Data from: Body reserves persist as fitness correlate in a long-distance migrant released from food constraints

Long-distance migratory birds rely on acquisition of body reserves to fuel their migration and reproduction. Breeding success depends on the amount of body reserve acquired prior to migration, which is thought to increase with access to food at the fuelling site. Here we studied how food abundance during fuelling affected time budgets and reproductive success. In a regime of plenty, we expected that (1) limitations on food harvesting would become lifted, allowing birds to frequently idle, and (2) that birds would reach sufficient fuel loads, such that departure weight would no longer affect reproductive success. Our study system comprised brent geese (Branta b. bernicla) staging on high-quality agricultural pastures. Fuelling conditions were assessed by a combination of high-resolution GPS-tracking, acceleration-based behavioural classification, thermoregulation modelling, and measurements of food digestibility and excretion rates. Mark-resighting analysis was used to test for correlations between departure weight and offspring recruitment. Our results confirm that birds loafed extensively, actively postponed fuelling in early spring, and took frequent digestion pauses, suggesting that traditional time constraints on harvest and fuelling rates are absent on modern-day fertilized grasslands. Nonetheless, departure weight remained correlated with recruitment success. The persistence of this correlation after a prolonged stopover with access to abundant high-quality food, suggests that between-individual differences in departure condition are not so much enforced by food quality and availability during stopover, but reflect individual quality and longer-lived life-history traits, such as health status and digestive capacity, which may be developed before the fuelling period.

长途迁徙鸟类需积累体内储备以支撑迁徙与繁殖活动。繁殖成功率取决于迁徙前积累的体内储备量，而该储备量被认为会随着在补给停歇地获取食物的机会增加而提升。本研究探讨了补给阶段食物丰度如何影响鸟类的时间分配与繁殖成功率。在食物充足的环境中，我们提出两项预期：其一，食物获取的限制将被解除，鸟类得以频繁闲栖休息；其二，鸟类能够积累足够的身体储备，使得离迁体重不再对繁殖成功率产生影响。本研究的研究对象为在优质农业牧场中途停歇的指名亚种黑雁（Branta b. bernicla）。本研究通过高分辨率GPS追踪、基于加速度的行为分类、体温调节模型构建，以及食物消化率与排泄速率测定的组合方法，对补给停歇的环境条件进行评估。研究采用标记重见分析（mark-resighting analysis）方法，检验离迁体重与后代招募率之间的相关性。研究结果证实，黑雁会大量闲栖、在早春主动推迟补给行为，并频繁暂停进食以进行消化，这表明在现代施肥草地中，传统的觅食速率与补给速率的时间限制已不复存在。尽管如此，离迁体重仍与招募成功率显著相关。在拥有充足优质食物的长期停栖之后，该相关性依然存在，这表明个体间离迁状态的差异，并非主要由停栖期间的食物质量与可获得性所决定，而是反映了个体自身质量以及寿命相关的生活史特征——例如健康状况与消化能力——这些特征或可在补给期之前就已形成。