Optimal Choice of Neighbour: Predator Protection among Tundra Birds

Abstract

The distribution of breeding birds on Siberian tundra was studied around nests of Long-tailed Skuas Stercorarius skua, Grey Plovers Pluvialis squatarola, Pacific Golden Plovers Pluvialisfulva and Bar-tailed Godwits Limosa lapponica, all of which have been observed attacking avian predators entering their nesting territories. Only the skua and the Grey Plover turned out to do so regularly, however. The efficiency of defence was measured using artificial nests 30, 70 and 150 m from nests of the four species. The survival of nests was significantly higher than the survival of control group nests only around Grey Plover nests. Long-tailed Skuas defended their own nests fiercely, but were observed preying on artificial nests inside their territories. Nest distribution of local birds around the potential protectors reflected the efficiency with which the protectors defended their territory, but most of all it reflected the survival probabilities found for artificial nests: the number of nests located within 100 m from Grey Plover nests was significantly higher than in control plots. The Long-tailed Skua did not attract more birds than control points, presumably because it could not be trusted as a reliable neighbour when rodent numbers were decreasing. It is concluded that tundra birds are able to make optimal decisions about the choice of protective neighbour.