title: Migratory diversity predicts population declines in birds.
abstract: Declines in migratory species are a pressing concern worldwide, but the mechanisms underpinning these declines are not fully understood. We hypothesised that species with greater within-population variability in migratory movements and destinations, here termed 'migratory diversity', might be more resilient to environmental change. To test this, we related map-based metrics of migratory diversity to recent population trends for 340 European breeding birds. Species that occupy larger non-breeding ranges relative to breeding, a characteristic we term 'migratory dispersion', were less likely to be declining than those with more restricted non-breeding ranges. Species with partial migration strategies (i.e. overlapping breeding and non-breeding ranges) were also less likely to be declining than full migrants or full residents, an effect that was independent of migration distance. Recent rates of advancement in Europe-wide spring arrival date were greater for partial migrants than full migrants, suggesting that migratory diversity may also help facilitate species responses to climate change.
authors.affiliation: School of Environmental Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK.
authors.forename: James J
authors.initials: JJ
authors.lastname: Gilroy
authors.affiliation: School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Gill
authors.affiliation: BirdLife International, Wellbrook Court, Cambridge, CB30NA, UK.|Department of Zoology, University of Cambridge, Downing St, Cambridge, CB23EJ, UK.
authors.forename: Stuart H M
authors.initials: SH
authors.lastname: Butchart
authors.affiliation: BirdLife International, Wellbrook Court, Cambridge, CB30NA, UK.
authors.forename: Victoria R
authors.initials: VR
authors.lastname: Jones
authors.affiliation: School of Environmental Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK.
authors.forename: Aldina M A
authors.initials: AM
authors.lastname: Franco
mesh_terms: D063147:Animal Distribution; D025041:Animal Migration; D000818:Animals; D001717:Birds / Q000502:physiology*; D057231:Climate Change; D005060:Europe; D011157:Population Dynamics; D012621:Seasons
keywords: Afrotropical migrants; European birds; behavioural plasticity; climate change; migratory strategy; partial migration; population trends