Influence of different weather aspects on breeding performance, food supply and nest-space use in hoopoe offspring

In this study, we investigated the influence of different weather aspects on breeding performance, food supply and nest-space use in hoopoe offspring (Upupa epops). Camera recordings of 88 nests were used to examine how ambient environmental conditions influence food supply, offspring nest-space use and the trade-off nestlings face regarding the two mainly used locations in the nest. Therefore, we provide a comprehensive analysis involving different factors including weather parameters together with food provisioned to nestlings on different temporal scales to identify the factors having the most influence on nest-space use. We found that different breeding conditions significantly influenced how nestlings used the nest. During excessively humid weather, nestlings spent more time under the entrance hole when small food was delivered. However, nestlings supplied with large prey more often remained hidden in the distant area, despite the adverse weather situation. In all three aspects and temporal scales, our analysis confirmed that prey was the most important factor influencing offspring nest-space use, suggesting a crucial role of large insects for hoopoes. Finally, we found that long-term effects of weather affect overall food provisioned to nestlings and thus offspring behaviour. We provide evidence that parental feeding location and prey size, which are in turn influenced by weather conditions, are the most influential factors for nest-space use. This study expands our knowledge of parent–offspring communication and how environmental factors may lead to differential nest-space use, which may be regarded as the earliest form of habitat preference in birds. Significance statement Nests are usually constrained in space but designed to protect offspring from the environment while giving them limited possibilities to express behavioural diversity. This is particularly true for bird nests, where nestlings are usually packed in close contact with one another and without much space for movement, except begging. Here we demonstrate that nest features, such as available nest space together with environmental conditions surrounding a nest, influence nestling strategies and behaviours, including social interactions between nest mates, which further leads to fitness consequences. Our results seem to be of great importance for habitat selection theory in birds, in particular regarding the early development of habitat preferences (imprinting) and use. On the other hand, the result may also have important implications for conservation issues given that nestling behaviour may be used as a determinant of environmental quality.

Effect of Artificial Regime Shifts and Biotic Factors on the Intensity of Foraging of Planktivorous Fish

It is still to be confirmed whether global warming with its predicted elevated water temperature will cause an increase in predation and alter phenological and physiological processes leading to changes in the size of aquatic organisms. In an experimental system of water column stratification simulating a natural combination of field conditions, we created artificial abiotic factors that mimicked the natural environment, i.e., light intensity, oxygen conditions, and thermal stratification. Subsequently, we added biotic factors such as algae, Daphnia, and planktivorous fish. We studied the intensity of foraging of planktivorous fish on individuals of Daphnia per min in different conditions of biotic and abiotic gradients. We demonstrated a possible scenario involving the risk of elimination of large prey within macrocladocera communities by predatory pressure as a result of climate change. A higher intensity of foraging of planktivorous fish caused or increased the occurrence of larger groups of planktonic animals with a smaller body size. The mechanisms of a future scenario were discovered at a higher trophic level in the aquatic environment.

Prey preference of a wasp determined by nest size supports the role of natural selection in body size evolution in Cassidinae leaf beetles

The prey preference of a predator can impose natural selection on prey phenotypes, including body size. Despite evidence that large body size protects against predation in insects, the determinants of body size variation in Cassidinae leaf beetles are not well understood. We examined the prey preference of the digger wasp Cerceris albofasciata, a specialist predator of adult Cassidinae leaf beetles, and found evidence for natural selection on prey body size. The wasp hunted prey smaller than the size of their nest entrance. However, the wasp preferred larger prey species among those that could be carried into their nest. Thus, the benefits of large prey and the cost associated with nest expansion might determine the prey size preference. As expected from the prey species preference, the wasp preferred small individuals of the largest prey species, Thlaspida biramosa, and large individuals of the smallest prey species, Cassida piperata, resulting in natural selection on body sizes. In intermediate-sized prey species, however, there was no evidence for selection on body size. Natural selection on body size might explain the variation of prey morphologies that increase body size, such as explanate margins, in this group.

Feeding ecology of broadbill swordfish (Xiphias gladius) in the California Current

The feeding ecology of broadbill swordfish (Xiphias gladius) in the California Current was described based on analysis of stomach contents collected by federal fishery observers aboard commercial drift gillnet boats from 2007 to 2014. Prey were identified to the lowest taxonomic level and diet composition was analyzed using univariate and multivariate methods. Of 299 swordfish sampled (74 to 245 cm eye-to-fork length), 292 non-empty stomachs contained remains from 60 prey taxa. Diet consisted mainly of cephalopods but also included epipelagic and mesopelagic teleosts. Jumbo squid (Dosidicus gigas) and Gonatopsis borealis were the most important prey based on the geometric index of importance. Swordfish diet varied with body size, location and year. Jumbo squid, Gonatus spp. and Pacific hake (Merluccius productus) were more important for larger swordfish, reflecting the ability of larger specimens to catch large prey. Jumbo squid, Gonatus spp. and market squid (Doryteuthis opalescens) were more important in swordfish diet in inshore waters, while G. borealis and Pacific hake predominated offshore. Jumbo squid was more important from 2007-2010 than in 2011-2014, with Pacific hake the most important prey item in the latter period. Diet variation by area and year probably reflects differences in swordfish preference, prey availability, prey distribution, and prey abundance. The range expansion of jumbo squid that occurred during the first decade of this century may particularly explain their prominence in swordfish diet from 2007-2010. Some factors that may influence dietary variation in swordfish were identified. Standardization could make future studies more comparable for conservation monitoring purposes.

Towards a better characterisation of deep-diving whales’ distributions by using prey distribution model outputs?

In habitat modelling, environmental variables are assumed to be proxies of lower trophic levels distribution and by extension, of marine top predator distributions. More proximal variables, such as potential prey fields, could refine relationships between top predator distributions and their environment. In situ data on prey distributions are not available over large spatial scales but, a numerical model, the Spatial Ecosystem And POpulation DYnamics Model (SEAPODYM), provides simulations of the biomass and production of zooplankton and six functional groups of micronekton at the global scale. Here, we explored whether generalised additive models fitted to simulated prey distribution data better predicted deep-diver densities (here beaked whales Ziphiidae and sperm whales Physeter macrocephalus) than models fitted to environmental variables. We assessed whether the combination of environmental and prey distribution data would further improve model fit by comparing their explanatory power. For both taxa, results were suggestive of a preference for habitats associated with topographic features and thermal fronts but also for habitats with an extended euphotic zone and with large prey of the lower mesopelagic layer. For beaked whales, no SEAPODYM variable was selected in the best model that combined the two types of variables, possibly because SEAPODYM does not accurately simulate the organisms on which beaked whales feed on. For sperm whales, the increase model performance was only marginal. SEAPODYM outputs were at best weakly correlated with sightings of deep-diving cetaceans, suggesting SEAPODYM may not accurately predict the prey fields of these taxa. This study was a first investigation and mostly highlighted the importance of the physiographic variables to understand mechanisms that influence the distribution of deep-diving cetaceans. A more systematic use of SEAPODYM could allow to better define the limits of its use and a development of the model that would simulate larger prey beyond 1,000 m would probably better characterise the prey of deep-diving cetaceans.

Food Habits of American Kestrels In the Southern High Plains of Texas

ABSTRACT The American Kestrel (Falco sparverius) is in general decline across its North American distribution. In contrast to widespread patterns of decline, kestrel populations appear stable in the southern Great Plains region. Historically, this region had a very low occurrence of kestrels, and their current abundance is highly likely due to vegetation and structures associated with settlement by people of European descent. To determine prey use by breeding kestrels, we placed motion-activated video cameras at preexisting kestrel nest boxes located in the Southern High Plains in 2017. We recorded over 4200 prey deliveries during 1748 hr of observation at five nests over the 4-wk brood-rearing period. On basis of frequency, these deliveries were dominated by reptiles (74.8%), with invertebrates (18.2%), mammals (4.4%), birds (2.9%), and unidentified (1.2%) prey used to lesser extents. Prey delivery rates were high relative to other studies; across the brood-rearing period we recorded an average of 2.3 deliveries/hr, equating to an average of 0.49 deliveries and 3.85 g of prey/nestling/hr. Because invertebrates dominate the diet reported in most kestrel food habit studies, the volume of reptiles captured as prey was unexpected. Even more unanticipated was the number of large prey captured, including juvenile eastern cottontails (Sylvilagus floridanus) and ground squirrels (Ictidomys tridecemlineatus, Xerospermophilus spilosoma). We suspect the proportion of vertebrate prey captured during the nesting season may explain the local high rates of nesting success and number of young fledged.

Five ixodid tick species including two morphotypes of Rhipicephalus turanicus on nestlings of Eurasian eagle owl (Bubo bubo) from south-eastern Bulgaria

Background Birds are major hosts for many tick species (Acari: Ixodidae, Argasidae), and their role is especially important in transporting ticks over large distances along their seasonal migratory routes. Accordingly, most studies across Europe focus on the importance of avian hosts in tick dispersal, and less emphasis is laid on resident birds and their role in supporting tick life cycles. Eurasian eagle owls (Bubo bubo) exemplify the latter, but all the few studies on their tick infestation were carried out in Western Europe and even those did not involve a large sample size and did not assess infestation prevalence in natural habitats. Methods In this study, 320 ixodid ticks were collected from nestlings of Eurasian eagle owls during the period 2018–2020 in Bulgaria in south-eastern Europe. These ticks were analysed morphologically, and selected specimens molecularly based on cytochrome c oxidase subunit I (cox1) gene. The effects of environmental and habitat-related conditions and of the species of prey eaten by eagle owls on tick infestation were also evaluated. Results The majority of ticks were identified as adults of Rhipicephalus turanicus (n = 296). In addition, 15 Hyalomma marginatum (three males, 11 nymphs and a larva), one female of Haemaphysalis erinacei and of Ha. punctata, and a nymph of Ixodes ricinus were found. Among R. turanicus, two distinct morphotypes were observed, but they do not form a monophyletic clade in the phylogenetic tree based on the mitochondrial gene cox1. We found a positive correlation between the total number of ticks on nestlings from a particular nest and the number of medium-sized to large prey mammals brought to the nestling owls. Also, the most important predictor for tick abundance was the effect of the extent of arable land (negative), while forests and grasslands contributed less, with no effect observed in case of urbanized areas and watercourses. Conclusions The intensity of tick infestation can be high on nestling Eurasian eagle owls (mean intensity 16.59 ticks/nestling). In this study, five different tick species were recorded, among which R. turanicus dominated. Two male morphotypes of this tick species were found, but their morphological differences were not reflected by genetic diversity or phylogenetic clustering. The most important factor determining tick abundance was the land-use structure. Graphic Abstract

Variation in the sacroiliac joint in Felidae

Felidae species show a great diversity in their diet, foraging and hunting strategies, from small to large prey. Whether they belong to solitary or group hunters, the behavior of cats to subdue resisting small or large prey presents crucial differences. It is assumed that pack hunting reduces the per capita risk of each individual. We hypothesize that the sacroiliac articulation plays a key role in stabilizing the predator while subduing and killing prey. Using CT-scan from 59 felid coxal bones, we calculated the angle between both iliac articular surfaces. Correlation of this inter-iliac angle with body size was calculated and ecological stressors were evaluated on inter-iliac angle. Body size significantly influences inter-iliac angle with small cats having a wider angle than big cats. Arboreal species have a significantly larger angle compared to cursorial felids with the smallest value, and to scansorial and terrestrial species with intermediate angles. Felids hunting large prey have a smaller angle than felids hunting small and mixed prey. Within the Panthera lineage, pack hunters (lions) have a larger angle than all other species using solitary hunting strategy. According to the inter-iliac angle, two main groups of felids are determined: (i) predators with an angle of around 40° include small cats (i.e., Felis silvestris, Leopardus wiedii, Leptailurus serval, Lynx Canadensis, L. rufus; median = 43.45°), the only pack-hunting species (i.e., Panthera leo; median = 37.90°), and arboreal cats (i.e., L. wiedii, Neofelis nebulosa; median = 49.05°), (ii) predators with an angle of around 30° include solitary-hunting big cats (i.e., Acinonyx jubatus, P. onca, P. pardus, P. tigris, P. uncia; median = 31.80°). We suggest different pressures of selection to interpret these results. The tightening of the iliac wings around the sacrum probably enhances big cats’ ability for high speed and large prey control. In contrast, pack hunting in lions reduced the selective pressure for large prey.