Seabird plastic ingestion differs among collection methods: Examples from the short-tailed shearwater

Area of Science:

• Marine Biology
• Environmental Science
• Conservation Science

Background:

• Seabird plastic ingestion is a growing concern, yet studies often rely on naturally deceased birds.
• Naturally deceased seabirds may present biased data due to factors like poor health or predation.
• Accidental mortality may provide a more representative sample of the population's exposure to marine debris.

Purpose of the Study:

• To compare plastic loads and physiological condition between naturally beached and accidentally road-killed short-tailed shearwater fledglings.
• To evaluate the representativeness of different sampling methods for assessing seabird plastic ingestion.
• To inform long-term monitoring programs for marine debris impacts on seabird populations.

Main Methods:

• Collected and necropsied naturally beached and road-killed short-tailed shearwater (Ardenna tenuirostris) fledglings.
• Quantified plastic loads in the gastrointestinal tracts of sampled birds.
• Assessed body condition and analyzed feather stable isotopes (δ13C and δ15N) to infer feeding strategies.

Main Results:

• Beached fledglings exhibited significantly higher plastic loads compared to road-killed fledglings.
• Naturally deceased birds displayed poorer body condition and reduced isotopic niche breadth.
• These findings indicate that naturally beached seabirds are not a representative subsample of the population.

Conclusions:

• Relying on naturally deceased seabirds for plastic ingestion monitoring can overestimate population-level exposure to marine debris.
• Accidentally killed fledglings, particularly those affected by light pollution, offer a more accurate temporal and population-representative sample.
• Refined monitoring strategies using specific cohorts, like grounded fledglings, are recommended for more reliable data on plastic pollution impacts.