Longevity record of arctic skua (Stercorarius parasiticus)

The arctic skua (Stercorarius parasiticus) is one of the most long‐lived bird species. In 2010, we captured in Finland an adult, female arctic skua which had been ringed as a nestling in 1987. We tagged it also with a color ring. The bird has last been seen in July 2020 at the age of 33 years, making it most likely the oldest known arctic skua of the world. In 2010–2011 the bird carried a light‐level measuring geolocator, the data of which revealed that the bird had spent the nonbreeding season in the Canary Current area on the west coast of Africa. Breeding populations of arctic skuas have declined recently especially in British Isles, thus it is useful to get longevity data of this species with a high breeding site fidelity.     

Faster migration in autumn than in spring: seasonal migration patterns and non‐breeding distribution of Icelandic whimbrels Numenius phaeopus islandicus

Migration is fundamental in the life of many birds and entails significant energetic and time investments. Given the importance of arrival time in the breeding area and the relatively short period available to reproduce (particularly at high latitudes), it is expected that birds reduce spring migration duration to a greater extent than autumn migration, assuming that pressure to arrive into the wintering area might be relaxed. This has previously been shown for several avian groups, but recent evidence from four tracked Icelandic whimbrels Numenius phaeopus islandicus, a long distance migratory wader, suggests that this subspecies tends to migrate faster in autumn than in spring. Here, we 1) investigate differences in seasonal migration duration, migration speed and ground speed of whimbrels using 56 migrations from 19 individuals tracked with geolocators and 2) map the migration routes, wintering and stopover areas for this population. Tracking methods only provide temporal information on the migration period between departure and arrival. However, migration starts with the fuelling that takes place ahead of departure. Here we estimate the period of first fuelling using published fuel deposition rates and thus explore migration speed using tracking data. We found that migration duration was shorter in autumn than in spring. Migration speed was higher in autumn, with all individuals undertaking a direct flight to the wintering areas, while in spring most made a stopover. Wind patterns could drive whimbrels to stop in spring, but be more favourable during autumn migration and allow a direct flight. Additionally, the stopover might allow the appraisal of weather conditions closer to the breeding areas and/or improve body condition in order to arrive at the breeding sites with reserves.     

Spring migration strategies of Whinchat Saxicola rubetra when successfully crossing potential barriers of the Sahara and the Mediterranean Sea

The flexibility for migrant land birds to be able to travel long distances rapidly without stopovers, and thus to cross wide inhospitable areas such as deserts and oceans, is likely to be a major determinant of their survival during migration. We measured variation in flight distance, speed and duration of major stopovers (more than 2 days), using geolocator tracks of 35 Whinchats Saxicola rubetra that migrated successfully from central Nigeria to Eastern Europe in spring, and examined how these measures changed, or depended on age, when crossing the barriers of the Sahara or the Mediterranean Sea. In all, 31% of Whinchats crossed at least the Sahara and the Mediterranean before a major stopover and 17% travelled over 4751 km on average without any major stopovers. Flight distance and speed during, and duration of major stopovers after, crossing the Mediterranean Sea were indistinguishable from migration over Continental Europe. Speed during a migration leg was lowest crossing Continental Europe and fastest, with longer duration major stopovers afterwards, when crossing the Sahara, but there was much individual variation, and start date of migration was also a good predictor of stopover duration. As the distance travelled during a leg increased, so major stopover duration afterwards increased (1 day for every 1000 km), but the speed of travel during the leg had no effect. There were no differences in any migration characteristics with age, other than an earlier start date for adult birds. The results suggest that adaptive shortening or even dropping of daily stopovers may occur often, allowing rapid, long‐distance migration at the cost of major stopovers afterwards, but such behaviour is not restricted to or always found when crossing barriers, even for birds on their first spring migration. The results may highlight the importance of stopover sites rather than barrier width as the likely key component to successful migration. Individual variation in spring migration may indicate that small passerine migrants like Whinchats may be resilient to future changes in the extent of barriers they encounter, although this may not be true of first autumn migrations or if stopover sites are lost.     

Variable detours in long‐distance migration across ecological barriers and their relation to habitat availability at ground

Migration detours, the spatial deviation from the shortest route, are a widespread phenomenon in migratory species, especially if barriers must be crossed. Moving longer distances causes additional efforts in energy and time, and to be adaptive, this should be counterbalanced by favorable condition en route. We compared migration patterns of nightingales that travelled along different flyways from their European breeding sites to the African nonbreeding sites. We tested for deviations from shortest routes and related the observed and expected routes to the habitat availability at ground during autumn and spring migration. All individuals flew detours of varying extent. Detours were largest and seasonally consistent in western flyway birds, whereas birds on the central and eastern flyways showed less detours during autumn migration, but large detours during spring migration (eastern flyway birds). Neither migration durations nor the time of arrival at destination were related to the lengths of detours. Arrival at the breeding site was nearly synchronous in birds flying different detours. Flying detours increased the potential availability of suitable broad‐scale habitats en route only along the western flyway. Habitat availability on observed routes remained similar or even decreased for individuals flying detours on the central or the eastern flyway as compared to shortest routes. Thus, broad‐scale habitat distribution may partially explain detour performance, but the weak detour‐habitat association along central and eastern flyways suggests that other factors shape detour extent regionally. Prime candidate factors are the distribution of small suitable habitat patches at local scale as well as winds specific for the region and altitude.     

Weak migratory connectivity,loop migration and multiple non-breeding site use in British breeding Whinchats Saxicola rubetra

Determining the links between breeding populations and the pressures, threats and conditions they experience presents a challenge for the conservation of migratory birds which can use multiple sites separated by hundreds to thousands of kilometres. Furthermore, migratory connectivity – the connections made by migrating individuals between networks of breeding and non-breeding sites – has important implications for population dynamics. The Whinchat Saxicola rubetra is declining across its range, and tracking data from a single African non-breeding site implies high migratory spread. We used geolocators to describe the migration routes and non-breeding areas of 20 Whinchats from three British breeding populations. As expected, migratory spread was high, with birds from the three populations overlapping across a wide area of West Africa. On average, in non-breeding areas, British breeding Whinchats were located 652 km apart from one another, with some likely to share non-breeding areas with individuals from breeding populations as far east as Russia. Four males made a direct non-breeding season movement to a second, more westerly, non-breeding location in January. Autumn migration was through Iberia and around the western edge of the Sahara Desert, whereas spring migration was more direct, indicating an anticlockwise loop migration. Weak migratory connectivity implies that Whinchat populations are somewhat buffered against local changes in non-breeding conditions. If non-breeding season processes have played a role in the species’ decline, then large-scale drivers are likely to be the cause, although processes operating on migration, or interactions between breeding and non-breeding processes, cannot be ruled out.     

Migration routes and timing of Mountain Plovers revealed by geolocators

Understanding the migratory movements and habitats used during the annual cycle of migrants is essential to developing comprehensive conservation strategies. Mountain Plovers (Charadrius montanus) are short‐distance migrants listed as a species of conservation concern in many states across their range, however, little is known about their migratory ecology. We used data from geolocators to describe the first direct estimates of migratory routes and migration schedules for Mountain Plovers breeding in Phillips County, Montana. We attached geolocators to 36 Mountain Plovers in 2010–2012 and recovered five (13.9%; three males and two females). Four of five Mountain Plovers in our study overwintered in Texas, and one overwintered in Arizona. Migration routes were relatively linear, with the exception of one plover that moved south and then west to reach its winter range in Arizona. Two plovers left breeding areas in mid‐July and the other three left in late September. All plovers used stopover sites near either eastern Colorado or southwest Kansas. Plovers that departed earlier used stopover sites for ~100 d, whereas those that left later used them for ~35 d. All plovers in our study arrived in wintering areas by early November and departed by late March. Our results suggest that eastern Colorado and southwest Kansas are important stopover areas during migration, and highlight the need to better understand how these locations support non‐breeding plovers.     

Migratory pathways,stopover zones and wintering destinations of Western European Nightjars Caprimulgus europaeus

Little is known about the wintering distribution of the European Nightjar Caprimulgus europaeus. We combined geolocator and GPS‐logger data from different sites in Western Europe to analyse migration routes and migration timing of this trans‐equatorial migrant. Nightjars followed a loop migration route during which they cross two ecological barriers, and converged near common stopover zones in Northern, Central and Western Africa, where they stayed for 2–3 weeks. Nightjars used the same stopover sites as several other European migrants, relying on small and discrete wintering areas within the Democratic Republic of Congo. This confirms the importance of these specific zones and highlights the vulnerability of Western European populations to habitat loss in their non‐breeding areas.     

Short‐ and long‐term effects of tracking devices on the European Roller Coracias garrulus

Tracking devices have contributed enormously to our knowledge of avian migration, although their effects on birds are controversial. Here, we study the short‐ and long‐term effects of deploying geolocators on European Rollers Coracias garrulus and assess the optimal weight of tracking devices to use. In nests in which both parents had geolocators, brood mass was lighter than in nests where only one or neither parent had a geolocator. The year‐to‐year recapture rate for Rollers tagged with geolocators was lower than that for control birds and the recapture rate in different populations was negatively related to the device‐to‐bird weight ratio, decreasing greatly when the weight ratio exceeded 2.5%.     

Survival probability in a small shorebird decreases with the time an individual carries a tracking device

Effects of tracking devices on survival are generally considered to be small. However, most studies to date have been conducted over a time-period of only one year, neglecting the possible accumulation of negative effects and consequently stronger negative impacts on survival when the individuals have carried the tracking devices for longer periods. We studied the effects of geolocators in a closely monitored and colour-ringed southern dunlin Calidris alpina schinzii population breeding in Finland. Our capture–recapture data spans 2002–2018 and includes individual histories of 338 colour-ringed breeding adult dunlins (the term ‘recapture' includes resightings of colour-ringed and individually recognizable birds). These data include 53 adults that were fitted with leg-flag mounted geolocators in 2013–2014. We followed their fates together with other colour-ringed birds not equipped with geolocators until 2018. Geolocators were removed within 1–2 years of attachment or were not removed at all, which allowed us to examine whether carrying a geolocator reduces survival and whether the reduction in survival becomes stronger when geolocators are carried for more than one year. We fit multi-state open population capture–recapture models to the encounter history data. When assessing geolocator effects, we accounted for recapture probabilities, time since marking, and sex and year effects on survival. We found that carrying a geolocator reduced survival, which contrasts with many studies that examined return rates after one year. Importantly, survival declined with the time the individual had carried a geolocator, suggesting that the negative effects accumulate over time. Hence, the longer monitoring of birds carrying a geolocator may explain the difference from previous studies. Despite their larger mass, females tended to be more strongly affected by geolocators than males. Our results warrant caution in conducting tracking studies and suggest that short-term studies examining return rates may not reveal all possible effects of tracking devices on survival.     

Regional wind patterns likely shape a seasonal migration detour

Migrating animals should optimise time and energy use when migrating, travelling directly to their destination. Detours from the most direct route may arise however because of barriers and weather conditions. Identifying how such situations arise from variable weather conditions is crucial to understand population response in the light of increased anthropogenic climate change. Here we used light-level geolocators to follow Cyprus wheatears for their full annual cycle in two separate years migrating between Cyprus, over the Mediterranean and the Sahara to winter in north–east sub-Saharan Africa. We predicted that any route detours would be related to wind conditions experienced during migration. We found that spring migration for all birds included an eastern detour, whilst autumn migrations were direct across the Sahara. The direct autumn migration was likely a consequence of consistent tail-winds, whilst the eastern detour in spring is likely to be more efficient given the wind conditions which are against a direct route. Such variable migration routes shaped by coincidence with prevailing winds are probably common suggesting that some birds may be able to adapt to future changes in wind conditions.