Feeding Ecology of Cory's Shearwater in the Portuguese Atlantic

This thesis considers aspects of the morphology, diet and feeding ecology of Cory's shearwater Calonectris diomedea in the Portuguese Atlantic (sub-tropical and temperate north east Atlantic). Morphological variability among colonies in measurements of adult Cory's shearwater in the Mediterranean, Atlantic and Cape Verde is described. Discriminant methods are employed to enable identification of each sex from bill measurements, in some Atlantic colonies. Relationships between the size and weight of several species of prey fish and the dimensions of diagnostic hard structures (vertebrae, otoliths) are presented, to enable back-calculation of size of prey from remains found in diet samples. The importance of using information from all hard remains present in food samples is discussed in the context of biases in dietary studies of piscivorous animals. The diet of Cory's shearwater in the archipelago of the Azores is described, and comparisons are made with the diet of other marine predators occurring in this area. The use of shearwaters as monitors of pelagic environments is briefly discussed. An interspecific study is described to test the existence of a causal relationship linking mercury levels in the plumage of seabirds with the levels found in the organisms that constitute their prey. The implications for the use of seabirds as monitors of mercury contamination are examined. The patterns of activity and burrow attendance of breeding Cory's shearwaters are analysed, using a novel logging system. The system records data on date, time, identity, of marked birds entering and leaving their nests. Data on the reliability of the system are presented, and its potential use in studies of other burrow-nesting animals is discussed. Existing methods developed to assess the natural patterns of food delivery to nestling Procellariiformes are critically examined, using independent information on parental behaviour provided by the logging system. Some implications of errors in the underlying assumptions of these methods on the understanding of the adaptive significance of reproductive traits of Procellariiformes are discussed. A flexible foraging behaviour of Cory's shearwater in a year of presumed low food availability is documented, and this behaviour is interpreted in relation to a situation of "normal" abundance of food resources. The ability of Cory's shearwaters to adopt alternative long and short foraging trips is discussed in the context of the life-history strategies of long-lived seabirds. An experimental study testing the influence of the nutritional status of the chicks on the provisioning behaviour of Cory's shearwater is presented. Results are discussed in light of current hypotheses explaining regulation of food delivery in Procellariiformes

Use of stable isotope fingerprints to assign wintering origin and trace shorebird movements along the East Atlantic Flyway

Migratory connectivity can be defined as the flux of individuals or populations among areas between stages of an animal's life cycle. Many shorebird species perform long-distance migrations and while moving between breeding and wintering grounds, they depend on a network of intermediate wetlands (stopover sites) where populations of different origins extensively overlap. The difficulty to discriminate such populations represents a serious obstacle to the identification of the links between breeding or wintering areas and stopover sites, and also precludes the estimation of demographic parameters for each population. In this study, we test if linear discriminant models based on stable carbon and nitrogen isotope ratios in toenails can he used to identify populations of several shorebird species of different wintering origins overlapping at two stopover sites of the East Atlantic Flyway. In addition, we evaluate the ability of this approach to infer migratory phenological patterns of shorebirds. Linear discriminant analyses performed overall well in distinguishing the isotopic signals of birds from wintering areas (in France, Portugal, Morocco, Mauritania and Guinea-Bissau) most species, correctly classifying over 80% (n = 542) of all wintering individuals sampled at these areas. Assignment rates of shorebirds captured during spring migration were also high (96%, n=323) at the Tejo estuary, Portugal, but lower (40%, 0 = 185) at Marennes-Oleron Bay in France, and also differed among species. A large proportion of spring migrants captured in Portugal and France were assigned to Banc d' Arguin in Mauritania, the most important wintering area in the flyway. Phenological patterns derived for dunlins (Calidris alpina), common ringed plovers (Charadrius hiaticula) and grey plovers (Pluvialis squatarola) suggest that the first northward migrants started arriving at the Tejo estuary during the second half of March, with peaking numbers occurring during April or May.</p

Data from: Quantifying population size of migrant birds at stopover sites: combining count data with stopover length estimated from stable isotope analysis

1. 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. 2. Here, we developed a new method to quantify the total number of migrant birds using stopover areas hosting overlapping populations of local (breeding, wintering or resident) 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. 3. 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, i.e., 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 ca. 30000 passage dunlins using the study site. 4. Our novel approach is not strict in its assumptions, and therefore can be customized 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

Carbon and nitrogen stable isotopic ratios of Dunlin (Calidris alpina)

Carbon and nitrogen stable isotopic signatures of dunlin (Calidris alpina) toenails, red blood cells (RBC) and plasma collected at the Tagus estuary (Portugal) and Banc d'Arguin (Mauritania) during the winters of 2012-2013 and 2013-2014, and at the Tagus estuary (Portugal) during spring migration of 2013 and 2014. Wintering origins of dunlins sampled during spring migration at the Tagus estuary, as determined by a discriminant analysis based on isotopic signatures of toenails (see Catry et al. 2016, 10.1016/j.baae.2015.10.005), are also included. Birds identified as originating from wintering areas outside Mauritania and Portugal (e.g. Morocco) are included in the dataset but were excluded from further analyses, as well as two birds with low classification scores

Dunlin (Calidris alpina) counts

Total number of dunlins (Calidris alpina) counted in high-tide roost regular counts at the Tagus estuary (Portugal) during spring migration

Breaking the routine: individual Cory's shearwaters shift winter destinations between hemispheres and across ocean basins

There is growing evidence that migratory species are particularly vulnerable to rapid environmental changes arising from human activity. Species are expected to vary in their capacity to respond to these changes: long-distance migrants and those lacking variability in migratory traits are probably at considerable disadvantage. The few studies that have assessed the degree of plasticity in behaviour of marine animals suggest that fidelity to non-breeding destinations is usually high. In the present study, we evaluated individual flexibility in migration strategy of a highly pelagic seabird, the Cory's shearwater Calonectris diomedea. Geolocation data from 72 different migrations, including 14 birds that were tracked for more than one non-breeding season, showed a remarkable capacity to change winter destinations between years. Although some birds exhibited high site fidelity, others shifted from the South to North Atlantic, from the western to eastern South Atlantic, and from the Atlantic to Indian Ocean. Individuals also showed flexibility in stopover behaviour and migratory schedule. Although their K-selected life-history strategy has the disadvantage that the chances of microevolution are slight if circumstances alter rapidly, these results suggest that Cory's shearwaters may be in a better position than many other long-distance migrants to face the consequences of a changing environment

Flexible migratory choices of Cory’s shearwaters are not driven by shifts in prevailing air currents

International audienceWind conditions strongly affect migratory costs and shape flyways and detours for many birds, especially soaring birds. However, whether winds also influence individual variability in migratory choices is an unexplored question. Cory's shearwaters (Calonectris borealis) exhibit migratory flexibility, changing non-breeding destination across the Atlantic Ocean within and between years. Here, we investigated how wind dynamics affect the spatiotemporal migratory behaviour and whether they influence individual choices of non-breeding destination. We analysed 168 GLS tracks of migratory Cory's shearwaters over five years in relation to concurrent wind data. We found no evidence for an association of the use of specific paths or destinations with particular wind conditions. Our results suggest that shearwaters deliberately choose their non-breeding destination, even when the choice entails longer distances and higher energetic costs for displacement due to unfavourable wind conditions en route. Favourable winds trigger migration only when directed towards specific areas but not to others. Despite their dependence on wind for dynamic soaring, Cory's shearwaters show a high individuality in migratory behaviour that cannot be explained by individual birds encountering different meteorological conditions at departure or during migratory movements

Solea senegalensis skeletal ossification and gene expression patterns during metamorphosis : new clues on the onset of skeletal deformities during larval to juvenile transition

Farmed Senegalese sole (Solea senegalensis) still show a high incidence of vertebral anomalies that limit its intensive production and hamper its economic profitability. A great effort towards understanding how fish species develops and grows in captivity has been undertaken in the last decade, with particular emphasis to how different biotic and abiotic factors affect its skeletal development. Although some work has been performed on its skeletal development and expression patterns of key genes in developmental signaling pathways, a detailed description of the above-mentioned processes is still lacking. Here, the progression of skeletal development of cranial, appendicular and axial skeleton has been described through the implementation of an acid free double staining protocol; while the gene expression pattern of vitamin A (VA) and thyroid hormones (THs) signaling pathways were assessed through quantitative PCR (qPCR) during larval fish development under a standard larval rearing protocol and in Senegalese sole larvae fed with increased dietary VA levels (8-fold increase) during the Anemia feeding phase (from 6 to 27 dph). The ontogenetic study allowed us to identify the onset and follow-up the development of most skeletal structures in this fish species, and to gather some insights on the potential onset of deformities originated at the larval to juvenile transition affecting Senegalese sole rearing. The pro-meta-morphosis stage is when the caudal fin vertebrae are formed, where the most common skeletal deformities are found in Senegalese sole. A highly coordinated expression of VA- and TH-related genes has been revealed during larval to juvenile transition, while a comparative gene expression analysis in larvae fed control and high dietary VA content identified the specific timing of VA and THs signaling disruption through which VA and THs directly or indirectly might increase the incidence of skeletal deformities in this species. The present research work represents an important step forward towards the proper identification of the onset of some skeletal deformities and urge the investigation of nutritional and rearing conditions during the switch of larval behavior - from pelagic to benthonic - in order to overcome them in this important species for southwestern European aquaculture