Abstract
AbstractAimGlobal declines in the populations of migratory species have been attributed largely to climate change and anthropogenic habitat change. However, the relative contribution of these factors on species’ breeding and non‐breeding ranges is unclear. Here, we present the first large‐scale assessment of the relative importance of climatic conditions and land cover on both the breeding and non‐breeding grounds in driving the long‐term population trends of migratory species.LocationEurope and Africa.MethodsWe use data on the long‐term population trends of 61 short‐ and 39 long‐distance migratory species of European breeding birds. We analyse these population trends in relation to changes in climate and land cover across species’ breeding and non‐breeding ranges over a 36‐year period, along with species’ migratory behaviour.ResultsThe population trends of European migratory birds appear to be more closely related to changes in climate than changes in land cover on their breeding grounds, but the converse is true on their non‐breeding grounds. While improvements in climate suitability across the breeding ranges of short‐distance migrants led to increasing population trends, the same was not true for long‐distance migrants. The combined effects of changes in climate and land cover account for approximately 40% of the variation in migratory species’ population trends, suggesting that factors other than climate and land cover as we have measured them, such as habitat quality, also affect the population trends of migrant birds.Main ConclusionsOver recent decades, population trends of most migrant species are most strongly related to climatic conditions on the breeding grounds but land cover change on the non‐breeding grounds. This suggests that management to stem the declines of migrant birds requires an integrated approach that considers all processes affecting migrant birds across their dynamic distributions throughout the year.
Highlights
Climate change is implicated in an emerging global trend whereby migratory species are experiencing more rapid rates of population decline than their resident counterparts (Runge et al, 2015; Studds et al, 2017; Wilcove & Wikelski, 2008)
Our models indicated that higher CSTb and LCSTnb, greater body mass and increased dispersion during the non-breeding season were all positively related to species’ population trends (Figure 2)
We have demonstrated that the variables of greatest importance for driving the long-term population trends of migratory species differ between their breeding and non-breeding grounds
Summary
Climate change is implicated in an emerging global trend whereby migratory species are experiencing more rapid rates of population decline than their resident counterparts (Runge et al, 2015; Studds et al, 2017; Wilcove & Wikelski, 2008). The dependence of migrants on conditions in multiple areas, and on the phenology of events in these areas, renders them more vulnerable to environmental changes than their resident counterparts (Finch, Pearce-Higgins, Leech, & Evans, 2014; Runge, Martini, Possingham, Willis, & Fuller, 2014) Elucidating drivers of their population change is further complicated by the need to understand in which of the various parts of the annual life cycle the population is critically limited (Ockendon, Hewson, Johnston, & Atkinson, 2012). We control for species’ habitat affinities because similar trends among species with shared habitat associations may indicate that processes affecting the condition of specific habitats that are not captured within the LCSTs, for example agricultural intensification, are affecting populations By analysing these effects separately for long- and short-distance migrants, we evaluate whether the drivers of population changes differ for different types of migrant birds
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