Time and energy budgets of the grey plover (Pluvialis squatarola) at Teesmouth

Abstract

The time and energy budgets of Grey Plovers (Pluvialis squatarola) at Teesmouth were investigated by observation of birds both by day and night, supplemented by additional information from a radio telemetry study and laboratory measurements of metabolic rates. The radio telemetry study of Grey Plovers confirmed that, on Seal Sands, some birds defended low water feeding territories, whilst others were non-territorial. This behaviour was maintained both diurnally and nocturnally, with territorial birds defending the same areas at night as by day. However territorial birds occasionally vacated their territories to forage on other areas at Teesmouth. Multivariate statistical methods characterised the conditions under which these birds changed foraging locations. The low-water time budgets of territorial birds were determined for both diurnal and nocturnal periods. No statistical differences could be found between these two budgets. The birds spent an extremely high (in excess of 90%) percentage of time foraging over the low water observation period. The diurnal low water time budget of non-territorial individuals was also determined and compared with that of territorial birds. The calorific intake rates of territorial birds during the daylight hours showed significant seasonal changes, characterised by a rise to a mid-winter peak, followed by a steady decline to mid March. This pattern may have been influenced by the temperature on the day of measurement. Respirometric measurements on Grey Plovers produced an estimate of their fasting metabolic rate, together with values for lower critical temperature and the rate of increase of metabolic rate with temperature below lower critical temperature. These measurements were consistent with estimates produced from general allometric equations. Information on the time budgets of territorial Grey Plovers, and measurements of metabolic parameters, enabled a simple energy budget to be constructed for the birds at Teesmouth.