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A novel method for detecting extra-home range movements (EHRMs) by animals and recommendations for future EHRM studies

Citation

Jacobsen, Todd; Wiskirchen, Kevyn; Ditchkoff, Stephen (2020), A novel method for detecting extra-home range movements (EHRMs) by animals and recommendations for future EHRM studies, Dryad, Dataset, https://doi.org/10.5061/dryad.jsxksn05t

Abstract

Infrequent, long-distance animal movements outside of typical home range areas provide useful insights into resource acquisition, gene flow, and disease transmission within the fields of conservation and wildlife management, yet understanding of these movements is still limited across taxa. To detect these extra-home range movements (EHRMs) in spatial relocation datasets, most previous studies compare relocation points against fixed spatial and temporal bounds, typified by seasonal home ranges (referred to here as the “Fixed-Period” method). However, utilizing home ranges modelled over fixed time periods to detect EHRMs within those periods likely results in many EHRMs going undocumented, particularly when an animal’s space use changes within that period of time. To address this, we propose a novel, “Moving-Window” method of detecting EHRMs through an iterative process, comparing each day’s relocation data to the preceding period of space use only. We compared the number and characteristics of EHRM detections by both the Moving-Window and Fixed-Period methods using GPS relocations from 33 white-tailed deer (Odocoileus virginianus) in Alabama, USA. The Moving-Window method detected 1.5 times as many EHRMs as the Fixed-Period method and identified 120 unique movements that were undetected by the Fixed-Period method, including some movements that extended nearly 5 km outside of home range boundaries. Additionally, we utilized our EHRM dataset to highlight and evaluate potential sources of variation in EHRM summary statistics stemming from differences in definition criteria among previous EHRM literature. We found that this spectrum of criteria identified between 15.6% and 100.0% of the EHRMs within our dataset. We conclude that variability in terminology and definition criteria previously used for EHRM detection hinders useful comparisons between studies. The Moving-Window approach to EHRM detection introduced here, along with proposed methodology guidelines for future EHRM studies, should allow researchers to better investigate and understand these behaviors across a variety of taxa.

Methods

This dataset was collected by deploying store-on-board GPS collars on free-ranging white-tailed deer in Alabama. Data was collected from the collars and compiled. Raw data (included here in the repository) were processed in R to create home ranges for both the Moving-Window method and the Fixed-Period method described in the article. Home ranges and associated point data were analyzed to detect extra-home range movements. Processed data from the extra-home range movement analysis were used to perform statistical analyses as well as create tables and figures.

Usage Notes

There are no missing values in this dataset.

Funding

Alabama Division of Wildlife and Freshwater Fisheries

Auburn University

The Westervelt Company

Timothy Couvillion

Bradley Bishop

Jerry Gaddy