As Christmas approaches, children expect Santa Claus to arrive with gifts on his sleigh. However, reindeer like Rudolph, who pull the sleigh, inevitably experience stress as they have to travel around the world. Scientists have developed a method to measure the stress levels of reindeer by using a camera to assess how much blood accumulates in their eyes.
Every year, scientists have published studies on reindeer in anticipation of Christmas for Rudolph. They have discovered the physical traits that allow reindeer to withstand the strenuous labor of delivering gifts. They can multitask, even eating while sleeping, and have keen eyes for finding hidden grass in the snow. Their noses provide ventilation depending on the conditions. This is a small Christmas gift from science for Rudolph.
◇Instant stress detection in reindeer using infrared
Virpi Lummaa, a professor in biology at the University of Turku, Finland, and her research team developed a method to detect the stress of reindeer from a distance using infrared thermal imaging technology. Their findings were published in September in the international journal 'Animal Behavior and Cognition.'
Evaluating animal stress is particularly important in livestock farming, usually determined by analyzing blood components. The problem is that even inserting a syringe causes stress to the animals. It is difficult to help stressed reindeer, who are already under pressure with Christmas gift deliveries, by inserting needles.
Professor Lummaa and her team focused on the idea that infrared thermal cameras can measure how much heat is emitted from various parts of an animal's body from a distance. Stress is related to the animal's body temperature. When reindeer face stressful situations, they prepare to either fight or flee, which results in blood pooling in their legs and a reduction in blood flow to other areas like the nose or eyes. Consequently, the temperature rises in the area where blood has pooled and decreases in other areas.
The research team filmed eight male reindeer used for tourism in the far northern Lapland region of Finland while a stranger petted them for one minute with a thermal camera. According to shepherds, reindeer are not accustomed to human contact. In reality, they avoided human touch, indicating that they were under stress.
The experiment showed that the infrared thermal camera footage revealed that the tail temperature of the reindeer decreased when a stranger petted them, and began to rise again gradually once the petting stopped. According to previous studies, emotional stress has been shown to lower nasal temperatures in both humans and primates. These temperature changes can occur rapidly within seconds and may persist for several minutes.
The researchers discovered that measuring the temperature around the hairless area of the eyes in reindeer could be an effective way to assess stress levels. They stated that this method could improve the management and treatment of reindeer in tourist areas. Santa will have to ensure he has an infrared thermal camera at hand before sending out gift deliveries.
◇Sleeping while chewing grass and accumulating fat in a short summer
Santa may have asked Rudolph to pull the sleigh because the reindeer possess a body suitable for the labor of delivery. Research teams led by Gabriela Wagner, a professor of Arctic and marine biology at the University of Tromsø, Norway, and Reto Huber, a professor at Zurich Children's Hospital in Switzerland, discovered last year that reindeer combine sleeping and digestion. This means they can work even without time to eat separately.
The research team attached electrodes to the scalp surface of four female reindeer to measure brain waves. They found that disrupting the reindeer's sleep resulted in an increase in slow waves, which decreased in frequency in the brain. Slow waves are evident during deep sleep stages. An increase in slow waves indicates a sense of drowsiness.
On the other hand, when reindeer chew feed while sleeping, slow wave activity decreases. This suggests that they can chew their feed without feeling drowsy while actually sleeping. If they sleep lightly, they enter a state of REM (rapid eye movement) sleep, while during deep sleep, they enter a non-REM state. According to the research team, it was found that during rumination, the reindeer enter a state similar to non-REM sleep.
In the Arctic, the summer brings continuous midnight sun with plenty of food, allowing reindeer to sleep while ruminating to accumulate fat in preparation for winter.
◇Eyes and noses are perfect for running in the snow
Research teams led by Nathaniel Dominy, a professor of anthropology at Dartmouth College, and Julie Harris, a professor of psychological neuroscience at the University of St Andrews in Scotland, revealed that Rudolph can locate food in snowy areas without having to prepare additional feed. Their findings were published in the international journal 'i-Perception' late last year.
During winter, reindeer dig through the snow to find 'Cladonia rangiferina'. Although commonly known as 'reindeer moss,' it is technically different from moss (bryophytes) and is classified as a lichen. The research team noted that 'the eyes of reindeer change shape to effectively detect ultraviolet light during winter, allowing them to easily find lichens that absorb UV rays in the snow.'
The eyes of reindeer appear golden in summer and turn blue in winter. Animals possess a reflective layer in their retinas called the tapetum, which enhances visibility in dark areas. The Arctic experiences polar night during winter when the sun is below the horizon, resulting in blue light dominating the sunlight. This is because the ozone layer only allows blue light to pass through the horizon. Reindeer modify the color of their reflective layer to blue, allowing them to accept blue light better, thereby making the most of even dim light.
The blue reflective layer is also highly sensitive to ultraviolet light. Consequently, reindeer can distinguish well between substances that absorb UV rays and those that reflect them, as the eyes reflect UV light while reindeer moss absorbs it. In the reindeer's eyes, white snow appears brighter while the normally pale-colored reindeer moss appears darker, making it easier to find.
Rudolph's red nose is a result of enduring the cold. Researchers from the University of Tromsø, Norway, noted in a 2012 study published in the 'British Medical Journal (BMJ)' that reindeer have 20 capillaries per square millimeter in their noses, which is 25% more vascular than humans. Consequently, when pulling a sleigh and running, the nose may become red. In laboratory tests, when reindeer were made to run, infrared cameras showed high blood temperatures around the nose along with the legs that were exerting effort. Researchers explain that reindeer can accumulate blood in their noses, preventing the tips from freezing during runs.
References
Animal Behavior and Cognition(2024), https://www.animalbehaviorandcognition.org/article.php?id=1380
Current Biology(2023), DOI: https://doi.org/10.1016/j.cub.2023.12.012
i-Perception(2023), DOI: https://doi.org/10.1177/20416695231218520
BMJ(2012), DOI: https://doi.org/10.1136/bmj.e8311