Movement Ecology最新文献

Background: Each spring, migratory birds converge along the Croatian coast from various directions, creating a dynamic intersection of flight paths. Many birds are thought to cross the Adriatic Sea, while others follow a northward route along the coastline. As most migratory birds initiate flight shortly after sunset, we hypothesized that sea-crossing migrants would arrive with a delay at the Croatian coast, compared to migrants that were following the coast, resulting in potentially intricate spatiotemporal patterns that remain poorly understood.

Methods: We deployed four ornithological radar devices along the Croatian coastline: two in southwestern Istria and two in northern Dalmatia. These radars tracked migratory bird activity up to 1000 m above ground, recording intensity and flight directions and their variations across sites, seasons, and individual nights. We conducted an exploratory analysis of these variations, applied functional principal component analysis and hierarchical clustering to summarise within-night activity profiles, and compared these profiles between sites and across the migration season, alongside associated flight direction distributions.

Results: During the early migration season, migration intensity was similar across all technically active sites, but site-to-site variation increased markedly in May. In March, flight directions were predominantly towards NNE, indicating mainly sea-crossing migration throughout the night. In April, NW directions dominated the first half of the night, shifting to scattered N directions later; in Dalmatia, even strong W components were observed early in the night. By May, W to NW movement towards the Italian coast were typical for early-night activity. Later in the night, flight directions shifted towards NE over Istria and N at the Dalmatian site in Zadar, while the site at Vrana exhibited a wide scatter, warranting further discussion. Contrary to our expectations, within-night intensity profiles could not be fully linked to specific directional patterns.

Conclusion: This study points to the complex interplay between coastal and sea-crossing migration along the Croatian coast. Our results demonstrate significant variability in the timing of migration within single nights in the context of aquatic barriers. Crossing such a barrier results in downstream delays compared to birds migrating along the barrier. Between nights, one behaviour or the other may dominate the overall activity, causing the shifts in within-night timing. In addition, barrier crossing is likely to be strongly influenced by weather conditions, contributing to the variability in the within-night timing of migration. However, measured flight directions were not always consistent with within-night timing, highlighting the complexity of avian migration in the context of aquatic barriers. This highlights the need for further research wit

The conditions regulating long distance migrations of large animal groups remain elusive in ecology. It has been suggested that individual interactions, environmental constraints and social dynamics play a major role in group formation and migration processes. The challenge is in how to incorporate those dynamics within a framework that reproduces observed dynamics and allows to investigate conditions for the persistence or collapse of migrations. We introduce a general model for seasonally migratory populations where individuals belong to separate contingents each representing a specific migration strategy. Contingents mix during the reproductive phase while the feeding migration is regulated by group formation and social learning. The model is solved numerically, illustrating key factors shaping population dynamics and migration. We identify non-linear critical thresholds in social learning regulating successful migrations. We also determine the conditions for similar thresholds in the behavioural adaptation of the species. This indicates that migration strategies could disappear from a population given social and environmental constraints. These results offer new perspectives on animal conservation and environmental management. Indeed, the removal of individual migrants may have long term consequences for the migratory strategies of the population, possibly leading to irreversible shifts in social behaviour and disruptions of local communities.

Background: Anthropogenic activity can modify how wildlife perceives risks and rewards across the landscape (the 'Landscape of Fear') and affect animal movement and behavior. Studying movement patterns allows researchers to infer anti-predator behaviors and their drivers that affect survival. We studied a game species, the Canada goose (Branta canadensis), to understand how hunting affects prey movement and in turn guide management decisions to maximize species abundance and hunting.

Methods: We used GPS receivers to track the movements of geese at two study sites in Pennsylvania during two hunting seasons. The hunting season in this system includes two distinct periods (hunting periods) in which hunting is permitted on alternating days (hunting days). We fitted hidden Markov models to analyze individual movement at three spatiotemporal scales and estimated how various environmental factors, such as habitat and hunting pressure, influenced the transition probabilities between behavioral states.

Results: We found that geese were less likely to take flight during hunting periods and on hunting days, and that geese were more likely to transition to a low ambulation state on hunting days. Overall, we found that resident Canada geese employed two nested anti-predator behaviors: individuals proactively decreased their movement during hunting, but as they neared the threat, they were more likely to take flight.

Conclusions: Our study provides further evidence that animals maintain a landscape of fear and a schedule of fear. We observed decreased movement during the hunting season and hypothesize that this was due to the stationary nature of risk (hunting blinds). Based on our results, we hypothesize that goose movement may be increased during hunting with an unpredictable spatial-temporal distribution of risk.

Background: Animal movement is influenced by both the physical environment and social environment. The effects of both environments are not independent from each other and identifying whether the resulting movement trajectories are shaped by interactions between individuals or whether they are the result of their physical environment, is important for understanding animal movement decisions.

Methods: Here, we assessed whether the commonly used methods for inferring interactions between moving individuals could discern the effects of environment and other moving individuals on the movement of the focal individual. We used three statistical methods: dynamic interaction index, and two methods based on step selection functions. We created five scenarios in which the animals' movements were influenced either by their physical environment alone or by inter-individual interactions. The physical environment is constructed such that it leads to a correlation between the movement trajectories of two individuals.

Results: We found that neglecting the effects of physical environmental features when analysing interactions between moving animals leads to biased inference, i.e. inter-individual interactions spuriously inferred as affecting the movement of the focal individual. We suggest that landscape data should always be included when analysing animal interactions from movement data. In the absence of landscape data, the inference of inter-individual interactions is improved by applying 'Spatial+', a recently introduced method that reduces the bias of unmeasured spatial factors.

Conclusions: This study contributes to improved inference of biotic and abiotic effects on individual movement obtained by telemetry data. Step selection functions are flexible tools that offer the possibility to include multiple factors of interest as well as combine it with Spatial+.

Background: Migrating birds do not always travel along the shortest possible routes between breeding and wintering sites. Rather, detours are a common phenomenon in response to availability of foraging habitats, generic wind patterns, predation risk, and ecological barriers. The Himalayas are a formidable ecological barrier within the Central Asian Flyway (CAF), but hitherto research has focused on high-altitude flights of species that cross the Himalayas, and thus information on species that circumvent this mountain range is lacking in this understudied migration system.

Methods: We tracked Montagu's Harriers Circus pygargus for 5 years from their wintering range in India, and found that these long-distance migrants travelled by a grand westward detour around the Himalayas to their breeding areas in Kazakhstan. We calculate the energetic optimality of the detour on the basis of a well-known theoretical model and explain the general migration patterns of Montagu's Harriers in the CAF. Additionally, we compare ecological factors such as ground elevation, habitat greenness (NDVI), land cover and wind patterns along the actual migration route with the hypothetical shortest route to explain why Montagu's Harriers follow a detour migration pattern in the CAF.

Results: The observed (detour) route was on average 1245 ± 94.4 km (27%) longer than the hypothetical shortest direct route. The detour did seem to be optimal for Montagu's Harriers as per the model that considers a distance of up to 1288 km to be optimal. With the detour, harriers circumvented the high altitudes of the Himalayan plateau, effectively avoiding high ground elevations over 4000 m above mean sea level (AMSL). Harriers followed the same detour during spring and autumn migrations, encountering both supporting and opposing winds, and thus the detour cannot be explained by generic wind patterns. The detour was facilitated by the availability of open natural ecosystems (ONEs) and stopover sites with higher productivity west of the mountain range along the floodplains of the Amu Darya river and in the Thar Desert during spring and autumn respectively.

Conclusion: We argue that circumventing the mountain range, as illustrated by our pioneer study on the Montagu's Harrier, could be a common behaviour among migrating landbirds in the CAF. We also emphasize the importance of the protecting ONEs along the western detour for the long term conservation of migratory birds in the CAF.

Background: How juvenile sea turtles disperse during their first years at sea, known as the "lost years", remains enigmatic. The oceanic circulation is known to play a major role, but the impact of the swimming activity is poorly understood, largely because juvenile tracking experiments rarely cover a significant fraction of the lost years' period. In addition, errors in commonly used ocean current estimates make it difficult to properly separate, in tracking data, the effect of the swimming activity from that of the drift velocity. In this paper, we re-analyze the largest extant tracking data set concerning juvenile North Pacific (NP) loggerhead turtles (Caretta caretta), attempting to more precisely characterize their lost years' swimming activity.

Methods: Juvenile loggerhead trajectories are jointly analyzed with surface drifter trajectories from the Global Drifter Program and novel operational oceanography products from the Copernicus Marine service. Combining these data sets, we present a new method to reliably separate, at least on the large scale, the turtles swimming velocity from the drift velocity which includes the impact of the current, the wind and the waves.

Results: Results reveal that the smallest juveniles perform large seasonal north-south migrations while drifting eastwards with ocean currents. As they grow larger, many individuals are observed to change behavior. While keeping their meridional seasonal migrations, they initiate their homing journey swimming vigorously westwards towards their natal area (Japan), against prevailing currents. The juvenile NP loggerheads' swimming activity is thus best described as a series of Drifting then Homing Seasonal Migrations. High interindividual synchronicity is observed during these migrations, especially around the fall equinox when individuals start swimming southwards.

Conclusion: While open-ocean dispersal of juvenile sea turtles is known to be largely governed by ocean currents, our results demonstrate that juvenile loggerheads' dispersal in the NP is also largely shaped by their well-organized large-scale swimming activity which involves ample seasonal migrations and vigorous homeward movements against adverse currents. Such an active swimming strategy comes with high energy expenditure probably balanced by increased foraging success. Analysis of forthcoming juvenile tracking experiments with our new data processing method should help reveal if juveniles from other sea turtle populations or species have evolved similar swimming strategies.

Background: Habitat fragmentation can influence the spatial ecology of wildlife populations, with downstream effects on population dynamics and sustainability. Row-crop farming is a common anthropogenic landscape alteration, yet the effects on animal movement and space use is understudied in some species. Cropland can benefit wildlife nutritionally but may result in habitat loss because of changes in landscape composition and human disturbance.

Methods: We quantified the influence of cropland presence and coverage on mule deer spatial ecology in the southern Great Plains. We GPS-collared 146 adult mule deer in four regions of the Texas Panhandle and monitored movement relative to spatio-temporal fluctuations in cropland and particular crop species availability for 2 years. We modeled the effects of cropland on space use and resource selection at multiple spatio-temporal scales to characterize population and individual habitat components of mule deer.

Results: We observed a functional response in cropland use, where at low coverage, use was proportional to availability but decreased with > 20% cropland coverage at the home range and within-home range scales. Few mule deer exhibited long-distance movements towards cropland. Individuals within 1.6 km of cropland exhibited greater cropland use, whereas deer > 4.2 km from cropland rarely used these areas. At the population level, mule deer selected cropland during the winter and late summer, probably for nutritional benefit when rangeland nutrients are low. At a finer scale, step-selection functions identified individual heterogeneity in crop species selection. Winter wheat, alfalfa, and fallow fields had greater use relative to other crop types. Generally, 15-60% of mule deer with access to cropland selected alfalfa year-round, and up to 63% of deer selected winter wheat post-reproduction.

Conclusions: Our results suggest that at a low spatial coverage, cropland alters the spatial ecology of mule deer at several spatio-temporal scales and may provide nutritional benefits, but at a cost of lost habitat when cropland exceeds 20% of the landscape. Declining groundwater resources and an exponentially growing human population will alter future farming practices. Understanding how species occupying these environments, such as mule deer, are influenced by human-induced landscape changes can enhance mitigation of human-wildlife interactions and aid conservation actions as policy and social pressures shape future agricultural practices.

Research on the direct effects of capture and tagging on post-release behaviour is typically limited to short-term deployments. To investigate the initial and longer-term behavioural responses to capture and tagging, we deployed eight Cefas G7 tags (1Hz depth and temperature, and 20 Hz triaxial acceleration) for 21-94 hours and 12 Wildlife Computers MiniPATs (depth, temperature, light and triaxial acceleration, each at 0.2 Hz) for 110-366 days on Atlantic bluefin tuna (ABT) in the English Channel. Post-release, ABT exhibited a strong, highly active initial swimming response, consistent with patterns reported in previous bluefin tuna, billfish and elasmobranch tracking studies. Accelerometry tags revealed that activity (VeDBA g), tailbeat amplitude (g) and dominant stroke frequency (Hz) were greater (2.4, 3.2 and 1.4 times respectively) within the first hour post-release than the subsequent 24 hours, stabilising at lower levels within 5-9 hours. However, lower resolution accelerometry data (0.2 Hz), obtained from longer periods from MiniPATs, revealed that fish then maintained this reduced activity for 11 ± 7.9 days (mean ± 1 SD; range: 2-26 days), during which they displayed disrupted diel patterns of activity and allocated on average 5 minutes of each day to burst energy events, compared to 14 minutes (max 74 minutes) during "recovered" periods. Subsequently, their activity levels increased again and were characterised by higher magnitude acceleration events (which may constitute feeding events) and became more active during the day than at night. Year-long deployments revealed that consistent diel vertical migration, diurnal patterns of activity, and increased time allocation to fast starts are normal for ABT off the British Isles in summer months, and their absence at the start of data collection may be related to the effect of capture and tagging, which may be longer lasting, and more complex than previously appreciated.

Background: Niche partitioning allows species to diversify resource utilisation and space allocation and reduce interspecific competition. Variations in abiotic and biotic conditions in different ecosystems may further influence resource availability and habitat utilisation, potentially reducing competition. The aim of this study is to investigate the effects of environmental variation on spatial and trophic niche overlap between two freshwater apex predators, the northern pike (Esox lucius) and the European catfish (Silurus glanis), in three different water bodies.

Methods: We used fine-scale acoustic telemetry to assess the spatial niche overlap of pike and catfish, analyzing their spatial and habitat use in relation to the thermocline and their presence in benthic versus open-water habitats. Stable isotope analysis (SIA) was used to quantify trophic niche overlap and dietary differences between the species. We compared the habitat use, spatial niche width and overlap, and trophic differentiation among waterbodies to determine how environmental conditions influence predator interactions.

Results: During summer, pike and catfish primarily occupied benthic habitats above the thermocline across all waterbodies and diel periods. However, catfish more frequently used open water above the thermocline, while pike were more often present in both open water and benthic habitats below it. While this general pattern of habitat use was consistent, its extent varied among lakes, suggesting that local environmental conditions shape species-specific habitat selection. Despite these variations, the species exhibited substantial spatial overlap, though its magnitude fluctuated across waterbodies and diel periods. Catfish occupied a broader spatial niche in two waterbodies, while pike had a broader niche in one. Across all lakes, catfish consistently maintained a broader trophic niche than pike. However, pike exhibited higher trophic overlap with catfish than vice versa, with nearly complete overlap in one lake and substantial but incomplete overlap in others. This suggests that pike relies more heavily on shared prey resources, while catfish exploits a broader range of food sources beyond those used by pike.These patterns were primarily driven by the position of the thermocline, prey availability, structural complexity and the greater foraging plasticity of catfish, highlighting the environmental dependence of niche partitioning in these predators.

Conclusions: Our findings demonstrate that spatial and trophic niche overlaps between pike and catfish are highly context-dependent, shaped by abiotic conditions, prey availability, and species-specific foraging strategies. This study highlights the importance of integrating spatial and trophic analyses to understand predator interactions in aquatic ecosystems.

Background: Parental care is exclusively provided by females in most mammals, and mothers use several spatiotemporal behavioral tactics to minimize risks to offspring and to enhance fitness of both the mother and offspring. In species with infanticide and varying maternal care duration, dependent offspring remain vulnerable to male infanticide until separation from the mother. However, extending maternal care likely results in parent-offspring conflicts. We investigated the spatiotemporal behavioral tactics of lone female brown bears and mothers accompanied by offspring of varying ages in relation to infanticide risk and offspring separation during the mating season.

Methods: We used data from 144 individuals (92 females and 52 males, 2003-2022) to characterize female spatiotemporal behavioral responses to males during the mating season by contrasting home range and encounter area sizes, proximity to males, and dyadic associations in relation to female reproductive status. We investigated the spatiotemporal behavioral responses of mothers from a socio-spatial perspective by connecting large-scale movement behavior (home range and overlap) and small-scale social behavior (proximity and associations) of adult females and males.

Results: We found that females with dependent offspring of any age avoided males during the mating season. In comparison, lone females or mothers that lost or separated from their offspring during the mating season used larger areas and moved in closer proximity to males. The home range of mothers that remained with their offspring still largely overlapped with male home ranges, however, they did not associate (< 100 m) with males. Additionally, mothers with yearlings had similar sized home ranges as solitary females, but larger home ranges in comparison to mothers with cubs-of-the-year. This suggests that mothers with yearlings are more conspicuous on the landscape which may result in a higher detectability by males.

Conclusion: Our results suggest that mothers with offspring of any age perceive adult males as potential source of infanticide and use spatiotemporal avoidance tactics. Generally, family groups had high home range overlap with adult males, but family groups that remained together throughout the mating season did not associate with any adult male. Mothers with yearlings used larger areas in comparison to mothers with cubs, potentially indicating their increasing energetic needs. The use of spatiotemporal behavioral tactics to avoid infanticide by females with dependent offspring irrespective of age likely disrupts movement, mating, and social dynamics and on the long-term potentially increases the risk of infanticide to older offspring.