Our Hypothesis Is That Female Chicks Are More Expensive to Rear Than Male Chicks

99700 The Effects of Brood Sex Ratio Manipulation on Parental Care Allocation in Zebra Finches, Taeniopygia guttata Diane Livio Mentor: Nancy Burley

Differences between male and female offspring can lead to one being more expensive to rear than the other, thus affecting the allocation of parental care and investment. Previous studies suggest that female chicks of zebra finches (Taeniopygia guttata) are more expensive to rear and cause greater costs to the parents’ fitness; thus we predict that male-biased broods would be in better condition and survive better that female-biased broods, receiving less allocation of care overall. To test this, we manipulated broods to all male, all female or a mix and recorded the parental care activities and durations at the nest. We also recorded the order of eggs laid, initial weight at switching, asynchrony among hatching dates, growth rates, survival and inter-clutch intervals (between nesting attempts). Our results showed that within the male-biased treatment, females fed more often, but in the female-biased treatment, males brooded more and were more defensive. Among the treatments though, the females spent more time in the nest in the mixed treatment than the sexually biased ones. There was a slight trend for the growth rate and percent survival to be higher for the female-biased treatment than the male-biased one. The egg order, initial weight and asynchrony of hatching did have a small effect on the survival of the nestlings. Overall, though, our data suggests trends that may support our hypotheses; we believe that we will find significantly stronger evidence when we complete analyses on the rest of our data.