Browsing by Author "Sapir, Nir"
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- Data packageData from: Early arrival at breeding grounds: causes, costs and a trade-off with overwintering latitude(2018-09-14) Rotics, Shay; Kaatz, Michael; Turjeman, Sondra Feldman; Zurell, Damaris; Wikelski, Martin; Sapir, Nir; Eggers, Ute; Fiedler, Wolfgang; Jeltsch, Florian; Nathan, Ran(1) Early arrival at breeding grounds is of prime importance for migrating birds as it is known to enhance breeding success. Adults, males and higher quality individuals typically arrive earlier, and across years, early arrival has been linked to warmer spring temperatures. However, the mechanisms and potential costs of early arrival are not well understood. (2) To deepen the understanding of arrival date differences between individuals and years, we studied them in light of the preceding spring migration behaviour and atmospheric conditions en route. (3) GPS and body‐acceleration (ACC) data were obtained for 35 adult white storks (Ciconia ciconia) over five years (2012‐2016). ACC records were translated to energy expenditure estimates (Overall Dynamic Body Acceleration; ODBA) and to behavioural modes, and GPS fixes were coupled with environmental parameters. (4) At the inter‐individual level (within years), early arrival was attributed primarily to departing earlier for migration and from more northern wintering sites (closer to breeding grounds), rather than to migration speed. In fact, early departing birds flew slower, experienced weaker thermal uplifts and expended more energy during flight, but still arrived earlier, emphasizing the cost and the significance of early departure. Individuals that wintered further south arrived later at the breeding grounds but did not produce fewer fledglings, presumably due to positive carry‐over effects of advantageous wintering conditions (increased precipitation, vegetation productivity and daylight time). Therefore, early arrival increased breeding success only after controlling for wintering latitude. Males arrived slightly ahead of females. Between years, late arrival was linked to colder temperatures en route through two different mechanisms: stronger headwinds causing slower migration and lower thermal uplifts resulting in longer stopovers. (5) This study showed that distinct migratory properties underlie arrival time variation within and between years. It highlighted: (a) an overlooked cost of early arrival induced by unfavourable atmospheric conditions during migration, (b) an important fitness trade‐off in storks between arrival date and wintering habitat quality, and (c) mechanistic explanations for the negative temperature‐arrival date correlation in soaring birds. Such understanding of arrival time can facilitate forecasting migrating species responses to climate changes.
- Data packageData from: Early life and acquired experiences interact in shaping migratory and flight behaviors(2023-11-21) Efrat, Ron; Hatzofe, Ohad; Mueller, Thomas; Sapir, Nir; Berger-Tal, OdedTwo types of experience affect animals' behavioral proficiencies and accordingly their fitness: early-life experience–an animal’s environment during its early development, and acquired experience–the repeated practice of a specific task. Yet, how these two experience types and their interactions affect different proficiencies is still an open question. Here, we study the interactions between these two types of experience during migration, a critical and challenging period. We do so by comparing migratory proficiencies between birds with different early-life experiences, and explain these differences by testing fine-scale flight mechanisms. We used data collected by GPS transmitters during autumn migrations of 65 individuals to study the flight proficiencies of two groups of Egyptian vultures (Neophron percnopterus), a long-distance, soaring raptor. The two groups differed greatly in their early-life experience, one group being captive-bred and the other wild-hatched. Both groups improved their migratory performance with acquired experience, exhibiting shorter migration times, longer daily progress, and improved flight skills, specifically more efficient soaring-gliding behavior. The observed improvements were mostly apparent for captive-bred vultures which were the least efficient during their first migration but were able to catch up in their migratory performance already in the second migration. Thus, we show how the strong negative effects of early-life experience were offset by acquired experience. Our findings uncover how the interaction between early-life and acquired experiences may shape animals' proficiencies and shed new light on the ontogeny of animal migration, suggesting possible effects of sensitive periods of learning on the acquisition of migratory skills.
- Data packageData from: The challenges of the first migration: movement and behavior of juvenile versus adult white storks with insights regarding juvenile mortality(2016-04-12) Rotics, Shay; Kaatz, Michael; Resheff, Yehezkel S.; Turjeman, Sondra Feldman; Zurell, Damaris; Sapir, Nir; Eggers, Ute; Flack, Andrea; Fiedler, Wolfgang; Jeltsch, Florian; Wikelski, Martin; Nathan, Ran(1) Migration conveys an immense challenge especially for juvenile birds coping with enduring and risky journeys shortly after fledging. Accordingly, juveniles exhibit considerably lower survival rates compared to adults, particularly during migration. Also, juvenile white storks (Ciconia ciconia), which are known to rely on adults during their first fall migration, presumably for navigational purposes, display much lower annual survival than adults. (2) Using detailed GPS and body acceleration data, we examined the patterns and potential causes of age-related differences in fall migration properties of white storks by comparing first-year juveniles and adults. We compared juvenile and adult parameters of movement, behavior and energy expenditure (estimated from overall dynamic body acceleration, ODBA) and placed this in the context of the juveniles’ lower survival rate. (3) Juveniles used flapping flight versus soaring flight 23% more than adults and were estimated to expend 14% more energy during flight. Juveniles did not compensate for increased flight costs by increased refueling or resting during migration. When juveniles and adults migrated together in the same flock, the juvenile flew mostly behind the adult and was left behind when they separated. Juveniles showed greater improvement in flight efficiency throughout migration compared to adults which appears crucial because juveniles exhibiting higher flight costs suffered increased mortality. (4) Our findings demonstrate the conflict between the juveniles’ inferior flight skills and their urge to keep up with mixed adult-juvenile flocks. We suggest that increased flight costs are an important proximate cause of juvenile mortality in white storks and likely in other soaring migrants, and that natural selection is operating on juvenile variation in flight efficiency.
- Data packageData from: The spatiotemporal properties of artificial feeding schemes influence the post-fledging movement of Egyptian Vultures(2024-03-13) Reznikov, Korin; Efrat, Ron; Berger-Tal, Oded; Sapir, NirMany vulture populations have severely declined in the past decades, showing high juvenile mortality. To support these populations, feeding stations are used to increase food availability and to supply food without antibiotics and toxic compounds. Yet, supplying food at feeding stations may affect vulture behavior. We present a large-scale field experiment testing how different food provision schemes affected the movement of Egyptian Vultures (Neophron percnopterus). We used GPS transmitters harnessed to 18 vulture chicks and described their movements post-fledging. We categorized the vultures into 3 groups according to the feeding scheme used at feeding stations near their nests: frequent and spatially dispersed food supply (FD); non-frequent and spatially dispersed food supply (NFD); and frequent food supply, concentrated in one location (FC). We found that birds from all three groups increased their roosting distances from the nest with fledgling age, with the NFD and FC groups showing a greater increase than the FD group. Additionally, all 3 groups increased their daily flight distances, with the NFD group presenting the largest increase and the FD group presenting the smallest increase. Our findings offer new insights into the relevance of spatiotemporal differences in the management of feeding stations and show its effect on movement during birds’ early life stages, creating 2 main movement patterns: local and regional. Our findings can help decide upon the preferable feeding scheme in a way that will either encourage or reduce the early dispersal distances of fledglings, according to long- and short-term conservation objectives. For example, local movements during the post fledging period to known and stable food resources may reduce the risk of anthropogenic-induced mortality, while it may negatively affect long-term survival by hindering foraging, flight, and exploring skills and affect dispersion to future breeding sites.