The homing behavior of red deer: A GPS assisted translocation experiment

doi:10.21203/rs.3.rs-3296212/v1

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The homing behavior of red deer: A GPS assisted translocation experiment

https://doi.org/10.21203/rs.3.rs-3296212/v1

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Background

Many animals move back to their home area (i.e., ‘homing’) after translocation to sites further away. Such translocations have traditionally been used in behavioral ecology to understand orientation and migration behavior of animals. The movement itself can then be followed by marking and recapturing of animals or by tracking, e.g., using GPS systems. Most detailed studies investigating this behavior were conducted with smaller vertebrates (e.g., birds, amphibians and mice), whereas information on larger mammals, such as red deer, is sparse.

Methods

We conducted GPS assisted translocation experiments with red deer at two sites in the Czech Republic. Individuals were translocated over a distance of about 11 km and their home journey was tracked. We used circular statistics to test for significant homeward orientation at 100, 500, 1000 and 5000 m distance to the release site. In addition, we applied a Lavielle trajectory segmentation, identifying different phases of the homing behavior.

Results

Thirty-one out of 35 translocations resulted in successful homing with a median time of 4.75 days (range: 1.23 to 100 days). Animals significantly oriented towards home immediately after release and again when they came closer to home; however, they did not show significant orientation at the distances in between. We were able to identify three homing phases, an initial ‘exploratory phase’, followed by a ‘homing phase’ which sometimes was again followed by an ‘arrival phase’. The ‘homing phase’ was characterized by the straightest paths and fastest movements. However, variation between translocation events was considerable.

Conclusions

We show good homing abilities of red deer after translocation. Our results show the feasibility to conduct experiments with environmental manipulations (e.g., to impede the use of sensory cues) close to the release site. The homing behavior of red deer is comparable to other species and might represent general homing behavior patterns in animals. Follow up studies should further dissect and investigate the drivers of the individual variations we observed, and try to identify the sensory cues used during homing.

Mammal navigation

satellite tracking

Cervus elaphus

Czech Republic

spatial orientation

Animal navigation and spatial cognition and memory are essential abilities that allow animals to reach specific destinations, such as food resources, mating grounds, nesting sites and to exploit spatially clustered resources efficiently [1, 2]. Many species display site fidelity, i.e., they return to specific locations every season, or stay in the same general area year around [3]. Typically, animals that show site fidelity return to their approximate capture location after translocation to a site outside their typical residency [4, 5]. The reason for such preference for certain ‘home areas’ can be manifold but is often associated with territorial behavior and/or mating sites [e.g., 6, 7] or spatial learning and memory-based home range formation[8, 9]. The return behavior to such specific sites is called ‘homing’ and has been studied extensively in smaller terrestrial vertebrate species such as birds [10, 11] and, to a lesser extent, amphibians [12], mice [13–15],rabbits [16, 17], bats [18] and dogs [19]. Large terrestrial mammals show good homing abilities as well [20] and some perform seasonal migrations [e.g., 21]. Spatial movements of large non-migratory mammals, however, have been subjected to far less experimental/manipulative investigations, probably due to practical issues with their translocation.

Studies across many species suggest that there are species specific limits of translocation distances beyond which the animals are no longer able to navigate back [20, 22]. These limits might be associated with the navigational cues used for homing, which might require familiarity with the environment. Homing abilities outside the previously visited (i.e. ‘familiar’) area are often termed ‘true navigation’, meaning that the animals can extrapolate the navigation cues beyond their home range. It is unknown what kind of sensory mechanisms large terrestrial mammals use for their navigation performance. However, in smaller mammals it has been shown that olfactory [23], visual [24] and magnetic cues [25] can be used for orientation. In principle, larger mammals, such as the red deer (Cervus elaphus), could use all of these cues if available. However, direct tests of the cues involved have not been performed yet.

Understanding the homing abilities of larger mammals is an important factor when managing populations either for the protection of endangered animals or for game management. For instance, bears are sometimes relocated to avoid conflicts with human settlements, which is considered a better alternative to sacrificing the animals [26]. However, such efforts are not successful if individuals return to their home sites. Bears can find their way home from up to 100 km [26], which likely is an especially well-developed homing ability for large terrestrial mammals. For white tailed deer (Odocoileus virginianus), studies on homing performance showed frequent settlement of the animals in an area of about 30 km to the release site [20]. For instance, in a study in Illinois out of 28 translocated individuals (distance 10–58 km), only two returned home [27]. Such studies usually rely on mark-recapture or radio telemetry, while advancements in remote sensing nowadays allow detailed movement monitoring of animals over long time periods, due to GPS-assisted tracking. Translocation studies with red deer are still missing, although they show high site fidelity for their home ranges, regardless if they show seasonal migration between home ranges or if they remain resident in an area during the year [28, 29].

In the current study, we performed translocation experiments with GPS-monitored red deer followed by detailed analyses of the homing performance and tracks. We show overall consistent and fast homing behavior, with most animals returning within days from 10 km distance.

Study site and species

The translocation experiments with the red deer (Cervus elaphus) were conducted in two different populations in the years 2019, 2020 and 2021 in the Czech Republic (Fig. 1) in two different locations in West Bohemia.. The first was one was in the Doupov Mountains, a military training site which is closed to the public and used only for military training, game species hunting and forestry. This area spans across 331 km². The second location was Kladska which is situated in the west and consist of a semi-natural coniferous forest. The total area is 140 km² and the forest stands are used for timber production and recreation. Stable deer populations are present at both locations and both are managed by hunting. In total we translocated 23 individuals at least once (15 animals in Doupov and eight animals in Kladska). Thirteen animals were translocated a second and two animals a third time. One animal was killed by hunters one day after translocation and was therefore not included in any of the analyses. One animal was male, the others were adult females. Translocations took place during early spring from February to April, which is the spring season without large-scale movements, while rutting season starts in the middle of September and continues until the mid of October.

Translocation procedure

Animals were anesthetized using a mixture of Ketamine and Xylazine in 3 ml for 100kg of the animal’s bodyweight. The concentration of Ketamine was 50 mg/ml and 250 mg/ml for Xylazine. The animals were then secured in the wooden transport box on the trailer behind a pick-up truck and driven to the release sites (11.9 +/- 1.8 km distance) which were either approximately towards North (n = 4 + 2), South (n = 15 + 7) or West (n = 8) of the capture location and 12 km away. Animal handling was performed in accordance with the decision of the Ethics Committee of the Ministry of the Environment of the Czech Republic number MZP/2019/630/361 which approved the procedures. All individuals were transported in wooden box which was developed for animal’s transport. The wooden box for the transport included the ventilation holes in the lower part the of construction. The animals were not able to see outside of the box during the transport. Time of translocation was lower than 90 minutes. The animals were released from the box after the translocation a visually checked by the veterinary stuff. All individuals left the box without injury and all of them didn’t need the antidote.

GPS tracking

Red deer individuals were tracked using GPS Vertex Plus collars (Vectronic Aerospace GmbH) (Fig. 2). The total mass of the collars was 750 g, the lifetime was approximately one year. The collar mass was lower than 3% of the animal’s body mass (Wilson 2021). GPS data were retrieved via GSM every eight hours and stored on servers. The frequency of GPS fixes was set to 30 min intervals and the collars included a VHF drop-off mechanism (Vectronic Aerospace GmbH) for non-invasive collar release after the end of the project or before the end of battery lifetime.

Track analysis

For the aim of this study we defined all animals that reached or crossed a circle of 1 km radius around their capture location within 180 days after translocation as “homed successful” and animals that did not reach this criterion as “did not home”. This does not necessarily mean that animals that were defined as “did not home” did not home at a later time point.

For all animals (“homed successful” and “did not home”) we calculated the homeward bearings at a distance of (at least) 100 m, 500 m, 1 km and 5 km from the release location. The bearings were calculated as the angle of the vector between the release location and the closest GPS fix after the individuals crossed the respective distance mark. The For the analysis we used the recently described MANOVA approach [30] and used an error term for the animals’ ID in cases where animals successfully homed more than once (we only applied this approach to distributions with at least five bearings). This approach was used to circumvent non-independency issues due to the retesting of the animals. Our aim was to test if animals would orient stronger towards home with increasing distance from the release location. The idea behind this analysis was that a deer might, at first, disperse at a random direction when released, after re-orienting itself and then following a homeward direction. Circular plots were generated using the wrapper function presented in Pail et al. [31] which is based on the plot.circular function from the package circular in R [32].

To analyze the different homing segments for all deer that successful homed we used the approach described by Lavielle [33, 34] using the function lavielle.ltraj from the R package adehabitatLT [35]. In this approach a track is partitioned using a contrast function, in our case we set the minimum length of a segment as four, used four as the maximum possible segments and set type of segmentation to “mean”, following the suggestions by Calenge [36]. We then applied the chooseseg function to find the optimum number of segments for the individual tracks. At the final step we applied the findpath function to divide the tracks in the suggested segments, this was only done if more than one segment was suggested from the chooseseg function. For each segment in each track we calculated the average speed, straightness (as the standardized vector length ‘r’) and proportion of entire track. We also correlated the number of days needed for homing with the number of trajectory segments using the function cor.test.

Of all deer translocations 89% (31 of 35) ended with successful homing, i.e., returned back to the capture location in a vicinity of a 1 km radius within 180 days. Of the four translocations without homing, two were individuals that had been translocated for the second time. Out of all individuals 19 homed at least once and two did not. One animal (shot by hunters) and one animal (killed by wolf) were not put inside the analyses of homing.

The median homing time was 4.75 days (range 1.23–100 days) (Fig. 3).

The initial orientation (100 m) of deer which homed successfully was significantly directed towards the home direction (Fig. 4.). The subsequent orientations at distances of 500 m and 1 km distance to the release site were randomly oriented, while at a distance of 5 km the animals were again oriented towards home. As only four releases were included in the analyses that did not home, we did not perform statistics on them. However, the general patterns, especially for the initial homeward trend, appeared comparable to the animals that did home.

The segmentation algorithm resulted in 10 trajectories which were not split up (i.e., one segment for the entire track, herein assigned to segment 1), 10 trajectories were split in two segments (assigned to segment 1 and 2) and 11 were split in three segments (Fig. 5). None were split into four segments (the highest segmentation possible in our analysis). The general trend for the trajectories showed that the animals had lower average speed and straightness in segment 1 than in segment 2 and again lower values in segment 3 (Fig. 5). In contrast, the segments’ relative proportion (i.e., the relative proportion of each segment on the entire trajectory) showed the opposite trend (lower proportion in segment 2 compared to 1 and 3). The two animals with directly opposite trends consisted of only two segments, suggesting that they might belong to segment 2 and 3 compared to the other animals (i.e., missing segment 1). Our results show a possible separation in three phases of homing which could be classified as an initial exploration of the release site, a faster homing phase and a (possible) exploration close to the home site, until our criteria of a 1 km radius around the release site was met. The number of days the animals needed to home was significantly negatively correlated with the number of segments (Pearson's product-moment correlation: -0.45, t = -2.7195, df = 29, p-value = 0.011), i.e., animals that needed longer were more likely to be classified into fewer segments by our segmentation algorithm.

Our study shows excellent homing abilities of red deer when translocated by about 11 km. This is surprising as selected release sites may be beyond the home ranges of the investigated deer, suggesting that the individuals likely navigated homewards from a novel location. Interestingly, the initial orientation at the release sites was significantly oriented towards the animals’ home. This suggests high navigational capabilities, potentially based on a global map cue, e.g., a magnetic or olfactory internal map [37, 38]. After this initial orientation the animals appeared to explore their release area before starting their journey home. This is again exemplified in the highly significant homeward orientation at a distance of 5 km to the release site. Overall, the homing abilities of red deer appear to be better than those of white tailed deer, at least according to the available literature [c.f., 20].

Despite considerable individual variation, the homeward navigation contained repeatable features between some individuals. There often was a first ‘exploratory phase’ immediately after release which is recognizable by its more irregular and slower movement. Then the animals started the ‘homing phase’, these trajectories are characterized by straight and fast movements. Close to home there often was a final ‘arrival phase’ where the animals are again moving slower and less straight. Typically, the homing phases are shorter than the other two (first and third segment). Two animals did not show the initial exploration phase and started immediately with the homing phase, and 10 animals did not have discrete phases according to our classifying algorithm. The arrival phase appeared in 11 of the animals and might only be entered when the animals miss the goal or if they assume they have reached ‘home’. The longer the animals needed to reach home the fewer phases our classifying algorithm detected. Possibly because they never entered the homing phase and slowly wandered towards home, never transitioning into a fast and straight movement.

Interestingly, our results are comparable to pigeon homing analyses, which also showed an initial phase with individually very variable duration and a homing phase with steeply increased steadiness (i.e., straightness) [39]. This suggests a common mechanism underlying the navigational process, presumably related to the cues used for homing as well as the individuals’ motivational state.

It would be highly interesting to gain further insights into the specific behavior the animals are performing during the identified homing phases. Furthermore, exploring what happens when they do not home could provide insights into the navigation cues deer are using. For instance, electromagnetic anomalies, obscured sun (cloud cover) or wind from other than home directions (lacking home odors) could interfere with the homing abilities and either delay homing or impede homing during the time interval we considered as homing. Manipulating the sensory environments of the release sites could be an option for discerning the sensory mechanisms used for homing (e.g., radio-frequency noise to disrupt a magnetic sense [c.f., 40]). This is possible, because the initial orientation of the animals did correspond well with the direction towards home. In conclusion, we provide evidence for excellent homing abilities of red deer, which fits well into the homing behavior found in other animals (e.g., the well-studied pigeons). Further studies regarding sensory cues as well as behavioral switches along the route would be a fruitful endeavor for the future.

Ethical approval:

The red deer trapping was realized in accordance with the decision of the Ethics Committee of the Ministry of the Environment of the Czech Republic number MZP/2019/630/361.

Consent for publication

Not applicable.

Availability of data and materials

The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests

The authors declare that they have no competing interests.

Funding

This study was supported by grant "EVA4.0" No. CZ.02.1.01/0.0/0.0/16_019/0000803 financed by OP RDE and Project B_11_21 of FFWS CZU.

Authors’ contributions:

V.S., L.L. and H.B. originated the idea. A.V. and M.J. did the animal handling and data collection. L.L., V.S., M.F. and M.S. wrote the manuscript and did data analyses with the contribution of L.B., and E.P.M., A.O., O.L. and M.H. contributed data and assisted with writing the final version of the manuscript.

Acknowledgements:

We are grateful to Václav Daněk, Vladislav Liška and Ladislav Baxa for facilitating the research and help during the field work.

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No competing interests reported.

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The homing behavior of red deer: A GPS assisted translocation experiment

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Abstract

Figures

Background

Methods

Study site and species

Translocation procedure

GPS tracking

Track analysis

Results

Discussion

Declarations

References

Additional Declarations

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