The main goal of this study was to investigate the effect of individual behavioral differences on the spatial ecology of western diamond-backed rattlesnakes. The main hypothesis was partially supported as bolder and more active individuals travelled more than shy, less active individuals during the non-mating season. Thus, shyer individuals increased their movement rate significantly more than bolder individuals during the mating season resulting in no significant difference in movement between personality types during the breeding season. Generally, these results support the pace-of-life syndrome hypothesis only during the non-breeding season.
Boldness had a significant effect on movement rate (m/day) during the non-mating season. Indeed, bolder individuals moved more on average than shyer individuals. The same relationship has been previously described in other species [19, 20]. For most of their time, rattlesnakes stay hidden in burrows or within vegetation to stay concealed from predators [51, 52]. When hunting, rattlesnakes stay immobile for long periods of time [53] rendering them difficult to spot by predators, even if the rattlesnake is not under the cover of vegetation [42]. Because of this, moving is risky for rattlesnakes as they are more likely to get killed while moving on the surface [54]. Although boldness has been correlated with habitat use [18], dispersal rate [44], and home range size [17] in other species, no significant correlation between boldness and home range size was found in this study. In the case of home range size, bolder individuals usually exhibit larger home range and core use area [18, 26] indicating a potential relationship between boldness and territoriality. Territoriality has been described in one species of snake [55], but generally snakes do not appear to be territorial. The lack of a relationship between boldness and home range size in the western diamond-backed rattlesnakes might be explained by their non-territorial nature.
Although activity did not have a significant effect on the total distance travelled according to the Bonferroni correction, the level of significance was still under 0.05. The Bonferroni correction has been subject to numerous critics, especially in the field of ecology (e.g. Moran 2003; García 2004). For this reason, the influence of activity is still discussed but these results must be interpreted with caution. Activity has been related to several spatial metrics in other species including core area size [58] and dispersal [59, 60]. In C. atrox, activity, boldness, and sociability form a behavioral syndrome [36] meaning that in this study, bolder individuals are also more active. In this study, active and bold individuals tend to travel longer distances at a faster rate than less active and shy individuals. These characteristics are commonly found in superficial (or fast) explorer individuals [61] showing that these results support the pace-of-life syndrome hypothesis [10]. Superficial explorers tend to move rapidly while being less sensitive to environmental stimuli and changes [16]. Superficial explorers reduce their stay at a specific spot, exploiting less resources [62]. Because of this, these individuals might need to travel longer distances to reach their resources requirements, even if it means taking more risks. On the other hand, less active and shy individuals are usually considered slow explorers, moving less and slower than fast explorers [61]. Slow explorers tend to carefully explore their environment, making them more sensitive to environmental variations [16]. These different behavioral types are maintained in the population as they each perform better in different conditions [62]. Indeed, slow explorers might be more successful than fast explorers when resources are unequally distributed on the landscape but might be outperformed by fast explorers when resources are unpredictable [16]. In general, boldness and activity are known to influence growth, survival, and reproduction success (reviewed in Réale et al. 2007). For example, bolder bighorn sheep (Ovis canadensis) males had higher lifetime reproductive success [63] and higher survival rates than shyer individuals [64]. Boldness also influenced positively body mass gain in several species [65, 66].While individuals were found to move differently across the landscape based on their personality during the non-mating season in this study, the biological implications of this difference remain to be investigated.
In this study, personality influenced the movement ecology of C. atrox only during the non-mating season (April-July), showing that this relationship was dependent on the reproductive state of this species. The non-mating season represents four out of the seven active months of this species, and thus personality influenced the majority of the active season. During the mating season, male rattlesnakes face a trade-off between searching for mates and hunting due to their ambush foraging strategy that requires they remain sedentary [67]. As a result, males usually choose to decrease their foraging activity to invest more in their reproductive output [67, 68]. Rattlesnake males actively locate females and as a result, often travel more during the mating season [37, 69]. The movement of males is closely linked to their reproductive success, and males who travel along straighter paths or longer distances tend to experience a higher frequency of mating events [69, 70]. Therefore, increased movement of all males regardless of personality type during the mating season might be a result of sexual selection to increase reproductive success [69].
While on average, males increased their movement during the mating season, the difference in movement rate varied between individuals and was dependent on boldness. Shyer individuals increased their movement rate significantly more than bolder individuals during the mating season. According to the pace-of-life syndrome hypothesis, slow explorers should be more responsive than superficial explorers to environmental and social changes, such as reproductive status of other individuals [16, 71, 72]. Thus, the results of this study support the pace-of-life syndrome hypothesis as slow explorers responded more to a change in reproductive status. Slow-explorers tend to act based upon prior knowledge from personal and social origins whereas fast-explorers tend to make decisions independently from information available [73, 74]. These differences might be explained by variation in the incorporation of information based on personality type [74] with slow-explorers being more behaviorally flexible than fast-explorers when incorporating information [75, 76]. These contrasting strategies can be beneficial or maladaptive depending on the environmental context [74]. Although using prior knowledge might generally be safer [77], especially in a more constant or resource-scarce environment, ignoring prior knowledge might be more rewarding, particularly in more variable and higher quality habitats [78, 79]. Male rattlesnakes are hypothesized to use three different strategies to find receptive females: 1) following scent-trails left by females; 2) using efficient search patterns to locate females; or 3) using prior experience to return to locations where females were previously found [80]. Scent-trailing does not appear to be an effective method to locate mates over extensive distances, as it largely relies on the chances of a male to encounter the trail of a female. In line with evidence showing that slow-explorers tend to base their decisions on prior knowledge and social cues [74], slow-explorer rattlesnakes might use a combination of all three strategies to locate mates leading to an increase in movement rate during the mating season. On the other hand, fast-explorers are less accurate when incorporating information in their decision-making processes [74].
In conclusion, this study demonstrated that western diamond-backed rattlesnakes exhibit differences in their movement ecology according to their personality. The effect of behavioral differences on movement was dependent on the reproductive status of individuals. During the mating season, males adjusted their movements, with shy individuals showing a larger increase in movement rate than bold individuals. The results of this study suggest the existence of two different strategies for resources acquisition, thus supporting the pace-of-life syndrome hypothesis under specific contexts (i.e. non-breeding season) [10, 16]. While this study provides new insights into the relationship between personality and ecology, further research is required to validate and uncover the mechanisms and consequences of these strategies for this species.