Seabirds have been used as indicators of ecosystem health in marine environments. That is due to the fact that these animals are more susceptible to the ingestion of debris in coastal areas as much as in high seas because of their long migrations and diverse diets. Another factor involved is the tendency that, while feeding their chicks through regurgitation, the undigested matter might be also transferred, along with the food, and that means plastics too, the most common form of marine debris. The ingestion of plastics could be even more troublesome to chicks for these animals can not obtain any nutrition necessary for their development, leading them to death.
Various studies seek to understand what drives birds to ingest plastic. It is believed that plastic fragments may resemble items from their usual diet. For instance, nurdles (small plastic beads that are melted and treated to be transformed in plastic products) could be mistaken as fish eggs, a common item in most seabirds’ diet.
A recent study in Australia took advantage of stranding events at Main Beach, North Stradbroke Island, in two ocasions (2010 and 2012) to investigate the ingestion of plastics by these birds and to compare if there was any difference in color, type and quantity of debris according to the age and sex of the animals.
The research reports that over 67% of the birds had ingested some form of debris, in its majority, plastic (n=102 adults and n=27 juveniles). In total, 399 pieces of anthropogenic debris were colected. Statistical tests did not find a significant relation between the body condition of the animals and the ingestion of debris. However, it was proved that juveniles ingest significantly more debris than do adult birds. Differences were not detected regarding the amount of debris in relation to sex. However, in a comparison between the debris ingested by the birds and the one collected on boat-based tows, following the species’s migration route, it has been found a significant difference, suggesting that the birds could be actively selecting for pieces of hard plastic, rubber and balloon fragments.
The characterization of the ‘preferred’ items by certain species and ages is an important factor that could be helpful when addressing preventive and mitigation measures to tackle the marine debris issue.
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Image by Heidi Acampora
Published by Heidi Acampora