Action: Use nest covers to reduce the impact of research on predation of ground-nesting seabirds
A before-and-after study in Canada found that protecting Caspian tern Sterna caspia nests after researchers disturbed parents from them significantly increased hatching success. This was due to a reduction in predation by ring-billed gulls Larus delawarensis.
Researchers arriving at nesting colonies may disturb birds and, particularly with ground-nesting species, may leave them vulnerable to opportunistic predators. This predation might be reduced by protecting the nests with cages or individual barriers.
Studies describing the more general use of nest cages and predator barriers are discussed in ‘Reduce nest predation by excluding predators from nests or nesting areas’.
Supporting evidence from individual studies
A before-and-after study at a site on the South Limestone Islands, Lake Huron, Canada (Quinn 1984), found that the hatching rate in a Caspian tern Sterna caspia colony was significantly higher in 1979 when researchers visiting the site added nest covers to nests when they arrived at the colony and removed them as they left, compared to in 1978, when covers were not used (77% of 156 eggs hatching in 1979 vs. 62% of 188 in 1978). This difference was mainly due to large numbers of eggs being eaten by ring-billed gulls Larus delawarensis in 1978. The author notes that two eggs in 1978 were crushed by poor placement of the covers. Covers were 38 cm diameter hemisphere made from wood, steel and chicken wire.