Modelling small-scale foraging habitat use in breeding Eurasian oystercatchers (Haematopus ostralegus) in relation to prey distribution and environmental predictors

Spatiotemporal variations in migratory bird diversity and abundance along the coast of Gochang getbol

Tidal flats provide critical habitat for migratory waterbird species; however, populations of migratory waterbirds have significantly declined due to tidal flat loss and degradation caused by human activities, particularly in Asia. Gochang getbol is one of tidal flats located on the southwest coast of South Korea and a center of clam production. Using bird monitoring data collected at five zones (zone1 to zone5) established across Gochang getbol and near coastal area, we examined distribution patterns of migratory bird diversity and conservation-related species along the coast of Gochang getbol. The intensity of human activity ‒ mudflat culture (mostly bivalve) and aquaculture was relatively high at zone2 and zone3, occupying > 30% of 2km circular area surrounding most sample points of these zones. Zone1 and particularly zone4 contained more natural/semi-natural habitats (less disturbed mudflats and wetlands) and zone5 had smallest mudflat than others. Shannon diversity, species richness, and abundance of migratory birds differed between zones (Anova test, P ≤ 0.02) except Shannon diversity in winter. In fall, all values were higher at zone4 than zone3 and zone5. In winter, zone1 showed greatest species richness and higher abundance than zone2, zone3, and zone5. In spring, while most differences were found between zone4 and zone5, abundance at zone4 was somewhat higher than zone2. The results from the fourth corner analysis indicated that abundance of species foraging at mudflat level was positively associated with zone1 (winter) but negatively with zone3 (fall). Sandpipers were positively associated with zone4. Abundance distribution maps of conservation-related species, created by inverse distance-weighted interpolation modeling, also showed high abundance of most conservation-related species at zone4 and 1. The findings of our study suggest the importance of natural/semi-natural habitat, and the possible link between human activity and distribution patterns of migratory birds in Gochang getbol. While we need further investigation on direct response of migratory birds to human activity, areas with low human activity with more natural/semi-natural habitat, e.g., zone4 and zone1 may be crucial for the conservation of migratory birds.

Urban rooftops near sports pitches provide a safe haven for a declining shorebird

Urbanisation has contributed to a severe decline in biodiversity worldwide. However, urban ecosystems can also play an important role in the conservation of threatened species, including ground-nesting birds such as the Eurasian Oystercatcher (Haematopus ostralegus). While the coastal populations of this shorebird have declined sharply, there is growing evidence that pairs nesting on urban flat roofs have high reproductive success. However, the reasons for rooftop nesting and the species' habitat use in urban areas remain poorly understood. In this study, we investigate the territory selection and foraging behaviour of the Eurasian Oystercatcher in the city of Münster (NW Germany). All nesting sites were located on flat roofs (N = 24), most of which were covered with gravel. Overall, reproductive success was high. This was mainly because the roofs provided protection from mammalian predators, leading to increased nest and chick survival. Moreover, breeding performance in the study area was favoured by the proximity of sports pitches. According to our observations, they provided a large amount of easily accessible prey throughout the breeding season. Overall, our study highlights that the reproductive success of the Eurasian Oystercatcher in urban environments is highly dependent on both safe nesting sites on flat roofs and the availability of suitable foraging habitats. Although our study suggests that breeding in urban areas can be beneficial for the model organism, the species' strong territory fidelity makes it very sensitive to the rapid environmental changes occurring in cities. The value of urban ecosystems for bird conservation should therefore be better integrated into urban planning and management.

Coping with unpredictable environments: fine-tune foraging microhabitat use in relation to prey availability in an alpine species

Microhabitat utilisation holds a pivotal role in shaping a species' ecological dynamics and stands as a crucial concern for effective conservation strategies. Despite its critical importance, microhabitat use has frequently been addressed as static, centering on microhabitat preference. Yet, a dynamic microhabitat use that allows individuals to adjust to fine-scale spatio-temporal prey fluctuations, becomes imperative for species thriving in challenging environments. High-elevation ecosystems, marked by brief growing seasons and distinct abiotic processes like snowmelt, winds, and solar radiation, feature an ephemeral distribution of key resources. To better understand species' strategies in coping with these rapidly changing environments, we delved into the foraging behaviour of the white-winged snowfinch Montifringilla nivalis, an emblematic high-elevation passerine. Through studying microhabitat preferences during breeding while assessing invertebrate prey availability, we unveiled a highly flexible microhabitat use process. Notably, snowfinches exhibited specific microhabitat preferences, favoring grass and melting snow margins, while also responding to local invertebrate availability. This behaviour was particularly evident in snow-associated microhabitats and less pronounced amid tall grass. Moreover, our investigation underscored snowfinches' fidelity to foraging sites, with over half located within 10 m of previous spots. This consistent use prevailed in snow-associated microhabitats and high-prey-density zones. These findings provide the first evidence of dynamic microhabitat use in high-elevation ecosystems and offer further insights into the crucial role of microhabitats for climate-sensitive species. They call for multi-faceted conservation strategies that go beyond identifying and protecting optimal thermal buffering areas in the face of global warming to also encompass locations hosting high invertebrate densities.

The importance of fine-scale predictors of wild boar habitat use in an isolated population

Predicting the likelihood of wildlife presence at potential wildlife-livestock interfaces is challenging. These interfaces are usually relatively small geographical areas where landscapes show large variation over small distances. Models of wildlife distribution based on coarse data over wide geographical ranges may not be representative of these interfaces. High-resolution data can help identify fine-scale predictors of wildlife habitat use at a local scale and provide more accurate predictions of species habitat use. These data may be used to inform knowledge of interface risks, such as disease transmission between wildlife and livestock, or human-wildlife conflict.This study uses fine-scale habitat use data from wild boar (Sus scrofa) based on activity signs and direct field observations in and around the Forest of Dean in Gloucestershire, England. Spatial logistic regression models fitted using a variant of penalized quasi-likelihood were used to identify habitat-based and anthropogenic predictors of wild boar signs.Our models showed that within the Forest of Dean, wild boar signs were more likely to be seen in spring, in forest-type habitats, closer to the center of the forest and near litter bins. In the area surrounding the Forest of Dean, wild boar signs were more likely to be seen in forest-type habitats and near recreational parks and less likely to be seen near livestock.This approach shows that wild boar habitat use can be predicted using fine-scale data over comparatively small areas and in human-dominated landscapes, while taking account of the spatial correlation from other nearby fine-scale data-points. The methods we use could be applied to map habitat use of other wildlife species in similar landscapes, or of movement-restricted, isolated, or fragmented wildlife populations.

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

Abstract

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.

Intercolony variations in movement patterns and foraging behaviors among herring gulls (Larus argentatus) breeding in the eastern Wadden Sea

Herring gulls (Larus argentatus) are opportunistic predators that prefer to forage in the intertidal zone, but an increasing degree of terrestrial foraging has recently been observed. We therefore aimed to analyze the factors influencing foraging behavior and diet composition in the German Wadden Sea. Gulls from three breeding colonies on islands at different distances from the mainland were equipped with GPS data loggers during the incubation seasons in 2012-2015. Logger data were analyzed for 37 individuals, including 1,115 foraging trips. Herring gulls breeding on the island furthest from the mainland had shorter trips (mean total distance = 12.3 km; mean maximum distance = 4.2 km) and preferred to feed on the tidal flats close to the colony, mainly feeding on common cockles (Cerastoderma edule) and shore crabs (Carcinus maenas). In contrast, herring gulls breeding close to the mainland carried out trips with a mean total distance of 26.7 km (mean maximum distance = 9.2 km). These gulls fed on the neobiotic razor clams (Ensis leei) in the intertidal zone, and a larger proportion of time was spent in distant terrestrial habitats on the mainland, feeding on earthworms. δ13C and δ15N values were higher at the colony furthest from the mainland and confirmed a geographical gradient in foraging strategy. Analyses of logger data, pellets, and stable isotopes revealed that herring gulls preferred to forage in intertidal habitats close to the breeding colony, but shifted to terrestrial habitats on the mainland as the tide rose and during the daytime. Reduced prey availability in the vicinity of the breeding colony might force herring gulls to switch to feed on razor clams in the intertidal zone or to use distant terrestrial habitats. Herring gulls may thus act as an indicator for the state of the intertidal system close to their breeding colony.

The timing of energy allocation to reproduction in an important group of marine consumers

Organisms may energetically finance reproductive effort using energy stored prior to the reproductive period (termed capital breeders) or using energy acquired during the reproductive period (termed income breeders). The specific strategy used has implications for population dynamics as well as for the response to environmental variation. Crabs and other crustaceans have generally been assumed to be capital breeders. Here I demonstrate an experimental procedure used to determine whether crabs are capable of using an income breeding strategy. I then examine data from several published studies from a range of crab species across a broad phylogenetic spectrum that conducted similar experiments to look for evidence of income breeding strategy. I show that income breeding does occur in crabs, but that it appears to be taxon-specific. In particular, I show that income breeding occurs in two species from the family Portunidae, but fail to find evidence for income breeding in other taxa examined. This finding has a range of implications for this ecologically and economically important group of consumers, including implications for their response to human-induced environmental change, their response to fishing pressure, and best practices for aquaculture. The implications of breeding strategy in crabs likely depends on phylogeny (morphology) and ecology, both of which influence the space available for energy storage inside the carapace.

Interaction between birds and macrofauna within food webs of six intertidal habitats of the Wadden Sea

The determination of food web structures using Ecological Network Analysis (ENA) is a helpful tool to get insight into complex ecosystem processes. The intertidal area of the Wadden Sea is structured into diverse habitat types which differ in their ecological functioning. In the present study, six different intertidal habitats (i.e. cockle field, razor clam field, mud flat, mussel bank, sand flat and seagrass meadow) were analyzed using ENA to determine similarities and characteristic differences in the food web structure of the systems. All six systems were well balanced between their degree of organization and their robustness. However, they differed in their detailed features. The cockle field and the mussel bank exhibited a strong dependency on external imports. The razor clam field appeared to be a rather small system with low energy transfer. In the mud flat microphytobenthos was used as a main food source and the system appeared to be sensitive to perturbations. Bird predation was the most pronounced in the sand flat and the seagrass meadow and led to an increase in energy transfer and parallel trophic cycles in these habitats. Habitat diversity appears to be an important trait for the Wadden Sea as each subsystem seems to have a specific role in the overall functioning of the entire ecosystem.

A fundamental study revisited: Quantitative evidence for territory quality in oystercatchers (Haematopus ostralegus) using GPS data loggers

A fundamental study by Ens et al. (1992, Journal of Animal Ecology, 61, 703) developed the concept of two different nest-territory qualities in Eurasian oystercatchers (Haematopus ostralegus, L.), resulting in different reproductive successes. "Resident" oystercatchers use breeding territories close to the high-tide line and occupy adjacent foraging territories on mudflats. "Leapfrog" oystercatchers breed further away from their foraging territories. In accordance with this concept, we hypothesized that both foraging trip duration and trip distance from the high-tide line to the foraging territory would be linearly related to distance between the nest site and the high tide line. We also expected tidal stage and time of day to affect this relationship. The former study used visual observations of marked oystercatchers, which could not be permanently tracked. This concept model can now be tested using miniaturized GPS devices able to record data at high temporal and spatial resolutions. Twenty-nine oystercatchers from two study sites were equipped with GPS devices during the incubation periods (however, not during chick rearing) over 3 years, providing data for 548 foraging trips. Trip distances from the high-tide line were related to distance between the nest and high-tide line. Tidal stage and time of day were included in a mixing model. Foraging trip distance, but not duration (which was likely more impacted by intake rate), increased with increasing distance between the nest and high-tide line. There was a site-specific effect of tidal stage on both trip parameters. Foraging trip duration, but not distance, was significantly longer during the hours of darkness. Our findings support and additionally quantify the previously developed concept. Furthermore, rather than separating breeding territory quality into two discrete classes, this classification should be extended by the linear relationship between nest-site and foraging location. Finally, oystercatcher's foraging territories overlapped strongly in areas of high food abundance.