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

Foreign egg retention by avian hosts in repeated brood parasitism: Why do rejecters accept?

Great reed warblers (Acrocephalus arundinaceus) are frequently parasitized by egg-mimetic common cuckoos (Cuculus canorus) in Hungary, and these hosts reject about a third of parasitic eggs. The timing of parasitism is important, in that the probability of rejection decreases with advancing breeding stages in this host. Also, egg rejection is more common when a clutch is parasitized by a single foreign egg, compared to parasitism by multiple eggs. We repeatedly parasitized great reed warbler clutches with moderately mimetic foreign eggs, either with (1) one foreign egg (single parasitism) and, after 3 days, by all foreign eggs (multiple parasitism), or (2) all foreign eggs and, 3 days later, by only one foreign egg. Hosts ejected 26-53 % of the experimental parasitic eggs in the first stage of the repeated parasitism, but almost all eggs were accepted in the second stage, irrespective of whether the clutch was singly or multiply parasitized. Video-taping of the behavioural responses of hosts to experimental parasitism revealed no evidence for sensory constraints on foreign-egg recognition, because hosts recognized and pecked the parasitic eggs as frequently in the second stage of repeated parasitism, as they did in the first stage. We suggest that the relative timing of parasitism (laying vs. incubation stage), rather than learning to accept earlier-laid foreign eggs, results in higher acceptance rates of cuckoo eggs in repeated parasitism, because there is decreasing natural cuckoo parasitism on this host species and, hence, less need for antiparasitic defences, with the advancing stages of breeding

Little directional change in the timing of Arctic spring phenology over the past 25 years

With the global change in climate, the Arctic has been pinpointed as the region experiencing the fastest rates of change. As a result, Arctic biological responses-such as shifts in phenology-are expected to outpace those at lower latitudes. 15 years ago, a decade-long dataset from Zackenberg in High Arctic Greenland revealed rapid rates of phenological change.1 To explore how the timing of spring phenology has developed since, we revisit the Zackenberg time series on flowering plants, arthropods, and birds. Drawing on the full 25-year period of 1996-2020, we find little directional change in the timing of events despite ongoing climatic change. We attribute this finding to a shift in the temporal patterns of climate conditions, from previous directional change to current high inter-annual variability. Additionally, some taxa appear to have reached the limits of their phenological responses, resulting in a leveling off in their phenological responses in warm years. Our findings demonstrate the importance of long-term monitoring of taxa from across trophic levels within the community, allowing for detecting shifts in sensitivities and responses and thus for updated inference in the light of added information.</p