Humans make it difficult for seabirds to breed
Many northern hemisphere seabirds struggle to breed – and in the southern hemisphere, they may not be far behind.
These are the conclusions of a study on Science analysis of over 50 years of breeding records for 67 species of seabirds around the world.
Researchers found that reproductive success had declined over the past half century for piscivorous seabirds north of the equator. The northern hemisphere has suffered greater effects from human-caused climate change and other human activities, such as overfishing.
Seabirds include albatrosses, puffins, murres, penguins, and other birds. Whether they soar or swim, all seabirds are adapted to feed and live near ocean waters. Many scientists view seabirds as sentinels of habitat health, as their life and well-being depend on healthy conditions both on land and at sea, says co-author P. Dee Boersma, professor of biology at the University of Washington and director of the Center for Ecosystem. Sentinels.
“When seabirds aren’t doing well, it’s a red flag that something bigger is happening below the ocean’s surface…”
“Seabirds travel long distances – some going from one hemisphere to another – chasing their food in the ocean,” says Boersma. “This makes them very sensitive to changes in things like the productivity of the oceans, often over a large area.”
In addition, seabirds congregate at particular sites along the coasts to breed and raise their young, making them vulnerable to changing shore and surface conditions and limiting the distance they can travel for food while at the same time. successfully raising their chicks, says Boersma.
The diets of seabirds play a major role in their ability to raise chicks. In the north, piscivorous seabirds experienced a significant decline in reproductive success during the study period. Additionally, surface feeding birds in both hemispheres were more prone to reproductive failure, whether they ate fish or smaller plankton, such as krill.
Deep-sea diving birds, such as puffins, have done better in terms of reproductive success.
Red flag for healthy oceans
Researchers believe the changing environmental conditions are to blame. Seabirds must travel far to feed and eat a lot – murres, for example, must consume half their body weight in fish per day. Nearly one million murres starved to death and breeding colonies crashed in 2015-16 due to a long wave of marine heat that disrupted food webs in the northeast Pacific. Climate change is causing more frequent and extreme events like these heat waves, and seabirds in the ocean face other threats as well.
“They have to compete with us for food. They can get caught in our fishing nets. They eat our plastic, which they think is food, ”says Boersma. “All of these factors can kill a large number of long-lived seabirds.”
These changes have implications beyond seabirds.
“What is also at stake is the health of fish populations like salmon and cod, as well as marine mammals and large invertebrates, like squid, which eat the same small forage fish and plankton as birds. of sea, ”says William Sydeman of the Farallon Institute in California.
“When seabirds aren’t doing well, it’s a red flag that something more important is happening below the ocean’s surface, which is of concern as we depend on healthy oceans for quality. of life.”
Harsh conditions hurt female seabirds the most
The team found great variability in reproductive success between species, indicating that more research is needed to understand all of the factors that shape the diet and reproduction of these species.
Boersma’s research on South American penguins illustrates how local conditions at sea and on land affect breeding success. For the study, she provided more than 35 years of data on breeding success at Punta Tombo, a site with one of the largest Magellanic penguin breeding colonies in southern Argentina. In almost four decades, Punta Tombo has evolved rapidly.
“Today, the breeding population of Punta Tombo is about half of what it was in the early 1980s,” says Boersma.
During the breeding season each summer, Magellanic parents must frequently return to the water to catch fish for their chicks. Changing ocean conditions mean adults have to travel further from Punta Tombo to find food, which increases the risk of starvation for chicks, Boersma says. Conditions on land, such as frequent storms, can also destroy nests and kill chicks, she adds.
The distant conditions at sea, where Magellanic penguins spend months feeding each winter after the breeding season, also shapes Punta Tombo. The proportion of male Magellanic penguins at this site has increased over the years and as a result many males cannot find mates. Boersma and her team discovered that harsh oceanographic conditions punish women more than men. Additionally, juvenile females are more likely to die at sea while trying to find food.
Protect seabirds from curious tourists
Southern seabirds performed better overall, the researchers said. But over time, conditions in the south could catch up with already bad conditions in the north, Boersma says.
The findings may be a call to protect sentinels like seabirds, as well as other species affected by growing ecosystem stress, the researchers say. This requires protecting seabirds in all their habitats, on land and at sea.
On land, seabirds can attract a lot of people’s attention, especially during the breeding seasons. But this does not necessarily translate into better protection of breeding colonies.
For example, Boersma and two colleagues recently investigated nearly 300 penguin breeding colonies 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 creation of marine reserves would protect seabirds feeding waters from overfishing, shipping traffic, pollution and energy extraction – giving these birds a much needed boost in the face of change climate.
“By knowing what is important for the success of a species, we can make the world a better place for its survival,” says Boersma.
Source: University of Washington