Changepoint analysis: a new approach for revealing animal movements and behaviors from satellite telemetry data

Abstract

Abstract. While telemetry is an invaluable tool for tracking animal movement patterns, the data generated by this technique is often challenging to interpret. Here, we addressed this issue by developing a novel method, based on changepoint analysis, which incorporated both the horizontal and vertical movement metrics and compared this output to that from a switching state-space model (SSSM) that categorized behavior based on horizontal movement metrics. We deployed 20 satellite transmitters on postnesting loggerhead turtles at Rethymno, Crete, Greece between 2010 and 2011 to monitor their at-sea behavior. We used both models to identify behavioral changes, such as the switches from migration to foraging, and from foraging to overwintering. The satellite-tracked turtles exhibited three discrete migratory strategies, with 9 turtles migrating southwards to the coast of northern Africa, 6 turtles migrating northwards into the Aegean Sea, and 4 turtles remaining resident in the waters of Crete. The SSSM readily identified the switch from transiting to ARS behavior in most animals, but the CPA model was able to distinguish multiple modes and more subtle shifts in behavior corresponding with shifts from migration to foraging to overwintering behaviors. We have shown that by incorporating vertical movement metrics into the analysis of telemetry data, previously hidden shifts in behavior can be revealed. The resulting increase in ability to discern complex behavioral patterns of animals remotely will likely yield better management and conservation decisions for a wide array of organisms.

Spatial ecology of loggerhead turtles: Insights from stable isotope markers and satellite telemetry

“…It is estimated that there are approximately 16,000 adult loggerhead turtles in the Mediterranean of which ~3,500 females nest annually (Casale & Heppell, 2016). The major foraging regions for these nesting females have been identified using flipper tag returns and satellite telemetry and include the northern Adriatic Sea, Aegean Sea, Turkey, Egypt and the Tunisian Plateau (Broderick, Coyne, Fuller, Glen, & Godley, 2007;Godley, Broderick, Glen, & Hays, 2003;Hays, Fossette, Katselidis, Mariani, & Schofield, 2010;Hays, Mazaris, & Schofield, 2014;Lazar, Margaritoulis, & Tvrtkovic, 2004;Margaritoulis & Rees, 2011;Patel et al, 2015;Schofield et al, 2013;Snape et al, 2016;Zbinden, Aebischer, Margaritoulis, & Arlettaz, 2008;Zbinden et al, 2011; see also reviews by Margaritoulis et al, 2003;Luschi & Casale, 2014;Casale et al, 2018). However, this information currently exists for only a small sample of these populations.…”

Coastal leatherback turtles reveal conservation hotspot

“…The movements of these coastally foraging loggerhead turtles tend to be far more direct than their oceanic counterparts19 and many often closely follow the coastal line20. Moreover, these coastal migrations tend to be shorter and the shallow-water foraging areas are often relatively localized and consistent between years2122.…”

Videography Reveals In-Water Behavior of Loggerhead Turtles (Caretta caretta) at a Foraging Ground

“…First, the development of an ethogram for loggerheads at a foraging ground may provide a standard by which researchers can compare behaviors across populations. As the use satellite telemetry increased, researchers developed analytical tools to allow for easy comparison of data (e.g., Jonsen et al, 2007;Dodge et al, 2014;Patel et al, 2015b;Bestley et al, 2015). We expect a similar trend to occur as the use of videography increases in marine research.…”