Action: Control predators not on islands for seabirds
Key messagesRead our guidance on Key messages before continuing
- A before-and-after study from New Zealand found an increase in a tern population following intensive trapping of invasive mammals.
- A before-and-after study from Canada found increases in tern fledging success following gull control.
Seabirds frequently nest on the ground, where they are vulnerable to predation by both mammals and other birds. In addition, they are often poor walkers, as they are specialised for flying and swimming, and are poor at evading predators.
Supporting evidence from individual studies
A before-and-after study at a common tern Sterna hirundo colony in eastern Canada (Guillemette & Brousseau 2001) found that fledging success was higher in 1994 when chick-predating gulls (four herring gulls Larus argentatus and one great black-backed gull Larus marinus) were selectively shot, compared with 1993 and 1995, when no gulls were culled (16% of 115 eggs fledged vs. no chicks fledging from 165 eggs).
A before-and-after study at three sites in northern North Island, New Zealand (Wilson & Hansen), found that the population of New Zealand fairy terns Sterna nereis davisae increased from a low of five breeding pairs in 1987 and an annual decline of 1.5% to between 35 and 40 individuals in 2005 and an annual increase of 1.4%, following the continual trapping of introduced mammalian predators (feral cats Felis catus, hedgehogs Erinaceus europaeus, stoats Mustela erminia, ferrets M. putorius, weasels M. nivalis, Australian brush-tailed possums Trichosurus vulpecula and rats Rattus spp.) from 1992 onwards. On average 100 hedgehogs and 12 cats were trapped each year.
- Guillemette M. & Brousseau P. (2001) Does culling of predatory gulls enhance the productivity of breeding common terns? Journal of Applied Ecology, 38, 1-8
- Wilson T. & Hansen K. (2005) Predator control to enhance breeding success of the New Zealand fairy tern Sterna nereis davisae, North Island, New Zealand. Conservation Evidence, 2, 89-89