower mean abundance of prey. More importantly, predation is a stronger destabilizing force when selection for calves is negatively frequency dependent. That stronger destabilizing force is indicated by greater variability in the abundance of prey and predators, prey populations being less resilient and a steeper negative slope of the relationship between predation rate and prey population growth rate. As such, our simulation analyses suggest that some of the observed patterns of negative-frequency dependent selection may have important consequences for predator–prey dynamics. • Wolves showed negative frequency-dependent selection for calves and senescent prey. • Wolves did not exhibit prey-switching behaviour when preferred prey became rare. • Selection is likely driven by the predator's interest to reduce their risk of injury. • Selection for calves may result in more efficient predators and less resilient prey.

Does Habitat Diversity Modify the Dietary and Reproductive Response to Prey Fluctuations in a Generalist Raptor Predator, the Eurasian Buzzard Buteo buteo?

Predators can modify their diet and demography in response to changes in food availability and habitat quality. I tested the prediction that some species can change their predation pattern, between specialist type and generalist type, depending on the complexity of habitat structure. It was hypothesized that their dietary response is stronger in diversified habitats than in simplified ones, but the opposite tendency occurs in the case of reproductive response. The nestling diet and breeding success of the Eurasian Buzzard Buteo buteo, the abundance of its main prey (the common vole Microtus arvalis), and that of the most important alternative prey group (passerines) were estimated over ten years in two types of agricultural habitat in western Poland, i.e., in the diversified habitat of small fields and the simplified habitat of large fields. The vole abundance was higher in large fields, but the abundance of passerines was greater in small fields. The frequency of voles in the Eurasian Buzzard nestling diet was higher in large fields than in small fields and increased with the abundance of this prey in crop fields. However, no difference in the relationship between the vole frequency in the diet of Eurasian Buzzards and the abundance of voles was found between the two habitat types. The breeding success of Eurasian Buzzards was dependent on the vole abundance, but this relationship did not differ between the two field types. It seems that the pattern of dietary and reproductive response of Eurasian Buzzards depends on the actual availability of individual prey species, which can be modified by habitat quality, rather than on relative prey abundance.

Unravelling diet composition and niche segregation of colonial waterbirds in a Mediterranean wetland using stable isotopes

Rice fields and waterbirds are an example of a synergy that can occur between agriculture and conservation. This connection is especially relevant during the farming period, when nesting waterbirds need to obtain resources to cover their energy requirements and those of their chicks in rice fields. However, new farming techniques may potentially put fulfilling this role at risk. Studies on how species use rice fields to feed during this critical period are essential to understand waterbird population dynamics and to optimize conservation measures. At present, several species of colonial birds in l’Albufera de València (Spain) that depend on trophic resources available in rice fields have decling populations and decreases in productivity. We therefore assessed trophic niche segregation in the diet of chicks of a waterbird community composed of seven species through stable isotope analyses of carbon (δ13C) and nitrogen (δ15N) obtained from chick blood and tissue samples of potential prey. According to trophic niche widths, chicks of Black‐headed GullChroicocephalus ridibundusand Gull‐billed TernGelochelidon niloticashowed a similar diet, although Gull‐billed Tern had a major trophic specialization. The Western Cattle EgretBubulcus ibisfed its chicks in a wider range of different habitats, with organisms located at the base of the food chain and with a greater importance of terrestrial prey than other species. Conversely, the Glossy IbisPlegadis falcinellushad a more differentiated diet, mostly in freshwater habitats and mainly consuming odonates. Grey HeronArdea cinerea, Little EgretEgretta garzettaand Squacco HeronArdeola ralloidesshowed overlap between their niches, largely explained by the presence and abundance of cyprinid fish and odonates in their diets. Our results suggest a less important role than expected of Red‐swamp CrayfishProcambarus clarkii, and a more important role of odonates despite being a less energy‐rich prey. In conclusion, the diet of generalistic species of waterbirds in this study suggests that their trophic niches can overlap when relative prey abundance is high.