Does hatching failure breed infidelity?

In socially monogamous species, the reasons for female infidelity are still controversial. It has been suggested that females could seek extra-pair copulations as an insurance against hatching failure caused by male infertility or incompatibility. In species where couples breed repeatedly, females could use previous hatching success as a cue to assess their partner’s infertility (or incompatibility). Hence, it has been predicted that females should increase their infidelity after experiencing hatching failures, but to our knowledge this hypothesis has never been tested experimentally. We manipulated hatching success of pairs in a captive population of zebra finches (Taeniopygia guttata), a species that forms lifelong pair bonds, and measured female willingness to engage in extra-pair copulation. By experimentally cross-fostering fertile and infertile eggs, couples either experienced 100% or about 35% hatching success in each of three consecutive clutches. Contrary to our prediction, females that experienced repeated hatching failure did not increase their responsiveness toward extra-pair males relative to those females with 100% hatching success. Moreover, there was no difference in female calling rate for the partner after male removal and no occurrence of divorce when the opportunity was given. These findings seem to contradict the common view that reproductive failure weakens the pair bond. Furthermore, a critical review of the literature suggests that there is no convincing evidence supporting this hypothesis in other species either. We therefore highlight that this fundamental area of behavioral ecology research is still much in need of specific experimental work that controls for confounding factors. Key words: divorce, extra-pair mating, fertility insurance, hatching failure, pair bond, zebra finch