Incorporation of anthropogenic debris into double-crested cormorant nests, Toronto, Ontario

Abstract

Prior research suggested using double-crested cormorants (Phalacrocorax auritus) as an indicator species to track anthropogenic debris in inland aquatic environments such as the Great Lakes. In this study, we sampled cormorant nests on the ground (n = 50) for the presence and type of debris at the Leslie Street Spit, a human built peninsula in Toronto, Ontario. We also compared the proportion of debris type to the Great Canadian Shoreline Cleanup data (2011–2018) for this site. All of the nests sampled had anthropogenic debris present, including plastic items, metal bars and clothing (average ± SD: 28.7 ± 22.0 g debris per nest). Out of four broad categories of debris type (plastic, building materials, miscellaneous and mixed materials), plastic had the highest proportion for nests (53.6%) and shoreline cleanup (63.9%), though plastic type differed. Nests (32.4%) had proportionally more building materials specific to the site, such as electrical wires compared to the shoreline cleanup data (4.7%). Because the Leslie Street Spit is a human-constructed site and cormorants accessed local construction material for their nests, the site should not be used to track changes in debris over time. We recommend that other ground-nesting colonies be used to: monitor changes in debris type and quantity; determine the proportion of nest material from terrestrial and aquatic environments; and estimate the distance cormorants will travel to gather nest material.