title: How many routes lead to migration? Comparison of methods to assess and characterize migratory movements.
abstract: Decreasing rate of migration in several species as a consequence of climate change and anthropic pressure, together with increasing evidence of space-use strategies intermediate between residency and complete migration, are very strong motivations to evaluate migration occurrence and features in animal populations. The main goal of this paper was to perform a relative comparison between methods for identifying and characterizing migration at the individual and population level on the basis of animal location data. We classified 104 yearly individual trajectories from five populations of three deer species as migratory or non-migratory, by means of three methods: seasonal home range overlap, spatio-temporal separation of seasonal clusters and the Net Squared Displacement (NSD) method. For migratory cases, we also measured timing and distance of migration and residence time on the summer range. Finally, we compared the classification in migration cases across methods and populations. All methods consistently identified migration at the population level, that is, they coherently distinguished between complete or almost complete migratory populations and partially migratory populations. However, in the latter case, methods coherently classified only about 50% of the single cases, that is they classified differently at the individual-animal level. We therefore infer that the comparison of methods may help point to 'less-stereotyped' cases in the residency-to-migration continuum. For cases consistently classified by all methods, no significant differences were found in migration distance, or residence time on summer ranges. Timing of migration estimated by NSD was earlier than by the other two methods, both for spring and autumn migrations. We suggest three steps to identify improper inferences from migration data and to enhance understanding of intermediate space-use strategies. We recommend (i) classifying migration behaviours using more than one method, (ii) performing sensitivity analysis on method parameters to identify the extent of the differences and (iii) investigating inconsistently classified cases as these may often be ecologically interesting (i.e. less-stereotyped migratory behaviours).
authors.affiliation: Biodiversity and Molecular Ecology Department, Research and Innovation Centre, Fondazione Edmund Mach, Via Mach 1, 38010, San Michele all'Adige, TN, Italy.|Organismic and Evolutionary Biology Department, Harvard University, 26 Oxford Street, Cambridge, MA, 02138, USA.
authors.forename: Francesca
authors.initials: F
authors.lastname: Cagnacci
authors.affiliation: Istituto dei Sistemi Compessi, Sezione di Firenze, via Madonna del Piano 10, 50019, Sesto Fiorentino, FI, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Focardi
authors.affiliation: Koloniestrasse 70, 13359, Berlin, Germany.
authors.forename: Anne
authors.initials: A
authors.lastname: Ghisla
authors.affiliation: Norwegian Institute for Nature Research (NINA), PO Box 5685 Sluppen, NO-7485, Trondheim, Norway.
authors.forename: Bram
authors.initials: B
authors.lastname: van Moorter
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada.
authors.forename: Evelyn H
authors.initials: EH
authors.lastname: Merrill
authors.affiliation: Department of Biology, University of Maryland, College Park, MD, 20742, USA.|School of Environmental and Forest Sciences, University of Washington, Seattle, WA, 98195, USA.
authors.forename: Eliezer
authors.initials: E
authors.lastname: Gurarie
authors.affiliation: Department of Research and Documentation, Bavarian Forest National Park, Freyunger Str 2, 94481, Grafenau, Germany.
authors.forename: Marco
authors.initials: M
authors.lastname: Heurich
authors.affiliation: Centre for Ecological and Evolutionary Synthesis, Department Biosciences, University of Oslo, PO Box 1066, Blindern, NO-0316, Oslo, Norway.
authors.forename: Atle
authors.initials: A
authors.lastname: Mysterud
authors.affiliation: Norwegian Institute for Nature Research (NINA), PO Box 5685 Sluppen, NO-7485, Trondheim, Norway.
authors.forename: John
authors.initials: J
authors.lastname: Linnell
authors.affiliation: Norwegian Institute for Nature Research (NINA), PO Box 5685 Sluppen, NO-7485, Trondheim, Norway.
authors.forename: Manuela
authors.initials: M
authors.lastname: Panzacchi
authors.affiliation: Norwegian Institute for Nature Research (NINA), PO Box 5685 Sluppen, NO-7485, Trondheim, Norway.
authors.forename: Roel
authors.initials: R
authors.lastname: May
authors.affiliation: Norwegian Institute for Nature Research (NINA), PO Box 5685 Sluppen, NO-7485, Trondheim, Norway.
authors.forename: Torgeir
authors.initials: T
authors.lastname: Nygård
authors.affiliation: Norwegian Institute for Nature Research (NINA), PO Box 5685 Sluppen, NO-7485, Trondheim, Norway.
authors.forename: Christer
authors.initials: C
authors.lastname: Rolandsen
authors.affiliation: Biodiversity and Molecular Ecology Department, Research and Innovation Centre, Fondazione Edmund Mach, Via Mach 1, 38010, San Michele all'Adige, TN, Italy.|Wildlife Biology Program, Department of Ecosystem and Conservation Science, University of Montana, Missoula, MT, 59812, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Hebblewhite
mesh_terms: D025041:Animal Migration; D000818:Animals; D003670:Deer / Q000502:physiology*; D004463:Ecology / Q000379:methods*; D005010:Ethology / Q000379:methods*; D005858:Germany; D006702:Homing Behavior; D009068:Movement; D009664:Norway; D012053:Reindeer / Q000502:physiology; D058998:Remote Sensing Technology / Q000662:veterinary; D012621:Seasons
keywords: Net Squared Displacement; adehabitat; home range overlap; movement patterns; red deer; reindeer; residence behaviour; roe deer; spatial clusters