Shearwaters are medium-sized long-winged seabirds that belong to the bird family Procellariidae. There are around 30 different species of shearwater that are found across the world’s oceans. Shearwaters are migratory birds that breed on islands and remote coastal cliffs and spend the rest of the year foraging at sea. Some species like the Manx shearwater have extremely long migrations from their breeding grounds in the northern hemisphere to their wintering areas in the southern hemisphere.
Typical Shearwater Lifespan
The typical lifespan of most shearwater species is around 15 to 20 years. However, the maximum recorded lifespan can be over double this length in some species. For example, the oldest recorded Manx shearwater was over 50 years old. Here is a breakdown of the typical and maximum recorded lifespans of some of the most common shearwater species:
| Species | Typical Lifespan | Maximum Recorded Lifespan |
|---|---|---|
| Manx Shearwater | 15-20 years | 51 years |
| Sooty Shearwater | 15-20 years | 41 years |
| Short-tailed Shearwater | 15-20 years | 34 years |
| Great Shearwater | 12-15 years | 23 years |
| Pink-footed Shearwater | 10-15 years | 22 years |
As you can see from the table, the Manx shearwater far outlives the other species, with a maximum recorded lifespan of over 50 years. The other species tend to max out their lifespans in the 20s and 30s. But even the shortest-lived shearwaters like Great shearwaters and Pink-footed shearwaters regularly live 10 to 15 years or longer.
What Factors Influence Shearwater Lifespan?
There are several key factors that account for the differences in typical and maximum lifespan across the shearwater species:
Genetics
Genetics play a major role in determining shearwater lifespan. The large variations between species are partly due to genetic differences. Some types of shearwaters are simply longer-lived birds. The Manx shearwater stands out with exceptional longevity compared to its close relatives.
Breeding Strategy
Shearwaters have a breeding strategy that is taxing on the parents but enables longevity. Unlike many seabirds, shearwaters lay only one egg per breeding season. They invest a massive amount of energy incubating the egg and then provisioning the chick over many months. This is energetically costly for the parents in the short-term but enables a longer lifespan over many breeding seasons.
Predation Pressures
Shearwaters have fewer predators to contend with than many other seabirds thanks to nesting on remote islands and cliffs. Their ability to live long is aided by the lack of predators at their breeding colonies. Species that nest on islands with more predators like gulls and rats tend to have higher adult mortality and shorter average lifespans.
Migratory Habits
The long migrations that some shearwaters undertake take their toll and cut into maximum lifespan Achievements. For example, the Manx shearwater that holds the record for oldest at 51 years bred on islands off the coast of Wales and did not migrate long distances. In contrast, populations of Manx shearwaters breeding on islands off eastern North America migrate down to South America annually, a journey of thousands of miles, and do not live as long.
Foraging Abilities & Diet
Shearwaters rely on their physical stamina and flying prowess to forage over vast ocean territories. Greater aerial maneuverability to dive and pursue prey enables some species like Manx shearwaters to get sufficient nutrition to sustain their long lives. Meanwhile, species with more limited diving abilities may work harder for less reward and wear out faster.
How Do Shearwaters Live So Long?
Beyond the differences between shearwater species, there are some general traits and behaviors that enable shearwaters as a group to achieve long lifespans relative to other birds:
Low Annual Mortality
Once shearwaters survive to adulthood, their annual mortality rates are very low thanks to a lack of predators and accidents. Studies of banded Manx shearwaters show annual adult mortality may be under 5% per year. Their chances of surviving year to year are high.
Resilience to Environmental Stressors
Shearwaters are resilient when facing environmental disruptions at sea thanks to being generalist foragers. This enables them to withstand seasonal shifts in prey availability or occasional food shortages that might cripple more specialized feeders.
Investment in Few Offspring
The single egg clutch size of shearwaters means they invest heavily in raising one chick at a time rather than spreading effort across multiple offspring. This conserves resources for adult survival and future breeding attempts.
Advanced Age Doesn’t Diminish Success
Unlike many birds, shearwater breeding success rates don’t decline with advanced age. Older birds are just as capable parents thanks to their foraging abilities not diminishing. This gives shearwaters the ability to keep reproducing successfully at older ages.
Lower Metabolic Rates
Shearwaters have relatively low metabolic rates compared to other birds their size due to adaptations for long stretches of gliding flight over water. The low day-to-day energy requirements help minimize damage and deterioration.
How Long Do Baby Shearwaters Live?
Shearwater chicks typically fledge from their remote breeding colony burrows at around 3 months of age. However, their chances of survival from that point on are low. Studies of shearwaters show that first year mortality ranges from 47% to 69% across different species. Causes of death include starvation, predators, adverse weather, and human activities like fishing bycatch.
If a young shearwater can survive that hazardous first year and learn to forage competently, their odds of survival greatly improve. Those that make it to 2 years old tend to go on to live the typical lifespan of 10-20 years for their species.
Why Don’t All Shearwaters Live as Long as Manx Shearwaters?
The record longevity of Manx shearwaters far outpaces other shearwater species. So why don’t they all live so long?
Manx shearwaters have a combination of advantages that enables their exceptional lifespans compared to their relatives:
- Breed on predator-free islands off the British Isles
- Forage on abundant Atlantic prey like lanternfish, sandeels, sprat
- Shorter migration distances minimizes energy expenditure
- Genetic lineages bred for UK colony conditions over centuries
In contrast, a Sooty shearwater that migrates from New Zealand to Alaska faces a much more arduous annual routine. And a Pink-footed shearwater breeding on the Galapagos doesn’t have access to the consistent food resources of a Manx off the British coast. Each species faces a different set of challenges that prevents them from maximizing lifespan achievements like the Manx.
Do Shearwater Lifespans Vary By Sex?
Research shows that female shearwaters tend to outlive males across species. On average females live 1-3 years longer. This is believed to be related to the extra physical burdens on males.
Male shearwaters invest more energy into courtship displays like aerial flight maneuvers early in each breeding season. Their skies also dive more aggressively when provisioning for chicks. The additional physical exertion takes a cumulative toll that shortens the lifespans of males relative to females.
How Do Scientists Study Shearwater Lifespans?
Ornithologists rely on several methods to study shearwater longevity:
- Banding birds with unique leg bands and tracking individuals over decades.
- Monitoring color-banded birds at breeding colonies to count survival year-to-year.
- Compiling breeding records over generations to track long-lived family lineages.
- Analyzing survival rates based on bird age data from recovered bands.
- Collecting remains of shearwaters from hunters and museums to determine age.
Combining data from these sorts of long-running studies enables scientists to learn about shearwater lifespans, mortality rates, breeding success, and survival conditions. Tracking banded birds like the 51-year-old Manx shearwater provides the individual record lifespans, while large scale banding studies reveal the average expected lifespans for various populations and species.
Threats to Long-Lived Shearwaters
Human activities have become one of the greatest dangers jeopardizing the longevity of shearwaters worldwide:
- Overfishing of prey species depletes shearwater food sources
- Ingestion of plastics causes adult mortality
- Bycatch in longline fisheries drowns shearwaters
- Introduced predators attack breeding colonies
- Habitat degradation by development
- Climate change disrupts migration and breeding
- Pollution exposure impairs health and reproduction
All of these modern threats have the potential to overtax shearwaters and shorten lifespans. Aggressive conservation action is needed to ensure shearwaters can continue achieving their remarkable longevity into the future.
Conclusion
Shearwaters are remarkably long-lived seabirds thanks to their adaptations for offshore living. Different species demonstrate a wide range of lifespan achievements. Manx shearwaters stand out as the most elderly, with lifespans exceeding 50 years. This longevity results from successful breeding strategies, low predation pressure, and foraging resilience. With proper protections of their island habitats and marine food webs, shearwaters can continue their reign as some of the world’s longest-lived avians for decades to come.
