Migration triggers in a large herbivore: Galápagos giant tortoises navigating resource gradients on volcanoes

Abstract

To understand how migratory behavior evolved and to predict how migratory species will respond to global environmental change it is important to quantify the fitness consequences of intra‐ and inter‐individual variation in migratory behavior. Intra‐individual variation includes behavioral responses to changing environmental conditions and hence behavioral plasticity in the context of novel or variable conditions. Inter‐individual variation determines the degree of variation on which selection can act and the rate of evolutionary responses to changes in average and extreme environmental conditions. Here we focus on variation in the partial migratory behavior of giant Galápagos tortoises (Chelonoidis spp.) and its energetic consequences. We evaluate the extent and mechanisms by which tortoises adjust migration timing in response to varying annual environmental conditions, and integrate movement data within a bioenergetic model of tortoise migration to quantify the fitness consequences of migration timing. We find strong inter‐individual variation in the timing of migration, which was not affected by environmental conditions prevailing at the time of migration but rather by average expectations estimated from multi‐annual averaged conditions. This variation is associated with an average annual loss in efficiency of ~15% relative to optimal timing based on year‐specific conditions. These results point towards a limited ability of tortoises to adjust the timing of their migrations based on prevailing (and, by extension, future) conditions, suggesting that the adaptability of tortoise migratory behavior to changing conditions is predicated more by past “normal” conditions than responses to prevailing, changing conditions. Our work offers insights into the level of environmental‐tuning in migratory behavior and a general framework for future research across taxa.

Tactical departures and strategic arrivals: Divergent effects of climate and weather on caribou spring migrations

“…), though this trend has also been observed for terrestrial herbivores (Bastille‐Rousseau et al. ). Analogous long‐range strategies have been observed for migratory red deer that “jump the green wave” to maximize resources at the end of their migration (Bischof et al.…”

“…In contrast, many long-distance migrants cannot rely on local information and must anticipate disparate, often unpredictable changes in the seasonality of abiotic conditions and vegetation phenology from great distances to encounter favorable conditions and exploit maximum resources. This is particularly true for birds (Both et al 2009, Møller et al 2010), many of which are shifting the timing of their arrival to breeding grounds to match changes in local climate and phenology (Cotton 2003, Marra et al 2005, Rubolini et al 2007, Barrett 2011, Ward et al 2016, though this trend has also been observed for terrestrial herbivores (Bastille-Rousseau et al 2019). Analogous long-range strategies have been observed for migratory red deer that "jump the green wave" to maximize resources at the end of their migration (Bischof et al 2012), and for zebras (Equus burchelli), that show evidence of memory-based forecasting of water resources (Bracis and Mueller 2017).…”

Accounting for space and uncertainty in real‐time location system‐derived contact networks

“…Data sets generated by RTLSs are incredibly versatile and can be used in conjunction with other geographic data (e.g., remotely sensed data) to answer a wide variety of ecological research questions pertaining to individual‐ and population‐level animal behaviors (Kays, Crofoot, Jetz, & Wikelski, 2015). Previous studies have used RTLS data to draw inferences about (a) animals' movement speed and tortuosity (Bastille‐Rousseau et al, 2019; Liu, Xu, & Jiang, 2015; Schiffner, Fuhrmann, Reimann, & Wiltschko, 2018), (b) energy expenditures (Williams et al, 2014), (c) habitat use (Keeley, Beier, & Gagnon, 2016; Thomson et al, 2017; Tsalyuk, Kilian, Reineking, & Marcus, 2019), (d) survival and mortality rates (Klaassen et al, 2013), (e) responses to environmental stimuli (Bastille‐Rousseau et al, 2019; Tsalyuk et al, 2019), and (f) interactions with other individuals, specific locations, or environmental substrates (Chen, Sanderson, White, Amrine, & Lanzas, 2013; Chen & Lanzas, 2016; Dawson, Farthing, Sanderson, & Lanzas, 2019; Spiegel, Leu, Sih, & Bull, 2016; Theurer et al, 2012).…”

Haematology and plasma biochemistry reference intervals for the critically endangered western Santa Cruz Galapagos tortoise (Chelonoidis porteri)

“…Much research has been conducted to assess the ecology, biology and genetics of giant tortoises, whereas very little is known about the health status of these species. Current threats include habitat loss and fragmentation, illegal trade, introduced and invasive species, global warming, egg loss due to introduced predators, disease, trauma and possibly antimicrobial resistance ( Blake et al , 2012 ; Ellis-Soto et al , 2017 ; Bastille-Rousseau et al , 2019 ; Nieto-Claudin et al , 2019 ). Several studies have been published to describe RI for chelonian species globally; however, there was only one study on giant tortoises describing haematology and blood biochemistry parameters for 32 giant tortoises ( Chelonoidis chathamensis ) at a captive-breeding facility on San Cristóbal Island ( Lewbart et al , 2018 ), and no morphological evaluation of blood cells was documented.…”