2017-10-23, Mahoney, Peter J., Ebinger, Michael, Jaeger, Michael, Shivik, John A., Young, Julie K.

(1) Space use by animals has important implications for individual fitness. However, resource requirements often vary throughout the course of a lifetime and are a reflection of the demands associated with daily tasks or specific life-history phases, from food acquisition to reproduction, and emphasize the need to classify resource selection relative to specific behavioural states. Site fidelity is often indicative of behaviours important for individual maintenance (e.g. foraging), species' life history (e.g. seasonal site selection), social communication (e.g. scent-marking) and species interactions (e.g. predation, competition). Thus, resolving site fidelity patterns associated with key behaviours is essential to accurately quantify behavioural-dependent resource needs and the fitness consequences of space use. (2) We propose a novel method for identifying site fidelity patterns in animal location data using a convex hull clustering program called R Animal Site Fidelity (rASF). We also provide a means of integrating activity as a measure of behavioural state. We demonstrate the utility of the approach in identifying cougar (Puma concolor) predation events, coyote (Canis latrans) den and rendezvous sites, and coyote territorial boundaries. (3) We parameterized rASF based on site fidelity characteristics that best characterized the clustering behaviour of interest and estimated behavioural state from either dual-axial accelerometer data or movement trajectory statistics. When behaviour was used in conjunction with cluster-specific metrics (duration, proportion of diurnal fixes and landscape composition), we could accurately predict prey species associated with cougar kills and differentiate pup-rearing from scent-marking sites in coyotes. (4) Site fidelity patterns and activities associated with animal revisitation will be key to identifying the behavioural motivations behind observed patterns of space use. Our approach provides an efficient, rigorous and repeatable means of identifying site fidelity patterns associated with specific behavioural states without the need for direct observations, which are often impossible to collect at large spatial scales and in dense habitat. As such, this framework has significant potential to inform theory in behavioural ecology while providing managers with better resolution on appropriate management targets associated with key aspects of a species' life history.

2019-09-05, Silva, João Paulo, Gudka, Mishal, Abad-Gómez, José Maria, Santos, Carlos David

Most species-climate models relate range margins to long-term mean climate but lack mechanistic understanding of the ecological or demographic processes underlying the climate response. We examined the case of a climatically limited edge-of-range population of a medium-sized grassland bird, for which climate responses may involve a behavioural trade-off between temperature stress and reproduction. We hypothesised that temperature will be a limiting factor for the conspicuous, male snort-call display behaviour, and high temperatures would reduce the display activity of male birds. Using remote tracking technology with tri-axial accelerometers we classified and studied the display behaviour of 17 free-ranging male little bustards, Tetrax tetrax, at 5 sites in the Iberian Peninsula. Display behaviour was related to temperature using two classes of Generalized Additive Mixed Models (GAMMs) at different temporal resolutions. GAMMs showed that temperature, time of the day and Julian date explained variation in display behaviour within the day, with birds snort-calling significantly less during higher temperatures. We also showed that variation in daily snort-call activity was related to average daytime temperatures, with our model predicting an average decrease in daytime snort-call display activity of up to 10.4% for the temperature increases projected by 2100 in this region due to global warming. For lekking birds and mammals undertaking energetically-costly displays in a warming climate, reduced display behaviour could impact inter- and intra-sex mating behaviour interactions through sexual selection and mate choice mechanisms, with possible consequences on mating and reproductive success. The study provides a reproducible example for how accelerometer data can be used to answer research questions with important conservation inferences related to the impacts of climate change on a range of taxonomic groups.

2016-05-20, Kölzsch, Andrea, Müskens, Gerhard J.D.M., Nolet, Bart A., Wikelski, Martin

(1) With increasing numbers of many herbivorous waterfowl species, often foraging on farmland, the conflict with agriculture has intensified. One popular management tool is to scare birds off the land, often in association with shooting. However, the energy costs of flying are considerably higher than those of resting. Therefore, when birds fly off after a disturbance, they use extra energy that subsequently needs to be compensated. (2) We used the white-fronted goose Anser albifrons, the most common (grass-eating) species wintering in western Europe, as a model species. We measured flight durations by high-frequency accelerometer recordings over 2 × 24 h in 9 focal geese that were only incidentally disturbed. We also made direct observations on these days to determine whether the flight durations were reliably recorded. Using both a simple and a more realistic model of the energy balance, we calculated the extra grass consumption resulting from additional intentional disturbances. (3) On average, the geese flew daily 2 × 323 s (from and to their roosting sites at 3200 m), and furthermore took to the air 5.3 times during a day (and 1.9 times a night). Multiplied with the average flight durations of 195 s, this gives a total flying time of almost 0.6 h day-1 and a total foraging time of 7.4 h day-1. The extra foraging time needed to compensate for additional intentional disturbances strongly depends on the frequency of such disturbances and the following flight duration. If, for example, flights when intentionally disturbed are twice as long (2 × 195 s), the extra foraging time will be 3.7% day-1 (2.3–3.2% day-1 in the more realistic model) for each intentional disturbance, and the geese will no longer be able to cover their energy requirements when intentionally disturbed six times per day. (4) Synthesis and applications. Recent experiments suggest that geese have to be scared frequently in order to reduce goose visitation to particular fields. With an intentional disturbance rate e.g. of five times a day, the birds’ compensation for the increased energy expenditure will lead to a higher overall consumption of grass of 11.5–16 % day-1. Accommodation schemes have to take such increases in total grass consumption into account when deciding on the refuge areas to be set aside.

2019-08-08, Efrat, Ron, Hatzofe, Ohad, Nathan, Ran

1. During migration, birds are often forced to cross ecological barriers, facing challenges due to scarcity of resources and suitable habitats. While crossing such barriers, birds are expected to adjust their behaviour to reduce time, energy expenditure and associated risks. 2. We studied the crossing of the Sahara Desert by the Great White Pelican (Pelecanus onocrotalus), a large wetland‐specialist. We focused on decisions made by migrating pelicans along different parts of the southbound autumn migration, their response to local environmental conditions, and the implications for time and energy optimisations. We compared the observed pelicans' migration routes with simulated “direct‐pass” (shortest, mostly across the desert) and “corridor‐pass” (along the Nile River) routes, and used GPS, body acceleration and atmospheric modelling to compare flight behaviour along the Nile River versus the desert. 3. The observed route was significantly shorter and faster than the simulated corridor‐pass route and not significantly different from the simulated direct‐pass one. Daily flights over the desert were longer than along the Nile River, with flying time extending to late hours of the day despite unfavourable atmospheric conditions for soaring‐gliding flight. Moreover, the pelicans behavioural response to atmospheric conditions changed according to the landscape over which they flew. Overall, the pelicans showed stronger behavioural adjustments to atmospheric conditions over the desert than along the Nile River. 4. Our findings suggest that migrating pelicans primarily acted as time minimisers while crossing the Sahara Desert, whereas energetic optimisation was only considered when it did not substantially compromise time optimisation. The pelicans took the almost shortest possible route, only following the Nile River along its south‐oriented parts, and frequently staged overnight in the desert far from water, despite being large, wet‐habitat specialists. Correspondingly, their behavioural response to atmospheric conditions changed according to the landscape over which they were flying, switching between time (over the desert) and energy (over the Nile River) optimisation strategies. Our results suggest that the interaction between landscape and atmospheric conditions depict a flexible, yet primarily time‐dominated, migration optimisation strategy.

2019-11-15, Gatt, Marie Claire, Quetting, Michael, Cheng, Yachang, Wikelski, Martin

Despite our knowledge of the biophysical and behavioural changes during flight ontogeny in juvenile birds, little is known about the changes in the mechanical aspects of energy expenditure during early flight development, particularly in migratory species. Here, we investigate in a unique experimental setup how energy expended during flights changes over time beginning with early ontogeny. We calculate overall dynamic body acceleration (ODBA) as a proxy for energy expenditure in a group of hand raised Greylag Geese (Anser anser) trained to fly behind a microlight aircraft. We propose two potential hypotheses; energy expenditure either increases with increasing physiological suitability (the ‘physical development hypothesis’), or decreases as a result of behavioural improvements mitigating flight costs (the ‘behavioural development hypothesis’). There was a significant temporal increase of flight duration and ODBA over time, supporting the ‘physical development hypothesis’. This suggests that early on in flight ontogeny behavioural development leading to flight efficiency plays a weaker role in shaping ODBA changes than the increased physical ability to expend energy in flight. We discuss these findings and the implications of flight development on the life history of migratory species.

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.

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.

2019-12-31, Boiko, Dmitrijs, Wikelski, Martin, Fiedler, Wolfgang

Previous studies on Whooper Swan Cygnus cygnus cygnets hatched in Latvia have shown that c. 99% leave the country each year to moult elsewhere in their 2nd to 6th calendar years. To reveal the exact moulting sites, in 2016 ten cygnets were fitted with 91g solar-powered neck-collar-mounted GPS-GSM loggers. Moulting sites were recorded for four individuals in their 2nd calendar year, and for two of these birds in their 3rd calendar year; four birds in total. All of these moulted at sites in Russia; one was in the Republic of Karelia and three were in the Arkhangelsk Region. The mean average straight-line distance between the hatching and moulting sites was 1,451 km (range = 1,038–2,524 km). Although the data were less comprehensive, another tracked swan probably moulted in the western part of the White Sea in the Republic of Karelia. The conservation of these moulting sites is essential for the Latvian Whooper Swans to thrive.

2015-06-13, Flack, Andrea, Fiedler, Wolfgang, Blas, Julio, Pokrovsky, Ivan, Mitropolsky, B., Kaatz, Michael, Aghababyan, Karen, Khachatryan, A., Fakriadis, Ioannis, Makrigianni, Eleni, Jerzak, Leszek, Shamin, M., Shamina, C., Azafzaf, H., Mokotjomela, Thabiso M., Feltrup-Azafzaf, Claudia, Wikelski, Martin

Annual migratory movements can range from a few tens to thousands of kilometers, creating unique energetic requirements for each specific species and journey. Even within the same species, migration costs can vary largely because of flexible, opportunistic life history strategies. We uncover the large extent of variation in the lifetime migratory decisions of young white storks originating from eight populations. Not only did juvenile storks differ in their geographically distinct wintering locations, their diverse migration patterns also affected the amount of energy individuals invested for locomotion during the first months of their life. Overwintering in areas with higher human population reduced the stork’s overall energy expenditure because of shorter daily foraging trips, closer wintering grounds, or a complete suppression of migration. Because migrants can change ecological processes in several distinct communities simultaneously, understanding their life history decisions helps not only to protect migratory species but also to conserve stable ecosystems.

2016-10-24, Sherub, Sherub, Wikelski, Martin, Fiedler, Wolfgang, Davidson, Sarah C.

Soaring raptors can fly at high altitudes of up to 9000 m. The behavioural adjustments to high-altitude flights are largely unknown. We studied thermal- ling flights of Himalayan vultures (Gyps himalayensis) from 50 to 6500 m above sea level, a twofold range of air densities. To create the necessary lift to support the same weight and maintain soaring flight in thin air birds might modify lift coefficient by biophysical changes, such as wing posture and increasing the power expenditure. Alternatively, they can change their flight characteristics. We show that vultures use the latter and increase circle radius by 35% and airspeed by 21% over their flight altitude range. These simple behavioural adjustments enable vultures to move seamlessly during their annual migrations over the Himalaya without increasing energy output to flight in high elevations.