Many seabirds in the northern hemisphere struggle to breed – and in the southern hemisphere they may not be far from it. These are the conclusions of a study published today in Science that analyzed more than 50 years of breeding records for 67 species of seabirds around the world.
The international team of scientists, led by William Sydeman of the Farallon Institute in California, discovered that reproductive success in fish-eating seabirds north of the equator has declined over the past half century. The northern hemisphere is having a greater impact from man-made climate change and other human activities such as overfishing.
“Our study shows that the prognosis for sustained breeding productivity of piscivorous and omnivorous breeding seabirds in the northern hemisphere is poor if the availability of food resources is not improved,” the researchers write.
Sea birds include albatrosses, puffins, murres, penguins, and other birds. Whether they hover or swim, all seabirds are adapted to feed and live near marine waters. Many scientists view seabirds as guardians of habitat health because their lives and well-being depend on good conditions both on land and at sea, said co-author P. Dee Boersma, professor of biology at the University of Washington and director of the center for Ecosystem Guardians.
“Seabirds travel long distances – some go from one hemisphere to another – hunting for their food in the sea,” said Boersma. “That makes them very sensitive to changes such as ocean productivity, often over a large area.”
In addition, seabirds congregate in specific locations along the coast to breed and rear their young, making them vulnerable to changing bank and surface conditions and limiting the distance they can find for food while they are still successfully raising their chicks added Boersma.
Reproductive success down
The diet of seabirds played an important role in their ability to raise chicks. In the north, fish-eating seabirds recorded a significant decline in reproductive success during the study period. In addition, surface-eating birds were more prone to reproductive disorders in both hemispheres, whether they ate fish or smaller plankton such as krill. Deep-diving birds, such as puffins, performed best in terms of reproductive success.
The team is to blame for the changing environmental conditions. Seabirds have to travel far to forage and eat a lot – Murres, for example, consume half their body weight in fish every day. Nearly a million Murres starved to death and breeding colonies crashed in 2015-2016 due to a long-term ocean heat wave that destroyed food webs in the northeast Pacific. Climate change is causing more frequent and extreme events like these heat waves, and sea birds in the ocean are also exposed to other threats.
“You have to compete with us for food. You can get caught in our fishing nets. They eat our plastic, which they think is food, ”Boersma said. “All of these factors can kill large numbers of long-lived seabirds.”
These changes have effects beyond seabirds.
“Also at stake is the health of fish populations like salmon and cod, as well as marine mammals and large invertebrates like octopus, which eat the same small feeder fish and plankton as seabirds,” said Sydeman. “When seabirds are not doing well, this is a warning sign that something bigger is happening below the surface of the sea, which is worrying as we depend on healthy oceans for quality of life.”
The team found high variability in reproductive success between species, indicating that additional research is needed to understand all of the factors influencing the feeding and breeding of these species.
This map shows the seabird locations used in this study. Red dots indicate locations in the northern hemisphere, while black dots indicate locations in the southern hemisphere. Image by Brian Hoover / P. Dee Boersma
Penguin numbers are falling
Boersma’s research on South American penguins shows how much local conditions at sea and on land influence reproductive success. For the study, she contributed more than 35 years of breeding success data in Punta Tombo, a location with one of the largest breeding colonies for Magellanic penguins in southern Argentina. In almost four decades, Punta Tombo has changed rapidly.
“Today the breeding population in Punta Tombo is about half what it was in the early 1980s,” said Boersma.
During the breeding season each summer, the Magellanic parents have to return to the water frequently to catch fish for their chicks. Changing sea conditions mean adults will have to travel farther from Punta Tombo to find food, increasing the risk of chicks starving, Boersma said. Land conditions, like frequent storms, can also destroy nests and kill chicks, she added.
The conditions far out at sea, where Magellanic penguins feed for months after the breeding season each winter, also characterize Punta Tombo. The proportion of male Magellanic penguins at this point has increased over the years, and many males fail to find a partner. Boersma and her team found that harsh oceanographic conditions punish women more than men. In addition, young females are more likely to die at sea while trying to find food.
Southern seabirds did better overall, according to the new study. But over time, conditions in the south could catch up with already poor conditions in the north, Boersma said.
These results may be a call to protect guardians like seabirds as well as other species affected by increasing ecosystem stress, the researchers said. This requires the protection of seabirds in all their habitats, on land and at sea.
On land, seabirds can draw a lot of attention from humans, especially during the breeding season. However, this does not necessarily mean greater protection for breeding colonies. Boersma and two colleagues recently examined almost 300 breeding colonies for penguins around the world that are open to tourists. Less than half had management plans to protect the environment, parents, and chicks from curious human visitors.
At sea, the establishment of marine protected areas would protect the feeding waters of seabirds from overfishing, shipping, pollution and energy generation – and give these birds a much-needed boost in the face of climate change.
“By knowing what is important for a species to succeed, we can make the world a better place for it to survive,” said Boersma.
Thank you to the University of Washington for providing this message.
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