The behavioural consequences of translocation: how do invasive cane toads (Rhinella marina) respond to transport and release to novel environments?

Abstract: Invasive species must respond appropriately to novel habitats as they expand their ranges. The degree of habitat novelty is likely to be the highest immediately following human-mediated range-expansion, which can move an individual very large distances beyond its home range within a short space of time. How does translocation affect those critically important initial colonists? We collected cane toads (Rhinella marina) in eastern Australia in heath and woodland habitats, simulated either short-distance or long-distance transport (level of transport stress) and then either returned toads to their exact collection point or reciprocally translocated them to a novel site. Following release, we radio-tracked toads for 5 days and recorded their shelter types and microhabitat use daily. We also examined the thermal and hydric conditions experienced by toads and tested if prey intake, stomach mass and body condition of translocated toads differed from those of resident conspecifics. Translocated toads used different types of diurnal shelters, were more exposed by day and experienced higher diurnal temperatures (but not more desiccating conditions). Analysis of stomach contents indicated that translocation per se did not reduce feeding rates, nor reduce body condition. However, toads exposed to higher transport stress (simulating long-distance displacement) exhibited changes to body condition and hydric balance. Shifts in toad shelter site use induced by translocation may increase the toads’ visibility to diurnal predators, thereby reducing toad survival but also exacerbating the ecological impact of toads during the initial phase of post-translocation dispersal. Significance statement: Each stage of the invasion process poses unique challenges for invading taxa, and very few species possess the full suite of behavioural, physiological or morphological traits required to pass through all stages of the invasion pathway. Although the study of invasion biology has grown exponentially, most research has focused on the determinants of invasion success during the later stages of establishment and spread, neglecting the earlier stages of transport and introduction. Understanding how species respond to all stages of the invasion process can clarify the non-random traits that allow certain species to become successful invaders.