W. Cresswell, VARIATION IN THE STRENGTH OF INTERFERENCE COMPETITION WITH RESOURCE DENSITY IN BLACKBIRDS, TURDUS-MERULA, Oikos, 81(1), 1998, pp. 152-160
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.