Biology subjects

Vansteelant, W. M. G.

Publications and source records attributed to Vansteelant, W. M. G..

7 recordsLinked to original sources

bioRxiv2025

Falcons use wind assistance and remote islands to mitigate risk during ocean-crossings

Wind conditions play a major role in determining how birds negotiate ecological barriers during long-distance migration. Migrants typically minimize flights over barriers in opposing winds, while crossing the same barriers directly in supportive winds. Nevertheless, even in supportive conditions, barrier-crossings likely involve a number of risk-mitigating behaviors, including the use of stepping stones. We aimed to understand how seasonal ocean-crossings of Eleonoras falcons (Falco eleonorae) compare in terms of wind support and flight effort, and whether falcons use islands to cross safely in variable wind conditions. To do this we combined GPS-tracking data from 19 individuals over a decade (2012-2022) with wind data from an atmospheric reanalysis model. Despite major differences in wind support, falcons achieved similar ground speeds in both seasons. That is because falcons reduce instantaneous flight effort by flying at lower airspeeds in supportive spring winds (31.5 {+/-} 6.0 km h-1) than in adverse autumn winds (47.4 {+/-} 9.3 km h-1). Overall, it took falcons twice as many flight hours to complete the spring crossings that were 40% greater in terms of air distance compared to autumn crossings. Islands were more frequently used during spring crossings (57.9% individuals in spring vs 21.1% in autumn), and the probability of a falcon using an island significantly increased with weaker wind support in spring (but not in autumn). While wind support partially offsets the extra distance flown over the ocean in spring, isolated islands offer emergency stop-over opportunities when Eleonoras falcons experience relatively weak wind support during protracted ocean crossings.

animal behavior and cognition↗

bioRxiv2025

Gradual ontogenetic shifts in the mobility and space use of long-lived migratory greater flamingos

O_LIHow early-life exploration shapes the adult annual cycle routines of migratory animals remains challenging to study, especially in long-lived species. Delayed recruitment often observed in long-lived migratory birds suggests that the first breeding attempt may be constrained by a protracted learning process in which individuals develop their annual itinerary, which may involve extensive exploration of the winter and breeding sites, potentially causing inexperienced young to wander beyond traditional population areas. C_LIO_LIUsing greater flamingo Phoenicopterus roseus GPS tracking data from 83 individuals tagged as nestlings in the Mediterranean, we analyzed ontogenetic changes in mobility and space use for up to 8 years of age. We segmented autumn-winter and spring-summer tracks (n = 223 device-bird-year combinations) into staging events (n = 1914). We then computed seasonal staging metrics and analysed how they changed with age. We map the traditional congregation sites of flamingos to investigate age-related changes in space use between males and females. C_LIO_LIFlamingos were more exploratory during their early years, gradually transitioning to a more sedentary lifestyle as they grew older. With each additional year of age, the number of staging events decreased by 16%, while the average duration of staging events increased by 8 days. C_LIO_LIBirds remained faithful to the non-breeding staging sites where they spent most of their time during the first year of life. Over time, they returned progressively closer to their natal sites, even after years of exploration at non-traditional locations. Breeding was rare (8%) and occurred at a relatively late age ([≥]5 years), highlighting an extended exploratory phase, a pattern observed in other long-lived species. C_LIO_LIOlder birds were more likely to use traditional sites and spent more time at these sites, particularly after age 5. Our study reveals the individual exploration process underlying natal and non-breeding dispersal patterns previously laid bare by ring-resighting studies and shows that flamingos retain long-term memory of sites learned in early life. C_LI

ecology↗

bioRxiv2025

Eurasian Spoonbill chicks receive parental care up to several months after fledging, but not into migration

Despite its potential role in affecting survival, habitat use and migration strategies of juvenile birds, post-fledging parental care is poorly studied, as it requires that families can be followed over large distances. Here we combine visual observations of colour-ringed chicks being fed after fledging with GPS-tracking and accelerometer-based behavioural classification of fledged chicks and their parent(s) to quantify post-fledging parental care in Eurasian spoonbills in relation to age of the chick and sex of the chick or parent. We show that the number of observed feedings and the amount of overall contact between chicks and parents, i.e. when chick and parent were <10 m apart, strongly decreased with chick age. Chicks were observed being fed until 125 d old, always within 40 km of the natal colony. The amount of contact strongly varied among the 16 GPS-tagged chick-parent pairs, on average decreasing from 8% of contact time at 40 d old to <2% at 90 d. The last contact occurred at chick ages of 44-136 d (median: 88 d). All contact occurred within 18 km of the natal colony except for the first outbound migratory flight of one chick-parent pair. Both mothers and fathers engaged in post-fledging care, with some evidence that mothers had slightly more contact with chicks than fathers, overall as well as while the chick was begging or foraging. In 10 out of 11 cases that both chick and parent embarked on autumn migration, they did not migrate together: post-fledging care ended on average one week before the adults departure and four weeks before the chicks departure on autumn migration. Significance statementProlonged parental care may have positive effects on the survival and influence the habitat use and migration strategies of juvenile birds, as parents may continue to feed their young, show them suitable sites for foraging or resting or suitable routes for migration. Nonetheless, the duration of post-fledging parental care is poorly studied as it requires that parents and their young can be followed over large distances. Based on feeding observations and GPS-tracking of fledged chicks and their parent(s), we show that in Eurasian spoonbills Platalea leucorodia, the duration of post-fledging parental care is highly variable but ends before the onset of migration. This has important implications for the development of migration routines of juvenile spoonbills.

animal behavior and cognition↗

bioRxiv2024

Full-season spring migration counts reveal seasonal contrasts in raptor migration through the eastern Black Sea flyway

The extent to which geographical features like coastlines and mountain ranges funnel migrating birds depends on the seasonal context and direction of migration. Near Batumi, in the Republic of Georgia, the eastern Black Sea coast and Lesser Caucasus funnel over one million raptors through a 10-20 km wide coastal strip every autumn. The funnelling effect of the Lesser Caucasus appears much less evident for northbound migrants. Yet historical data suggest tens of thousands of raptors pass through the region in spring. To elucidate the composition and timing of spring raptor migration we conducted full-season migration surveys near Batumi in 2019, 2020 and 2022. In total, we recorded 33 species and, on average, counted 542,161 raptors (min. 455,799 - max. 618,848) annually. The bulk of the spring passage consisted of Black Kite Milvus migrans (239,649 {+/-} 22,547) and Steppe Buzzard Buteo buteo vulpinus (194,029 {+/-} 102,702). The most diverse and intense spring migration occurred from late March through mid-April, when the median passage date of 12 of 15 common species (>100 ind. y-1) occurred. Species with longer autumn migration periods tended to have longer spring migration periods, and most species had a longer migration period in spring than in autumn, likely due to larger age differences in timing during spring. Species abundance was up to an order of magnitude lower in spring than in autumn, consistent with a weaker bottleneck-effect in spring. Nevertheless, our results confirm the eastern Black Sea coast as a principal spring flyway and help redraw the map of East African-Eurasian migration for several Palearctic raptors. While we will not continue annual spring migration surveys, our data provides a baseline for detecting changes in raptor migration through short-term surveys and can help plan migration-based conservation and research at Batumi in spring.

ecology↗

bioRxiv2022

Itinerant lifestyle and congregation of lesser kestrels in West Africa

Migratory birds often spend a large proportion of their annual cycle in their non-breeding areas. While some species are sedentary after arriving in their non-breeding areas, others engage in itinerary or nomadic movements. Using GPS-tracking we aimed to investigate the little known non-breeding movements of the lesser kestrel Falco namumanni in sub-Saharan Africa. We segment non-breeding tracks (n = 78 tracks by 54 individuals) into staging events (131{+/-} 25 days), itinerant movements between staging sites (11 {+/-} 10 days), and non-directed exploratory movements (6 {+/-} 5 days). We then describe timing and directionality of itinerary movements by male and female kestrels, and explore shifts in habitat use throughout the non-breeding season. Regardless of sex, lesser kestrels spent on average 89% of the non-breeding season at 2-3 staging sites in West Africa. Upon arrival at the end of September, kestrels used disparate sites throughout the Sahel. By December, however, they congregated into two clearly delineated areas in Senegal and along the Malian-Mauritanian border. The birds stayed longer and showed greater daily activity in the latter areas, which were situated closer to wetlands compared to their first and intermediate ones. While 20 of 24 individuals tracked across multiple annual cycles showed consistent staging sites, a few switched between the Senegal and Mauritanian/Malian staging clusters. These results show that rather than tracking suitable climatic conditions southward, lesser kestrels survive the West African dry season by moving into wetland areas within the Sahelian climatic belt. Our findings match reports of lesser kestrel super-roosts in West Africa and stress the conservation value of wetlands along the Senegal River and the Inner Niger Delta in West Africa for the Spanish lesser kestrel population. These areas host 81% of lesser kestrels during 20% of their annual cycle.

animal behavior and cognition↗

bioRxiv2022

Experience does not change the importance of wind support for migratory route selection by a soaring bird

Migration is a complex behavior that is costly in terms of time, energy, and risk of mortality. Thermal soaring birds rely on airflow, specifically wind support and uplift, to offset their energetic costs of flight. Their migratory routes are a record of movement decisions to negotiate the atmospheric environment and achieve efficiency. Because thermal soaring is a complex flight type that young birds need to learn, we expected that, as individuals gain more experience, their movement decisions will also increasingly favor the best thermal uplift conditions. We quantified how route choice during autumn migration of young European honey buzzards (Pernis apivorus) was adjusted to wind support and uplift over up to four years of migration and compared this to the choices of adult birds. We found that wind support was important in all migrations. However, we did not find an increase in the use of thermal uplifts, which could be an artifact of the uplift proxies that we used. Age-specific variations in response to airflow might occur at a smaller spatio-temporal scale than we investigated.

animal behavior and cognition↗

bioRxiv2019

Age-specific migration timing affects the energy seascape over an ecological barrier

Thermal soaring birds extract energy from the atmosphere to achieve energetically low-cost movement. When encountering regions that are energetically costly to fly over, such as open seas, they attempt to adjust the spatio-temporal pattern of their passage to maximize energy extraction from the atmosphere over these ecological barriers. We apply the concept of energy landscapes to investigate the spatio-temporal dynamics of energy availability over the open sea for soaring flight. We specifically investigated how the \"energy seascape\" may shape age-specific sea-crossing behaviour of European honey buzzards Pernis apivorus over the Mediterranean Sea in autumn. We found uplift potential over the sea to be the main determinant of sea-crossing length, rather than wind conditions. Considering this variable as a proxy for available energy over the sea, we constructed the energy seascape for the autumn migration season using forty years of temperature data. Our results indicate that early-migrating adult buzzards are likely to encounter adverse energy subsidence over the Mediterranean, whereas late-migrating juveniles face less adverse flight conditions, and even conditions conducive to soaring flight. Our study provides evidence that the dynamics of the energy landscape can explain intra-specific variation in migratory behaviour also at sea.

ecology↗