Low fitness at low latitudes: Wintering in the tropics increases migratory delays and mortality rates in an Arctic breeding shorebird

Publisher's version (útgefin grein)Evolutionary theories of seasonal migration generally assume that the costs of longer migrations are balanced by benefits at the non-breeding destinations. We tested, and rejected, the null hypothesis of equal survival and timing of spring migration for High Arctic breeding sanderling Calidris alba using six and eight winter destinations between 55°N and 25°S, respectively. Annual apparent survival was considerably lower for adult birds wintering in tropical West Africa (Mauritania: 0.74 and Ghana: 0.75) than in three European sites (0.84, 0.84 and 0.87) and in subtropical Namibia (0.85). Moreover, compared with adults, second calendar-year sanderlings in the tropics, but not in Europe, often refrained from migrating north during the first possible breeding season. During northward migration, tropical-wintering sanderlings occurred at their final staging site in Iceland 5–15 days later than birds wintering further north or south. Namibia-wintering sanderlings tracked with solar geolocators only staged in West Africa during southward migration. The low annual survival, the later age of first northward migration and the later passage through Iceland during northward migration of tropical-wintering sanderlings, in addition to the skipping of this area during northward but not southward migration by Namibia-wintering sanderlings, all suggest they face issues during the late non-breeding season in West Africa. Migrating sanderlings defy long distances but may end up in winter areas with poor fitness prospects. We suggest that ecological conditions in tropical West Africa make the fuelling prior to northward departure problematic.Annual expeditions to Mauritania were organized by NIOZ, and we especially thank Maarten Brugge, Anne Dekinga, Jutta Leyrer and Bernard Spaans for their contributions. The Parc National du Banc d'Arguin granted research permits and facilitated access. J.R. and T.S.L.V. thank Aarhus University for logistical support at Zackenberg. Benoît Sittler organized expeditions to Karupelv Valley. The Farlington Ringing Group provided cannon‐net equipment. This work was supported by two grants from the Netherlands Polar Programme (851.40.072 and 866.15.207) of the Netherlands Organisation for Scientific research (NWO) and from the Metawad project awarded by Waddenfonds (WF209925) to JR and TP. The measurements in Mauritania had their beginnings in the Prins Bernhard Cultuurfondsprijs to TP. JR and TP also received INTERACT grants for Transnational Access from the European Community's Seventh Framework Programme (grant agreement No262693). JR received a generous donation from World Wildlife Fund Netherlands. JAA was supported by FCT (SFRH/BPD/91527/2012). OG and Loïc Bollache were supported by the French Polar Institute (IPEV; program ‘1036 Interactions') and TL by a Veni grant (no. 016.Veni.192.245) from NWO. The authors declare no conflict of interest. This study is based on the efforts of more than 2,000 observers reporting colour‐ringed sanderlings. We especially thank Guðmundur Örn Benediktsson, John Bowler, Ruth Croger, Anne de Potier, Benjamin Gnep, Kim Fischer, Kirsten Grond, Eileen Hughes, Hilger Lemke, Pedro Lourenço, Andy Johnson, Pierre Leon, Jelle Loonstra, Sebastien Nedellec, Afonso Rocha, Brian Rogers, Ron Summers, Jan van Dijk and Hein Verkade. Anneke Bol, Marco van der Velde and Yvonne Verkuil molecularly sexed the majority of birds, Maria Teixeira and Jérôme Moreau sexed eight individuals. Ron Porter created flags for geolocator attachment. Eldar Rakhimberdiev answered questions concerning FLightR and Allert Bijleveld, Jesse Conklin, Rosemarie Kentie, Thomas Oudman, Janne Ouwehand, Emma Penning, Eldar Rakhimberdiev, Brett Sandercock, Ron Summers, Yvonne Verkuil and two reviewers critically commented on drafts. Benjamin Gnep created Figure.Peer Reviewe

Interspecific variation in non-breeding aggregation: a multi-colony tracking study of two sympatric seabirds

Migration is a widespread strategy for escaping unfavourable conditions during winter, but the extent to which populations that segregate during the breeding season aggregate during the non-breeding season is poorly understood. Low non-breeding season aggregation may be associated with higher likelihood of overlap with threats, but with fewer populations affected, whereas high aggregation may result in a lower probability of exposure to threats, but higher overall severity. We investigated non-breeding distributions and extent of population aggregation in 2 sympatrically breeding auks. We deployed geolocation-immersion loggers on common guillemots Uria aalge and razorbills Alca torda at 11 colonies around the northern UK and tracked their movements across 2 non-breeding seasons (2017-18 and 2018-19). Using 290 guillemot and 135 razorbill tracks, we mapped population distributions of each species and compared population aggregation during key periods of the non-breeding season (post-breeding moult and mid-winter), observing clear interspecific differences. Razorbills were largely distributed in the North Sea, whereas guillemot distributions were spread throughout Scottish coastal waters and the North, Norwegian and Barents Seas. We found high levels of aggregation in razorbills and a strong tendency for colony-specific distributions in guillemots. Therefore, razorbills are predicted to have a lower likelihood of exposure to marine threats, but more severe potential impact due to the larger number of colonies affected. This interspecific difference may result in divergent population trajectories, despite the species sharing protection at their breeding sites. We highlight the importance of taking whole-year distributions into account in spatial planning to adequately protect migratory species.</jats:p

Data from: Low fitness at low latitudes: wintering in the tropics increases migratory delays and mortality rates in an Arctic breeding shorebird

1. Evolutionary theories of seasonal migration generally assume that the costs of longer migrations are balanced by benefits at the non-breeding destinations. 2. We tested, and rejected, the null hypothesis of equal survival and timing of spring migration for High Arctic breeding sanderling Calidris alba using six and eight winter destinations between 55° N and 25° S, respectively. 3. Annual apparent survival was considerably lower for adult birds wintering in tropical West-Africa (Mauritania: 0.74 and Ghana: 0.75) than in three European sites (0.84, 0.84 and 0.87) and in subtropical Namibia (0.85). Moreover, compared with adults, second calendar-year sanderlings in the tropics, but not in Europe, often refrained from migrating north during the first possible breeding season. During northward migration, tropical-wintering sanderlings occurred at their final staging site in Iceland 5-15 days later than birds wintering further north or south. Namibia-wintering sanderlings tracked with solar geolocators only staged in West-Africa during southward migration. 4. The low annual survival, the later age of first northward migration and the later passage through Iceland during northward migration of tropical-wintering sanderlings, in addition to the skipping of this area during northward but not southward migration by Namibia-wintering sanderlings, all suggest they face issues during the late non-breeding season in West-Africa. 5. Migrating sanderlings defy long distances but may end up in winter areas with poor fitness prospects. We suggest that ecological conditions in tropical West-Africa make the fuelling prior to northward departure problematic. The material includes R-script