Nest attendance does not predict offspring desertion by Eurasian Penduline Tit parents

Parental care is costly, and in many organisms, the male or the female parent benefits from reducing its own care which may be compensated for by its mate. One of the parents may even face all costs of parental care if its mate deserts and leaves him/her to care for the offspring alone. Theoretical models have generated contrasting predictions as to how parents negotiate a resolution of this sexual conflict over care, although empirical tests are largely lacking. We investigated pre-desertion behaviour (nest attendance) of a highly polygamous passerine, the Eurasian penduline tit ( Remiz pendulinus) that exhibits intense sexual conflict over care culminating in clutch desertion by the male, by the female or by both parents. We conjectured that nest attendance of parents should predict desertion, so that the lack of care provided by the deserting parent may be compensated for. By analysing over 200 000 video frames (2.50 +/- 1.36 d per pair, 302 +/- 170 min/d) of 20 pairs, we show that nest desertion is not a gradual process and cannot be predicted by nest attendance. These results are consistent with the argument that the predictable desertion may not be evolutionarily stable, and suggest that male and female penduline tits do not negotiate clutch desertion.