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.
The ontogeny of migratory strategies in long‐lived animals with slow maturation remains enigmatic. This long‐term study provides empirical support to the hypothesis that in long‐lived species as Cory's shearwater, 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.
Individuals in free‐living animal populations generally differ substantially in reproductive success, lifespan and other fitness‐related traits, but the molecular mechanisms underlying this variation ...are poorly understood. Telomere length and dynamics are candidate traits explaining this variation, as long telomeres predict a higher survival probability and telomere loss has been shown to reflect experienced “life stress.” However, telomere dynamics among very long‐lived species are unresolved. Additionally, it is generally not well understood how telomeres relate to reproductive success or sex. We measured telomere length and dynamics in erythrocytes to assess their relationship to age, sex and reproduction in Cory's shearwaters (Calonectris borealis), a long‐lived seabird, in the context of a long‐term study. Adult males had on average 231 bp longer telomeres than females, independent of age. In females, telomere length changed relatively little with age, whereas male telomere length declined significantly. Telomere shortening within males from one year to the next was three times higher than the interannual shortening rate based on cross‐sectional data of males. Past long‐term reproductive success was sex‐specifically reflected in age‐corrected telomere length: males with on average high fledgling production were characterized by shorter telomeres, whereas successful females had longer telomeres, and we discuss hypotheses that may explain this contrast. In conclusion, telomere length and dynamics in relation to age and reproduction are sex‐dependent in Cory's shearwaters and these findings contribute to our understanding of what characterises individual variation in fitness.
Seabirds must often travel vast distances to exploit heterogeneously distributed oceanic resources, but how routes and destinations of foraging trips are optimized remains poorly understood. Among ...the seabirds, gadfly petrels (
spp.) are supremely adapted for making efficient use of wind energy in dynamic soaring flight. We used GPS tracking data to investigate the role of wind in the flight behaviour and foraging strategy of the Desertas petrel,
. We found that rather than visiting foraging hotspots, Desertas petrels maximize prey encounter by covering some of the longest distances known in any animal in a single foraging trip (up to 12 000 km) over deep, pelagic waters. Petrels flew with consistent crosswind (relative wind angle 60°), close to that which maximizes their groundspeed. By combining state-space modelling with a series of comparisons to simulated foraging trips (reshuffled-random, rotated, time-shifted, reversed), we show that this resulted in trajectories that were close to the fastest possible, given the location and time. This wind use is thus consistent both with birds using current winds to fine-tune their routes and, impressively, with an
knowledge of predictable regional-scale wind regimes, facilitating efficient flight over great distances before returning to the home colony.
Migratory strategies dictate stopover ecology, particularly concerning decisions of when, where and how long to stop, and what to do at stationary periods. In birds, individuals stop primarily to ...replenish energy stores, although the functions of stopover events vary among and within species, particularly between pre- and post-breeding seasons. Here, we combined plasma metabolite levels and haematological parameters to compare refuelling rates and physiological state within (early, mid, late) and between (spring, autumn) migratory periods, aiming to identify potentially different migratory strategies in a shorebird, the dunlin Calidris alpina, using a key stopover site in Iberia. Plasma triglycerides and β-hydroxybutyrate concentrations did not differ between seasons, and small differences were found in haematological profiles (higher haemoglobin and hematocrit levels in spring). Similar refuelling rates and physiological status suggests a single migratory strategy in spring and autumn. During both seasons, dunlins arrive at the Tagus estuary with medium-to-high fuel loads, indicating they do not engage in prolonged fuelling. This agrees with a skipping migratory strategy, where birds fly short-to-medium distances while fuelling at moderate rates along a network of sites. Although we may expect late spring migrants to experience stronger pressures to optimally schedule migratory events, we found no significant differences in physiological profiles among early, mid and late migrants. Unexpectedly, such differences were found in autumn: early birds showed the highest triglycerides and haemoglobin levels and lowest β-hydroxybutyrate concentrations. These results denote enhanced refuelling rates and blood oxygen-carrying capacity in early autumn migrants, which is typical of jumpers, i.e., birds travelling with larger fuel loads and performing fewer stops. Our study adds substantially to previous knowledge of stopover ecology in migratory shorebirds in the East Atlantic Flyway. Importantly, it indicates that the Tagus estuary is a high-quality stopover site for intermediate fuelling. Yet, understanding non-fuelling stopping functions is needed to ultimately inform conservation planning.
We present the first assessment of the diet of the blackchin guitarfish Glaucostegus cemiculus (Geoffroy Saint-Hilaire, 1817) for West Africa using DNA metabarcoding on stomach contents of ...individuals captured in the Bijagós Archipelago, Guinea-Bissau. The diet was dominated by crustaceans, particularly caramote prawn Penaeus kerathurus (frequency of occurrence FO = 74%, numerical frequency NF = 54%) and fiddler crab Afruca tangeri (FO = 74%, NF = 12%). Bony fishes were present in 30% of the stomachs. We highlight the importance of conservation action for intertidal habitats and their associated benthic invertebrates for the survival of the critically endangered blackchin guitarfish.
Migratory birds must fit three costly life‐history events within the annual cycle, reproduction, moult and migration, to minimize their overlap and maximize survival and breeding success. However, ...some seabirds, such as Cory's Shearwater Calonectris borealis, overlap body moult and breeding, with flight feather renewal occurring in late chick‐rearing. In contrast, the moult patterns of non‐breeding adult (sabbatical) and immature Cory's Shearwaters, which also attend the colony during the breeding season, remain poorly understood. Furthermore, the potential implications of life‐stage and breeding status trade‐offs on moult status and colony attendance in non‐breeders has rarely been investigated. Surveying different areas within one colony between June and September 2013 and 2014, we studied the age and breeding status composition of birds attending the breeding colony and scored moult of their body (breast and upper‐neck), wing and tail feathers. We found that in addition to breeders (n = 165), 57.6% of the birds (n = 389) attending the colony were 4‐ to 10‐year‐old immatures (n = 132) and adult sabbatical shearwaters (n = 92). Sabbaticals and 8‐ to 10‐year‐old immatures (n = 28) were present at the colony during incubation, whereas only three sabbatical birds and no 8‐ to 10‐year‐old immatures were captured in late chick‐rearing. Conversely, 4‐ to 7‐year‐old immatures arrived later in the season but were still present in late chick‐rearing. Sabbatical and 8‐ to 10‐year‐old immatures were moulting body feathers at the same time as adult breeders, whereas, among 4‐ to 7‐year‐old immatures, older birds moulted earlier than younger birds. A larger proportion of sabbatical birds were replacing tail feathers compared with adult breeders. However, there was no evidence that sabbaticals or 8‐ to 10‐year‐old immatures differed in wing moult from adult breeders until August. Overall, our study shows that colony attendance by non‐breeding adults and immatures is widespread in this population. The synchronous moult schedule of flight and body feathers across age groups at different life‐history stages may suggest that this aspect of moult is controlled by environmental conditions.
Mercury is a heavy metal, which is pervasive and persistent in the marine environment. It bioaccumulates within organisms and biomagnifies in the marine food chain. Due to its high toxicity, mercury ...contamination is a major concern for wildlife and human health. Telomere length is a biomarker of aging and health, because it predicts survival, making it a potential tool to investigate sublethal effects of mercury contamination. However, the relationship between telomeres and mercury contamination is unclear. We measured feather mercury concentration in Cory's Shearwaters Calonectris borealis, long-lived seabirds and top predators, between 9 and 35 years of age and related it to telomere length in erythrocytes. Cory's Shearwaters with higher mercury concentrations had shorter telomeres and the effect was sex-dependent, reaching significance in males only. This may be explained by the fact that males have longer telomeres and higher and more variable mercury concentrations than females in this population. The mercury effect on telomere length was stronger on longer telomeres in the genome within individuals. We discuss the hypotheses that the negative correlation could either be a direct effect of mercury on telomere shortening and/or a consequence of variation in phenotypic quality among individuals that results in a covariation between mercury contamination and telomere length.
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•We investigated the relationship between mercury contamination and telomere length in the Cory’s shearwater.•Higher feather mercury concentration was associated with shorter telomeres, and this effect was stronger in males.•Maleshad longer telomeres and higher, more variable mercury concentrations than females in this population.•The telomere-mercury relationship could reflect a direct effect and/or have resulted from phenotypic quality differences.
Shorebirds and seabirds are abundant predators in coastal habitats worldwide, relying upon a high diversity of benthic invertebrates and fish, respectively. While occupying different trophic guilds, ...they are differently exposed to element contamination entering the coastal food web. Therefore, these birds have been used as bioindicators of environmental contamination in marine ecosystems. We analysed the concentration of trace elements in blood samples of 16 shorebird and seabird migratory species in a major non-breeding site, the Bijagós Archipelago, in regard to their trophic ecology. Overall, our study shows low exposure of this bird community to toxic elements, except for Hg. Most species presented Hg burdens within the moderate toxicity threshold, but one species (Dunlin) presented values at a potential high Hg toxicity risk. We found a positive relationship between Se and Ni concentrations and δ15N values (a proxy for trophic level). In addition, a positive relationship was found between δ13C (a proxy for habitat characteristics) and Hg, Fe, Cu and Mn, while the opposite pattern was recorded for As. Differences were also shown for several trace elements between the two studied trophic guilds: concentrations of As, Pb and Se were higher in pelagic fish consumers (seabirds), whereas Cr, Fe and Sr burdens were higher in benthic invertebrate consumers (shorebirds). Although previous studies in the same site revealed very high concentrations of Cd and Pb in some of the prey species of shorebirds and seabirds (bivalves and fishes), values found in birds for these two elements suggest no toxicological risk. Thus, exposure to toxic elements is not currently a threat to coastal bird populations, namely those facing apparent local declines in Guinea-Bissau, one of the most important non-breeding quarters for of West Africa. Still, Hg burdens were high in some species, deserving further monitoring.
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•We present the first trace elements assessment on migratory birds in West Africa.•Most bird species were little exposed to toxic elements in the Bijagós Archipelago.•Dunlins are at a potential high Hg toxicity risk.•Se and Ni significantly increased with δ15N.•As, Pb and Se were higher in seabirds; Cr, Fe and Sr were higher in shorebirds.
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.
Monitoring mercury concentration in the marine environment is pivotal due to the risks that mercury intake poses to the ecosystem and human health. It is therefore of interest to make reliable, ...comparative measurements over large geographic areas. Here, the utility of wide-ranging generalist seabirds as mercury biomonitors at an ocean basin scale was assessed, using the Cory's Shearwater as a model species. The mercury concentration in flight feathers moulted at distant non-breeding areas of geolocator-tracked birds was quantified, reflecting contamination in various geographic areas. Compound-specific isotope analysis of amino acids was used to obtain comparable trophic positionestimates controlled for baseline isoscape. Birds that remained resident in the Canary Current integrated less mercury into their feathers than those that migrated to either the Benguela or Agulhas currents. Residents also occupied a significantly lower trophic position during the non-breeding season than migrants, largely explaining the difference in mercury exposure. Both mercury concentration and trophic position were similar in individuals spending the non-breeding period in the Benguela and Agulhas currents. This paper highlights the importance of accurate trophic position calculation in order to understand mercury exposure in wide-ranging predators and for meaningful spatial comparisons.
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•The Cory's Shearwater was assessed as a Hg biomonitor at an ocean basin scale.•Feather Hg of partial migrants reflects exposure in different oceanic areas.•Feather Hg concentrations were higher in migrants than in residents.•CSIA-AA-derived trophic position was also higher in migrants than residents.•Trophic position correlated strongly with Hg concentrations.
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