stables isotopes, and tracking: unraveling the trophic ecology of a winter-breeding storm petrel (Hydrobates castro) with a multimethod approach. Marine Biology 167 ( 14) , -

The global decline of many insect communities (Sánchez-Bayo & Wyckhuys, 2019; Saunders et al., 2020; Wagner, 2020) is negatively affecting higher trophic levels such as mammals, amphibians, and birds (Hallmann et al., 2017). Populations of avian aerial insectivores, such as swallows, swifts, and nightjars, are believed to be declining due to the loss of their prey (Ng et al., 2018; Smith et al., 2015). In most cases, the diet composition of these predatory species is unknown and it is still unclear when and where they collect their food within their summer home-range. With the advent of modern tracking technologies and molecular techniques, we have the opportunity to combine information on the space use of such species (

Changes in phenology and distribution are being widely reported for many migratory species in response to shifting environmental conditions. Understanding these changes and the situations in which they occur can be aided by understanding consistent individual differences in phenology and distribution and the situations in which consistency varies in strength or detectability. Studies tracking the same individuals over consecutive years are increasingly reporting migratory timings to be a repeatable trait, suggesting that flexible individual responses to environmental conditions may contribute little to population‐level changes in phenology and distribution. However, how this varies across species and sexes, across the annual cycle and in relation to study (tracking method, study design) and/or ecosystem characteristics is not yet clear. Here, we take advantage of the growing number of publications in movement ecology to perform a phylogenetic multilevel meta‐analysis of repeatability estimates for avian migratory timings to investigate these questions. Of 2,433 reviewed studies, 54 contained suitable information for meta‐analysis, resulting in 177 effect sizes from 47 species. Individual repeatability of avian migratory timings averaged 0.414 (95% confidence interval: 0.3–0.5) across landbirds, waterbirds and seabirds, suggesting consistent individual differences in migratory timings is a common feature of migratory systems. Timing of departure from the non‐breeding grounds was more repeatable than timings of arrival at or departure from breeding grounds, suggesting that conditions encountered on migratory journeys and outcome of breeding attempts can influence individual variation. Population‐level shifts in phenology could arise through individual timings changing with environmental conditions and/or through shifts in the numbers of individuals with different timings. Our findings suggest that, in addition to identifying the conditions associated with individual variation in phenology, exploring the causes of between‐individual variation will be key in predicting future rates and directions of changes in migratory timings. We therefore encourage researchers to report the within‐ and between‐ individual variance components underpinning the reported repeatability estimates to aid interpretation of migration behaviour. In addition, the lack of studies in the tropics means that levels of repeatability in less strongly seasonal environments are not yet clear.