In a new study from the Queensland University of Technology, researchers have solved the mystery of what killed millions of shearwater birds in 2013. The team found evidence that migrating seabirds are eating materials that are not even food, including pumice stones, because they are starving.
Study lead author Dr. Lauren Roman is a researcher at Australia’s national science agency CSIRO. She said there was much discussion in the scientific community about the causes of mass mortality of seabirds which are often found with plastic and other non-food items in their stomach.
“We found that in the instance of the shearwater bird deaths in 2013, these birds were starving, and in their starved state had reduced prey discrimination,” said Dr. Roman.
“Our study investigates the chicken-and-egg dilemma – do animals starve from eating non-food or do animals eat non-food because they are starving?””
Seabirds are indicator species that can be used to monitor the health of marine ecosystems. Mass mortalities are often indicative of changing food webs and ecological conditions.
The study was focused on short-tailed shearwaters, which migrate from Australia to the North Pacific in April and return late in the year. Among 172 deceased seabirds that were recovered from the New South Wales and Queensland, 96.7 percent had ingested pumice or plastic.
The researchers used satellite systems to track the 2013 shearwater migration and compared the data to locations of a large pumice raft produced by the 2012 Havre eruption north of New Zealand.
“We proposed that a short time period between non-food ingestion and death would indicate that birds were already starving at the time of non-food ingestion, and a starving state would be reflected by poor body condition and reduced muscle mass,” explained study co-author Professor Scott Bryan, who has been studying pumice rafts for over 20 years.
“Death after a longer period would indicate that birds starved following ingestion of non-food.”
Professor Bryan said detailed information about the route of the pumice raft was an integral part to determining the answer of where the birds had consumed the pumice.
“We combined the tracking information data of the short-tailed shearwaters, using location tags on migrating birds, and the geological signature of the ingested pumice.”
“By October 2013 when the shearwaters were returning to Australia on their annual migration from the North Pacific, the floating pumice was now located along their flight path as they approached Australia.”
Once the experts had established when the birds ate the pumice, and their physical condition at the time, they were able to conclude that the birds were already starving when they ate the pumice. Furthermore, the study revealed that the seabirds had ingested the pumice about 12 to 41 hours before death.
“With a projected increase in challenging times for wildlife because of threats such as climate change, marine pollution and over exploitation of resources, this study has implications for mass mortalities and exacerbation of existing threats to marine species,” said Dr. Roman.
The study is published in the journal Marine Ecology Progress Series.
By Chrissy Sexton, Earth.com Staff Writer