Behavioural flexibility in migratory behaviour in a long‐lived large herbivore

Abstract

Migratory animals are predicted to enhance lifetime fitness by obtaining higher quality forage and/or reducing predation risk compared to non-migratory conspecifics. Despite evidence for behavioural flexibility in other taxa, previous research on large mammals has often assumed that migratory behaviour is a fixed behavioural trait. Migratory behaviour may be plastic for many species, although few studies have tested for individual-level flexibility using long-term monitoring of marked individuals, especially in large mammals such as ungulates. We tested variability in individual migratory behaviour using a 10-year telemetry data set of 223 adult female elk (Cervus elaphus) in the partially migratory Ya Ha Tinda population in Alberta, Canada. We used net squared displacement (NSD) to classify migratory strategy for each individual elk-year. Individuals switched between migrant and resident strategies at a mean rate of 15% per year, and migrants were more likely to switch than residents. We then tested how extrinsic (climate, elk/wolf abundance) and intrinsic (age) factors affected the probability of migrating, and, secondly, the decision to switch between migratory strategies. Over 630 individual elk-years, the probability of an individual elk migrating increased following a severe winter, in years of higher wolf abundance, and with increasing age. At an individual elk level, we observed 148 switching events of 430 possible transitions in elk monitored at least 2 years. We found switching was density-dependent, where migrants switched to a resident strategy at low elk abundance, but residents switched more to a migrant strategy at high elk abundance. Precipitation during the previous summer had a weak carryover effect, with migrants switching slightly more following wetter summers, whereas residents showed the opposite pattern. Older migrant elk rarely switched, whereas resident elk switched more frequently to migrate at older ages. Our results show migratory behaviour in ungulates is an individually variable trait that can respond to intrinsic, environmental and density-dependent forces. Different strategies had opposing responses to density-dependent and intrinsic drivers, providing a stabilizing mechanism for the maintenance of partial migration and demographic fitness in this population.

Migratory plasticity is not ubiquitous among large herbivores

“…We also evaluated the influence of age and reproductive status on switching behaviour and fidelity, because they are individually variable traits (Eggeman et al, 2016) and are expected to change depending upon state of the animal (Jachowski & Singh, 2015;Monteith et al, 2011;Mysterud et al, 2011;Singh et al, 2012). Upon initial capture for 142 animals in six of the study populations, we extracted the incisiform TA B L E 1 Study duration, sample sizes for animal and migration sequences, and monitoring duration of GPS-collared mule deer in nine study populations across the Intermountain West, USA canine using standardized methods to facilitate ageing via cementum annuli (Bleich et al, 2003;Swift et al, 2002).…”

“…The decision of whether to migrate often refers to facultative migration or "switching" behaviour, where animals may migrate one year, but not the next. However, several recent studies that monitored individual animals for multiple years have shown varying degrees of switching behaviour, including impala (Aepyceros melampus) (Gaidet & Lecomte, 2013), moose (Alces alces) (White, Barten, Crouse, & Crouse, 2014), roe deer (Capreolus capreolus) (Cagnacci et al, 2011;Gurarie et al, 2017;Peters et al, 2017), white-tailed deer (Odocoileus hemionus) (Fieberg, Kuehn, & Delgiudice, 2008;Sabine et al, 2002), red deer (Cervus elaphus) (Martin et al, 2018;Mysterud et al, 2011) and North American elk (Cervus canadensis) (Eggeman et al, 2016;Hebblewhite & Merrill, 2011). However, several recent studies that monitored individual animals for multiple years have shown varying degrees of switching behaviour, including impala (Aepyceros melampus) (Gaidet & Lecomte, 2013), moose (Alces alces) (White, Barten, Crouse, & Crouse, 2014), roe deer (Capreolus capreolus) (Cagnacci et al, 2011;Gurarie et al, 2017;Peters et al, 2017), white-tailed deer (Odocoileus hemionus) (Fieberg, Kuehn, & Delgiudice, 2008;Sabine et al, 2002), red deer (Cervus elaphus) (Martin et al, 2018;Mysterud et al, 2011) and North American elk (Cervus canadensis) (Eggeman et al, 2016;Hebblewhite & Merrill, 2011).…”

“…Although switching behaviour has been documented in a wide range of taxa, including fish, birds, amphibians and insects Grayson, Bailey, & Wilbur, 2011;Skov et al, 2011;Sutherland, 1998), researchers have traditionally assumed that the migratory status of large herbivores was fixed (Eggeman et al, 2016). Together, these studies led Eggeman et al (2016) to conclude that all large herbivores can, and do, switch between the two basic movement tactics of residency and migration. Together, these studies led Eggeman et al (2016) to conclude that all large herbivores can, and do, switch between the two basic movement tactics of residency and migration.…”

“…For instance, for some marine mammals, weak fidelity during migration may result in greater rewards in terms of mass gain during anomalous weather conditions, which are predicted to increase in frequency with climate change (Abrahms et al, 2018). Until recently, the extent of flexibility in migratory behaviours had not been widely explored in large herbivores (Eggeman et al, 2016), but such work is critical to understanding the adaptive capacity of migratory herbivores in a rapidly changing world (Shaw, 2016).…”

Advances and Environmental Conditions of Spring Migration Phenology of American White Pelicans

“…S1)48. Net squared displacement has been successfully used to estimate the migration timing and summer range of migratory ungulates tracked by GPS transmitters4950. We used the R function identify to determine the start and end locations of the net squared displacement plateau.…”