Animal movement behaviors, such as natal dispersal, migration, and territoriality, are important components in the life history and ecological interactions of a species (Nathan, 2008). However, when animals undergo involuntary movement such as translocation to an unfamiliar, novel area, their natural movement behavior can be substantially altered (Heidinger et al., 2009; Le Gouar et al., 2012). Some individuals may exhibit homing behavior, even when released extremely long distances from their place of origin (Dickens et al., 2010). Translocated individuals may be forced to settle in lower-quality habitats (Burns, 2005), disperse if territorial resident conspecifics already occupy high-quality habitat (McNicol et al., 2020), or move away from their release sites in search of mates (Mihoub et al., 2011). In addition, animals may be translocated in response to human–wildlife conflict, but they can again become problem individuals if released in an area that is too small to account for long-range movements or has inadequate resources (Weilenmann et al., 2010; Le Gouar et al., 2012). Difficulties with animal behavior post-translocation, primarily movement or dispersal activities, are some of the most common obstacles to translocation success (Berger-Tal et al., 2020). Therefore, identifying movement patterns post-translocation can help to set expectations and anticipate behavioral responses in future translocation efforts, and ultimately guide conservation and management.

Beaver (American beaver, Castor canadensis, and Eurasian beaver, C. fiber) translocation is a popular method of human-wildlife conflict mitigation and ecosystem restoration. Once overexploited during the fur trade of the 1700s and 1800s (Baker and Hill, 2003; Halley et al., 2021), beaver populations have now recovered in some areas and come in close contact with humans, sometimes causing unwanted flooding, damaging trees, and jeopardizing infrastructure. Translocation provides an alternative method to lethal control by removing beavers from conflict situations and allowing them the opportunity to play a critical role in restoration initiatives. American and Eurasian beavers are ecologically similar (Rosell et al., 2005), and as ecosystem engineers, both species can significantly alter the system they inhabit, primarily through dam building (Mills et al., 1993; Larsen et al., 2021). Beaver dams retain water and mitigate the effects of drought, add heterogeneity to stream channels, impact riparian vegetation, and benefit many other species (Naiman et al., 1988; Rosell et al., 2005; Pollock et al., 2014). However, retaining translocated beavers at a targeted site and encouraging the initiation of passive restoration through dam-building can be challenging, and translocated individuals may not behave similarly to naturally occurring, dam-building beavers, at least initially (Pilliod et al., 2018; Nash et al., 2021).

Beavers are central-place foragers, and dams are most commonly built by territorial colonies to create pools as cover near their lodge or burrow for predator avoidance and transport of wood; beavers rarely build dams during natal dispersal or transience (DeStefano et al., 2006; McClintic et al., 2014b; Ritter, 2018). The home range of established beavers typically covers 1.6–3.9 river kilometers (Breck et al., 2001; Herr and Rosell, 2004; Havens et al., 2013), while dispersing subadult beavers typically travel 3.5–19.8 km before settling (Beer, 1955; Sun et al., 2000; Ritter, 2018). Autonomous displacement recorded for translocated beavers ranges widely from 3.3 to 238 km, leading to variable dam-building success post-translocation (Hibbard, 1958; McKinstry and Anderson, 2002; Petro et al., 2015).

Beavers can play a vital role in desert rivers, sustaining water and increasing habitat complexity with their dams, especially because many arid systems have become imperiled by altered flow regimes and drought, habitat simplification, invasive species, and climate change (Harper, 2001; Stromberg, 2001; Mott Lacroix et al., 2017). However, the ecology of naturally occurring (hereafter, resident) beavers is understudied in desert rivers, and few translocation studies have been conducted in such systems (Gibson and Olden, 2014; Barela and Frey, 2016). Further, post-release movement behavior of translocated beavers, into a novel degraded desert river where resources may be more patchy, scarce, and unpredictable, may be different from other environments where the majority of beaver studies have occurred (Gibson and Olden, 2014; Barela and Frey, 2016).

We investigated the post-release movements of translocated American beavers (hereafter, beavers) on multiple spatiotemporal scales for 6 months post-release, using resident beavers for baseline comparison of movement behavior. We hypothesized that, at a landscape scale, translocated beavers would initially move farther and more quickly than resident adult (RA) beavers, similar to subadult beavers during dispersal. Farther and faster movement of translocated beavers was expected since they would likely be exploring their novel environment, potentially searching for a mate and a suitable site to settle, whereas RA beavers have established territories and would not need to move as far or as quickly. We also hypothesized translocated beavers would initially be more active than adult resident beavers on a fine-scale (1-h sampling sessions), continuously exploring their new environment, leading to faster movement speeds. In contrast, resident beavers using a familiar territory with set activity patterns would result in slower movement speeds. Our final hypothesis is that after establishing territories, translocated beavers would eventually settle into similar fine- and coarse-scale movement patterns that are similar to territorial adult resident beavers. A better understanding of the movement patterns of translocated beavers in this novel system can help develop an expectation framework of beaver movement behavior for future beaver-assisted restoration efforts in desert systems.

We captured and PIT-tagged 41 translocated beavers and fit 35 translocated beavers (21 adults, 14 subadults) with radio transmitters. We PIT-tagged 16 resident beavers and fit 12 resident beavers with radio transmitters (9 adults, 3 subadults). We censored three additional resident beavers from analyses because they died from capture- or processing-related events. We released resident beavers at their capture sites, at Cottonwood Wash (2019; n = 3, 2 adults and 1 subadult) and in the Price River (2019 and 2020; n = 13, 8 adults and 5 subadults). We released 36 translocated beavers (76.5%) as family groups or as pairs formed during quarantine. We released 33 translocated beavers (16 adults and 17 subadults) in unoccupied portions of the Price River targeted restoration site both years, but only released 8 translocated beavers (5 adults and 3 subadults) near BDAs at Moonshine Wash in 2019. Drought in 2020 caused extremely low flows in the San Rafael River, resulting in unsuitable conditions for translocation at Moonshine Wash.

We detected RS and translocated beavers over significantly longer stretches of river than RA beavers (Table 3; Figure 1). The average time passed between an individuals' most up- and down-stream locations was 54.1 ± 31.5 days for RA beavers, 35.9 ± 30.1 days for RS beavers, 38.1 ± 23.6 days for TA beavers, and 40.6 ± 12.1 days for TS beavers. We detected 41.4% of all TA and subadult beavers (n = 17) >20 km from their release site (Figure 2), and 61.4% of RS and translocated beavers were downstream of their release site at their final detection (25.0% of RS, 66.7% of TA, and 63.2% of TS). Eleven translocated beavers (four adults at the Price River, two adults at Moonshine Wash, and five subadults at the Price River) settled in transient resting sites within the targeted restoration sites for an average of 16.2 ± 2.7 days before moving to other areas. We did not observe any transient resting sites for RS beavers. Four translocated beavers (two adults, two subadults) permanently settled outside the targeted restoration sites 8.6–155.4 days after release (72.2 ± 34.6 days); three near the confluence of the Green and Price Rivers, and one subadult beaver farther downstream, near the town of Green River. We detected these beavers for an average of 134.8 ± 7.5 days with PIAs at these settlement sites.

Based on the displacement model, we observed distinct differences between RA beavers and RS or translocated beavers in the relationship between the distance traveled from their release sites and time (Table 3; Figure 3). For RAs, ln(time since release) had no detectable effect on ln(distance from release)—RA beavers did not change their displacement from their release site over time. In contrast, translocated beavers and RS beavers moved farther from their release sites during the monitoring period, albeit at a diminishing rate (Table 3; Figure 3). The random effects of Beaver ID on both the intercept and the effect of ln(time since release) substantially improved model fit [likelihood-ratio χ(2, n=1,110)2 = 225.29, p < 0.001; marginal R² = 0.45, conditional R² = 0.86].

Based on the step-length model, we observed differences between the displacement rates of RA beavers and RS or translocated beavers (Table 3). Passive integrated antennae detections were associated with higher displacement rates, while neither river discharge category nor NDVI value at the start of a step affected displacement rates in the model. Resident adult beavers moved more slowly than the beavers in other state categories, although the confidence intervals of all state categories overlapped to some extent (Figure 4). When all other covariates were held constant, RA, and translocated beavers exhibited acceleration initially, followed later by gradual deceleration in increasing step duration. Resident subadult beavers exhibited quick deceleration initially, followed later by gradual deceleration in increasing step duration (Figure 4). Resident subadult beavers displaced fastest over short time periods (i.e., hours and days), while translocated beavers displaced fastest over long time periods (i.e., months, Figures 4, 5). Resident adult beavers moved the slowest at all temporal scales (Figure 5). Resident adults also reduced their speed as time since release increased, whereas the three other beaver state categories demonstrated a slight increase in speed as time since release increased (Figure 5). Similar to the displacement model, the random effects of Beaver ID on both the intercept and the effect of ln(step duration) substantially improved model fit [likelihood-ratio χ(2, n=600)2 = 11.66, p < 0.01; marginal R² = 0.30, conditional R² = 0.51].

The fine-scale movement rates of RA and translocated beavers were similar (Table 3; Figure 6). Time of day (i.e., day vs. night) was an important parameter explaining fine-scale beaver movement patterns, with beavers being more active at night. Including a random effect of Beaver ID on the intercept in the fine-scale movement rate model did not improve model fit [likelihood ratio χ(1, n=1,110)2 = 0.28, p = 0.6; marginal R² = 0.20, conditional R² = 0.28], but was necessary to account for the repeated sampling events for individual beavers.

Our findings suggest translocated beavers exhibited movement behavior similar to dispersing RS beavers, likely moving through their new environment in search of a mate and a suitable site to settle. We found that translocated beavers demonstrated movement patterns similar to RS beavers in the first 6 months post-release, with an exploratory dispersive phase following release gradually decaying into more sedentary space-use indicative of home range establishment. Translocated beavers moved substantially farther and faster than RA beavers, beavers which already had established territories and therefore likely had no need for such exploratory movement patterns. However, contrary to our fine-scale movement rate hypothesis, we observed no differences in median distance moved between translocated and RA beavers over a short time span (5 min), suggesting day-to-day activity patterns such as foraging and resting were not greatly impacted by dispersal or translocation. These results suggest that although translocated beavers typically demonstrated wide-ranging movement patterns initially, movement behavior patterns will eventually mimic RA beavers.

Resident adult beavers remained in small stretches of river throughout time, with maximum distance detected between the most upstream and downstream locations of each beaver averaging 0.86 ± 0.21, suggesting they held established home ranges and territories. The distance we observed was smaller than naturally occurring American and Eurasian beaver home ranges reported in other studies (3.6 ± 0.3 km, Graf et al., 2016b; 2.2 ± 0.5 km, Breck et al., 2001; 1.8 ± 0.3 km in smaller streams and 3.6 ± 0.5 km in larger rivers, Havens et al., 2013). Smaller home ranges may be caused by resources being less dispersed and less diverse in smaller rivers (Havens et al., 2013). Our findings are consistent with previous findings in smaller streams, such as a small creek in Oregon where mean linear home range size was 1.56 ± 0.71 km (1 SE; Maenhout, 2013). Alternatively, home ranges may have been small because seasonal resource availability affects beaver movement (Bloomquist et al., 2012; McClintic et al., 2014a; Korbelová et al., 2016), which may be intensified in a desert ecosystem. Summer temperatures in our study system were extremely high and food resources were often localized; these two factors potentially contribute to reduced movements. In addition, we tracked many beavers during drought periods when river discharges were low, increasing the difficulty for beaver to evade predators when far from the safety of a burrow or lodge.

The maximum distances we detected between the most upstream and downstream locations for each RS were similar to or larger than movement patterns recorded in other studies. In Montana, mean dispersal-settlement distance for subadult American beavers was 10.9 ± 3.1 km (Ritter, 2018), and in Oregon, it was 16.2 ± 9.3 km (Maenhout, 2013), yet mean dispersal distance of Eurasian beavers in Norway was 4.5 ± 5.4 km (Mayer et al., 2017). The four RS beavers in our study dispersed following release; three moved >9.0 km. One beaver only moved 2.38 km from its natal colony to another colony, an indication of successful dispersal (Sun et al., 2000). While it is possible that capture, quarantine, and handling could have induced these dispersal events (e.g., Kukalová et al., 2013), a study in Norway demonstrated no change in short-term Eurasian beaver space use post-capture and post-tagging, although only dominant adults were included in their study (Graf et al., 2016a).

Similar to other studies, translocated beavers were detected to have moved similar maximum distances as RS beavers. The mean distances moved for beavers translocated in North Dakota was 14.6 ± 2.1 km (Hibbard, 1958), 7.4 straight-line km for beavers translocated to streams in Wisconsin (Knudsen and Hale, 1965), and >10 km from their release sites for 51% of translocated beavers in Wyoming (McKinstry and Anderson, 2002). Conversely, translocated beavers only moved a mean distance of 3.3 ± 0.2 km from their release sites in Oregon, indicating their model-based method of release-site selection may have identified high-quality vacant habitat, encouraging beavers to stay (Petro et al., 2015). Translocated individuals may also roam much farther than naturally dispersing individuals. Along with our study, where translocated beavers moved up to 101.8 km, beavers have been reported to move 238 km in North Dakota (Hibbard, 1958) and 76.2 km in Wisconsin (Knudsen and Hale, 1965).

Results of our displacement model showed that RS and translocated beavers moved farther from their release sites than RA beavers. Spatiotemporal autocorrelation may exist due to our use of sequential observations in this model and despite accounting for repeated observations using random effects. Nonetheless, our results serve as an effective demonstration of the considerably larger distances traveled by dispersing subadult and translocated beavers compared to RA beavers, even soon after release. Final detections for 61.4% of our translocated and RS beavers were downstream of their release sites, similar to previous studies of dispersing subadult beavers that reported that the predominant direction of travel is downstream (Leege, 1968; Sun et al., 2000). Beavers likely exert less energy while covering longer distances when traveling with the current. Results from our displacement model show TA beavers demonstrated lower displacement from release than resident and TS beavers, potentially indicating these individuals settled more quickly, although this result should be interpreted with some caution because the confidence intervals overlapped. Most adult translocated beavers likely already experienced natal dispersal through an unfamiliar environment and territory establishment in their lifetime (Baker and Hill, 2003). Perhaps this previous experience led them to more quickly settle in the closest suitable site, find a mate, and defend their new territory from subordinate subadult beavers, who may not have dispersed before. Knowledge on previous experience by beavers slated for translocations may be difficult to obtain but could improve which individuals would exhibit philopatry and should be considered in future research.

Dispersing beavers may need to travel longer distances to find an area to settle with sufficient resources for survival in desert rivers because they have patchier and more unpredictable resources (Gibson and Olden, 2014; Barela and Frey, 2016). Rivers in our study had low existing beaver densities (Macfarlane et al., 2017). This may have allowed RS and translocated beavers to be choosier about selecting high-quality sites for settlement because there was reduced “social resistance” effects (Armansin et al., 2020) with more unoccupied territories and less potential for aggressive encounters with conspecifics (DeStefano et al., 2006). Some of our translocated beavers used temporary settlement sites centered around a discovered burrow or hiding place as a known safety refuge from which to conduct exploratory movements; this has been documented in dispersing subadult beavers (Sun et al., 2000; McNew and Woolf, 2005; Ritter, 2018).

When existing resident populations are low, as is common in conservation translocation or reintroduction efforts (Seddon et al., 2014), translocated individuals may have to travel farther to find a mate. One week post-release we observed no translocated beavers who were released as a pair or family group in close proximity to each other, indicating that translocated beavers were likely unable to find their original release groups and instead were searching for new mates. This group fission is similar to a study in Kazakhstan in which translocated kulan (Equus hemionus kulan) had difficulty reconnecting with other translocated individuals once breaking from the group, negatively impacting reproduction in the reintroduced herd (Kaczensky et al., 2021). These findings emphasize the importance of translocating large numbers of individuals or releasing individuals near existing populations to increase conspecific encounter rates and increase recruitment, a key to conservation translocation success.

Our results also demonstrated RS and translocated beavers move more quickly than RA beavers, although there was some overlap in confidence intervals. Resident adult beavers were likely already settled in the best quality habitat, spending more time in concentrated areas of high resource availability with a known place of safety nearby, therefore moving more slowly to reduce their encounter rates with predators (Prokopenko et al., 2017; Dickie et al., 2020). Conversely, the fact that RS and translocated beavers were in an unfamiliar, novel environment may have heightened their perceived predation risk, causing them to move faster. Beavers moved faster the farther they were from their lodge to minimize increased predation risk from alligators in less familiar areas of Alabama (McClintic et al., 2014b).

Fine-scale movement behavior did not differ among categories of beaver, suggesting environmental factors had a larger effect on median distance moved over short time periods (5 min intervals). In general, beavers exhibit crepuscular or nocturnal activity patterns, a common predator avoidance strategy (Swinnen et al., 2015). Translocation or dispersal did not alter this behavior; all beavers moved less during the day, likely resting in burrows or lodges to insulate against the extreme desert temperatures (Buech et al., 1989). During dispersal or translocation, beavers must still forage and rest to survive, and our fine-scale movement patterns suggest that these short-term behaviors remained similar to RA beavers. We note that there is likely some error in our estimation of the true location of beavers during fine-scale monitoring. We used single azimuths to estimate locations, but the error remained generally the same at various sampling distances from the river based on calibration tests using stationary test transmitters, and among different beaver state categories. As such this bias was fairly uniform across sampling sessions and should not affect relative comparisons.

Inference from our results are somewhat limited due to sample size once individuals were classified among the beaver categories. For example, we did not include sex because it was confounded with other parameters in the models: both male and female beavers are territorial and disperse, so we did not expect sex to have a strong effect on movement as compared to beaver category (Baker and Hill, 2003). Results for RS beavers demonstrated the largest variation and widest confidence intervals of the four beaver categories, likely due to the small sample size of this state category (n = 4). In future studies, the use of more detailed habitat covariates or conducting a habitat selection analysis may reveal more about the external drivers of coarse-scale movement behavior in desert systems (e.g., Wang et al., 2019; Ritter et al., 2020). Despite our unsurprisingly low small sample size and thus limited inferential power, the patterns we observed were clear and supported most of our original hypotheses.

In terms of displacement, though translocated beavers tended to move more similarly to dispersing RS beavers overall, we observed a gradual leveling-off of differences among beaver categories, suggesting these individuals will eventually establish a home range similar to RA beavers and may subsequently build dams which contribute to restoration. Logistical challenges limited our monitoring period to 6 months post-release, or shorter periods for some individuals due to transmitter failure (Doden, 2021), so confirming settlement site establishment was challenging. However, we observed four translocated beavers permanently settle outside of the targeted restoration sites 8.6–155.4 days post-release, supporting our expectation that translocated beavers will eventually settle and behave similarly to RA beavers in regard to movement. Indeed, translocated individuals of any species must adjust to their novel environment to survive but need time to learn and explore their new surroundings in order to make appropriate changes to their behavior. For example, translocated “alalā” (Corvus hawaiiensis) in Hawaii learned to be more vigilant over time to limit predation at supplemental feeding sites (Lee et al., 2021), and swift foxes (Vulpes velox) translocated in Canada exhibited distinct post-release movement stages (initial acclimation, establishment, final settlement) as they adjusted to their new surroundings over time (Moehrenschlager and Macdonald, 2003).

The comparative technique we used here to monitor naturally occurring resident individuals to translocated individuals should inform translocation expectations and outcomes for the conservation of beavers as well as other species. Results from a concurrent study demonstrated that 40.4% of translocated beavers included in this study were detected outside of targeted restoration sites, while no RA beavers were detected outside of the targeted restoration sites (Doden, 2021). Despite the variable site fidelity of translocated beavers, 22 dams were constructed by resident and translocated beavers in the targeted restoration sites during the study, suggesting that translocations had some success in supplementing resident beaver dam-building and contributing to restoration objectives. Identifying ways to improve the proportion of translocated beavers that settle within targeted restoration sites is an important next step. Previous studies have observed increases in beaver dams near structural features such as BDAs installed in rivers, and these structures create deep pools which may help improve translocation success (Bouwes et al., 2016; Pollock et al., 2018). However, this approach has yet to be studied simultaneously with translocations in desert systems. In addition, even beavers that settled outside of targeted restoration sites should be considered to contribute to restoration success at a more riverscape scale. These desert tributaries have, in some cases 50–100 km of very degraded habitat, and native fishes are challenged by this flow-related habitat simplification at very large scales (Budy et al., 2015; Pennock et al., 2021). Our study presents novel research critical to informing future beaver translocation efforts in desert rivers, because this study is the first to compare naturally occurring resident beaver movement behavior to translocated beaver movement behavior in the same system and is one of few studies of beaver movement ecology in desert systems (Gibson and Olden, 2014).

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation or at Dryad, doi: 10.3389/fcosc.2022.777797

All procedures in this study including animal capture, handling, tagging, and monitoring were approved the Institute for Animal Care and Use Committees at Utah State University (No. 10128) and USDA-National Wildlife Research Center (QA-3171).

ED participated in methodology, data collection, data analysis, writing of the original manuscript draft, and review and editing. PB took part in conceptualization, funding and resource acquisition, supervision, and review and editing. TA participated in methodology, data analysis, and review and editing. JY engaged in conceptualization, methodology, funding, resource acquisition, supervision, and review and editing. All authors contributed to the article and approved the submitted version.

Funding for this study was provided by the U.S. Bureau of Land Management (Agreement L18AC00121), the Utah Division of Wildlife Resources (in-kind), the U.S. Bureau of Reclamation (Agreement R19AC00153), the Ecology Center at Utah State University, the Utah Chapter of the Wildlife Society, the U.S. Department of Agriculture-National Wildlife Research Center, and the U.S. Geological Survey, Utah Cooperative Fish and Wildlife Unit (in-kind).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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