Seasonal migration is intrinsically connected to the balance of survival and reproduction, but whether migratory behavior influences species’ position on the slow-fast continuum of life history is poorly understood. We found that boreal-breeding birds that migrate long distances exhibit higher annual adult survival and lower annual reproductive investment relative to co-distributed boreal species that migrate shorter distances to winter closer to their breeding grounds. Our study uses “vital rates” data on reproductive output and survivorship compiled from the literature for a species assemblage of 45 species of mostly passerine birds. These species breed sympatrically in North American boreal forests but migrate to a diversity of environments for the northern winter. After controlling for body size and phylogeny, migration distance and apparent annual adult survival are positively related across species. Both migration distance and survival are positively correlated with wintering in environments that are warmer, wetter, and greener. At the same time, longer migrations are associated with reduced time spent on the breeding grounds, lower clutch sizes, and lower fecundity (clutch size × maximum number of broods per year). Although seasonal migration is often associated with high mortality, our results suggest that long-distance migration imposes selection pressures that both confer and demand high adult survival rates. That is, owing to the reproductive cost of long-distance migration, this strategy can only persist if balanced by high adult survival. Our study supports the idea that migration evolves to promote survival of species breeding in seasonal environments. In boreal birds, the evolution of the longest migrations yields the highest survival, but at an inherent cost to annual fecundity. Our results therefore reveal migratory distance as a fundamental axis of the slow-fast continuum that predicts, and is inextricable from, the balance of survival and reproduction.

中文翻译：

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迁徙距离是北方鸟类生活史慢快连续体的基本轴

季节性迁徙与生存和繁殖的平衡有着内在的联系，但迁徙行为是否会影响物种在生命史慢快连续体中的位置却知之甚少。我们发现，长距离迁徙的北方繁殖鸟类表现出较高的年度成虫存活率和较低的年度繁殖投资，而共同分布的北方物种相对于较短距离迁移到靠近其繁殖地的冬季。我们的研究使用从文献中汇编的关于繁殖产量和存活率的“生命率”数据，用于 45 种主要是雀形目鸟类的物种组合。这些物种在北美北方森林中同域繁殖，但在北部冬季迁移到多样化的环境中。在控制了体型和系统发育后，迁移距离和成年表观年存活率在物种间呈正相关。迁徙距离和生存都与在更温暖、更潮湿和更绿色的环境中越冬呈正相关。同时，迁徙时间越长，在繁殖地停留的时间越短，离合器尺寸越小，繁殖力越低（离合器尺寸×每年的最大育雏数量）。尽管季节性迁徙通常与高死亡率相关，但我们的研究结果表明，长距离迁徙会带来选择压力，既赋予并要求高成人存活率。也就是说，由于长距离迁徙的繁殖成本，这种策略只有在成年人存活率高的情况下才能持续下去。我们的研究支持这样的观点，即迁移进化以促进季节性环境中物种繁殖的生存。在北方鸟类中，迁徙时间最长的进化产生了最高的存活率，但其固有的成本是每年的繁殖力。因此，我们的研究结果揭示了迁徙距离是慢-快连续体的基本轴，它预测了生存和繁殖的平衡，并且与此密不可分。