Data from: Male zebra finches have limited ability to identify high-fecundity females

In species with biparental care and lifetime monogamy, the fecundity of a male’s partner can be a major component of his fitness but it is unclear whether males can assess female fecundity before breeding. We carried out an experiment in which we measured variation in female fecundity (repeatability 39%, 213 females) in a captive zebra finch population and tested whether males preferred unfamiliar females of high fecundity (approximately top 10% of the population; 30 eggs laid on average) over those of low fecundity (bottom 10%; 6 eggs). We first tested whether naïve human observers could identify the high-fecundity female when confronted with duos of high and low fecundity. Humans guessed correctly in 58% of the cases (95% confidence interval [CI] 50–66%) indicating that differences in female condition were not highly obvious to humans. Zebra finch males preferred the high-fecundity female in 59% of choice tests that lasted 20 min (CI 52–66%). When extending such choice tests over several days, male “success” in associating with the high-fecundity female was still modest (61% correct choices, CI 44–76%). Overall, male zebra finches seem to have only limited abilities to identify the better mate when faced with a choice between extremes in terms of female fecundity. We found no male preference for heavier females. We speculate that such a preference may not have evolved because, in contrast to many ectothermic species, predicting fecundity from female weight is not sufficiently accurate (r2 = 0.04) for the benefits to outweigh the costs of increased male–male competition for heavy females.

在双亲抚育且终生实行单配制的物种中，雄性配偶的繁殖力是其适合度的核心组成部分，但目前尚不清楚雄性能否在繁殖前评估雌性的繁殖力。我们开展了一项实验，在圈养斑胸草雀（zebra finch）种群中测量了雌性繁殖力的变异（重复率39%，共纳入213只雌性个体），并检验雄性是否更偏好陌生的高繁殖力雌性（约为种群前10%，平均产卵30枚），而非低繁殖力雌性（种群后10%，平均产卵6枚）。我们首先测试了未经过训练的人类观察者在面对高、低繁殖力雌性配对时，能否识别出高繁殖力个体。人类在58%的试次中做出了正确判断（95%置信区间[confidence interval，CI]为50%~66%），这表明雌性身体状态的差异对人类而言并不十分显著。在持续20分钟的选择实验中，斑胸草雀雄性在59%的试次中表现出对高繁殖力雌性的偏好（95%置信区间为52%~66%）。当将此类选择实验延长至数天时，雄性与高繁殖力雌性建立关联的"成功率"依然有限（正确选择率为61%，置信区间44%~76%）。总体而言，当需要在雌性繁殖力差异悬殊的个体间做出选择时，斑胸草雀雄性识别更优质配偶的能力较为有限。我们未发现雄性存在对体重更大雌性的偏好。我们推测，此类偏好之所以未演化形成，是因为与许多外温动物（ectothermic species）不同，通过雌性体重预测其繁殖力的准确性不足（决定系数r²=0.04），以至于相较于雄性间为争夺大体型雌性而增加的竞争成本，该偏好带来的收益并不足以覆盖其成本。