Common Tern - Predators and Parasites

Predators and Parasites

Rats will take tern eggs, and may even store large numbers in caches, and the American mink is an important predator of hatched chicks, both in North America, and in Scotland where it has been introduced. The red fox can also be a local problem. Because Common Terns nest on islands, the most common predators are normally other birds rather than mammals. The Ruddy Turnstone will take eggs from unattended nests, and gulls may take chicks. Great Horned Owls and Short-eared Owls will kill both adults and chicks, and Black-crowned Night Herons will also eat small chicks. Merlins and Peregrine Falcons may attack flying terns; as with other birds, it seems likely that one advantage of flocking behaviour is to confuse fast-flying predators.

The Common Tern hosts feather lice, which are quite different from those found in Arctic Terns, despite the close relationship of the two birds. It may also be infected by parasitic worms, such as the widespread Diphyllobothrium species, the duck parasite Ligula intestinalis, and Schistocephalus species carried initially by fish. Tapeworms of the family Cyclophyllidea may also infect this species. The mite Reighardia sternae has been found in Common Terns from Italy, North America and China. A study of 75 breeding Common Terns found that none carried blood parasites. Colonies have been affected by avian cholera and ornithosis, and it is possible that the Common Tern may be threatened in the future by outbreaks of avian influenza to which it is susceptible. In 1961 the Common Tern was the first wild bird species identified as infected with avian influenza, the H5N3 variant being found in an outbreak of South African birds.