José P. Granadeiro

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 Corys 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 Corys shearwaters may be in a better position than many other long-distance migrants to face the consequences of a changing environment.

Albatrosses following fishing vessels: how badly hooked are they on an easy meal?

Fisheries have major impacts on seabirds, both by changing food availability and by causing direct mortality of birds during trawling and longline setting. However, little is known about the nature and the spatial-temporal extent of the interactions between individual birds and vessels. By studying a system in which we had fine-scale data on bird movements and activity, and near real-time information on vessel distribution, we provide new insights on the association of a threatened albatross with fisheries. During early chick-rearing, black-browed albatrosses Thalassarche melanophris from two different colonies (separated by only 75 km) showed significant differences in the degree of association with fisheries, despite being nearly equidistant to the Falklands fishing fleet. Most foraging trips from either colony did not bring tracked individuals close to vessels, and proportionally little time and foraging effort was spent near ships. Nevertheless, a few individuals repeatedly visited fishing vessels, which may indicate they specialise on fisheries-linked food sources and so are potentially more vulnerable to bycatch. The evidence suggests that this population has little reliance on fisheries discards at a critical stage of its nesting cycle, and hence measures to limit fisheries waste on the Patagonian shelf that also reduce vessel attractiveness and the risk of incidental mortality, would be of high overall conservation benefit.

Carry‐over effects from breeding modulate the annual cycle of a long‐distance migrant: an experimental demonstration

Carry-over effects relate to events or processes that influence individual performance in a subsequent season, but their occurrence in the annual cycle of migratory avian taxa is seldom studied. We investigated if different levels of resource allocation to reproduction may result in carry-over effects that change the timing and destination of long-distance migration. We reduced the parental investment of Corys Shearwaters Calonectris diomedea by removing their chick at an early stage. When compared to individuals with greater parental investment (controls that raised chicks to close to fledging), manipulated birds started most stages of migration sooner and returned to the colony earlier at the start of the following breeding season. Late arrival in the subsequent nesting season increased the probability of skipping a breeding year. Manipulated males were less likely to engage in long-distance migration, which supports the idea that partial migration is condition dependent. Our study demonstrates experimentally that energetic or time-dependent costs of reproduction may have an enduring impact on migration schedule and on nonbreeding geographical distribution of long-distance migrants, which may also influence the ability to breed in the following season.

Numbers and population trends of Cory’s Shearwater Calonectris diomedea at Selvagem Grande, Northeast Atlantic

Abstract The island of Selvagem Grande holds one of the most important colonies of Cory’s Shearwater (Calonectris diomedea) in the Atlantic. Historical records suggest a stable population well in excess of 100,000 pairs. A succession of massacres in 1975 and 1976 dramatically reduced this population to less than 10% of the original numbers. Since 1977 strict protection was enforced and the population started a steady recovery. However, between 1995 and 1998 an alarming decline, of more than 13% of the birds, was reported and concurrently the monitoring work was interrupted. Data from other colonies in the Atlantic and the Mediterranean also indicated significant regional declines, some of which appear to be driven by unsustainable levels of accidental mortality in fishing gear. In order to investigate the persistence of the regressive trend at Selvagem Grande, we carried out a global census of the colony in June 2005. We counted 20,555 occupied nests and estimated the total breeding population at 29,540 pairs. The population still appears to be recovering from the massacres of 1975-1976, at an average rate of about 4.6% per year over the past 25 years. Our data reveal that Selvagem Grande now harbors the largest known Cory’s Shearwater colony in the World. Results from this study suggest that this population is not, as yet, suffering from unsustainable fisheries-related mortality, which would be reflected in a decline in numbers. This situation contrasts with that of the Mediterranean, where significant mortality in fishing gear has been linked to shearwater population declines.

Different means to the same end: long-distance migrant seabirds from two colonies differ in behaviour, despite common wintering grounds.

Although seabirds that are trans-equatorial migrants show apparently broad overlap among populations in the non-breeding season, such large-scale pattern may conceal subtle but nevertheless key differences in migratory behaviour. These specializations could reflect adaptation to different environments during the breeding season, carry-over effects from the breeding to the nonbreeding period, or asymmetries in competitive ability of birds of different origin. We compared the migratory and wintering behaviour of Corys shearwaters Calonectris diomedea nesting in Berlengas and in the Selvagens, two colonies in contrasting oceanographic environments, separated by ca. 1200 km. Although no differences were found in winter distribution, there was a marked divergence in timing, route and the use of staging areas during the postbreeding (autumn) migration. Birds from Berlengas typically travelled to oceanic waters in the North Atlantic for an extended stopover, whereas those from Selvagens rarely did so. In the South Atlantic, birds from Selvagens spent more time in flight, perhaps because they had higher energy and nutrient requirements for feather replacement compared to birds from Berlengas, which moult more flight feathers during breeding. Stable isotope analyses of feathers suggested that this variation in activity patterns was unrelated to trophic ecology. Differences in migration routes and stopovers may expose populations to distinct threats, and should be taken into consideration when defining units for conservation purposes and developing appropriate management strategies.

Environmental factors drive habitat partitioning in birds feeding in intertidal flats: implications for conservation

We present data on the low-tide distribution of shorebirds in the Tagus estuary, Portugal, and relate the distribution of the bird assemblage with environmental factors. The study was based on an extensive survey of the majority of the intertidal flats, carried out with a high spatial resolution. The environmental factors that mostly affected the distribution of shorebirds were the exposure period, the type of sediment and the extent of the shell banks. The feeding bird assemblage could be divided into four main groups of species, and these occupied distinct areas of the estuary. These findings imply that maintaining the overall value of the estuaries for foraging shorebirds requires relatively extensive intertidal areas, encompassing sediment flats with the large diversity of ecological characteristics required by different species.

Breeding Biology of the White-Faced Storm-Petrel on Selvagem Grande Island, North-East Atlantic

-The White-faced Storm-petrel (Pelagodroma marina) breeds on several tropical, sub-tropical and temperate islands in both hemispheres, but some aspects of its breeding biology are still poorly known. The European subspecies hypoleuca is almost confined to a small archipelago, the Salvage Islands, about 300 km south of Madeira Island, North-east Atlantic. Because of its very localized distribution, this subspecies is relatively vulnerable to extinction and its population dynamics need to be understood and monitored. We studied the breeding biology of the White-faced Storm-petrel at Selvagem Grande Island in 1996. Birds first arrived at the colony in mid-December, eggs were laid from mid-March to early June, and the last chicks fledged in mid-August. Mean incubation period was 53.7 days, but was highly variable due to frequent egg-neglect that affected at least two thirds of the clutches. Mean nestling period was 60.3 days. Chick growth (body mass and wing length) is described. Hatching success was 60.7% (N = 89) and fledging success was 88.9% (N = 54). Breeding success (53.9%) was not low, in spite of frequent predation by house mice (Mus musculus), the main cause of nesting failures. Rabbits (Oryctolagus cunniculus) and Yellow-legged Gulls (Larus cachinnans), two species thought to pose threats to other seabirds of the region, had no measurable negative effect on breeding performance at our study nests. However, we had some evidence that gulls prey upon chicks and adult birds. Breeding success did not correlate with egg size. There was a highly significant seasonal decline in both hatching and fledging success. Using data on burrow density and occupancy obtained in the main colony, we estimated the breeding population on Selvagem Grande at around 36,000 pairs. Received 30 November 1988, accepted 16January 1999.

Long-term declines of wader populations at the Tagus estuary, Portugal : a response to global or local factors?

Summary Migratory wader populations face global threats, mainly related to increasing rates of habitat loss and disturbance driven by human activities. To a large extent, the long-term survival of these populations requires the conservation of networks of sites along their migratory flyways. The Tagus estuary, Portugal, is among the most important wetlands for waders in the East Atlantic Flyway. Annual winter wader counts have been carried in this wetland since 1975 and a monthly roost-monitoring programme was implemented in 2007. Wintering populations of three out of the five most abundant species, Dunlin Calidris alpina, Grey Plover Pluvialis squatarola and Redshank Tringa totanus, showed significant population declines over the past three decades, which are most likely due to the loss and degradation of roost sites as a result of increasing human activity. The situation is unlikely to improve, as a high proportion of the wintering waders use roost sites that are situated in highly urbanised areas with no legal protection. The use of different roost sites by waders is highly variable both temporally and spatially, thus emphasizing the need for a network of good quality roost sites. Additionally, during migration, 60–80% of all the waders of the Tagus estuary concentrate at a single refuge, thus increasing the risk for wader populations during these periods.

Searching behaviour of foraging waders: does feeding success influence their walking?

Predators that feed on clustered prey tend to have an ‘area-restricted search’ (ARS), characterized by a combination of a slow and tortuous movement in prey-rich areas, and a fast and straight movement in poorer areas. Waders that forage in intertidal areas usually prey upon buried macroinvertebrates, whose distribution is often clustered. However, wader species differ in the strategy used to find their prey: some rely mainly on visual cues, some rely on tactile cues, and others follow a more generalist method, simply sweeping the sediment surface with the bill. We hypothesized that these strategies influence the adoption of an ARS by waders. We analysed this hypothesis by comparing the fine-scale movement of a ‘tactile’ predator (black-tailed godwit, Limosa limosa ), with that of a ‘visual’ predator (redshank, Tringa totanus ) and a ‘sweeper’ (avocet, Recurvirostra avosetta ). We filmed 190 individuals of the three species and, using GIS facilities, obtained more than 12 000 spatial positions, along with detailed records of feeding activity. We analysed several parameters of fine-scale movement of waders, such as foraging and searching speeds, tortuosity, and the relationship between these parameters and foraging success. Only the tactile predator, the black-tailed godwit, followed an ARS, reducing searching speed and increasing spatial turning rate whenever the prey intake was higher. Furthermore, its foraging strategy involved short-term adjustments of movement that maximized the likelihood of finding subsequent prey, suggesting a prior knowledge or an ability to perceive rapidly the distribution pattern of its prey.

An holistic ecological analysis of the diet of Cory's shearwaters using prey morphological characters and DNA barcoding

Knowledge of the dietary choices and trophic niches of organisms is the key to understanding their roles in ecosystems. In seabird diet studies, prey identification is a difficult challenge, often yielding results with technique‐specific biases. Additionally, sampling efforts are often not extensive enough to reveal intrapopulational variation. Immature animals, which may constitute up to 50% of a population, may occupy a significantly different trophic niche to more experienced birds, but this remains largely unexplored. We investigated the diet of Corys shearwater (Calonectris diomedea) from Selvagem Grande, an island located off the northwest African coast, collecting a total of 698 regurgitate samples over three consecutive breeding seasons. The diet was assessed using two complementary approaches for prey identification: conventional morphological analysis (using fish vertebrae, otoliths and cephalopod beaks) and DNA barcoding of the 16S rRNA mitochondrial gene, in cases where a positive identification could not be retrieved. Species assignments employed BLAST and distance‐based methods, as well as direct optimization of the tree length based on unaligned sequences in POY. This method resulted in robust tree estimates and species assignments, showing its potential for DNA barcoding of stomach contents using hypervariable markers such as the 16S. The molecular approach increased taxonomic resolution and revealed an additional 17 taxa. Diet differed significantly according to breeding status, sex, breeding phase (prelaying and chick rearing) and year. Such direct evidence of trophic segregation within the same population has rarely been shown in seabirds and highlights the importance of including such variables in ecosystem‐based management approaches.