Plastic is likely the cause of declining shearwater chick health

Flesh-footed Shearwater

New research shows how the body condition of nestlings in a shearwater colony rapidly declined in just over a decade. Human impacts are considered the most likely cause.

Researchers collected data on how body condition, which includes wing, head and beak mass and length, changed in flesh-footed shearwaters on Lord Howe Island between 2010 and 2022. This new study reveals that body condition in young birds has declined significantly in the colony over the past decade. Lord Howe Island lies 600 kilometers off the east coast of Australia and is home to the largest colony of flesh-footed shearwaters in the world.

“We were speechless”

Alex Bond, curator in charge of birds at the Natural History Museum in London and co-author of the study published in the ICES Marine Science Journal, says: “When we looked at the data collected over the past 13 years, it was only an empty thought to wonder how the body condition of the chicks had changed. We expected it to fluctuate up and down with good and bad years, but we were speechless when we saw the results.

“That’s when we realized we hadn’t seen any of the really heavy birds that we often saw in the early years. So putting it together and seeing it in the larger context of the last 13 years was surprising because it wasn’t what we expected.

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The island’s biodiversity faces many pressures, including habitat loss, invasive species, fishing and plastic pollution.

Shearwater chicks spend about 90 days in their burrow after hatching and are nursed by their parents. After this time, the parents will abandon their young, leaving them to fend for themselves, flying off to Japan and not returning to earth for five to eight years until they are of breeding age. As the chicks must now feed themselves, they must be fed well enough to survive on their own.

The scientists captured the nestlings in the colony and on the adjacent beaches, weighed them and measured the length of their wings, beaks and heads. Using this data collected over the past 13 years, they were able to see how their physical condition has changed over a decade.

“Even healthier birds get lighter, which is concerning because body mass is probably one of the biggest predictors of survival in the first two years,” Bond says.

“Imagine your parents supporting you all your life, and then you’re told you now have to run a marathon without any training or knowledge of how to gather food. It’s sort of the equivalent of what these birds are dealing with.

“Obviously, the more stores you have and the more fat you have on your body, the longer you can endure this learning curve during your first year as you learn to survive on your own.”

Young flesh-footed shearwaters weigh 42% less

At the start of the study in 2010, most birds weighed around 690 grams, but scientists have found that in recent years less than half of the birds weigh more than 400g, a critical threshold for survival in their first year. This equates to a 42% drop in body weight over 13 years.

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As these changes do not appear to be related to food availability or El Niño or La Niña climate oscillations, the researchers believe this indicates a stressor impacting the population.

The most plastic contaminated birds in the world

The team previously found that Lord Howe Island’s flesh-footed shearwaters are the most plastic-contaminated birds in the world, as they consume pieces of plastic at sea after mistaking them for food. Therefore, researchers believe it is the most likely candidate for reduced fitness.

When the stomach is full of plastic, it impairs the blood and causes scarring. It also moves space for more nutritious foods, such as squid, which the chicks would normally eat.

“We can’t say conclusively that plastic is driving this massive decline, but it’s pretty high up on the list of candidates.” said Bond. “We have been studying this colony for 15 years, and we can see in the data the changes that are taking place.

“Chicks that fledge with smaller mass and with shorter wings have lower survival, and we know that from a bunch of seabird species. first eight years to return to breeding.

Thanks to the Natural History Museum in London for this news.

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