Macro-microscopic Research in Reideer (Rangifer Tarandus) Hoof Suitable for Efficient Locomotion on Complex Grounds

Quantifying effects of snow depth on caribou winter range selection and movement in Arctic Alaska

BACKGROUND

Caribou and reindeer across the Arctic spend more than two thirds of their lives moving in snow. Yet snow-specific mechanisms driving their winter ecology and potentially influencing herd health and movement patterns are not well known. Integrative research coupling snow and wildlife sciences using observations, models, and wildlife tracking technologies can help fill this knowledge void.

METHODS

Here, we quantified the effects of snow depth on caribou winter range selection and movement. We used location data of Central Arctic Herd (CAH) caribou in Arctic Alaska collected from 2014 to 2020 and spatially distributed and temporally evolving snow depth data produced by SnowModel. These landscape-scale (90 m), daily snow depth data reproduced the observed spatial snow-depth variability across typical areal extents occupied by a wintering caribou during a 24-h period.

RESULTS

We found that fall snow depths encountered by the herd north of the Brooks Range exerted a strong influence on selection of two distinct winter range locations. In winters with relatively shallow fall snow depth (2016/17, 2018/19, and 2019/20), the majority of the CAH wintered on the tundra north of the Brooks Range mountains. In contrast, during the winters with relatively deep fall snow depth (2014/15, 2015/16, and 2017/18), the majority of the CAH caribou wintered in the mountainous boreal forest south of the Brooks Range. Long-term (19 winters; 2001-2020) monitoring of CAH caribou winter distributions confirmed this relationship. Additionally, snow depth affected movement and selection differently within these two habitats: in the mountainous boreal forest, caribou avoided areas with deeper snow, but when on the tundra, snow depth did not trigger significant deep-snow avoidance. In both wintering habitats, CAH caribou selected areas with higher lichen abundance, and they moved significantly slower when encountering deeper snow.

CONCLUSIONS

In general, our findings indicate that regional-scale selection of winter range is influenced by snow depth at or prior to fall migration. During winter, daily decision-making within the winter range is driven largely by snow depth. This integrative approach of coupling snow and wildlife observations with snow-evolution and caribou-movement modeling to quantify the multi-facetted effects of snow on wildlife ecology is applicable to caribou and reindeer herds throughout the Arctic.

Forelimb joints contribute to locomotor performance in reindeer (Rangifer tarandus) by maintaining stability and storing energy

Reindeer (Rangifer tarandus) have lengthy seasonal migrations on land and their feet possess excellent locomotor characteristics that can adapt to complex terrains. In this study, the kinematics and vertical ground reaction force (GRF) of reindeer forelimb joints (interphalangeal joint b, metacarpophalangeal joint c, and wrist joint d) under walk, trot 1, and trot 2 were measured using a motion tracking system and Footscan pressure plates. Significant differences among different locomotor activities were observed in the joint angles, but not in changes of the joint angles (α_b, α_c, α_d) during the stance phase. Peak vertical GRF increased as locomotor speed increased. Net joint moment, power, and work at the forelimb joints were calculated via inverse dynamics. The peak joint moment and net joint power related to the vertical GRF increased as locomotor speed increased. The feet absorbed and generated more energy at the joints. During different locomotor activities, the contribution of work of the forelimbs changed with both gait and speed. In the stance phase, the metacarpophalangeal joint absorbed more energy than the other two joints while trotting and thus performed better in elastic energy storage. The joint angles changed very little (∼5°) from 0 to 75% of the stance phase, which reflected the stability of reindeer wrist joints. Compared to typical ungulates, reindeer toe joints are more stable and the stability and energy storage of forelimb joints contribute to locomotor performance in reindeer.

Structure, morphology and composition of fur on different parts of reindeer (Rangifer Tarandus) foot

In the long-distance migration of reindeer in winter, furs of reindeer foot, as the part in direct contacting with the external environment, can play the role of protection and heat preservation. With furs on different parts of the right posterior foot (fibular side, tibial side and planta pedis) as research objects, the microstructure of reindeer foot furs was observed with a scanning electron microscope. The image displayed that the reindeer foot furs was divided into 3 layers, namely cuticular layer, cortical layer and medulla layer. It was observed from the fur surface that the scales of fur on tibial side had smooth edge, with the scale structure in mosaic and coronary types. The scale structure of furs on the other parts showed the irregular waves due to abrasion to different degrees. From the cross-section view of fur, there was a non-medullated segment on the medial part of fur on planta pedis. The medulla layer of fibular and tibial sides showed a porous foam structure. The medulla index (MI) of fur on fibular side and tibial side at distal part was 70.35% and 81.79%, respectively, and MI at medial part was 77.88% and 88.08%. The composition of reindeer foot fur was measured through infrared spectroscopy and energy spectrum analysis respectively. The element contents of foot fur varied on different parts. The content of sulfur of the furs on planta pedis was higher than that on other parts. The research results can provide foundations for the functional study and bionic design of reindeer foot furs during long distance migration and swimming.