Nest predation lowers the polygyny threshold: a new compensation mInfanticide
in great reed warblers: secondary females destroy eggs of primary females
Hansson, B., Bensch, S. & Hasselquist, D.
Animal Behavior, 54, 297-304. 1997.
In 1993-1995 artificial nests with attached model eggs
were put into territories that were known to have been occupied by male
great reed warblers, Acrocephalus arundinaceus, in previous years. Because
the eggs were made of soft plasticine, predators left peckmarks in them
and this enabled us to identify predators by comparing peckmarks with reference
marks made by. Various species. Previous field data had suggested that
infanticidal behaviour existed in our study population, as nests of primary
females suffered a three times higher rate of nest loss during the egg-laying
period than nests of secondary and monogamous females. The presence of
infanticide was supported by the experiment. Small peckmarks resembling
those of a great reed warbler occurred almost exclusively in territories
occupied by great reed warblers, in particular when a new female settled
in the territory. The newly settled females built nests closer to depredated
than non-depredated nests. That small peckmarks occurred when new females
settled strongly suggests that it is secondary female great reed warblers
that commit infanticide on eggs of primary females. Females of low harem
rank are expected to gain from infanticidal behaviour because a low ranked
female gets a higher proportion of male parental investment when the nest
of the primary female fails.