Non-Breeding Territoriality: Causes and Consequences of Seasonal and Individual Variation in Grey Plover Pluvialis squatarola Behaviour

Abstract

1. Approximately 65% of grey plovers at the Zwartkops estuary, South Africa, defended feeding territories throughout the austral summer. Territories were established during the arrival period (September), once the foraging densities of grey plovers exceeded 4.6 birds ha -1 . Territories ranged in size from 490 to 2800 m 2 . 2. Average territory size decreased over the season and was significantly and inversely related to the total number of grey plovers on the estuary, rather than to resource patterns. Individual variation in territory size was inversely related to resource density. 3. Territorial encounter frequency decreased from September to March, probably due to neighbour familiarity, and was also reduced by avoidance behaviour. The frequency of aggressive encounters was significantly higher for owners of smaller territories. 4. The owners of large territories spent significantly more time foraging during the low tide period than did owners of small territories. However, energy intake rates were negatively correlated with territory size, with the result that the total low tide intake was approximately equal, irrespective of territory size. 5. Non-territorial grey plovers foraged at higher densities than territorial birds. These birds achieved a decreasing proportion of the energy intake rate of territorial birds over the season, and may have had to depart later on northward migration.