TEMPORAL VARIATION IN THE SOCIAL RANK OF ADULT OYSTERCATCHERS HAEMATOPUS OSTRALEGUS

The success in interactions with conspecifics (the dominance score) of eleven out of 26 adult Oystercatchers changed significantly over seve ral years. Since dominance score predicts dominance within dyads and h ence rank within a linear hierarchy, these results suggest that hierar chies which are stable within one winter, change over longer periods. This was verified by a group of eight individuals of which six showed contested reversals of rank over four years. On the basis of external measurements it appears that individuals which increased in status and achieved high social rank were predominantly male. Comparison of the dominance scores of 'residents' and 'movers' were contrary to predicti ons generated by the idea that an individual's rank is determined larg ely by passive means as a result oi the cumulative effect of prior res idence. However, several comparisons were in the direction expected by this hypothesis. The relative importance of passive and active proces ses in determining an individual Oystercatcher's social rank remains t o be evaluated. Empirical relationships indicated that changes in domi nance score resulted in changes in intake rate of between -10% and +12 %. Whether this effect of social rank influences fitness remains to be determined.