Shearwater Calonectris Borealis Research Articles

Nest predation of Cory's shearwater Calonectrisborealis (Aves, Procellariiformes) by introduced mammals on Terceira Island, Azores.

The Azores holds the largest population of Cory's shearwater Calonectrisborealis (Cory, 1881) (Aves, Procellariiformes) in the world. Apart from a few mammal-free islets, the bulk of the population breeds in coastal areas on the main human-inhabited islands, where several non-native predators have been introduced. Throughout the entire year of the 2019 breeding season, we used motion-triggered cameras and regularly visited three colonies of Cory's shearwater to identify nest predators and the factors affecting nest predation. A total of 292,624 photos were obtained, of which 97.7% were of Cory's shearwaters, 1.7% of non-target species (e.g. other birds, rabbits) and 0.52% of potential predators. Of the monitored nests, 25.7% were predated (n = 9), mainly by black rats (n = 8), but also by cats (n = 1). The relative abundance of black rats in the nests was the main factor explaining nest mortality. This variable was significantly and negatively related with the daily survival rate of Cory's shearwater nestlings. Identification of the main nest predators is crucial for the management and conservation of native bird populations, particularly on oceanic islands, which harbour an important number of threatened and endemic species.

Colony attendance and moult pattern of Cory's Shearwaters (Calonectris borealis) differing in breeding status and age

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.

Surveying Cory Shearwater colonies with camera traps and identifying potential invasive nest predators.

The Azores holds the largest population of Cory's shearwater Calonectrisborealis (Cory, 1881) (Aves, Procellariiformes, Procellariidae) in the world. One of the major threats of this species in the Azores is the predation by invasive mammals, which were introduced during European colonisation of the islands.The present study provides a dataset from a camera-trapping survey performed in colonies of Cory's shearwater. The sampling was conducted between 7 April and 23 October 2019, covering the entire breeding season, in three colonies of the Terceira Island (Azores). A total of 32 nests were sampled using motion-triggered cameras. The aims of this study are to provide information about the ecological patterns of the Cory shearwater and to identify potential nest predators. Our results include a total of 6972 records of 15 species (nine species of birds, five of mammals and one reptile), of which 5414 records are of Cory's shearwater, 478 of potential mammal predators and 1080 of another vertebrate species. Information about the biology of the species is also provided, as species circadian behaviour and habitat description.

Tracking Flights to Investigate Seabird Mortality Induced by Artificial Lights

Light pollution causes attraction and/or disorientation of seabirds, leading to mortality events due to multiple threats. This is a poorly understood phenomenon, largely because of the challenge to track seabirds at night from their nests to the grounding light-polluted locations. New tracking technologies can inform about this phenomenon. Here, we used GPS transmitters with remote download to track the flights of Cory’s shearwaterCalonectris borealisfledglings from an inland experimental releasing site to the ocean. We released birds assigned to three experimental groups: GPS tagged, tape-labelled, and control birds. We assessed how both intrinsic (such as body mass, body condition, body size, and down abundance) and extrinsic (i.e., flight descriptors, such as distance, straightness, and flight duration, wind speed, or moon luminance) factors influenced light-induced groundings by using two datasets: one including the three groups and another including just the GPS tagged birds (as GPS devices provide unique information). We tested whether the probability of being grounded by artificial lights was related to intrinsic factors. With the use of the whole dataset, we found that birds with a higher down abundance had a higher probability of being grounded. GPS data revealed that the probability of being grounded was positively related to the tortuosity of flights and the overflown light pollution levels. Also, birds with slower flights were more likely to be grounded than birds with fast flights. Tortuosity increased with light pollution levels but decreased with the ambient light of the moon. GPSs with remote data download provided information on birds reaching the ocean, this being a substantial improvement to previous studies requiring recapture of the individuals to retrieve the data. GPS tracks of birds reaching the ocean allowed us to know that some birds overflew coastal urban areas so light-polluted as the landing sites of grounded birds. We provide novel scientific-based information to manage seabird mortality induced by artificial lights.

Feeding of Atlantic bluefin tuna Thunnus thynnus around the Canary Islands assessed from stomach content and stable isotope analyses

The Canary archipelago, which is part of the Atlantic biogeographical region of Macaronesia, provides suitable habitat for tropical and temperate-water large pelagic species. Atlantic bluefin tuna (ABFT) Thunnus thynnus occur year round in the Canary Islands. Life history traits of ABFT, specifically foraging patterns, have not been studied thus far in this region. We investigated ABFT trophic biology, combining stomach content and stable isotope analyses. A high proportion (~77%) of the stomachs contained prey, indicating active foraging. The diet primarily consisted of fishes, among which the snipefish Macroramphosus sp. was the major prey. Cephalopods and crustaceans were less important diet components. Moreover, a well-preserved specimen of Cory’s shearwater Calonectris borealis was found in a stomach sampled in 2018. Besides natural prey, 16.7% of the stomachs contained plastic debris. Inter-annual isotopic differences were detected in liver tissue samples, reflecting a dietary shift in 2018, where δ15N values were lower than in 2016 and 2017. Isotopic niche width estimations from stable isotope Bayesian ellipse in R and kernel utilization density analyses suggested a more diverse diet in 2017. Corrected and Bayesian standard ellipse area values from muscle and liver data indicated that the diet of ABFT in the Canary Islands is more euryphagous than in the Strait of Gibraltar (East Atlantic) but more stenophagous than it is in the Gulf of Saint Lawrence (West Atlantic). The present results show that the Canary archipelago represents a foraging ground for ABFT in spring.

Breeding Success of Cory's Shearwater in Relation to Nest Characteristics and Predation by Alien Mammals

Procellariiformes are one of the most threatened groups of birds of the world so knowledge of nesting habitat and factors affecting breeding rates are vital issues for their conservation. Although Cory's Shearwater Calonectris borealis is a well-studied seabird species on the whole, information on the relationship between its breeding parameters and nest site characteristics is quite limited. To address this gap, during 2017-2019, we conducted a study on its breeding performance on Tenerife, the largest and the most densely populated island of the Canarian archipelago. We constructed generalized linear mixed models to evaluate the potential effects of nest features on breeding performance. Two variables explained breeding success: the distance from the nest to the nearest paved road, and the presence of pebbles at the entrance of the nest-burrow, which correlated negatively and positively with breeding success, respectively. The majority of failures occurred during the incubation period. Breeding failures were mainly related to egg abandonment and rat predation upon eggs or chicks. Effective measures mitigating human-instigated disturbance (e.g. control of dogs, rats and feral cat populations, and reducing light pollution), together with studies on factors affecting demographic parameters, are needed to guarantee the long-term conservation of Cory's Shearwater and other seabird species on the main Canary Islands.—Rodríguez, B., Siverio, F., Acosta, Y. & Rodríguez, A. (2022). Breeding success of Cory's Shearwater in relation to nest characteristics and predation by alien mammals. Ardeola, 69: 115-128.

Year-round element quantification of a wide-ranging seabird and their relationships with oxidative stress, trophic ecology, and foraging patterns

Multidisciplinary approaches are essential to diligently assess environmental health status of ecosystems. In this study, year-round chemical elements' exposure and impacts were assessed on the wide-ranging Cory's shearwater Calonectris borealis breeding in Berlenga Island, offshore Portugal, North Atlantic Ocean. The aim was to identify potential contamination and oxidative stress sources associated with trophic ecology, habitat and spatial use, and foraging patterns. A set of 20 chemical elements were quantified, along with oxidative stress biomarkers, stable isotope analyses, and GPS tracking data. Birds presented higher accumulation to some non-essential elements along the year (i.e. arsenic, As; cadmium, Cd; mercury, Hg; lead, Pb; and strontium, Sr), in which concentrations were similar or surpassed other procellariform seabird populations all over the world. No significant differences were found for any of the elements between different periods within the breeding season, with exception of Hg. However, a Principal Component Analysis taking into consideration a group of elements showed differences between pre-laying and chick-rearing periods, with overall higher concentrations in the former. Individuals spending more time engaging in an intensive search for food, and in more coastal environments, presented overall higher element concentrations, and particularly Hg. Contrary to expectations, no relationships were found between chemical elements and oxidative stress. On the other hand, spatial use and foraging patterns of Cory's shearwaters influenced their oxidative stress responses. Our results highlight the need for multidisciplinary approaches to deepen understanding of the large-scale vulnerability of bioindicators such as seabirds and, by extension, the overall environmental health of ecosystems in which they rely.

Leucistic Cory’s Shearwater Calonectris borealis off São Miguel, Azores, in November 2019

The Cory’s Shearwater Calonectris borealis is the most abundant seabird in the Azores. It breeds along the coast of all islands and on most islets in the archipelago (Monteiro et al. 1996a). Birds attend colonies and adjacent waters from late February to late October (Monteiro et al. 1996b), when they can be seen daily around most islands. From mid-November to late January most birds have migrated to wintering areas in the tropical and southern Atlantic (Camphuysen & van der Meer 2001; González-Solís et al. 2007). Aberrant colourations such as albinism, leucism, and melanism have been reported in a wide range of seabird species. One of the aberrant colourations, leucism, is defined as a loss of pigment of entire feathers. A loss of pigmentation may also occur in the legs and bill however, excluding a change in colour of the eyes (van Grouw 2006). This loss of pigmentation, or lack of eumelanin, is due to congenital and heritable failure of pigment-producing melanoblasts to reach some or all areas of the skin (van Grouw 2013). In this note, we document an observation of an aberrantly coloured Cory’s Shearwater in the Azores.

A geolocator-tagged fledgling provides first evidence on juvenile movements of Cory’s Shearwater Calonectris borealis

ABSTRACTUsing geolocator-immersion loggers, we tracked for the first time the migration of one Cory’s Shearwater Calonectris borealis fledgling, from its breeding colony in the Canary Islands, and along its first year of life. The juvenile bird initially followed the same migratory path as the adults but visited different areas of the Central and the South Atlantic Ocean.

Extra-pair paternity in socially monogamous Streaked Shearwaters: forced copulation or female solicitation?

Seabirds are long-lived birds that invest in offspring at very high levels, for which male parental care is indispensable. These characteristics are thought to explain seabirds’ generally low level of extra-pair paternity (EPP). Although the Streaked Shearwater (Calonectris leucomelas) is a socially monogamous seabird, it is known to copulate outside its social pair bond, which implies the frequent occurrence of EPP. In the closely related Cory’s Shearwater Calonectris borealis, cuckoldry is related to body size of the social male. To determine whether body-size-related EPP occurs among Streaked Shearwaters, we established 39 new microsatellite markers for parentage analysis and compared body size between cuckolded and non-cuckolded males. With the new markers, we found that extra-pair males sired 17 (15.0%) of 113 offspring during the 2014–2016 study period, which included three 1.5-month chick-rearing periods. This percentage is among the highest recorded for seabirds. We also found the bill and wing length of cuckolded males to be significantly shorter than those of non-cuckolded males, and that females can reject attempted copulations. These observations imply that EPP in this species is size related and involves female acceptance.

Noteworthy seabird records from Paraná state, southern Brazil

We inventoried seabird specimens—skeletons and skins—collected during beach surveys of Parana, south Brazil, both the mainland coast and offshore islets during the period 1992–94. We found 184 specimens comprising four orders and 17 species. This represents the most important collection of seabirds from Parana and includes three new records for the state, Cory's Shearwater Calonectris borealis, Sooty Shearwater Puffinus griseus and Snowy Sheathbill Chionis albus. We recommend the removal of two species from the avifauna of Parana—Shy Albatross Thalassarche cauta and Broad-billed Prion Pachyptila vittata—due to the lack of tangible evidence. All of this material is held in publicly accessible natural history museums.

Comparing the foraging strategies of a seabird predator when recovering from a drastic climatic event

Seabirds due to their status as sentinels of the marine environment can indicate qualitative changes at various levels of the food web. Furthermore, changes in marine productivity have been correlated with fluctuations in large-scale atmospheric conditions driven by global indices, such as the North Atlantic Oscillation (NAO) index. During the winter of 2009/2010, the second lowest NAO index in history was recorded leading to detrimental conditions that influenced productivity levels in the northeast Atlantic. The response of the Cory’s Shearwater Calonectris borealis, during the period of ameliorating climatic conditions from this drastic event, was monitored in two islands with contrasting productivity patterns: Berlenga, located on the rich upwelling area of the Portuguese shelf; and Cima Islet (Porto Santo Island), located in a poor oceanic environment in the Madeira Archipelago. We collected a multi-year GPS-tracking data set (2011–2015) from adult breeders during the chick-rearing season to examine their at-sea foraging distribution. During a year of low productivity, kernel estimations demonstrated that Cima Islet birds expanded their home ranges and core foraging areas all over the northeast Atlantic, whereas Berlenga birds maintained their distribution close to the breeding colony. Once oceanographic conditions ameliorated from 2012 to 2015, birds decreased significantly their foraging effort, and oceanic breeders concentrated their activity closer to the breeding colony. Analysis of habitat use by means of Maximum Entropy Modelling confirmed distance-to-colony as the most important predictor in the distribution of Cory’s Shearwater. Environmental variables describing sea surface temperature, bathymetry, and chlorophyll a were more influential in Porto Santo, indicating higher sensitivity of the oceanic population to marine productivity proxies. Our study confirms that the Cory’s Shearwater possesses enormous flexibility in its foraging tactics and that neither oceanic nor neritic populations disperse randomly from their breeding colonies to the open ocean even under conditions of environmental stochasticity. Instead, populations breeding in contrasting environments vary in their responses according to their strategies and to the changing levels of marine productivity in the surroundings of their colonies.

Sex and migratory strategy influence corticosterone levels in winter-grown feathers, with positive breeding effects in a migratory pelagic seabird.

To overcome unpredictable stressful transitory events, animals trigger an allostatic response involving the hypothalamic-pituitary-adrenal cortex. This hormonal response, which involves the release of glucocorticoids which in turn mediate between the main physiological mechanisms that regulate the energetic demands and resource allocation trade-off with behavioural responses to environmental perturbations and may ultimately lead to variation in fitness. We have used the Cory's shearwater Calonectris borealis, a sexually dimorphic pelagic seabird with a partial migratory strategy, as a model bird species to analyse a number of traits related to the stress response. We investigated whether the activation of a stressful response, mediated by corticosterone, during the wintering period (1) correlated with the previous breeding success, (2) was affected by the migratory behaviour of male birds and (3) had consequences in the fitness of the birds. Corticosterone levels in feathers grown overwinter were analysed in 61 adult birds during three consecutive migratory periods (2009-2012) and in 14 immature birds in the wintering period 2010-2011. Moreover, the levels of corticosterone were analysed in experimental birds which were freed from their reproductive duties and compared with control birds which raised fledglings to the end of the breeding period. The results show that the levels of corticosterone were sex dependent, differed between years and were affected by the migratory strategy performed by the birds. The activation of the stressful response over the wintering period generated residual carry-over effects that positively affected the reproductive output in the subsequent breeding stage, a phenomenon previously undescribed in a long-lived pelagic seabird. Our study provides evidence that the analysis of corticosterone from feathers is a useful tool to evaluate carry-over effects in birds far away from breeding sites, opening new possibilities for future studies in this field.

New species of the feather mite genus Promegninia Gaud & Atyeo (Acari: Avenzoariidae) from petrels and shearwaters (Procellariiformes: Procellariidae).

Two new species of the feather mite genus Promegninia Gaud & Atyeo, 1967 (Avenzoariidae: Bonnetellinae) are described from procellariids in the northeasterm Atlantic Ocean: Promegninia bulweriae n. sp. from the Bulwer's petrel Bulweria bulwerii (Jardine & Selby) and P. calonectris n. sp. from the Cory's shearwater Calonectris borealis (Cory) (Procellariiformes: Procellariidae). Males of P bulweriae n. sp. are most clearly distinguished from the other known species in the genus by having short legs III extending only to the level of lobar apices and short conical tarsi III with lanceolate ventral seta w; females of this species are characterised by the absence of additional sclerites at postero-lateral angles of the prodorsal shield. Males of P. calonectris differ from the other known species in having bidentate terminal lamellae on the lobar apices and the entire adanal shield; females of this species are distinguished by having well-developed pygidial shields and a hysteronotal shield encompassing the bases of setae c2. Sequence data of the mitochondrial cytochrome c oxidase subunit I gene fragment (COI) are also obtained for the new species. An updated diagnosis of Promegninia and a key to the known species are provided.

Spatial foraging segregation by close neighbours in a wide-ranging seabird.

Breeding seabirds are central-place foragers and therefore exploit food resources most intensively nearer their colonies. When nesting aggregations are close to one another density-dependent competition is likely to be high, potentially promoting foraging segregation (i.e. neighbouring colonies may segregate to search for food in different areas). However, little is known about spatial segregation in foraging behaviour between closely adjacent colonies, particularly in species that are wide-ranging foragers. Here, we tested for foraging segregation between two sub-colonies of a wide-ranging seabird, Cory's shearwater Calonectris borealis, separated by only 2 km, on a small Island in the North Atlantic. During the 2010 chick-rearing period, 43 breeding adults of both sexes were simultaneously sampled at both sub-colonies. A GPS logger was deployed on each individual and removed after several foraging trips at sea. Blood samples (plasma and red blood cells) were collected from each tracked individual for stable isotope analysis. Results indicated partial spatial segregation between the two sub-colonies during local foraging trips (i.e. those of ≤1 day duration and 216 km from the colony) accounting for 84.2% of all trips recorded. The location of the breeding sub-colony influenced the direction of travel of birds during local trips resulting in sub-colony-specific foraging areas. Although the oceanographic conditions associated with the foraging range of the two sub-colonies differed, no differences were found in the habitat exploited and in their estimated diets. This suggests that birds concentrated their feeding activity in patches of similar habitat and prey during the chick-rearing period.

Do Cory’s Shearwaters Calonectris borealis choose mates based on size?

Many bird species rely on visual cues for mate choice, including those provided by body size or by the size of a body appendage. Mate choice based on size may lead to size-assortative mating, which may in turn have consequences for reproductive performance. In this study, we examined whether body size influences mate choice decisions of Cory's Shearwater Calonectris borealis ,a seabird with nocturnal activity on land. We found evidence of negative assortative mating for bill morphology (nostril height and bill length), but found no assortative mating according to body mass, tarsus length, and wing length. In addition, we investigated the influence of negative assor- tative mating and individual body size-related traits on reproductive performance, i.e., laying date and breeding success. We found that laying date and breeding success were not correlated with the extent of assortative mating, i.e., the assortatively mating breeders did not lay earlier and were not more likely to breed successfully. However, we found that heavier females (body mass measured during pre-laying) laid later in the season. We discuss these results in the light of possible effects of acoustic signals and for- aging strategies on the mating pattern. Furthermore, we suggest that some female attributes may be crucial for breeding success in Cory's Shearwaters.