Data from: Fluff-thieving birds sabotage seed dispersal

Characterizing many species interactions as mutualisms can be misleading
because some members of the interaction derive greater fitness benefits at
the expense of other members. We provide detailed natural history data on
a suspected bird–plant mutualism in South Africa where many species of
birds use fluffy Eriocephalus seed material to construct their nests,
potentially dispersing seeds for the plant. We focus on a common bird,
Prinia maculosa, which invests heavily in gathering Eriocephalus material.
Prinias spent 5 of their median 6-day nest construction period adding seed
material to their nests and frequently travelled outside their territory
boundary to gather Eriocephalus material. Yet, prinias gathered primarily
Eriocephalus fluff and actively avoided gathering seeds. The average
prinia nest contained only 6.6 seeds, but contained fluff from 579 seeds.
These data suggest that prinias provide limited dispersal benefits to
Eriocephalus plants. By contrast, the large amounts of Eriocephalus fluff
in prinia nests, and the effort that prinias invest in gathering it,
suggest that prinias benefit from constructing their nests with
Eriocephalus material. We end by outlining hypotheses for possible fitness
benefits that Eriocephalus material could provide prinias and other birds.