The nesting of Ringed plovers was investigated in 1974 at Mestersvig, north-east Greenland, and in 1974–76 at Lindisfarne, north-east England. Difficulties in the use of Nest Record Cards for this species (to obtain information from more sites) are discussed. Territory sizes tended to be smaller, and more feeding took place within territories, at Lindisfarne than at Mestersvig. Clutch sizes were similar in different areas. Incubation (mean period about 25 days) was shared fairly equally by the two sexes. Longer incubation shifts at Mestersvig and some areas at Lindisfarne than at other Lindisfarne sites were associated with greater distances between nests and feeding areas. Most egg losses were probably due to predation, and were fewer in the Arctic than in Britain, where nesting success varied greatly in different areas and years, and in relation to timing within a season. Up to five nestings per pair per year were made at Lindisfarne, but only one at Mestersvig.
The timing of breeding is discussed, and it is concluded that the date of start of egg-laying in north-east Greenland is determined by the timing of snow clearance, while that at Lindisfarne is related to the decreasing probability of egg-predation later in the season. Because of the high nest losses, the production of young at many temperate sites, including parts of Lindisfarne, was probably inadequate for the population to be self-supporting. The reasons for the large seasonal, annual and geographical differences are discussed. It is concluded that increasing predation probably determines the southern nesting limits of Ringed plovers, but that this limit may be modified by varying degrees of different types of natural and artificial protection, and extent of habitat suitable for egg camouflage. Increased human usage of nesting beaches probably has an adverse effect on nesting success, but because of the complexity of the number of inter-related factors affecting the latter, without field experiments it is difficult to predict how this could best be offset by protection measures.