Arnekleiv Øyvind, Eldegard Katrine, Moa Pål F, Eriksen Lasse F, Nilsen Erlend B
Faculty of Environmental Sciences and Natural Resource Management Norwegian University of Life Sciences (NMBU) Ås Norway.
Faculty of Biosciences and Aquaculture Nord University Steinkjer Norway.
Ecol Evol. 2022 Mar 10;12(3):e8690. doi: 10.1002/ece3.8690. eCollection 2022 Mar.
Partial migration, where a portion of the population migrates between winter and summer (breeding) areas and the rest remain year-round resident, is a common phenomenon across several taxonomic groups. Several hypotheses have been put forward to explain why some individuals migrate while others stay resident, as well as the fitness consequences of the different strategies. Yet, the drivers and consequences of the decision to migrate or not are poorly understood.We used data from radio-tagged female ( = 73) willow ptarmigan in an alpine study area in Central Norway to test if (i) the decision to migrate was dependent on individual state variables (age and body weight), (ii) individuals repeated migratory decisions between seasons, and (iii) the choice of migratory strategy was related to reproductive success.Partially supporting our prediction that migratory strategy depends on individual state, we found that juvenile birds with small body sizes were more likely to migrate, whereas large juveniles remained resident. For adult females, we found no relationship between the decision to migrate or stay resident and body weight. We found evidence for high individual repeatability of migratory decision between seasons. Migratory strategy did not explain variation in clutch size or nest fate among individuals, suggesting no direct influence of the chosen strategy on reproductive success.Our results indicate that partial migration in willow ptarmigan is related to juvenile body weight, and that migratory behavior becomes a part of the individual life history as a fixed strategy. Nesting success was not affected by migratory strategy in our study population, but future studies should assess other traits to further test potential fitness consequences.
部分迁移是指一部分种群在冬季和夏季（繁殖）区域之间迁徙，而其余部分则全年留居，这是多个分类群中常见的现象。已经提出了几种假说来解释为什么一些个体迁徙而另一些个体留居，以及不同策略对适应性的影响。然而，决定迁徙与否的驱动因素和后果仍知之甚少。我们利用挪威中部一个高山研究区域中无线电追踪的73只雌性柳雷鸟的数据，来检验：（i）迁徙的决定是否取决于个体状态变量（年龄和体重）；（ii）个体在不同季节之间是否重复做出迁徙决定；（iii）迁徙策略的选择是否与繁殖成功率相关。我们部分支持了迁徙策略取决于个体状态这一预测，发现体型较小的幼鸟更有可能迁徙，而体型较大的幼鸟则留居。对于成年雌性，我们发现迁徙或留居的决定与体重之间没有关系。我们发现有证据表明个体在不同季节之间的迁徙决定具有高度的重复性。迁徙策略并不能解释个体之间窝卵数或巢命运的差异，这表明所选策略对繁殖成功率没有直接影响。我们的结果表明，柳雷鸟的部分迁移与幼鸟体重有关，并且迁徙行为作为一种固定策略成为个体生活史的一部分。在我们的研究种群中，筑巢成功率不受迁徙策略的影响，但未来的研究应该评估其他特征，以进一步测试潜在的适应性后果。
