Calonectris diomedea

Geographic Range

Calonectris diomedea (Scopoli’s Shearwater) is distributed across the Mediterranean Sea and the Atlantic Ocean, with small and rare breeding populations along the Iberian Atlantic coast, including Portugal and Biscay. Breeding populations are found primarily in Europe and the Mediterranean sea, though they will forage great distances across the Atlantic. Notably, the Almería-Oran Oceanic Front and the Siculo-Tunisian Strait serve as significant oceanographic breaks influencing population structure.

After the breeding season, most of the population is believed to migrate to the South Atlantic off the coast of South Africa and occasionally the east coast of Brazil for the winter, though some individuals remain in the Central Mediterranean, particularly south of Sicily. While there is substantial dispersal among colonies within each basin, the genetic structure aligns with these main oceanographic features. Scopoli’s Shearwater is an extremely rare visitor to the North Sea, with occasional records from Britain and Sweden.

• Biogeographic Regions
• oceanic islands oceanic islands
  • native native
• atlantic ocean atlantic ocean
  • native native
• mediterranean sea
  • native native

Habitat

While there is limited research available on the habitat preferences of Calonectris diomedea , it shares similar habitat characteristics with the closely related Calonectris borealis (Cory's Shearwater). Both species are primarily found in coastal regions, favoring inaccessible cliffs and coastal stacks for nesting. These species tend to avoid inland habitats and prefers burrows in sandy soil, crevices in cliffs, or spaces beneath boulders. In the Azores, nesting densities correlate with the surface area of cliffs, indicating their importance as breeding sites.

As a pelagic seabird, Scapoli's shearwater primarily inhabits open ocean environments outside of the breeding season. The open ocean offers a vast landscape with few physical barriers, yet the species shows high fidelity to breeding sites. The species breeds on islands and steep coastal areas, with colonies distributed across the Mediterranean and Atlantic regions.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial
• saltwater or marine saltwater or marine

• Terrestrial Biomes
• chaparral chaparral
• mountains mountains

• Aquatic Biomes
• pelagic pelagic
• coastal coastal

• Other Habitat Features
• caves

Physical Description

Calonectris diomedea (Scopoli’s Shearwater) is a large seabird measuring 45-52 cm in length with a wingspan of 112-122 cm. It is very similar in appearance to Calonectris borealis (Cory’s Shearwater). Until recently, the two were thought to be the same species. Adult Scopoli's shearwaters typically weigh between 535 and 800 grams, with variations attributed to factors such as age, sex, and geographic location. Its upperparts are brownish grey, with the outer wing slightly darker and faintly paler upper tail-coverts, which are typically only visible at close range. The underside is mostly white, with no dark markings on the underwing coverts or belly, but it has a distinctive brown-grey wash along the sides of the breast, neck, and head. The bill is dull and pale pinkish yellow with a dark area near the tip. Male individuals have greater body mass and larger bill dimensions compared to females.

Distinguishing Scopoli’s Shearwater from Cory’s Shearwater is often difficult, as individual or age-related variations, along with field conditions like lighting and distance, can make identification challenging. However, when observed in good lighting at close range or in photographs, there are several subtle differences. The inner webs of the primary feathers on the underwing are whitish, leaving less dark at the wingtip and rear edge, whereas Cory’s Shearwater has mostly dark primaries visible on the underwing. Scopoli’s Shearwater is slightly smaller overall, with a somewhat smaller bill than Cory’s Shearwater. Though there is considerable overlap between the two species, the bill is paler or duller yellow and not as bright as Cory’s Shearwater, and the upperparts are a slightly paler brown grey.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

Development

While not much is well-known about the development of Scopoli’s Shearwaters, they undergo physiological adjustments throughout the breeding season to meet the varying energy demands of migration, territory defense, egg formation, incubation, and chick provisioning. They lay a single-egg clutch, with both parents sharing incubation and chick-rearing responsibilities.

Reproduction

Mating pairs often consist of individuals with similar body sizes. This assortative mating may enhance reproductive success and coordination between partners during breeding activities. Scopoli's shearwaters exhibit long-term monogamous pair bonds, returning to the same nesting sites annually. Both sexes share responsibilities in incubating the egg and feeding the chick. The coordinated efforts between male and female shearwaters are crucial for the successful rearing of offspring.

• Mating System
• monogamous monogamous
• cooperative breeder cooperative breeder

Calonectris diomedea (Scopoli's Shearwater) is a colonial seabird that nests on remote islets and islands, showing strong monogamous behavior and a high degree of site fidelity, often returning to the same burrow year after year. Adults arrive at their breeding colonies in late February or early March. They breed on islands throughout the Mediterranean, with their largest colony located on Zembra Island. They build their nests on rocky cliffs and steep coastal areas. If breeding fails, they may change to a new nest location. Females lay a single egg by the end of May, and both parents take turns incubating it. Chicks hatch in mid to late July and typically fledge by late October. After the breeding season, both adults and juveniles leave the Mediterranean around the same time. It is generally believed that the entire species migrates each year to shared wintering grounds in the central and southern Atlantic, though a small number of individuals may remain in the Mediterranean over winter.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous

Both parents share the responsibility of raising offspring. In Mediterranean colonies, the species exhibits a dual-foraging strategy, alternating between short foraging trips (1–4 days) focused on chick provisioning and long trips (up to 10 days) for self-maintenance. However, in the Canary Islands, these birds undertake foraging trips from their nesting sites to the northwest African continental shelf. This indicates a foraging range that includes the marine areas between the Canary Islands and the African mainland.

Foraging locations are influenced by marine productivity levels, and environmental conditions in nearby waters and offspring demands often drive foraging decisions. Chick weight is an important factor influencing parental foraging behavior, with heavier chicks allowing parents to engage in longer self-maintenance trips.

• Parental Investment
• altricial altricial
• male parental care male parental care
• female parental care female parental care

Lifespan/Longevity

Calonectris diomedea (Scopoli’s Shearwater) are long-lived seabirds with low reproductive rates. The life expectancy of Scopoli's shearwater exceeds 20 years in the wild. There is no documented lifespan data for Scopoli’s Shearwater in captivity. As with most seabirds, they have relatively high reproductive performance. Scapoli’s Shearwater exhibit a hatching success rate of approximately 76.9%, indicating that about three-quarters of the eggs laid successfully hatched into chicks. The overall breeding success, defined as the proportion of fledged chicks per occupied nest annually, averages 66.6%. Notably, fledging success, representing the percentage of chicks that survived to fledge after hatching, is higher than hatching success, at 86.8%.

Behavior

Calonectris diomedea (Scopoli's Shearwater) exhibit behavior generally similar to that of Cory’s Shearwater. Both species exhibit distinct behavioral patterns both at sea and on land, particularly during the breeding season. Scapoli’s Shearwaters are highly social seabirds, often forming large rafts on the water near their breeding colonies before coming ashore after sunset. They are also known to interact with fisheries, scavenging discarded fish from fishing vessels.

Scopoli’s Shearwater displays a mix of diurnal and nocturnal behavior, depending on the activity and context. Most of their feeding activity occurs during daylight hours, when prey is more accessible near the surface. The species spends much of the day gliding over the ocean and searching for food such as small fish, squid, and crustaceans. At breeding colonies, they exhibit primarily nocturnal activity patterns. This nocturnal arrival helps them avoid predators, as they are clumsy and vulnerable on land. Once onshore, they use vocalizations to communicate with their mates and establish territory, a behavior most commonly observed at night. However, Shearwaters will sometimes vary their foraging timing to maximize feeding opportunities. A study observed that moonlight influences their nocturnal foraging efficiency, with increased activity during brighter nights, suggesting an adaptation to optimize feeding opportunities while minimizing predation risks.

• Key Behaviors
• flies
• glides
• diurnal diurnal
• nocturnal nocturnal
• motile motile
• migratory migratory
• colonial colonial

Home Range

Calonectris diomedea implements a combination of small breeding territories and large foraging areas, reflecting their adaptation to a pelagic lifestyle. While breeding, Scopoli's Shearwaters undertake extensive foraging trips to procure food. Studies employing the Adaptive Kernel method have estimated their core foraging area (50% utilization distribution) to be approximately 6,871 km², and their broader foraging range (95% utilization distribution) to extend up to 23,014 km². These expansive foraging ranges underscore the species' reliance on distant marine areas to meet their nutritional needs during the breeding season.

Communication and Perception

The calls of Scopoli’s Shearwater are very similar to those of Cory’s Shearwater but are described as being slightly less coarse and guttural. After dusk, the colonies are noisy, giving raw, crow-like sounds and a strained, nasal series of three similar notes, ending with a different note, roughly 'gaooha-gaooha-gaooha-waah'. Like many seabirds, Scopoli’s Shearwaters likely rely on vocalizations for mate attraction and territory defense, especially during nocturnal periods when visual cues are less effective.

• Communication Channels
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Calonectris diomedea (Scopoli's Shearwaters) exhibit a diverse and adaptable foraging strategy, incorporating both natural prey capture and scavenging behaviors. They primarily feed on small fish and cephalopods, often foraging in association with marine predators such as tunas and sea turtles, which drive prey to the surface and enhance feeding opportunities. They have also been documented eating small pelagic fish, including trumpet fish and boarfish, which are abundant near the Azores, Portugal, and the Canary Islands, and even squid.

Their foraging behavior is highly social, with individuals frequently gathering in groups to locate and capture food. The species catches prey by gliding close to the water and snatching food from the surface, a technique known as surface seizing. Unlike some other seabirds, it rarely dives fully underwater while foraging. Additionally, Scopoli's Shearwaters take advantage of fishery discards, scavenging from fishing vessels to obtain readily available food with minimal energy expenditure. This opportunistic feeding strategy allows them to exploit both natural and anthropogenic food sources, demonstrating their ecological flexibility in a marine environment.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore

• Animal Foods
• fish
• mollusks
• aquatic crustaceans
• other marine invertebrates

Predation

Predators of Scapoli’s Shearwater include introduced species such as Rattus rattus (Black Rats) and Larus michahellis atlantis (Atlantis Yellow-legged gulls), both of which significantly impact breeding success by preying on eggs and chicks. The species faces significant predation pressure from introduced ship rats, which adversely affects their breeding success. The presence of ship rats leads to increased predation on eggs and chicks, thereby reducing breeding success. Atlantis Yellow-legged gulls are also known to prey on the eggs and chicks of Scopoli's shearwaters, especially during the breeding season when shearwaters nest in colonies on Mediterranean islands. Eradication of Rattus rattus has been shown to be effective and efficient in the long term for enhancing Scapoli's Shearwater breeding success. It is critical to manage invasive predators like ship rats to improve the reproductive outcomes of Scapoli’s Shearwater and other colonial seabirds.

Though not technically considered a predator, bycatch poses a major conservation threat to Scapoli’s Shearwaters, as they are long-lived seabirds with low reproductive rates, making population recovery from losses slow. Birds are more likely to be caught on non-working days when long line vessels operated over continental shelf areas and when more hooks were deployed. Conservation strategies such as nighttime setting of longlines, using bird-scaring devices, and modifying baiting techniques could help mitigate mortality. Managing fisheries to minimize bycatch is crucial for ensuring the stability of Scapoli’s Shearwater populations, particularly in the Mediterranean, where they are already facing other pressures like habitat degradation and invasive predators. Additionally, human-induced environmental changes, including habitat degradation and pollution, indirectly affect adult survival and reproductive performance.

Ecosystem Roles

Calonectris diomedea (Scopoli’s Shearwater) play a crucial role in marine ecosystems as both predators and nutrient transporters. Their consumption of large amounts of fish and squid influences prey populations. As mid-trophic level predators, they help regulate populations of small pelagic fish, squid, and crustaceans, and contribute to maintaining ecological balance within marine food webs. Additionally, their ability to scavenge discarded fish indicates their role in utilizing human-altered food sources. They also contribute to nutrient cycling through their guano deposition on breeding islands. Their guano deposits enrich the soil with nitrogen and phosphorus, benefiting plant communities and other organisms in coastal ecosystems. By influencing coastal habitat characteristics, they provide nesting habitats for other seabirds and invertebrates. They aid in the exchange of marine-derived nutrients between oceanic and terrestrial environments, further reinforcing their ecological importance.

• Ecosystem Impact
• creates habitat
• biodegradation biodegradation

Economic Importance for Humans: Positive

While the direct economic importance of Calonectris diomedea (Scopoli’s Shearwater) is not well-documented, its ecological interactions suggest indirect economic impacts through fisheries dynamics and potential ecotourism opportunities. The presence of Scopoli's Shearwater colonies may attract birdwatchers and nature enthusiasts, contributing to local ecotourism industries. However, specific studies quantifying this economic contribution are currently lacking.

• Positive Impacts
• ecotourism ecotourism

Economic Importance for Humans: Negative

Calonectris diomedea (Scopoli’s Shearwater) can have negative economic impacts primarily through its interactions with fisheries. One of the most significant concerns is bycatch, as these birds are often accidentally caught on longline fishing gear, especially in the Mediterranean region. This not only threatens the bird population but can also result in economic losses for fisheries due to reduced gear efficiency and the need for mitigation measures. Additionally, in areas where they are numerous and compete for fish or follow fishing vessels for scraps, they may be seen as a nuisance by some fishers. However, it's important to note that these negative impacts are generally limited and context-dependent.

Conservation Status

Scopoli's Shearwater is currently classified as Least Concern on the IUCN Red List, meaning its population is considered stable. A total population estimate of 285,000-446,000 was reported in 2018. However, the current population trend is declining, and continued monitoring is important to ensure that this status remains unchanged.

Additional Links

Encyclopedia of Life

Contributors

Gwyneth Boyden (author), Texas State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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