EGG BURIAL IN PENDULINE TITS, REMIT PENDULINUS - ITS ROLE IN MATE DESERTION AND FEMALE POLYANDRY

One important component in the mating strategy of an already-mated ind ividual is the decision to remain with the partner and care for the of fspring or to desert. Almost ail research on nest desertion has focuse d on the costs and benefits of continued parental care versus desertio n of both parents. However, if it pays both parents to desert, the tim ing of desertion is most important. In birds, where all eggs are ferti lized well before the last egg is laid, males should be the first to d esert. Even if females try to hide their fertile period, it is likely that the appearance of eggs acts as a cue that males can use to calcul ate the timing of their desertion. Here we examine egg burial behavior in penduline tits and its possible effects on parental behavior and d esertion. Penduline tits perform uniparental care from the earliest po int of breeding, and both sexes try to become polygamous. We found tha t 36% of investigated males were polygynous and deserted as soon as th e first egg appeared. in their nest, and 12.5% of females became polya ndrous. About 27% of the nests were deserted by both sexes, which mean s high costs for females in terms of wasted energy in eggs and for mal es in terms of wasted energy and time in building elaborate nests. Fem ales cover the eggs, and several facts indicate that egg covering is a deceptive behavior of females: (1) females cover the eggs in the morn ing before leaving the nest for the first time, (2) females are more a ggressive toward their mates during the laying period than before layi ng, (3) females try to prevent males from entering the nest when eggs have been experimentally uncovered, and (4) females uncover the eggs a s soon as males are experimentally removed. Finally ive found that a f emale can only desert the nest before the male deserts when she covers the eggs. We conclude that the higher the proportion of eggs a female can hide, the greater her chance of becoming polyandrous.