VARIATION IN THE STRENGTH OF INTERFERENCE COMPETITION WITH RESOURCE DENSITY IN BLACKBIRDS, TURDUS-MERULA

The decline in feeding rate of single blackbirds when feeding with one or two competitors was measured over a range of prey densities, in tw o winters, to determine whether the degree of interference competition experienced by an individual was independent of resource density. ind ividual wild blackbirds feeding with one or two competitors in experim ental patches suffered high interference competition in both winters. In the absence of interactions (any observable despotic behaviour) the re was no significant variation in the degree of interference competit ion with prey density in tither winter. However, in the presence of in teractions (an incident of chasing or being chased by a conspecific wh ile feeding) there was significant variation in the degree of interfer ence competition with prey density: interference competition peaked at mid-prey densities in both winters.