BREEDING SUCCESS IN BRENT IN RELATION TO INDIVIDUAL FEEDING OPPORTUNITIES DURING SPRING STAGING IN THE WADDEN SEA

Brent Geese Branta bernicla individually marked with inscribed leg rings were intensively watched from permanent towers on the saltings of the island Schiermonnikoog in the Dutch Wadden Sea during the spring staging period April- May 1982 when 3,000 used the area. By observing geese on plots with enhanced vegetation (biomass, protein content) as a result of fertilizer treatment, it was found that individuals on the improved sites fought more and walked more slowly. The position of the marked individuals in relation to the total feeding minutes accumulated by the flock as the group grazed past the tower was determined by making use of a radial system of counting plots. Individuals tended to be consistent in their relative timing in the grazing sequence, and the highest rate of interaction and lowest pacing rate was found just behind the leading edge of the flock, in the second quartile of feeding minutes, and by inference birds in this sector experienced the best feeding conditions. Status of the males (proportion of interactions won) was highest for individuals habitually in this sector, and observation of the same birds in the fall revealed the highest incidence of breeding success (pairs accompanied by young) for this group. A number of measures reflecting a good food supply (low pace rate, highest percentage feeding times, and highest number of bites per step) were found to correlate positively with male status supporting the conclusions from the grouped data presented in relation to the grazing sequence. Though a causal relation cannot be proved from such correlations, we interpret these findings to indicate that males of high status can provide their mates with enhanced feeding opportunities, resulting in accumulation of more body reserves in the spring, and a heightened probability of successful breeding. Females subsequently found to prove successful had a larger proportion of Triglochin maritima in their spring diet but a larger sample of droppings will be needed to substantiate this hint of a difference of diet in birds of the same flock.