Plastic detected in 71% of examined petrel chicks

Even a small amount of plastic can leave a biological trace in the body of a young bird. Plastic was detected in 71.4% of the southern giant petrel chicks examined in Patagonia. Importantly, plastic begins to accumulate in their bodies, along with food delivered by their parents, before they even leave the nest.

Plastic in southern giant petrel chicks

The study was conducted jointly by scientists from Argentina’s CONICET and the University of California, Davis. During the breeding seasons of 2022 and 2023, they examined southern giant petrel chicks (Macronectes giganteus) from colonies in Chubut Province, in Argentine Patagonia. Each year, 30 nests were randomly selected, and the birds were assessed at two stages of development: at around 30 days of age and shortly before leaving the nest, at around 90 days.

Plastic was detected in 71.4% of the chicks examined. Individual birds contained between 1 and 14 pieces, with an average mass of 0.251 g, less than 0.1% of the chick’s body mass. The study included plastic pieces measuring at least 1 mm. These included small fragments of plastic, foam and tiny pellets.

The ocean is polluted by both microplastics and larger plastic waste. Animals may swallow them directly while foraging or together with their food. In this way, plastic present in the marine environment moves through food webs.

Jak mikroplastik w oceanach wpływa na zmianę klimatu?

How does plastic enter the bodies of young petrels?

Southern giant petrels often forage near the sea surface, where floating plastic accumulates. Adult birds may swallow it while obtaining food and then pass it on to their young. After returning to the colony, they feed their chicks by regurgitating food.

This means that young petrels are exposed to eating waste before they even begin foraging independently. The authors indicate that the high frequency of plastic detection suggests that parents are unknowingly delivering plastic to their chicks.

The impact of plastic on petrel chick physiology

The most important finding of the study, however, was not simply the confirmation that plastic was present in the birds’ bodies. In chicks around 30 days old, the amount of ingested plastic was associated with parameters related to nutritional status and condition, metabolism, and immune response. These relationships included cholesterol and calcium levels, body mass and condition, and the activity of enzymes associated with liver and muscle function.

This does not mean that plastic was the direct cause of all these changes. The researchers identified statistical associations, not a simple cause-and-effect relationship. Moreover, the associations between the amount of plastic and some of the enzymes analyzed were no longer significant after accounting for differences between the study years.

The closer the chicks were to leaving the nest, at around three months of age, the weaker most of the previously observed associations became, and some disappeared completely. Differences in calcium levels and the activity of one enzyme that helps cells cope with oxidative stress were still visible, however.

The scientists do not identify the cause of the changes with certainty. Possible explanations include physiological compensation, the effects of chemicals associated with plastic, and natural changes occurring during bird development.

Seabirds as indicators of ocean pollution

Seabirds are particularly useful for monitoring plastic pollution. They forage across large areas of the ocean and come into contact with waste floating on the surface. The contents of their digestive tracts can therefore provide reliable information about the presence of plastic in the marine environment. Another source of information, besides petrels, is the northern fulmar, which lives in the North Sea region.

This does not mean, however, that the figure of 71.4% can be applied to all seabirds. The study covered one species, the southern giant petrel, two colonies in Argentine Patagonia, and two breeding seasons. The findings should therefore not be generalized.

The results do show, however, that even a relatively small mass of ingested plastic can be associated with measurable physiological changes in young birds. Petrels are long-lived and reproduce slowly, so even subtle developmental disturbances may have significance over the longer term. The authors emphasize, however, that further research is needed to determine whether, and if so how, exposure to plastic early in life affects the survival, condition and lifetime reproductive success of birds after they leave the nest.