Movement Ecology最新文献

Each spring, migratory Gray Catbirds (Dumetella carolinensis, henceforth referred to as Catbirds) that have wintered in Central America and the Caribbean, fly across the Gulf of Mexico during their northern migration. These long-distance flights are primarily fueled by lipid reserves, but protein is also catabolized leading to significant depletions in organ and muscle tissue mass upon arrival at stopover sites. Here, Catbirds must not only recover from their previous intensive flight across the Gulf but must also provision for the next leg of migration as they continue to their breeding grounds in North America. There is still much to be known about how reduced lean mass at stopover may constrain refueling performance. Catbirds present a unique opportunity to study refueling performance relating to differential migratory strategies as these songbirds have significant geographic spread in their North American breeding grounds. We caught Catbirds during spring migration on St. George Island, FL over three consecutive years. We measured total fat and lean mass using non-invasive quantitative magnetic resonance, basal metabolic rate using standard flow-through respirometry techniques, and plasma triglycerides to determine refueling rate. We then used feather deuterium (δD) to estimate breeding location and migratory distance. We determined, with high probability, three migratory strategies used by this group of Catbirds at stopover, yet found no differences in total, fat, or lean body mass amongst birds attributed to be short, medium, or long-distance migrants. However, migratory distance explains the relationship between total mass and refueling rates, with long-distance migrants having a larger increase in plasma triglyceride concentration per unit increase of body mass compared to short-distance migrants. Furthermore, we document a physiological strategy whereby long-distance migrants can deposit greater amounts of lean and fat mass with a smaller associated increase of metabolic rate than predicted for their size.

Background: Movement of marine predators can connect different habitats and create links that are key for maintaining metapopulation dynamics, genetic diversity, energy flow and trophic links within and between systems. This key ecological process is known as ecological connectivity.

Methods: We used a combination of acoustic telemetry data, network analysis (graph theory), habitat modelling and machine learning methods to quantify movement patterns and habitat use of three coral reef predators (grey reef shark Carcharhinus amblyrhynchos, silvertip shark Carcharhinus albimarginatus and red bass Lutjanus bohar). We also assessed how movements and habitat preference influence connectivity in two remote reef systems (Rowley Shoals and Scott Reef) off Northwest Australia.

Results: Grey reef shark movements created more substantial connections within reef systems, greater than silvertip sharks and red bass, with occasional long-ranging movement linking distant atolls. Core use areas (nodes with high degree centrality) were represented by low complexity habitats in shallow areas near passages in the reef crest, but varied among species, time of the day and sex. Overall, female sharks had larger networks with greater movement extent than males indicating potential sex-specific patterns in movement and connectivity of sharks at both local (within an atoll) and regional (within reef system) spatial scales. Red bass movements resulted in local-scale connectivity between the lagoon and nearby forereef areas, whereas reef shark connectivity operated at broader scales with movement along the forereef creating stronger connections across distant areas within the reef systems.

Conclusions: The combination of animal tracking data, network analyses and machine learning allowed us to describe complex patterns of movement and habitat use within and between remote coral reef ecosystems and how they influence ecological connectivity over local and regional scales. Importantly, we suggest that the existing spatial protection across these remote coral reefs is effective in protecting the local-scale connectivity of mesopredators, yet broad-scale protection is required to effectively encompass the seascape connectivity of large predators which is crucial for the long-term health and stability of coral reef ecosystems.

The study of migration ecology is crucial for understanding the factors and pressures affecting migratory species. Here, we studied the migratory ecology of the little bustard (Tetrax tetrax), a steppe bird that has suffered a sharp decline over recent decades, mainly due to agricultural intensification. Using 105 adult birds tagged across the main Iberian regions where the species is present (Alentejo, Extremadura, Ebro Valley, Northern Plateau, Southern Plateau and Guadalquivir Valley), we analysed the ratio of migratory and resident birds in each population and assessed their connectivity during the three main migratory periods (summer, winter and pre-breeding). Additionally, we describe the features of the migrations recorded in terms of length, duration and day period. Our results corroborate that little bustards can be considered partial migrants across Iberia, although the proportion of residents versus migrants varied between populations: the Alentejo (94.74%) and Northern Plateau (93.75%) had the highest proportion of migrants, followed by Guadalquivir Valley (81.82%), Extremadura (65.38%), Southern Plateau (55.56%) and Ebro Valley (25.93%). Migratory connectivity varied between periods: the pre-breeding and summering migrations showed a trend to move northwards, while birds moved southwards for winter. Regarding the migratory corridors obtained from the 253 migrations identified, we found three main routes: one corridor that connects the Northern Plateau with the western part of the Southern Plateau and Extremadura, another one that connects the Southern Plateau, Extremadura, Alentejo and Guadalquivir Valley, and one corridor that concentrates migrations within the Ebro Valley, and between the Ebro Valley and the Southern Plateau. Finally, analyses showed that little bustards migrate at night through areas dominated by herbaceous cover (avoiding tree-covered land and water bodies) and of low elevation and terrain roughness. Our results highlight the importance of developing an international and inter-regional conservation strategy to protect not only the breeding and wintering quarters, but also this endangered species' migratory corridors, thus supporting the viability of the metapopulation.

Background: The degradation and loss of critical nodes in the East Asian-Australasian Flyway (EAAF) migration network could have implications for the migration of shorebirds. The conservation of critical nodes along the EAAF is important for maintaining the stability of migratory networks. However, identifying these nodes remains a major challenge.

Methods: We used a network method that integrates GPS tracking data and remote sensing data to identify critical nodes for three shorebird species (Black-tailed Godwit (Limosa limosa), Eurasian Curlew (Numenius arquata), and Pied Avocet (Recurvirostra avosetta)) in migratory networks along the EAAF and priority conservation areas to facilitate the development of conservation and management plans.

Results: A total of 111, 37, and 81 nodes in the migratory networks were identified for the Black-tailed Godwit, Eurasian Curlew, and Pied Avocet, respectively; these included 25, 13, and 16 critical nodes, respectively. Node importance (node betweenness) was higher in the migration period than in the breeding and wintering periods. Habitat loss was observed in most stopover nodes. A total of 23 unprotected critical nodes were identified as priority conservation areas.

Conclusions: Habitat loss was observed in most of the unprotected critical nodes in stopover regions for all three species. The inclusion of these sites such as Haoyao sumu forest farm and Tianjin coast, into flyway site networks (the East Asian-Australasian Flyway Partnership (EAAFP)) should be prioritized, and the habitat quality of nearby alternative nodes should be improved. Future studies should focus on developing new node indexes that integrate ecological variables with each node's role in maintaining network connectivity using data from a larger number of tracked individuals and birdwatching data. Such studies could help identify currently unknown regions with critical habitats.

Background: To complete their lifecycle, diadromous fish often need to pass anthropogenic barriers in regulated rivers and estuaries (e.g., pumping stations, weirs, hydropower facilities). The safe and timely passage of the endangered catadromous European eel (Anguilla anguilla), through pumping stations is a major concern and European legislation stipulates that safe downstream passage must be provided at hazardous intakes. To implement effective mitigation measures, specific knowledge on eel passage behaviour at barriers is needed.

Methods: We used acoustic telemetry with acceleration sensors tags, to understand eel movement and activity, migration routes, escapement success, and delay at a tidal pumping station. Tri-axes accelerometers measured eel acceleration in three directions and provide a root-mean-square (RMS) value over the measurement period, providing a proxy for eel activity. A network of 10 receivers was placed along the migration route to track 40 tagged individuals. Telemetry data were analysed using visual investigation of eel detections and Generalised Additive Mixed Models (GAMMs) for analysing acceleration data.

Results: We found that 75% of the tagged eels migrated to the estuary via the pumping station (PS), 5% used other routes, and 20% did not migrate seaward that season. Acceleration data showed that eels significantly increased their activity up until the moment of PS passage, from an overall mean RMS acceleration of 1.04 m/s² (95% CI = 0.93-1.18) when the pumping station started pumping (between 1 up to 4 h before eel passage), to 1.14 m/s² (95% CI = 1.04-1.26) at 10 min before the eels passed through the pumps, and 1.66 m/s² (95% CI = 1.32-2.08) 1 min before passage. Most eels passed the pumping station at night, and we found that eels had the highest movement activity between 15:00 and 00:00 with a peak around 19:00, which coincided with the moment of PS passage.

Conclusions: Acceleration provides a proxy for fish movement activity and our study demonstrates how including accelerometer sensors with telemetry can help understand movement of endangered species at migration barriers. This information is vital for implementing strategies to improve outward migration success, towards the spawning grounds in the Sargasso Sea, and thus the conservation and restoration of eel populations.

Background: Understanding how predatory animals efficiently locate prey with limited knowledge of its location is challenging. Optimal foraging theory suggests that animals improve their food intake through experience-based adjustments of search patterns. For example, animals feeding on clustered prey may repeatedly search successful areas and move farther away when unsuccessful (the 'win-stay, lose-shift' strategy). A related concept, area-restricted search, predicts that animals initially search broadly and then switch to a more localized, tortuous search upon finding clustered prey. However, few studies have empirically supported these predictions for large aquatic predators due to difficulties in recording their foraging success on known prey species.

Methods: We used biologging techniques to record the fine-scale foraging behaviour of Baikal seals in Lake Baikal, which hunt tiny, clustered, planktonic amphipods at high rates. We reconstructed their three-dimensional movement paths during dives and estimated the timing of prey capture events based on video-validated body acceleration data.

Results: Seals moved shorter horizontal distances and exhibited greater directional changes after more successful dives, supporting the 'win-stay, lose-shift' strategy. Consistent with area-restricted search, successful foraging dives led to decreased speed and increased tortuosity in the horizontal plane.

Conclusions: These findings suggest that experience-based behavioural adjustments at a dive-to-dive scale are crucial for Baikal seals-and possibly other large aquatic predators-to maintain high foraging rates. Furthermore, they illustrate how an exceptionally high predator-prey body mass ratio (> 500,000) for a single-prey-feeding (non-filter-feeding) predator is maintained in the unique Lake Baikal ecosystem.

Background: Large bodies of water are ecological barriers known to influence the migration properties of avian migrants. Among soaring raptors, various flight strategies are used during migration to overcome these obstacles. These raptors exploit favourable winds and thermals to successfully migrate since prolonged flapping flight is expensive energetically. Soaring migrants circumvent large expanses of water and cross at geographical bottlenecks, minimizing the amount of open water they cross to save energy. Few studies have directly investigated how atmospheric conditions influence water crossing behavior during northbound pre-breeding spring migration at a high concentration bottleneck.However,inefficientlycrossingecologicalbarriersduringspringmigrationcanleadtodelayedbreedingandfitness consequences for soaring raptors.

Methods: We use the Red-tailed Hawk (Buteo jamaicensis) as a model organism to investigate how atmospheric conditions influence the timing of water crossing at the Straits of Mackinac in Michigan, USA. We deployed 36 GPS transmitters during spring migrations spanning 2021-2023. Fifty-one water crossings from 33 adult individuals were used in this analysis. We annotated crossing events with atmospheric covariates including wind speed, wind support (V), crosswind (U), and uplift potential (temperature difference between water surface and air) to elucidate what conditions explain the probability of water crossing behavior by Red-tailed Hawks.

Results: We found that uplift over water was available in spring and that it positively affected the probability to cross. We also found that wind support and wind speed had a significant effect on crossing probability as low wind speeds and supportive wind increased the probability of crossing. The hawks had a higher probability to cross earlier in spring.

Conclusion: We provide evidence that uplift over water along with low overall wind speed and wind support facilitate water crossing behavior of Red-tailed hawks during pre-breeding spring migration. We also highlight that despite the general effects of uplift and wind there is substantial variation in crossing behavior among individuals. Our findings further contribute to the understanding of how soaring raptors overcome water barriers during migration.