Now showing 1 - 5 of 333
- Data packageData from: Study "Caracal movement ecology study in Cape Town, South Africa"(2024-02-21) Serieys, Laurel E.K.; Bishop, Jacqueline M.Human activities increasingly challenge wild animal populations by disrupting ecological connectivity and population persistence. Yet, human-modified habitats can provide resources, resulting in selection of disturbed areas by generalist species. To investigate spatial and temporal responses of a generalist carnivore to human disturbance, we investigated habitat selection and diel activity patterns in caracals (Caracal caracal). We GPS-collared 25 adults and subadults in urban and wildland-dominated subregions in Cape Town, South Africa. Selection responses for landscape variables were dependent on subregion, animal age class, and diel period. Contrary to expectations, caracals did not become more nocturnal in urban areas. Caracals increased their selection for proximity to urban areas as the proportion of urban area increased. Differences in habitat selection between urban and wildland caracals suggest that individuals of this generalist species exhibit high behavioral flexibility in response to anthropogenic disturbances that emerge as a function of habitat context.
- Data packageData from: Turbulence causes kinematic and behavioural adjustments in a flapping flier(2024-02-20) Lempidakis, Emmanouil; Ross, Andrew N.; Quetting, Michael; Krishnan, Krishnamoorthy; Garde, Baptiste; Wikelski, Martin; Shepard, Emily L.C.Turbulence is a widespread phenomenon in the natural world, but its influence on flapping fliers remains little studied. We assessed how freestream turbulence affected the kinematics, flight effort, and track properties of homing pigeons (Columba livia), using the fine-scale variations in flight height as a proxy for turbulence levels. Birds showed a small increase in their wingbeat amplitude with increasing turbulence (similar to laboratory studies), but this was accompanied by a reduction in mean wingbeat frequency, such that their flapping wing speed remained the same. Mean kinematic responses to turbulence may therefore enable birds to increase their stability without a reduction in propulsive efficiency. Nonetheless, the most marked response to turbulence was an increase in the variability of wingbeat frequency and amplitude. These stroke-to-stroke changes in kinematics provide instantaneous compensation for turbulence. They will also increase flight costs. Yet pigeons only made small adjustments to their flight altitude, likely resulting in little change in exposure to strong convective turbulence. Responses to turbulence were therefore distinct from responses to wind, with the costs of high turbulence being levied through an increase in the variability of their kinematics and airspeed. This highlights the value of investigating the variability in flight parameters in free-living animals.
- Data packageData from: Study "Green turtles (Chelonia Mydas); Hays; Chagos Archipelago, Western Indian Ocean"(2024-01-23) Hays, Graeme C.; Esteban, Nicole; Rattray, AlexEstimating the absolute number of individuals in populations and their fecundity is central to understanding the ecosystem role of species and their population dynamics as well as allowing informed conservation management for endangered species. Estimates of abundance and fecundity are often difficult to obtain for rare or cryptic species. Yet, in addition, here we show for a charismatic group, sea turtles, that are neither cryptic nor rare and whose nesting is easy to observe, that the traditional approach of direct observations of nesting has likely led to a gross overestimation of the number of individuals in populations and underestimation of their fecundity. We use high-resolution GPS satellite tags to track female green turtles throughout their nesting season in the Chagos Archipelago (Indian Ocean) and assess when and where they nested. For individual turtles, nest locations were often spread over several tens of kilometres of coastline. Assessed by satellite observations, a mean of 6.0 clutches (range 2–9, s.d. = 2.2) was laid by individuals, about twice as many as previously assumed, a finding also reported in other species and ocean basins. Taken together, these findings suggest that the actual number of nesting turtles may be almost 50% less than previously assumed.
- Data packageData from: Trans-equatorial migration links oceanic frontal habitats across the Pacific Ocean: year-round movements and foraging activity of a small gadfly petrel(2024-01-22) Clay, Thomas A.; Brooke, MdeL.Gadfly petrels are among the widest-ranging birds and inhabit oceanic regions beyond the legislative protection of national jurisdictions (the High Seas). Detailed information on breeding phenology, at-sea distributions, and habitat requirements is crucial for understanding threats and designing conservation measures for this highly threatened group. We tracked 10 Stejneger’s petrels Pterodroma longirostris, endemic to Isla Alejandro Selkirk, Juan Fernández Islands in the southeast Pacific Ocean, with geolocator-immersion loggers over two years to examine year-round movements, phenology, habitat use, and activity patterns. Birds conducted round-trip trans-equatorial migrations of 54,725 km to the northwest Pacific Ocean between Hawaii and Japan. Across the boreal summer, birds followed the c. 1000 km northward movement of the North Pacific Transition Zone Chlorophyll Front, before their return migration which took a long detour south toward New Zealand before heading east at 40–50°S, presumably benefitting from Antarctic circumpolar winds. To our knowledge, a comparable triangular migration is unique among seabirds. During the pre-laying exodus, birds traveled southwest to the Sub-Antarctic Front, and unlike congeners, there was no evidence of sexual segregation. Foraging areas during incubation were similar to pre-laying, with trips lasting 13 d and taking birds up to 4810 km southwest of the colony. Petrels spent > 75% of their time flying during breeding and migration, yet flight activity was substantially lower during non-breeding, presumably due to flight feather molt. Birds spent 87% of their time at sea within the High Seas and their apparent preference for oceanic frontal regions demonstrates the importance of protecting these remote habitats.
- Data packageData from: Study "LifeTrack White Stork Rheinland-Pfalz" (2015-2023)(2024-01-17) Fiedler, Wolfgang; Hilsendegen, Christiane; Reis, Christian; Lehmann, Jessica; Hilsendegen, Pirmin; Schmid, Heidi; Wikelski, MartinHuman-induced changes in climate and environment are challenging the existence of migratory species. Species with diverse and flexible migratory behaviour suffer less from population decline, as they are more capable to respond by altering migratory behaviour. At the individual-level, variations in migratory behaviour may lead to differences in fitness and subsequently influence demographic dynamics. Using lifetime GPS bio-logging data from 169 white storks (Ciconia ciconia), we answer whether their recently shortened migration has survival benefit during the juvenile stage, the riskiest life period for many migrants. We also explore how other variations in migratory decisions (i.e. time, destination), movement activity (measured by the overall body dynamic acceleration), and early life conditions influence juveniles’ survival. We observed that first autumn migration was the riskiest period for juvenile white storks. Individuals that migrated shorter distances and fledged earlier experienced lower mortality risk. In addition, higher movement activity and overwintering “closer-to-home” in Europe and North Africa (84.21% of tracked individuals adopted this new strategy) were associated with higher survival. Our study shows how avian migrants can change life history decisions linked to fitness over few decades and thus helps us to understand and predict how migrants respond to the changing world.