| In order to understand the effects of parental investment on learning, we conducted a series of experiments using zebra finches. The aspects of parental investment studied included deposition of maternally-derived hormones (MDH) into eggs, feeding and attention to chicks. Learning was assessed by song copying (mean accuracy, sequential matching and percent similarity to the father's song). We compared digit ratios, a marker for the amount of MDH chicks experienced in eggs, and song copying ability. Our data suggests that maternally-derived testosterone negatively affected the ability to sequentially match notes. To determine if parents were preferentially feeding chicks by hatch order, we weighed chicks at key developmental points prior to fledging. We found that chicks that hatched early were heavier than those who hatched late. Additionally, weight at day 10 was positively correlated with song learning. Acoustic cues are one obvious way that parents might differentiate chicks by hatch order. Therefore, we assessed the begging calls of 10 day old chicks. We found that early-hatched chicks begged at lower amplitudes than late-hatched chicks. We then conducted a playback experiment in which begging calls of 10 day old early- and late-hatched chicks were presented to breeding adults. Adults were more attentive during the early-hatched chicks' playbacks. To determine if attention, in the form of clumping or perching closely together, affected song learning, we observed family groups when chicks were beginning song acquisition (day 25). We found that while clumped with their mates, mothers clumped with first-hatched more than second- or third-hatched chicks. Moreover, clumping behavior was positively correlated with the percent similarity of song copying. Clumping with first-hatched sons may be a way for mothers to give additional access to the father and thereby enhance son's song learning. Finally, we used a multiple linear regression, combining all three forms of parental investment to determine which were more important in song learning. We found that digit ratio 2:3 was positively correlated with sequential matching, nestling weight positively correlated with mean accuracy and clumping with the mother positively correlated with the percent similarity score. |
