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Tuesday, January 26 • 4:20pm - 4:40pm
Brownian Bridge Movement Models Using Telemetry Data: A Case Study With Eastern Box Turtles Terrapene Carolina

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AUTHORS: Ethan J. Kessler*, Illinois Natural History Survey (INHS); Jason P. Ross, INHS; Christopher A. Phillips, INHS; Michael J. Dreslik, INHS

ABSTRACT: Accurate home range estimates inform management and are vital to studies of habitat use and selection. Currently, minimum convex polygons (MCP) and kernel density estimators (KDE) remain the predominant home range estimators for chelonian studies despite invalid assumptions (i.e. equal spatial distribution of points (MCP) and uncorrelated relocations (KDE)). The recent popularity of GPS satellite transmitters and automated telemetry systems has led to the development of new home range estimators to handle the numerous, spatially autocorrelated locations produced. One of these methods, Brownian bridge movement models (BBMM), uses the time between successive locations to incorporate movement behavior into the home range estimate. BBMM are most widely used in avian and mammalian studies using GPS satellite transmitter data, but are likely robust enough for wide use with smaller radio telemetry sample sizes. We investigated the application of BBMM using radio-telemetry data for 25 Eastern box turtles Terrapene carolina with an average of 92.8 radio-locations between May and November 2009. We calculated 50% and 95% BBMM for comparison with MCP and 50% and 95% KDE smoothed with the reference h value (KDE href). Despite the small sample size, the BBMM smoothing parameter reached convergence in all individuals, including one individual with only 32 relocations. The 95% KDE href produced the largest home range size followed by the MCP and 95% BBMM (F(2,72)=3.69, p=0.03). KDE href was also significantly larger than BBMM for estimates of 50% core areas (paired-t=-2.69, p=0.01). Additionally, many turtles utilized wooded corridors to move between forest patches. These corridors were represented in BBMM home range estimates whereas MCP included surrounding, unused habitats, and KDE href was simply unable to represent this behavior. Although the BBMM has a reputation as a data-hungry estimator, it can provide robust, biologically relevant results for chelonian radio-telemetry studies with realistic relocation schedules.

Tuesday January 26, 2016 4:20pm - 4:40pm EST