Plasticity of Noddy Parents and Offspring to Sea-Surface Temperature Anomalies

Behavioral and/or developmental plasticity is crucial for resisting the impacts of environmental stressors. We investigated the plasticity of adult foraging behavior and chick development in an offshore foraging seabird, the black noddy (Anous minutus), during two breeding seasons. The first season had anomalously high sea-surface temperatures and ‘low’ prey availability, while the second was a season of below average sea-surface temperatures and ‘normal’ food availability. During the second season, supplementary feeding of chicks was used to manipulate offspring nutritional status in order to mimic conditions of high prey availability. When sea-surface temperatures were hotter than average, provisioning rates were significantly and negatively impacted at the day-to-day scale. Adults fed chicks during this low-food season smaller meals but at the same rate as chicks in the unfed treatment the following season. Supplementary feeding of chicks during the second season also resulted in delivery of smaller meals by adults, but did not influence feeding rate. Chick begging and parental responses to cessation of food supplementation suggested smaller meals fed to artificially supplemented chicks resulted from a decrease in chick demands associated with satiation, rather than adult behavioral responses to chick condition. During periods of low prey abundance, chicks maintained structural growth while sacrificing body condition and were unable to take advantage of periods of high prey abundance by increasing growth rates. These results suggest that this species expresses limited plasticity in provisioning behavior and offspring development. Consequently, responses to future changes in sea-surface temperature and other environmental variation may be limited.     

Impacts of Agriculture on the Diet and Productivity of Mackinder's Eagle Owls (Bubo capensis mackinderi ) in Kenya

Land conversion for agriculture is an increasing threat to biodiversity conservation, but its ecological effects on African birds is practically unknown. We investigated the impacts of agriculture on the diet and productivity of a small, disjunct population of Mackinder's eagle owls ( Bubo capensis mackinderi  ) in central Kenya. Owl diet was determined by analysis of pellets and other remains and compared to small mammal populations estimated by live trapping in two habitats. Small mammal abundance was low and averaged 7.4 small mammals/ha in farms and 0.5 small mammals/ha in grassland. Owls consumed a wide diversity of prey. The majority were mammals (87%) followed by birds (7%) and insects (5%). The percentage of small mammals in owl diet correlated positively with the relative abundance of small mammals during monthly trapping sessions. Diet composition did not influence owl breeding success. Farming activities affected owl diet composition through crop production. The amount of maize, peas, and carrots growing in farms was correlated with the abundance of Mastomys sp. and Procavia sp. in the owl's diet. Agricultural activities had a large effect on Mackinder's eagle owl diet by increasing the abundance of certain small-mammal prey and attracting owl prey to farms, though farming practices harmful to owls were observed.     

The stress hormone corticosterone in a marine top predator reflects short‐term changes in food availability

In many seabird studies, single annual proxies of prey abundance have been used to explain variability in breeding performance, but much more important is probably the timing of prey availability relative to the breeding season when energy demand is at a maximum. Until now, intraseasonal variation in prey availability has been difficult to quantify in seabirds. Using a state‐of‐the‐art ocean drift model of larval cod Gadus morhua, an important constituent of the diet of common guillemots Uria aalge in the southwestern Barents Sea, we were able to show clear, short‐term correlations between food availability and measurements of the stress hormone corticosterone (CORT) in parental guillemots over a 3‐year period (2009–2011). The model allowed the extraction of abundance and size of cod larvae with very high spatial (4 km) and temporal resolutions (1 day) and showed that cod larvae from adjacent northern spawning grounds in Norway were always available near the guillemot breeding colony while those from more distant southerly spawning grounds were less frequent, but larger. The latter arrived in waves whose magnitude and timing, and thus overlap with the guillemot breeding season, varied between years. CORT levels in adult guillemots were lower in birds caught after a week with high frequencies of southern cod larvae. This pattern was restricted to the two years (2009 and 2010) in which southern larvae arrived before the end of the guillemot breeding season. Any such pattern was masked in 2011 by already exceptionally high numbers of cod larvae in the region throughout chick‐rearing period. The findings suggest that CORT levels in breeding birds increase when the arrival of southern sizable larvae does not match the period of peak energy requirements during breeding.     

Breeding success of an endangered island endemic kestrel increases with extent of invasion by an alien plant species

The Mauritius Kestrel Falco punctatus, once the rarest kestrel worldwide, became an icon of bird conservation after it recovered from four to six individuals in 1974 to some 800 by 2005 following intense conservation management. Its population however then halved within about a decade prompting a re-evaluation of the IUCN status and up listing of the species in 2014 and an increased conservation attention. Drivers of this new decline are unclear and the influence of habitat structure and diet on breeding success may be important contributors but have received relatively little attention, particularly in the way they may interact to influence production of new fledglings. We address this knowledge gap by studying whether breeding success is influenced by habitat structure (in terms of cover of the invasive Ravenala in native habitats, an alien plant causing strong structural shift in the forests that it invades, and extent of cleared area), diet composition and food pass frequency (as a proxy for food intake) and food quality at 28 nests of a re-introduced kestrel population in south east Mauritius during the 2015–2016 breeding season. The kestrel’s diet comprised native and alien birds, reptiles, insects, and small alien mammals, with a disproportionately high proportion of Phelsuma gecko. A higher frequency of food provisioning and percentage cover of Ravenala both contributed to higher breeding success. Ravenala may increase gecko density or increase gecko detectability and predation by the kestrel, or both, while changed land use (pasture and sugar cane fields) may increase prey diversity in the form of non-forest prey known to be eaten by Kestrels (e.g. alien agamids, small mammals and birds). These prey related influences on breeding suggest that the Bambou mountain range provides a human-generated novel ecosystem altering food availability and increasing the kestrel’s breeding success. However, Ravenala is an invasive alien species harmful to the wider forest biodiversity. Progressive weeding of Ravenala and concurrent re-introduction and augmentation of native palms and Pandanus species which geckos can use at comparable densities to Ravenala, is recommended. This would likely improve the kestrel’s hunting habitat quality and maintain high gecko density or detectability and the vegetation structure required for hunting manoeuvrability and prey availability without the negative consequences of invasive Ravenala.     

Factors influencing diet variation in a generalist predator across its range distribution

Factors linked with intraspecific variation in trophic diversity are still poorly understood in generalist species like the Montagu’s harrier (Circus pygargus) but may have important implications for conservation management at a wide scale. We described geographic patterns of Montagu’s harrier diet across Eurasia, gathering diet data from 30 studies in 41 areas from 11 countries. We grouped prey as invertebrates, reptiles, small mammals, large mammals, eggs, small birds and large birds, and calculated the contribution of each prey type to the diet (as % biomass) and Shannon’s Diversity Index for each study site. We analysed qualitative estimates of prey abundance in relation to latitude and longitude, then diet composition in relation to habitat of the study area and prey abundance estimates. Diet diversity of Montagu’s harriers increased from north to south, while abundance of all prey groups other than small mammals showed the opposite trends. Agricultural areas in northern latitudes seemed to hold high densities of small mammals, but low densities of alternative prey. Overall, birds were the main prey in most of Montagu’s harrier’s distribution range, although the relative importance of each prey type in the diet was significantly explained by its local abundance and habitat, confirming the opportunistic foraging strategy of this raptor species. Consumption of mammals was an exception to this trend, being negatively associated with the abundance of alternative prey, suggesting that this prey is not preferred. Trophic diversity in this species could be influenced by land-use changes through variations in the abundance and availability of prey, which could impact its population dynamics. This may be particularly important for northern populations of Montagu’s harriers breeding in agricultural habitats, where trophic diversity is already low.     

Food web structure and climate effects on the dynamics of small mammals and owls in semi-arid Chile

Population dynamics of small mammals and predators in semi-arid Chile is positively correlated with rainfall associated with incursions of El Niño (El Niño Southern Oscillation: ENSO). However, the causal relationships between small mammal fluctuations, predator oscillations, and climatic disturbances are poorly understood. Here, we report time series models for three species of small mammal prey and two species of owl predators. The large differences in population fluctuations between the three small mammal species are related to differences in their respective feedback structures. The analyses reveal that per capita growth rate of the leaf-eared mouse is a decreasing function of log density and of log barn owl abundance together with a positive rainfall effect. In turn, per capita population growth rate ( R -function) of the barn owl is a negative function of log barn owl abundance and a positive function of leaf-eared mouse abundance, suggesting a predator–prey interaction. The dramatic population fluctuations exhibited by leaf-eared mouse ( Phyllotis darwini ) are caused by climate effects coupled with a complex food web architecture.     

Seasonal differences in rainfall,food availability,and the foraging behavior of Tropical Kingbirds in the southern Amazon Basin

ABSTRACT Little is known about the relationship between seasonal food availability and the foraging strategies of insectivorous Neotropical birds. We studied a population of Tropical Kingbirds (Tyrannus melancholicus), a primarily insectivorous species, in eastern Bolivia to examine relationships between rainfall, food availability, and foraging strategies throughout the year. Our study site in the southern Amazon Basin was characterized by strong seasonal variation in the abundance of the kingbird's main insect prey (coleopterans and hymenopterans), with reduced abundance during the nonbreeding season which largely overlaps the dry season. Overall, mean search times for insect prey by Tropical Kingbirds during the breeding (96.9 ± 85.6 [SD] sec) and nonbreeding (83.7 ± 91.2 sec) seasons did not differ (P= 0.23). However, during the nonbreeding season, kingbird search times were negatively, but nonsignificantly, correlated with coleopteran abundance (r²= 0.43, P= 0.16) and significantly and negatively correlated with hymenopteran abundance (r²= 0.72, P= 0.03). Although insect abundance differed seasonally, kingbird search times did not, perhaps because kingbirds forage on a greater variety of insects during the nonbreeding season or, during the breeding season, kingbird search times may be influenced by the need to monitor and defend nests as well as constraints on the types of prey that can be fed to nestlings. However, the reduced abundance of their primary insect prey and negative relationships between the abundance of those prey and search times during the dry, nonbreeding season suggest that Tropical Kingbirds in southern Amazonia may be food limited, potentially explaining why some migrate and spend that season elsewhere.     

Biases in Studying the Diet of the Bearded Vulture

Abstract: We compared methods of assessing the diet of the bearded vulture (Gypaetus barbatus) during the nestling period in the Pyrenees, northeast Spain. We determined diet from direct observations of food items delivered to the nest, recent prey remains present in the nest, remains collected in the nests after fledging, and remains collected in the ossuaries (bone-breaking sites). Data suggest that direct observation (food items delivered and recent prey remains present in the nest) is the only valid method of assessing the bearded vulture's diet accurately. Remains overestimated the presence of large mammals, such as cows (Bos taurus) and horses (Equus caballus), Suidae, and birds; delivered samples contained a higher proportion of small mammals, medium-sized mammals, micromammals, and reptiles. Ossuaries also differed from delivered samples because remains collected there overestimated large and medium-sized mammals. Concerning the skeletal parts, ossuaries, compared to all other methods, underestimated extremities and overestimated long bones, such as femur, humeri and tibiae, scapulae, vertebrae, and skulls. Remains samples, which overestimated scapulae, also differed from delivered and present samples. Our results suggest that bearded vultures favor extremities of prey (78% of the mammal remains, which make up 95% of the diet). The prevalence of small carcasses (almost 17%) suggests that vultures select small animals for food for the young. Because food quality may influence breeding success, future conservation projects based on the selective provision of food to breeding pairs should add to food stations meat remains and small carcasses consistent with our assessment of the birds’ dietary needs.     

Episodic outbreaks of small mammals influence predator community dynamics in an east African savanna ecosystem

Little is known about the dynamics of small mammals in tropical savanna: a critical gap in our understanding of Africa's best known ecosystems. Historical evidence suggested small mammals peak in abundance (outbreak) in Serengeti National Park (SNP), as in agricultural systems. We asked 1) what are bottom–up drivers of small mammals and 2) do predators have top–down effects? We documented dynamics of small mammals, birds of prey, and mammalian carnivores in SNP and agricultural areas. We used climatic fluctuations and differences between unmodified and agricultural systems as perturbations to examine trophic processes, key to understanding responses to climate change and increasing human pressures. Data were derived from intermittent measures of abundance collected 1968–1999, combined with systematic sampling 2000–2010 to construct a 42‐year time series. Data on abundance of black‐shouldered kites (1968–2010), eight other species of rodent‐eating birds (1997–2010), and 10 carnivore species (1993–2010) were also collated. Outbreaks occurred every 3–5 years in SNP, with low or zero abundance between peaks. There was a positive relationship between rainfall in the wet season and 1) small mammal abundance and 2) the probability of an outbreak, both of which increased with negative Southern Oscillation Index values. Rodent‐eating birds and carnivores peaked 6–12 months after small mammals. In agricultural areas, abundance remained higher than in natural habitats. Abundances of birds of prey and mammalian carnivores were extremely low in these areas and not related to small mammal abundance. Small mammals are an important food resource for higher trophic levels in the Serengeti ecosystem. Changes in climate and land use may alter their future dynamics, with cascading consequences for higher trophic levels, including threatened carnivores. Although outbreaks cause substantial damage to crops in agricultural areas, small mammals also play a vital role in maintaining some of the diversity and complexity found in African savanna ecosystems.     

Variation in the feeding pattern of red foxes in relation to changes in anthropogenic resource availability in a rural habitat of western Poland

The feeding pattern of red foxes Vulpes vulpes, i.e., the composition of their diet and dietary responses to fluctuations in the abundance of common voles Microtus arvalis were compared in the periods before and after the limitation of anthropogenic food availability in a rural area in western Poland. During the winter seasons of 1996/97–2014/15, the diet of the foxes was estimated by analysing the stomach contents of individuals shot from November to March and the index of vole abundance was obtained by counting their burrow entrances. The major component of the fox diet over the entire study period was anthropogenic food (mainly, the remains of farm animals) that showed both the highest average proportion in the stomach content volume (53.4%) and the highest average frequency of occurrence in the stomachs (62.7%), whereas small mammals were the second important component (27.5% and 54.2%, respectively). The frequency of anthropogenic food decreased and the frequencies of wild ungulate carrion and other wild vertebrates (mainly birds) increased after the limitation of anthropogenic resources. The observed fluctuations in the index of vole abundance resulted in positive changes in the small mammal frequency and negative changes in the anthropogenic food frequency, but the course of these relationships did not significantly differ between the two periods. The frequency of hares in fox stomachs did not change significantly between these periods, but recently the occurrence of hares in the diet of foxes increased with vole abundance. This study indicated that the reduction of anthropogenic food availability for carnivorous mammals may result in their switching to other prey species and potentially may have a negative influence on the demography of such prey species.     

Oscillations in large mammal populations: are they related to predation or rainfall?

Cyclic population dynamics is relatively common among populations of small mammals in high latitudes but is not yet established among African savanna ungulates. However, oscillations may be expected in large mammal populations subject to quasi‐periodic oscillations in regional rainfall. We evaluated evidence for environmentally entrained oscillations in a large‐mammal predator–prey system in Kruger National Park (KNP), South Africa, where rainfall exhibits quasi‐periodic oscillations. The evaluation is based on analysis of comparative changes in the abundance of twelve ungulate species throughout South Africa's KNP using population counts over the period 1965–1996. We present evidence suggesting that (i) twelve ungulate populations display cyclic variability with half‐periods ranging between 10 and 18 years, (ii) this variability was associated with lagged rainfall between 3 and 10 years back in the past for different ungulate species, and (iii) the ungulate species respond in contrasting ways to rainfall, with some reaching highest abundance during periods of low rainfall and others under conditions of high rainfall. These findings are not consistent with the response pattern we would expect if the population oscillations were driven directly by the rainfall influence on food availability. Instead they seem to be an outcome of predator–prey interactions, which are entrained by the effect of rainfall on habitat conditions affecting the relative susceptibility of the different ungulate species to predation.     

The relevance of food peak architecture in trophic interactions

Phenological shifts and associated changes in the temporal match between trophic levels have been a major focus of the study of ecological consequences of climate change. Previously, the food peak has been thought to respond as an entity to warming temperatures. However, food peak architecture, that is, timings and abundances of prey species and the level of synchrony between them, determines the timing and shape of the food peak. We demonstrate this with a case example of three passerine prey species and their predator. We explored temporal trends in the timing, height, width, and peakedness of prey availabilities and explained their variation with food peak architecture and ambient temperatures of prebreeding and breeding seasons. We found a temporal match between the predator's breeding schedule and food availability. Temporal trends in the timing of the food peak or in the synchrony between the prey species were not found. However, the food peak has become wider and more peaked over time. With more peaked food availabilities, predator's breeding success will depend more on the temporal match between its breeding schedule and the food peak, ultimately affecting the timing of breeding in the predator population. The height and width of the food peak depended on the abundances and breeding season lengths of individual prey species and their reciprocal synchronies. Peakednesses of separate prey species' availability distributions alone explained the peakedness of the food peak. Timing and quantity of food production were associated with temperatures of various time periods with variable relevance in different prey species. Alternating abundances of early and late breeding prey species caused high annual fluctuation in the timing of the food peak. Interestingly, the food peak may become later even when prey species' schedules are advanced. Climate warming can thus produce unexpected changes in the food availabilities, intervening in trophic interactions.     

Habitat use by breeding Tree Sparrows Passer montanus

Tree Sparrows Passer montanus showed a strong preference for nest-sites adjacent to wetland habitats, and avoidance of sites on intensively managed mixed farmland distant from Rutland Water. A variety of wetland edge habitats were frequently used by foraging adult birds when provisioning nestlings, and invertebrate prey of aquatic origin was frequently recorded in chick diet. We suggest that the wetland edge habitats at the study sites played a key role in providing adequate diversity and availability of suitable invertebrate prey to allow successful chick rearing throughout the long breeding season of this multi-brooded passerine. It is possible that large areas of formerly occupied farmland in the UK no longer provide these invertebrate resources due to the effects of intensification in the late 20th century. There was no evidence that the availability of supplementary seed food within 1 km of the nest-site influenced nest-site choice, or affected productivity. It is probable that the importance of seed food resources to the persistence of Tree Sparrow populations operates on a larger spatial scale than that tested in this study, due to the greater mobility of Tree Sparrows in the non-breeding season, when seed resources are most likely to be a key limiting factor. When considering conservation management aimed at recovering breeding populations of Tree Sparrows, the key resources of seed food, invertebrate food and nest-sites must be made available at appropriate spatial scales.     

Diet and foraging opportunism of the Guiana dolphin (Sotalia guianensis) in the Abrolhos Bank,Brazil

Diet analysis allows exploring how coastal dolphins interact with the environment and their role in the marine food webs. We studied the diet and feeding ecology of the Guiana dolphin, Sotalia guianensis, through analysis of stomach content from 42 animals stranded on the eastern coast of Brazil. A total of 1,336 semidigested prey items (fish, otoliths, cephalopod beaks, and crustaceans) were identified. Teleost fish comprised the most frequent food item (92% of the total), followed by cephalopods, and crustaceans. Prey belonged to 34 taxa and richness in individual stomachs varied from 1 to 15 prey taxa. Prey were generally small, but showed a significant trend to increase in size with dolphin length. The main prey of Guiana dolphins were demersal, estuarine, and sound-making fish such as catfish and sciaenids. No sex-related differences in diet were found. Diet composition varied seasonally and occurrence of prey items was coherent with breeding or high abundance periods of some fish species and squids. Our study shows the importance of demersal prey from estuarine and soft-sediment habitats to Guiana dolphin in the Abrolhos Bank and reveals that feeding habits are generalist and opportunistic, with diet reflecting the seasonal abundance and availability of prey.     

Food partitioning between breeding White-tailed Kites (Elanus leucurus; Aves; Accipitridae) and Barn Owls (Tyto alba; Aves; Tytonidae) in southern Brazil.

I examined the diet of breeding White-tailed Kites (Elanus leucurus; Aves; Accipitridae) and Barn Owls (Tyto alba; Aves; Tytonidae) in an agrarian area of southern Brazil by analyzing regurgitated prey remains. The objective was to evaluate how these raptors, which differ markedly in their hunting activity periods (owls are nocturnal and kites diurnal), share their mammalian food component. 2,087 prey consumed by Barn Owls and 1,276 by White-tailed Kites were identified. They presented a high overlap of food-niches (Piankas index was 0.98). Based on the daily activity period of their main small mammal prey, a lower overlap would be expected. The crepuscular/nocturnal Mus musculus was the main prey for the diet of breeding Barn Owls (81%) and White-tailed Kites (63%). This small exotic rodent provided 63% of the small mammal biomass ingested by owls and 44% by kites. Larger native small mammals were also considered important for the diet of kites, mainly because of their biomass contribution. Although these raptors differ markedly in their hunting activity periods, Barn Owls and White-tailed Kites are very similar predators in southern Brazil, overlapping their diets.     

The effects of rainfall on different components of seasonal fecundity in a tropical forest passerine

Seasonal fecundity is a composite metric that is determined by component parameters such as clutch size, nest survival and re‐nesting probability. Many of these component parameters are known to vary with environmental conditions, in particular rainfall prior to or during the breeding season. In some species, seasonal fecundity is positively related to rainfall, but little is known about which component parameters of seasonal fecundity respond most strongly to rainfall. We used intensive nest monitoring of a multi‐brooded tropical forest passerine, the Montserrat Oriole Icterus oberi, to examine the effects of rainfall during the pre‐breeding season on component parameters of annual fecundity. We monitored all nests of a total of 42 pairs over 5 years in which rainfall varied substantially. We then related clutch size, nest survival, onset and length of the breeding season, re‐nesting probability and re‐nesting interval to pre‐breeding season rainfall using generalized linear mixed models that accounted for random variation across sites and individual pairs, and incorporated other variables known to affect the response. Higher pre‐breeding season rainfall led to an increase in clutch size and a decrease in re‐nesting interval, but nest survival, re‐nesting probability and length of the breeding season were not affected by variation in rainfall. The onset of the breeding season was delayed in very dry years. We conclude that higher rainfall is likely to increase food availability and thus body condition of female Montserrat Orioles, leading to an increase in fecundity due to larger clutch sizes.     

The impact of vegetation characteristics and prey availability on breeding habitat use and diet of Little Owls Athene noctua in Central European farmland

Capsule Foraging habitats are determined by vegetation characteristics rather than the availability of insect prey.

Aims To determine the diet composition of Little Owls in relation to the availability of insects at foraging sites, and to elucidate the main factors determining the owls’ habitat choice.

Methods The feeding ecology of Little Owls was studied during the 2002 breeding season in the agricultural landscape of western Bohemia (Czech Republic), where its population is in decline. Diet composition was determined by pellet analysis. Insect availability was studied using pitfall traps in the two most important Little Owl foraging habitats. For both habitats, we assessed the main vegetative characteristics (average and maximum vegetation height, vegetation density).

Results Based on number, insects were the most dominant prey, followed by small mammals; based on weight, insects comprised only a minor part of the diet. Among insect prey, Carabidae beetles were the most abundant. The proportion of insect numbers was strongly positively correlated with advancing day of the season and negatively correlated with the proportion of vertebrates. Although the highest densities of Carabidae were found in cornfields Little Owls significantly preferred grassland habitats, probably because of the lower vegetation cover.

Conclusions The availability of short sward vegetation in grassland habitats during the breeding season may play a key role in the conservation of Little Owls in central European farmland.     

Importance of feeding ecology to the reproductive success of Blackbirds Turdus merula nesting in rural habitats

The feeding ecology of Blackbirds Turdus merula breeding in contiguous woodland and farmland habitats was studied over three years. The aim of the study was to investigate how reproductive success was influenced by nestling diet and the provisioning rates of parents feeding nestlings. Parental provisioning rates increased with brood size, and consequently individual nestlings were no lighter in larger broods. None of the environmental factors measured had strong effects on parental provisioning rate. The nestling diet was dominated by caterpillars and earthworms, the former occurring in a short period in the middle of the breeding season. The availability of earthworms was higher in woodland and was dependent on rainfall in farmland. Nestling mass and provisioning rates were marginally higher under predominantly earthworm diets. Nestling mass increased with rainfall in farmland only, and was higher in farmland than in woodland or woodland-edge, although it is doubtful whether this result is of any significance for fledgling survival. Overall, Blackbirds were able to provision their nestlings adequately throughout the breeding season across a range of conditions. There was no evidence to suggest that reproductive success was constrained by aspects of feeding ecology within the natural range of brood size.     

Tawny owl prey remains indicate differences in the dynamics of coastal and inland vole populations in southern Finland

Some studies suggest that mild winters decrease overwinter survival of small mammals or coincide with decreased cyclicity in vole numbers, whereas other studies suggest non-significant or positive relationships between mild winter conditions and vole population dynamics. We expect for the number of voles to be higher in the rich and low-lying habitats of the coastal areas than in the less fertile areas inland. We assume that this geographical difference in vole abundances is diminished by mild winters especially in low-lying habitats. We examine these relationships by generalized linear mixed models using prey remains of breeding tawny owls Strix aluco as a proxy for the abundance of voles. The higher number of small voles in the coastal area than in the inland area suggest that vole populations were denser in the coastal area. Vole populations of both areas were affected by winter weather conditions particularly in March, but these relationships differed between areas. The mild ends of winter with frequent fluctuations of the ambient temperature around the freezing point (“frost seesaw”) constrained significantly the coastal vole populations, while deep snow cover, in general after hard winters, was followed by significantly lowered number of voles only in the inland populations. Our results suggest that coastal vole populations are more vulnerable to mild winters than inland ones. We also show that tawny owl prey remains can be used in a meaningful way to study vole population dynamics.     

Dietary overlap and seasonality in three species of mormoopid bats from a tropical dry forest

Competing hypotheses explaining species’ use of resources have been advanced. Resource limitations in habitat and/or food are factors that affect assemblages of species. These limitations could drive the evolution of morphological and/or behavioural specialization, permitting the coexistence of closely related species through resource partitioning and niche differentiation. Alternatively, when resources are unlimited, fluctuations in resources availability will cause concomitant shifts in resource use regardless of species identity. Here, we used next‐generation sequencing to test these hypotheses and characterize the diversity, overlap and seasonal variation in the diet of three species of insectivorous bats of the genus Pteronotus. We identified 465 prey (MOTUs) in the guano of 192 individuals. Lepidoptera and Diptera represented the most consumed insect orders. Diet of bats exhibited a moderate level of overlap, with the highest value between Pteronotus parnellii and Pteronotus personatus in the wet season. We found higher dietary overlap between species during the same seasons than within any single species across seasons. This suggests that diets of the three species are driven more by prey availability than by any particular predator‐specific characteristic. P. davyi and P. personatus increased their dietary breadth during the dry season, whereas P. parnellii diet was broader and had the highest effective number of prey species in all seasons. This supports the existence of dietary flexibility in generalist bats and dietary niche overlapping among groups of closely related species in highly seasonal ecosystems. Moreover, the abundance and availability of insect prey may drive the diet of insectivores.