Data from: Nest as an extended phenotype signal of female quality in the great reed warbler

Extended phenotypes with signalling function are mostly restricted to
animal taxa that use construction behaviour during courtship displays.
However, they can be used also as post-mating signals of mate quality,
allowing individuals to obtain reliable information about their partners.
Nest size may have such a signalling function and a lot of indirect
evidence supports this view. However, direct evidence based on an
experimental approach is still widely missing. Here we test the role of
nest size in post-mating signalling of mate quality in the great reed
warbler Acrocephalus arundinaceus, a passerine with female-restricted
nest-building behaviour. Based on observational data, clutch size,
nestling weight, brood size and fledglings’ propensity to return to their
natal site positively correlated with nest size. Moreover, we
experimentally enlarged great reed warbler nests to investigate whether
this manipulation affects male investment in feeding. We found that males
fed their nestlings significantly more intensively on enlarged nests than
those on control nests. This suggests that nest size in this species
serves as a signal of female quality or willingness to invest in
reproduction and that it pays males to enhance their feeding effort
according to this signal. Thus, we provide convincing evidence that animal
communication takes place through the extended phenotypes and that
post-mating signalling of quality is not restricted only to males, but may
function equally well in females.