Estimating migration parameters of individuals and populations is vital for their conservation and management. Studies on animal movements and migration often depend upon location data from tracked animals and it is important that such data are appropriately analyzed for reliable estimates of migration and effective management of moving animals. The Net Squared Displacement (NSD) approach for modelling animal movement is being increasingly used as it can objectively quantify migration characteristics and separate different types of movements from migration. However, the ability of NSD to properly classify the movement patterns of individuals has been criticized and issues related to study design arise with respect to starting locations of the data/animals, data sampling regime and extent of movement of species. We address the issues raised over NSD using tracking data from 319 moose (Alces alces) in Sweden. Moose is an ideal species to test this approach, as it can be sedentary, nomadic, dispersing or migratory and individuals vary in their extent, timing and duration of migration. We propose a two-step process of using the NSD approach by first classifying movement modes using mean squared displacement (MSD) instead of NSD and then estimating the extent, duration and timing of migration using NSD. We show that the NSD approach is robust to the choice of starting dates except when the start date occurs during the migratory phase. We also show that the starting location of the animal has a marginal influence on the correct quantification of migration characteristics. The number of locations per day (1-48) did not significantly affect the performance of non-linear mixed effects models, which correctly distinguished migration from other movement types, however, high-resolution data had a significant negative influence on estimates for the timing of migrations. The extent of movement, however, had an effect on the classification of movements, and individuals undertaking short- distance migrations can be misclassified as other movements such as sedentary or nomadic. Our study raises important considerations for designing, analysing and interpreting movement ecology studies, and how these should be determined by the biology of the species and the ecological and conservation questions in focus.
Notes
Cites: Ecol Lett. 2009 May;12(5):395-40819379134
Cites: Ecol Lett. 2008 Jan;11(1):63-7717897327
Cites: Ecol Appl. 2009 Dec;19(8):2016-2520014575
Cites: Philos Trans R Soc Lond B Biol Sci. 2010 Jul 27;365(1550):2157-6220566493
Cites: Philos Trans R Soc Lond B Biol Sci. 2010 Jul 27;365(1550):2303-1220566506
Cites: PLoS One. 2011;6(1):e1637021283536
Cites: J Anim Ecol. 2011 Mar;80(2):466-7621105872
Cites: PLoS One. 2012;7(5):e3652722570722
Cites: Ecol Appl. 2012 Oct;22(7):2007-2023210316
Cites: PLoS One. 2013;8(5):e6454823691246
Cites: Ecology. 2013 Jun;94(6):1245-5623923485
Cites: PLoS One. 2013;8(10):e7567324130732
Cites: Nat Commun. 2013;4:268824162104
Cites: Ecology. 2014 Jan;95(1):225-3724649661
Cites: PLoS One. 2014;9(4):e9475024722396
Cites: Am Nat. 2014 May;183(5):E154-6724739204
Cites: Biol Lett. 2014 Jun;10(6). pii: 20140379. doi: 10.1098/rsbl.2014.037924942710
Cites: PLoS One. 2015;10(4):e012475425905640
Cites: Science. 2015 Jun 12;348(6240):aaa247826068858
Cites: Science. 2015 Jun 12;348(6240):125564226068859