Sc. Whitehead et al., MEASURING THE IMPACT OF PARENTAL FORAGING BY STARLINGS (STURNUS-VULGARIS) ON SOIL INVERTEBRATE PREY AVAILABILITY - AN EXCLOSURE EXPERIMENT, Oikos, 76(3), 1996, pp. 511-521
Depletion of soil invertebrate availabilities by starling foraging dur
ing the breeding season was investigated by using exclosures to create
areas where the birds could not feed. A field 'preferred' by the wild
birds was compared with a 'non-preferred' field. Prey biomass was mea
sured from soil cores and the foraging success of individuals feeding
in experimental enclosures gave a measure of prey availability. Foragi
ng by these birds resulted in significant short-term depletion after a
few hours of foraging. Trials conducted after a 24-h interval showed
that this depletion was due to removal of prey by the birds rather tha
n invertebrate movements. Comparison with exclosure sites al the end o
f the chick-feeding period showed that foraging by the wild birds caus
ed significant long-term depletion. This depletion was greatest in the
'preferred' field. which offered a higher availability of leather jac
kets Tipula paludosa. The 'non-preferred' field yielded lower capture
rates, despite a higher earthworm biomass in the soil cores. These fin
dings suggest that soil core analysis alone is insufficient to predict
the foraging success of starlings and other birds feeding on soil inv
ertebrates. The significant reduction in prey availability to parent s
tarlings is discussed in relation to the number of parental foraging t
rips made to the two fields.