EXPERIMENTAL DEMONSTRATION OF A TRADE-OFF BETWEEN MATE ATTRACTION ANDPATERNAL CARE

Males should invest in mate attraction, mate guarding and paternal car e in relation to the marginal fitness value of each of those behaviour s. Since time and energy are limited, trade-offs between these activit ies are expected. This study demonstrates that monogamous male Europea n starlings (Sturnus vulgaris) decrease their paternal effort in respo nse to increased opportunities to attract additional mates and instead invest in mate attraction. Monogamous males' probabilities of attract ing additional females were increased by providing them with additiona l nestboxes. This resulted in both the rate at which males were visite d by prospecting females and the probability that they would obtain se condary mates increasing. Males with an additional nestbox sang more t han males with only one nestbox, both before laying and during incubat ion. Males with two nestboxes spent more time at their nest sites when their fertile females were away before, but not during, egg laying. T he experiment affected how much males incubated during the early, but not during the late, part of the incubation period. This makes sense, because males can attract additional females mainly during the early p art of the incubation period. Male feeding of nestlings was unaffected by the experiment. The fact that the potential to attract mates affec ts males' investment in parental care suggests that variation in this potential may contribute to the variation in paternal care between bir d species.