Data from: Cost of reproduction: a comparison of survival rates of breeding and non-breeding male ortolan buntings

The cost of reproduction is expected to influence survival or future reproduction. Most previous studies have assessed cost of reproduction in relation to natural and experimental variation in number of offspring produced. The ortolan bunting (Emberiza hortulana) is a passerine bird species with biparental care, and the Norwegian population of the species has an extraordinarily skewed sex ratio with only about half of the males attracting a female, and therefore provides a rare opportunity to compare survival of males that have paired and bred with that of non-breeders (unpaired males), which have not paid a cost of reproduction. Results showed that survival rates of paired (65.0%) and unpaired (64.2%) males did not differ. However, when comparisons were restricted to paired males that definitely had nestlings, their survival rate (76.8%) was significantly higher than that of unpaired males, and the same was the case when comparisons were further restricted to paired males that had offspring recruiting to the population the next year (76.8% survived). Males breeding successfully are likely to be a biased subset of high quality males. In analyses of a subset of males that had bred successfully when young, there was no difference in survival of paired and unpaired individuals when these males were older. In conclusion, breeding male ortolan buntings did not appear to pay a cost of reproduction in terms of reduced survival to the next year compared to non-breeding males. These results may be explained by non-breeding males also incurring extra costs during the breeding season, and that costs of reproduction are not shared equally among sexes in the ortolan bunting and other bird species with biparental care.

繁殖成本被认为会影响个体存活或未来繁殖成功率。既往多数研究均围绕繁殖后代数量的自然变异与实验操控，评估繁殖成本相关议题。
圃鹀（ortolan bunting，Emberiza hortulana）是一种实行双亲育幼的雀形目鸟类，其挪威种群的性比存在显著偏倚：仅约半数雄性能够成功配对获得配偶，这为比较已配对繁殖雄性与未繁殖（未配对）雄性的存活情况提供了罕见契机——后者无需付出繁殖成本。
研究结果显示，已配对雄性（存活率65.0%）与未配对雄性（存活率64.2%）的存活率并无显著差异。然而当仅纳入确定育有雏鸟的配对雄性时，其存活率（76.8%）显著高于未配对雄性；若进一步限定为次年子代成功招募至种群的配对雄性，该结果同样成立（存活率76.8%）。
成功繁殖的雄性个体，往往属于高质量雄性中的偏倚性亚群。针对年轻时曾成功繁殖的雄性亚群开展的分析显示，当这些雄性步入成熟个体阶段后，已配对与未配对个体的存活率并无差异。
综上，与未繁殖雄性相比，繁殖期雄性圃鹀并未表现出因繁殖而导致次年存活率降低的繁殖成本。上述结果可通过以下机制解释：未繁殖雄性在繁殖季同样需要承担额外成本，且在圃鹀及其他实行双亲育幼的鸟类类群中，繁殖成本并非在两性间均匀分配。