Search

Este artículo contiene 20 páginas, 6 figuras, 4 tablas., Aim: Over the last decades, the study of movement through tracking data has grown exceeding the expectations of movement ecologists. This has posed new challenges, specifically when using individual tracking data to infer higher- level distributions (e.g. population and species). Sources of variability such as individual site fidelity (ISF), en-vironmental stochasticity over time, and space-use variability across species ranges must be considered, and their effects identified and corrected, to produce accurate estimates of spatial distribution using tracking data. Innovation: We developed R functions to detect the effect of these sources of vari-ability in the distribution of animal groups when inferred from individual tracking data. These procedures can be adapted for their use in most tracking datasets and tracking techniques. We demonstrated our procedures with simulated datasets and showed their applicability on a real-world dataset containing 1346 year- round migratory trips from 805 individuals of three closely related seabird species breeding in 34 colonies in the Mediterranean Sea and the Atlantic Ocean, spanning 10 years. We detected an effect of ISF in one of the colonies, but no effect of the environmental stochasticity on the distribution of birds for any of the species. We also identified among-colony variability in nonbreeding space use for one species, with significant effects of popu-lation size and longitude. Main conclusions: This work provides a useful, much- needed tool for researchers using animal tracking data to model species distributions or establish conservation measures. This methodology may be applied in studies using individual tracking data to accurately infer the distribution of a population or species and support the deline-ation of important areas for conservation based on tracking data. This step, designed to precede any analysis, has become increasingly relevant with the proliferation of studies using large tracking datasets that has accompanied the globalization process in science driving collaborations and tracking data sharing initiatives., We thank the following institutions for funding: EU H2020 pro-gramme through grant 634495; Seventh Framework Programme (Research Executive Agency) through Marie Curie Career Integration Grant 618841 (FP7-PEOPLE-2013- CIG); ESFRI LifeWatch Project; LIFE programme of the European Commission through projects LIFE10 NAT/MT090 and LIFE11 NAT/IT/000093; Ministerio de Ciencia e Innovación/Ministerio de Economia y Competitividad (Spain) through projects CGL2009- 11278/BOS, CGL2013-42585-P, C G L 2 0 1 3 - 4 2 2 0 3 - R , C G L 2 0 16 - 7 8 5 3 0 - R a n d C G L 2 0 17- 8 52 10 - P ; Organismo Autónomo de Parques Nacionales (Spain) through pro-ject 1248/2014; Fundação para a Ciência e a Tecnologia (MCTES, Portugal) through projects MARE-UID/MAR/04292/2019; IF/00502/2013/CP1186/CT0003, PTDC/BIA-ANM/3743/2014, PTDC/MAR-PRO/0929/2014, UID/AMB/50017/2019 and UIDP/50017/2020 + UIDB/50017/2020 (to CESAM); Office Français de la Biodiversité (France), through the Programme PACOMM, Natura2000 en mer; Hellenic Bird Ringing Centre; MSDEC (Malta). VMP was supported by pre-doctoral contract BES-2014- 068025 of the Spanish Ministerio de Industria, Economía y Competitividad; MM by grant SFRH/BPD/47047/2008 from the Portuguese Foundation for Science and Technology; JMRG by Ph.D. grant AP2009-2163 from the Spanish Ministerio de Educación; GDO and MMü by Ornis italica and by the Regione Siciliana and Assessorato Risorse Agricole e Alimentari thoriugh a grant to the Ringing Unit of Palermo; VHP by grant SFRH/BPD/85024/2012 from the Portuguese Foundation for Science and Technology; VN by grant SFRH/BPD/88914/2012 from the Portuguese Foundation for Science and Technology; and JN by the Spanish National Programme Ramón y Cajal (RYC-2015- 17809); GK and SX were partially funded by the Operational Program “Environment and Sustainable Development” (EPPERAA) of the National Strategic Reference Framework (NSRF) 2007-2013, co- financed by the ERDF and Greek EDP; FdF by a Ph.D. grant from the Coordination for the Improvement of Higher Education Personnel (CAPES—Brazilian government agency; Bex Process 1307/13-4); ZZ by a PhD grant from the University of Barcelona (APIF/2012); MCF by a PhD grant from the University of Barcelona; and RR by post-doctoral contracts of the PLEAMAR programme from MINECO and Fundación Biodiversidad (2017/2349), and Ministerio de Ciencia, in-novación y Universidades (RYC-2017- 22055). This publication is part of the project I+D+i/PID2020-117155GB-I00, funded by MCIN/ AEI/10.13039/501100011033.

The processes that drive the ontogeny of migratory strategies in long-lived animals with slow maturation remain enigmatic. While some short-lived migrants are known or believed to repeat the same migratory patterns throughout their lives, little is known on the time required for immature long-lived migrants to progressively acquire adult-like migratory behaviours, or which aspects take longer to refine during the maturation process. Here, we studied the ontogeny of long-distance migratory strategies and related patterns of spatial distribution in a long-lived seabird species during the annual cycle. To do so, we deployed light-level geolocators on 4- to 9-year-old immature Cory's shearwaters (Calonectris borealis) and on breeding adults. We revealed that migratory timings and destinations of young shearwaters progressively changed with age. The effect of ageing was remarkably evident on spring migratory performance and phenology. Birds gradually shortened the duration of the non-breeding period by advancing departure date and reducing travelling time, which resulted in a sequential arrival at the colony of the various age contingents. Ageing immatures gradually changed from a more exploratory strategy to a more conservative way of exploiting resources, reducing both their year-round spatial spread across oceanic domains and the total distance travelled. Immatures always performed a trans-equatorial migration to the Southern Hemisphere, contrasting with 17% of the adults which remained in the North Atlantic year-round. Finally, during the breeding season immatures were widely dispersed through the North Atlantic reducing their overlap with breeding adults. Our long-term study provides empirical support to the hypothesis that in long-lived species, the refinement of migratory behaviour and year-round spatial distribution is a progressive process mediated by age and experience, where life stage constraints and competition for resources may also play a role. The emerging pattern suggests that for some avian taxa, the ontogeny of migratory strategy is a prolonged, complex and dynamic process. FEDER; FCT-Fundação para a Ciência e Tecnologia info:eu-repo/semantics/publishedVersion

Inter-individual variation in behaviour has been recognised as a major driver of population ecology, but its relationship to migratory strategy has been ill-explored. Here, we investigated whether male migrant and resident Cory’s shearwaters Calonectris borealis, a long-lived partially migratory seabird, are distinguishable by their temperament at the colony. We tracked a large number of individuals over two winters using GLS devices and assessed whether exploratory behaviour and reaction to extraction from the nest corresponded to migratory strategy over this period. While exploratory behaviour was unrelated to migratory strategy, birds that were resident were more likely to be unreactive towards extraction from the nest. This difference in behavioural stress response, together with previous findings that migrants display higher physiological stress over winter, suggests that migrants and residents may be distinguishable by their stress threshold. Fundação para a Ciência e a Tecnologia - FCT info:eu-repo/semantics/publishedVersion

Regular counts of migrating animals at stopover sites have been used as a measure of site importance at the global scale as well as for monitoring long-term population changes. However, migratory passage can last for several weeks and the turnover rate of individuals is often high, preventing the use of peak counts to estimate the total number of migrants. This estimate can be achieved, however, by combining count data with information on stopover length. Here, we developed a new method to quantify the total number of migrant birds using stopover areas hosting overlapping populations of local (breeding or wintering) and passage individuals of a given species. We illustrate the application of this method by estimating the number of spring migrant dunlins Calidris alpina stopping over at the Tagus estuary (Portugal). We used carbon and nitrogen isotopic signatures in toenails to identify migrants and to estimate their proportion in total counts. We then employed isotopic clock models to determine time since arrival (TSA) of individuals from signatures in red blood cells and plasma and, using a simulation approach, we derived the relationship between TSA and stopover length. Finally, by dividing the number of migrants.day (obtained from counts) by the stopover length, we assessed the size of the migrant population. We demonstrated that stopover length can be directly predicted from mean TSA values of birds sampled during migration, regardless of variations in (1) migratory rate, that is, the phenology of arrivals throughout the migratory period and (2) the number of birds involved in the migratory event. Migrant dunlins stayed on average 7.5 days at the Tagus estuary during spring migration, which combined with count data resulted in an estimate of c. 30,000 passage dunlins, using the study site. Our novel approach is not strict in its assumptions, and therefore can be customised to the specificities of different taxa and study areas. Estimates of total number of migrants along migratory flyways are critical to identify priority sites for conservation action. In fact, single stopover sites may host a very significant proportion of a global population albeit for a short period.

Length–weight relationships were estimated for six teleost fish species occurring in Bijagós Archipelago, Guinea-Bissau. Samples were collected seasonally during three dry seasons (2013/2014, 2014/2015, 2015/2016) and two rainy seasons (2015 and 2016). Fishes were captured by three methods: angled from the beach or a boat; using beach seine with a mesh size ranging 0.5–1 cm; drift netting from a boat (mesh size 2 cm). This work provides the length-weight relationship for three fish species that are not reported in FishBase (Citharichthys stampflii, Gerres nigri and Psettodes belcheri) as well as for three species from which we present a wider size range (Eucinostomus melanopterus, Scomberomorus tritor and Sphyraena afra). Fundação para a Ciência e a Tecnologia (FCT); MAVA Foundation through a project granted to IBAP (Guinea-Bissau) info:eu-repo/semantics/publishedVersion

Fisheries can have profound impacts on the structure and functioning of marine ecosystems and affect seabird populations. For seabirds, impacts can include direct mortality in fishing gear, but fisheries also represent an abundant source of food that may otherwise be inaccessible. Previous studies with seabirds have revealed the occurrence of individual foraging specializations, and therefore in scavenging species some individuals may have a higher propensity to feed on fisheries discharges than the rest of the population. Here we used recently developed techniques (spatio-temporal match of positions) to detect interactions between black-browed albatrosses Thalassarche melanophris and fishing vessels, and also stable isotope analysis of tissues with different turnovers, to investigate long-term individual specialization in fishery waste products. We combined global positioning system tracking data from 89 birds with vessel monitoring system data from the entire fleet operating around the Falklands Islands, in 2009 and 2011. Interactions with vessels (freezer/factory bottom trawlers) occurred in 15 out of 89 independent albatross trips. Among individuals tracked in both years, those that associated with fisheries in 2009 were not more likely to do so again in 2011. Carbon and nitrogen isotopic signatures in whole blood and feathers of albatrosses that interacted with trawlers were similar to those of individuals that did not. Also, we found no correlation between feather and blood isotopic ratios of carbon or nitrogen, indicating no long-term consistency in the isotopic niche of study birds. These results suggest no specialization of individual albatrosses with regard to fisheries. Studies of other albatrosses have also failed to show long-term trophic consistency, which may indicate that scavenging albatrosses, a group particularly threatened by fisheries activity, do not specialize in discards. Therefore, any management actions leading to a reduction of discards will be beneficial, decreasing the numbers of birds behind vessels and consequently the likelihood of incidental mortality.

In this study we test the potential of stable isotope analysis to reveal wintering origins of waders mixing at stopover sites, using the dunlin Calidris alpina as a case study. We determined stable carbon ( δ 13 C) and nitrogen ( δ 15 N) isotope signatures of toenails of dunlins captured during winter at reference sites along the East-Atlantic Flyway, from Mauritania to the United Kingdom. Afterwards, during spring migration, dunlins were sampled at the Tagus estuary, Portugal, and assigned to their wintering grounds according to their stable isotope signatures. Toenails from wintering dunlins at diff erent sites had signifi cantly diff erent δ 13 C and δ 15 N signatures, despite some overlap in isotopic carbon ratios of birds from Morocco, Portugal and the UK. Among birds sampled during migration in Portugal, we found a clear bimodal pattern in δ 13 C values, corresponding to passage migrants from Mauritania (enriched δ 13 C values) and wintering birds from the Tagus estuary (depleted δ 13 C values). Th e fi rst passage migrants from Mauritania appeared at the Tagus estuary by the end of March, with peak numbers during late April and early May. Our study provides evidence that isotopic signatures of toenails can play a determinant role in tracing the wintering origins of migrant dunlins at their stopover areas. Toenails, instead of feathers, can be the powerful and innovating tissue to sample in wader studies, allowing to bridge the gap in the fi eld of migratory connectivity between sites used in diff erent phases of the life cycle of waders.

In birds, the period spent brooding or guarding young chicks is highly variable, but such variation has seldom been studied. Previous single-year studies of Antarctic petrels Thalassoica antarctica and grey-headed albatrosses Thalassarche chrysostoma revealed a pronounced seasonal decline in brood-guarding duration and gave rise to the ‘synchronisation hypothesis’, which suggests that some of the variation in the length of the brood-guarding stage is related to predictable seasonal changes in the risk of chick predation. We tested the predictions of this and three other hypotheses in a two-site, four-year study of the black-browed albatross T. melanophris. The existence of a pronounced seasonal decline in broodguarding duration was apparent at both sites, and in years of contrasting food availability, providing further support for the ‘synchronisation hypothesis’. Alternative explanations for this pattern are that short brood-guarding periods for latehatched chicks result from a seasonal decline in food availability or from the fact that early nesting birds are of higher individual quality. However, these explanations are at odds with the absence of a seasonal decline in early chick growth or in probability of chick survival. Furthermore, adult quality (measured as past reproductive performance) had a weak and inconsistent effect on the duration of brood-guarding. Weather changes explained some of the variation in broodguarding, but there were no differences between regions of contrasting climates. Individual pairs displayed a degree of inter-annual consistency in brood-guarding duration and, at least in some years, longer brood-guarding resulted in higher fledging probability. We speculate that a higher investment in brood-guarding increases the cost of reproduction, which counteracts other selective pressures that would otherwise lead to longer brood-guarding durations.

Estuarine mudflats, among the most important foraging grounds for waders during the non-breeding season, consist of complex mosaics of shallow pools and dry areas during low tide. In this study, we carried out close-range focal observations to determine foraging parameters of dunlins Calidris alpina, foraging in the mudflat microhabitats of the Tagus estuary, Portugal. Birds foraging in wet patches mostly targeted the siphons of the bivalve Scrobicularia plana, while in dry patches they mostly fed on mudsnails Hydrobia ulvae. Surface visibility of prey, rather than their abundance in the sediment, explained the microhabitat-related differences in prey selection. Birds using dry patches obtained 40% less energy intake than those using wet patches, still many extensively used this poor microhabitat. Because siphons retract quickly when the sediment is disturbed, birds often failed to catch them. We found that birds that were less efficient in capturing siphons in wet patches tended to spend more time foraging on mudsnails in dry patches. This suggests that lack of skills in siphon cropping represents a major foraging constraint for dunlins wintering in the Tagus estuary. It may even cause them to forage during high tide in order to achieve their daily energetic requirements.

We monitored the attendance and activity of Cory's Shearwater Calonectris diomedea on Berlenga Island, Portugal, during the breeding season. To achieve this, we developed a novel logging technique to record the date and time of entrances and departures from the burrows, as well as the identity of each member of a pair. The technique enabled nonintrusive assessment of the activity of burrow-nesting animals over prolonged periods and provided very reliable information. Our study showed that males attended the nests more frequently than females during the pre-laying and chick-rearing periods. We did not find such differences during the incubation period, and both members spent similar amounts of time incubating the eggs. An index of activity (denned as number of entrances plus exits from the nest) achieved higher scores during the pre-laying and incubation periods, but the activity decreased significantly during the chick-rearing period. We did not find any effect of moonlight on the levels of activity, hour of arrival at the colony or time spent inside the burrows in breeding birds.

During the highest spring tides the intertidal sediment flats of estuaries are fully inundated at high water, and waders have no choice but to move to supratidal roosts, e.g. on open farmland, saltpans or beaches. However, in many estuaries during the lowest neap or intermediate tides there are sectors of upper intertidal sediment flats that remain exposed even at the peak of high water, and so waders have the choice of roosting either there or in supratidal sites. In the Tagus Estuary, Portugal, as elsewhere, waders use both types of roosts during high water. Our main objective was to understand what makes waders opt for one of these two types of available roosts. We monitored wader use of saltpans and intertidal roosts from spring to neap tides, and measured foraging and alarm behaviour, prey availability and disturbance by predators. Most of the wader species studied chose intertidal (mudflat) roosts whenever these were available, and only roosted in saltpans during the peak of spring tides. We hypothesized that this preference was explained either by an attempt (i) to continue feeding into the high water period, or (ii) to minimize predation risk. Extending feeding time into the high water period did not seem to be very relevant for roost choice because both prey availability and foraging activity were low in both types of roosts. However, predator disturbance was several times higher in the saltpans than in the intertidal roosts, suggesting that this factor may be the determinant in the choice of roost type.

Summary 1 Despite covering a relatively small area on a global scale, estuarine tidal flats are vital to many aquatic bird species during much of the yearly cycle. Small-scale features of tidal flats, such as water drainage channels, can influence the carrying capacity of estuarine wetlands, yet their ecological impact is poorly understood. In this study we evaluated the influence of drainage channels on the quality of feeding habitat for waders in the Tagus estuary, Portugal. 2 We measured the abundance of seven wader species at five distance classes from drainage channels, and analysed the variation in peck rates, step rates, turning rates and success rates. In addition we measured the density of macroinvertebrate prey and the sediment physical–chemical characteristics at different distances from the channels. 3 All wader species occurred at higher densities near the channels. In the study area 44% of the birds fed on just 12% of the available surface, less than 5 m away from drainage channels. Wader foraging behaviour also suggests a greater feeding effort near the channels. 4 While the characteristics of the sediments did not change significantly with distance from channels, prey abundance corresponded closely with wader abundance, suggesting that the small scale distribution of birds on the tidal flats may be related to the presence of their prey. 5 Synthesis and applications. Our study shows that the areas around drainage channels are particularly important feeding sites for waders foraging on tidal flats. Consequently, managers of estuarine wetlands should strive to preserve or improve channel networks. This can be achieved by (i) preserving saltmarshes and saltpans adjacent to tidal flats, (ii) minimizing the reclamation of upshore flats and (iii) avoiding embankments and canalizations of inland water flows that reduce the number of water entry points onto tidal flats.