title: Different location sampling frequencies by satellite tags yield different estimates of migration performance: pooling data requires a common protocol.
abstract: BACKGROUND
  Migration research is in rapid expansion and increasingly based on sophisticated satellite-tracking devices subject to constant technological refinement, but is still ripe with descriptive studies and in need of meta-analyses looking for emergent generalisations. In particular, coexistence of studies and devices with different frequency of location sampling and spatial accuracy generates doubts of data compatibility, potentially preventing meta-analyses. We used satellite-tracking data on a migratory raptor to: (1) test whether data based on different location sampling frequencies and on different position subsampling approaches are compatible, and (2) seek potential solutions that enhance compatibility and enable eventual meta-analyses.
  
  
  RESULTS
  We used linear mixed models to analyse the differences in the speed and route length of the migration tracks of 36 Black kites (Milvus migrans) satellite-tagged with two different types of devices (Argos vs GPS tags), entailing different regimes of position sampling frequency. We show that different location sampling frequencies and data subsampling approaches generate large (up to 33%) differences in the estimates of route length and migration speed of this migratory bird.
  
  
  CONCLUSIONS
  Our results show that the abundance of locations available for analysis affects the tortuosity and realism of the estimated migration path. To avoid flaws in future meta-analyses or unnecessary loss of data, we urge researchers to reach an agreement on a common protocol of data presentation, and to recognize that all transmitter-based studies are likely to underestimate the actual distance traveled by the marked animal. As ecological research becomes increasingly technological, new technologies should be matched with improvements in analytical capacity that guarantee data compatibility.
authors.affiliation: Department of Conservation Biology, Estación Biológica de Doñana, Consejo Superior de Investigación Científica, Sevilla, Spain. a.tanferna@ebd.csic.es
authors.forename: Alessandro
authors.initials: A
authors.lastname: Tanferna
authors.forename: Lidia
authors.initials: L
authors.lastname: López-Jiménez
authors.forename: Julio
authors.initials: J
authors.lastname: Blas
authors.forename: Fernando
authors.initials: F
authors.lastname: Hiraldo
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Sergio
mesh_terms: D025041:Animal Migration; D000818:Animals; D001717:Birds; D040362:Geographic Information Systems / Q000295:instrumentation; D016014:Linear Models; D017215:Satellite Communications / Q000295:instrumentation