The Manx shearwater (Puffinus puffinus) is a medium-sized seabird that breeds on islands off the coasts of the North Atlantic. Manx shearwaters nest in colonies, often in thousands, on remote islands and cliffs. Their habitat requirements are very specific which limits where they can breed successfully.
What kind of habitat do Manx shearwaters need for nesting?
Manx shearwaters require islands that are free from mammalian predators in order to breed successfully. This is because adult shearwaters, eggs, and chicks are vulnerable on the ground from predators like rats, cats, dogs, and foxes. Mammalian predators were introduced to many remote islands by humans over the centuries. This led to extirpation or extinction of shearwater colonies on many islands. Today, remaining shearwater colonies persist on islands that are too small or isolated to support populations of mammalian predators.
Manx shearwaters nest in underground burrows or crevices between rocks located on grassy slopes. They prefer islands with short vegetation and limited tree cover. This allows the birds to more easily access their nest sites. Rocky and sandy soils are ideal for constructing burrows. Wet, peaty soils can allow burrows to collapse.
What kinds of islands do Manx shearwaters colonize?
The main types of islands used for nesting by Manx shearwaters include:
– Small, rocky, isolated islands and islets located far offshore. These islands are too small to support introduced mammals.
– Large islands with inhospitable terrain, such as islands with mountainous cliffs and rocky shores. These areas provide natural protection from mammalian predators.
– Islands located far north, such as in Iceland and the Faroe Islands. Harsh winters prevent establishment of mammalian predator populations.
– Restored islands where invasive predators like rats have been eradicated. Conservation programs have successfully eliminated predators and allowed re-colonization by Manx shearwaters.
Where are the major Manx shearwater colonies located?
Some of the major breeding colonies of Manx shearwaters are found on these islands:
– Skomer, Skokholm, and Middleholm Islands off the coast of Wales
– Rum, Eigg, Canna, and Muck Islands off the coast of Scotland
– Copeland Islands off the coast of Northern Ireland
– Great Saltee Island off the coast of Ireland
– Grimsey, Vestmannaeyjar, and Heimaey Islands off the coast of Iceland
– Mykines Island in the Faroe Islands
– Islands off the coast of Newfoundland, Canada
– Islands off the coast of Massachusetts, USA
What ocean conditions do Manx shearwaters require?
Manx shearwaters spend most of their lives foraging at sea. Successful breeding requires access to productive marine waters to provide adequate food.
Key ocean habitat requirements for Manx shearwaters:
– Productive currents and upwellings that concentrate prey. Manx shearwaters feed on small fish, krill, and other marine invertebrates brought close to the surface by currents. Upwellings near colonies provide a consistent food source.
– Shelf breaks and seamounts. These underwater features cause upwelling and mixing that aggregates prey. Many colonies are located near shelf break fronts.
– Low sea surface temperatures. Manx shearwaters avoid tropical waters and breed at higher latitudes where sea surface temperatures are 50-59°F (10-15°C). Colder water increases productivity.
– Wintering habitat with productive waters. During the nonbreeding season, Manx shearwaters migrate long distances to productive waters off South America, southern Africa, and Australia to build energy reserves for the breeding season.
How far do Manx shearwaters travel to find food?
During the breeding season, Manx shearwaters regularly travel long distances from the colony to find adequate food. Foraging trips average around 300 miles but can extend up to 1900 miles one-way.
These marathon trips are fueled by the birds’ ability to extract oxygen while gliding. This allows them to cover vast distances with minimal wing flapping. Parents take turns foraging while the other remains at the nest to incubate the egg.
The duration of foraging trips increases through the breeding season as food becomes scarcer close to colonies. Trip length peaks when adults must provision growing chicks, which have higher energy demands.
How do Manx shearwaters interact with their environment?
Manx shearwaters are well-adapted to their island and marine environments. Some key interactions include:
– Nesting underground- Manx shearwaters dig burrows or use crevices to avoid aerial predators and shelter eggs and chicks. Their underground nests also protect against harsh weather.
– Nocturnal activity – At breeding colonies Manx shearwaters are most active after dark to avoid predators. Their eyes are adapted to function in low light.
– Soaring flight – Long, thin wings allow Manx shearwaters to soar dynamically for hours, traveling hundreds of miles to find prey patches.
– Foraging cooperation – Males and females coordinate their foraging trips and share incubation duties so that eggs or chicks are never left alone.
– Navigational abilities – Manx shearwaters migrate across entire oceans and return to the same nest sites each year, navigating using the sun, stars, magnetic fields, and sense of smell.
– Regurgitation feeding of chicks – Parents gulp down food at sea and return to chicks to regurgitate oily fish meal. This allows chicks to quickly gain weight.
– Colony synchronization – Nesting in dense colonies may facilitate mate finding and synchronize breeding using social cues.
How does climate change affect Manx shearwater habitat?
Climate change is expected to significantly impact both the nesting and marine habitats used by Manx shearwaters in the coming decades. Some potential effects include:
– Sea level rise flooding or destroying low-lying island breeding sites
– Increased storm frequency or severity damaging nests and colonies
– Warming ocean temperatures reducing prey availability near colonies
– Changes in ocean currents and upwellings affecting distribution and abundance of prey
– Increased competition and predation as subarctic species shift ranges northward
How can habitat loss from sea level rise impact Manx shearwaters?
Many Manx shearwater colonies are located near sea level on small islands that are vulnerable to sea level rise caused by climate change. Habitat loss and flooding of nesting areas could occur in the following ways:
– Permanent inundation of entire low-lying islands used for breeding
– Loss of grassy slopes and access to burrows due to coastal erosion and flooding
– Increased wave action and high tides washing away burrows and nesting habitat
– Saltwater intrusion degrading groundwater and vegetation around colonies
– colonization of islands by predators like rats, drawn to higher ground
Sea level rise could destroy or degrade breeding habitat, reducing nesting space. This may impact populations, as Manx shearwaters exhibit high nest site fidelity, limiting their ability to colonize new areas.
How can warming oceans affect the food supply of Manx shearwaters?
Manx shearwaters rely on cold, productive waters around their breeding colonies to provide reliable food sources like fish, krill, and zooplankton.
As climate change causes sea surface temperatures to rise, availability of key prey species near colonies during the breeding season may be reduced because:
– Warmer water holds less oxygen, reducing phytoplankton growth, which lowers productivity.
– Zooplankton abundance and distribution shifts away from colonies as waters warm. Krill rely on cold, nutrient-rich habitats.
– Fish prey may shift poleward or into deeper waters to find optimal temperatures as surface waters warm.
With less food near the colony, adult Manx shearwaters are forced to travel farther on foraging trips, increasing their energy expenditure and reducing provisioning rate to chicks. This has a negative impact on chick growth and survival.
How can Manx shearwater habitat be protected and restored?
Maintaining and increasing breeding habitat will be critical for the future survival of Manx shearwater populations given climate change impacts. Some conservation strategies include:
– Predator eradication on islands to allow recolonization. Removing invasive rats, cats, etc. can help restore degraded habitat.
– Preventing introduction of mammalian predators to additional islands. Strict biosecurity protects remaining predator-free sites.
– Artificial burrow construction to provide additional nesting habitat. This may facilitate colony expansion and buffer against sea level rise impacts.
– Minimizing other threats like overfishing, marine pollution, and bycatch mortality to help offset climate-driven food web changes.
– Monitoring and projecting impacts of warming oceans and currents on prey distribution so colonies can be protected.
– Establishing marine protected areas around key foraging zones and migration routes to improve food supply.
– Translocating chicks to establish new colonies at higher elevations or latitudes with cooler sea temperatures.
Protecting existing habitat and establishing additional nesting sites will provide the best chance for the survival of Manx shearwater populations facing threats from climate change.
Conclusion
Manx shearwaters have very specific habitat requirements that allow breeding colonies to persist on remote, predator-free islands with access to highly productive marine ecosystems. However, climate change presents severe threats to nesting habitat from sea level rise and to the food supply from warming ocean temperatures. Protecting colonies from other threats and developing adaptive conservation strategies will give this iconic seabird the best chance to withstand the impacts of a changing climate on the islands and oceans it relies on.
