Reindeer Games: 8 Surprising Facts About Reindeer

A reposting of an original article from December, 2017.

A Swedish reindeer watches you. Photo by Alexandre Buisse at Wikimedia Commons.

1. Reindeer are caribou (kinda): Reindeer are the same species as caribou (with the scientific name Rangifer tarandus), but the terms are not completely interchangeable. Rangifer tarandus is a species of deer that is native to Northern regions of Europe, Siberia and North America, which includes many different habitat types, like arctic, subarctic, tundra, snow forest and mountains. These variations in harsh environments have led to variations among populations, resulting in multiple subspecies. The Rangifer tarandus subspecies that live in North America are commonly called caribou and the subspecies that live in Europe and Siberia are commonly called reindeer. We also often refer to domesticated populations as reindeer, regardless of where they are.

A map of reindeer and caribou distributions. Image by TBjornstad at Wikimedia Commons.

2. Rudolf’s red nose was an adaptation: Technically, reindeer don’t have red noses, but they do have lots extra blood flow in them. The inside of their noses are twisted and vascularized so the warm blood can heat up the frigid Arctic air before it gets into the lungs.

3. Santa’s reindeer were probably girls: Not only do reindeer have the biggest antlers of all deer species (relative to body size), but they are the only deer species in which both males and females grow antlers. Both males and females use their antlers to scrape through the snow and look for food, but males also use their antlers to compete with one another and impress the ladies during the breeding season. Unlike horns, antlers shed and regrow every year, and this process is regulated by sex hormones. When the new antlers grow in spring, they are made up of cartilage and lots of blood vessels and are covered in a furry skin called velvet. The blood carries lots of calcium into the antlers, which helps them to grow and harden into bone. When testosterone levels drop in males at the end of their breeding season in early December, their antlers fall off. Females, however, generally keep their antlers until March or April. So, if Santa’s reindeer had antlers at the end of December, they were probably female!

4. If you’re going to pick an animal to travel the world in one night, reindeer are a good choice: Some North American caribou migrate over 3,000 miles a year (more than any other land mammal). They can run up to 50 miles per hour and swim over 6 miles per hour. Migration herds can be up to 500,000 animals and baby reindeer learn to run within two hours of birth!

A swimming caribou herd. Photo by Lestar Kovac at Wikimedia Commons.

5. Reindeer eat weird stuff: Like cows, reindeer are ruminants, which means their stomachs have multiple compartments, some of which specialize in maintaining microbial communities to help them digest. Unlike cows, reindeer predominantly eat lichen, which are combinations of algae and fungi that are typically high in carbohydrates and low in proteins. To make up for this low amount of protein in their diet, reindeer may occasionally eat rodents and bird eggs.

6. They have the coolest feet: Their hooves have four toes: two that splay out like snow shoes and two dew claws. Their hooves have sharp edges to dig for food and are paddle-shaped for swimming. Their hooves even change with the seasons to provide the best traction, being softer in the summer when the ground is soft and hard in the winter to walk on slippery snow and ice.

7. Some reindeer use clicking knees to communicate: Some subspecies have knees that click when tendons slip over bone extensions in their feet. They use this sound to stay with their herd, even when weather conditions limit visibility. But because larger reindeer have larger legs and therefore make louder knee-clicks, they also use these sounds to establish dominance.

8. Reindeer are the only mammals that can see UV light: They have a reflective layer in the back of their eyes that is golden in summer and blue in winter. When it is blue, this allows reindeer to see contrasts in UV light, such as lichen (which absorbs UV) versus snow (which reflects UV).

Reindeer Games: 8 Surprising Facts About Reindeer

A Swedish reindeer watches you. Photo by Alexandre Buisse at Wikimedia Commons.

1. Reindeer are caribou (kinda): Reindeer are the same species as caribou (with the scientific name Rangifer tarandus), but the terms are not completely interchangeable. Rangifer tarandus is a species of deer that is native to Northern regions of Europe, Siberia and North America, which includes many different habitat types, like arctic, subarctic, tundra, snow forest and mountains. These variations in harsh environments have led to variations among populations, resulting in multiple subspecies. The Rangifer tarandus subspecies that live in North America are commonly called caribou and the subspecies that live in Europe and Siberia are commonly called reindeer. We also often refer to domesticated populations as reindeer, regardless of where they are.

A map of reindeer and caribou distributions. Image by TBjornstad at Wikimedia Commons.

2. Rudolf’s red nose was an adaptation: Technically, reindeer don’t have red noses, but they do have lots extra blood flow in them. The inside of their noses are twisted and vascularized so the warm blood can heat up the frigid Arctic air before it gets into the lungs.

3. Santa’s reindeer were probably girls: Not only do reindeer have the biggest antlers of all deer species (relative to body size), but they are the only deer species in which both males and females grow antlers. Both males and females use their antlers to scrape through the snow and look for food, but males also use their antlers to compete with one another and impress the ladies during the breeding season. Unlike horns, antlers shed and regrow every year, and this process is regulated by sex hormones. When the new antlers grow in spring, they are made up of cartilage and lots of blood vessels and are covered in a furry skin called velvet. The blood carries lots of calcium into the antlers, which helps them to grow and harden into bone. When testosterone levels drop in males at the end of their breeding season in early December, their antlers fall off. Females, however, generally keep their antlers until March or April. So, if Santa’s reindeer had antlers at the end of December, they were probably female!

4. If you’re going to pick an animal to travel the world in one night, reindeer are a good choice: Some North American caribou migrate over 3,000 miles a year (more than any other land mammal). They can run up to 50 miles per hour and swim over 6 miles per hour. Migration herds can be up to 500,000 animals and baby reindeer learn to run within two hours of birth!

A swimming caribou herd. Photo by Lestar Kovac at Wikimedia Commons.

5. Reindeer eat weird stuff: Like cows, reindeer are ruminants, which means their stomachs have multiple compartments, some of which specialize in maintaining microbial communities to help them digest. Unlike cows, reindeer predominantly eat lichen, which are combinations of algae and fungi that are typically high in carbohydrates and low in proteins. To make up for this low amount of protein in their diet, reindeer may occasionally eat rodents and bird eggs.

6. They have the coolest feet: Their hooves have four toes: two that splay out like snow shoes and two dew claws. Their hooves have sharp edges to dig for food and are paddle-shaped for swimming. Their hooves even change with the seasons to provide the best traction, being softer in the summer when the ground is soft and hard in the winter to walk on slippery snow and ice.

7. Some reindeer use clicking knees to communicate: Some subspecies have knees that click when tendons slip over bone extensions in their feet. They use this sound to stay with their herd, even when weather conditions limit visibility. But because larger reindeer have larger legs and therefore make louder knee-clicks, they also use these sounds to establish dominance.

8. Reindeer are the only mammals that can see UV light: They have a reflective layer in the back of their eyes that is golden in summer and blue in winter. When it is blue, this allows reindeer to see contrasts in UV light, such as lichen (which absorbs UV) versus snow (which reflects UV).

Eye Didn’t See That

By Evan Hovey

A grandmother and her grandson watching the television.
The elder is straining to see while the young man is not having any troubles.
Photo by Evan Hovey.

It’s Thanksgiving and the family just finished stuffing their faces full of turkey and cranberry fluff. Everyone meanders into the living room to sit down, let the tryptophan sink in, and watch some football. As you sit there, you start to observe the older family members around you take out their glasses or bifocals and squint towards the television in attempts to see what is going on. You begin to ponder the thought, “am I going to start to lose my eye sight as well?” Well, as it turns out, as you age, the number of cells that respond to light and color (called photoreceptors) begins to decrease.

Songhomitra Panda-Jonas, Jost Jonas, and Martha Jakobczyk-Zmija at the University of Erlangen-Nurnberg, Germany, looked into the number of photoreceptors in the retina of the eye to determine whether there was a loss as you age. The retina is the thin layer of tissue that lines the back of the eye. It is the location where your eye transfers what you see to the brain. There are two different kinds of photoreceptors in your eyes: rods and cones. Rods are those that detect light at low levels, which is what helps us see at night. Cones, on the contrary, are those that take in high light levels and help decode color. The authors believed that there would be a decrease in both kinds of photoreceptors as the eye got older (the older the person, the fewer photoreceptors). They came up with this hypothesis in part because of prior knowledge of a loss of tissue associated with vision in other parts of the eye as you age.

The researchers approached this study by obtaining fifty-five eyes from human donors that died at ages ranging from 18-85. The eyes were removed from the bodies less than eleven hours after death. Then the eyes were cut open and tissue samples from the retina were obtained. To determine the amount of photoreceptors in the tissue samples, the researchers used an ultrasound to view the retina and counted the photoreceptors on a photograph taken with the ultrasound. The two different kinds of cells were distinguished by their sizes (the larger cells were the cones and the smaller cells were the rods).

The results they found were as expected: the older you get, the fewer photoreceptors you have and the worse your eyesight is. The decline of the number of photoreceptors was at a constant rate throughout all ages of life. However, the number of rods declined faster than the number of cones. The loss of these photoreceptors causes you to view things with more difficulty. As your rods die, you begin to develop night blindness (the inability to see well in poor lighting or darkness). When your cones die, you begin to lose more of your visual perception, which includes straining when looking at something from a distance, as well as affecting how you see fine detail such as reading a book or looking at a television. The combined loss of your rods and cones is part of what causes older individuals to have more vision problems.

As you progress through life, your photoreceptors decline, causing your vision to get worse. As you sit down after Thanksgiving to enjoy some good old-fashioned fall football and the elderly people strain to see the television, you now know that the oldest person in your family is most likely having the hardest time seeing that big touchdown.


If you would like to read the actual paper, the source is located below:

Panda-Jonas, S., Jonas J., Jakobczyk-Zmija, M. (1995). Retinal photoreceptor density decreases with age: Ophthalmology, 102 (12), 1853-1859

Vole Pee: An Epiphany (A Guest Post)

By Nate Kueffer

You’re driving down the road, looking out the window, and you see a large raptor hovering above a field. Have you ever wondered what exactly the raptor could see that you couldn’t? Well, it is thought that raptors may be able to sense ultraviolet light and use it to track voles through urine and feces trails.

A hovering kestrel, possibly tracking a vole. Photo by Mark Likner at Flickr.

Ultraviolet light is a non-detectable form of radiation by the human eye and is similar to X-rays and gamma rays. However, with the help of a black light human eyes can see different materials that we couldn’t see in visible light. The objects that humans can typically see under a black light are fluorescent. This means that the object has the ability to soak up ultraviolet light and then emit the light it took in and produce a light frequency that humans are able to detect.

Jussi Viitala from the University of Jyvaskyla in Finland, and Erkki Korpimäki, Päivi Palokangas (now Lundvall) and Minna Koivula from the University of Turku in Finland set out to find more conclusive evidence on raptors using ultraviolet light to hunt. The four researchers tested the hypothesis that in order to find prey patches, Eurasian kestrels, a species of raptor, look for vole scent marks visible in ultraviolet light. The voles’ scent marks are their urine and feces droppings, which show up under ultraviolet light. The researchers set up experiments in the field and in a laboratory setting.

Kestrel with a captured vole after a successful hunt. Photo by Eugene Beckes at Flickr.

In the laboratory setting, wild captured kestrels were released into a large area made up of four different arenas. All arenas were different, but did not allow any external visual cues. One arena had vole trails in ultraviolet light, another was clean with ultraviolet light, a third arena had visible light and vole trails, and the final arena was clean with visible light. The kestrels were then measured by their time spent over each arena. The kestrels in the laboratory seemed to prefer the arena with ultraviolet light and vole trails. The clean, ultraviolet-lit arena had the least amount of scans and time spent over that arena compared to the other three arenas. The kestrels had no preference over either arena with visible light.

The field setting had 3 experimental groups for 45 kestrel nest boxes: the first had artificial vole trails with urine and feces, the second had artificial vole trails, but no urine or feces, and the last was the control with no vole trails, urine, or feces. The 45 boxes were observed over 24 mornings when the researchers recorded the number of kestrels near each nest and their behavior (hunting, paired, or resting). For the field experiment, 27 of the 45 nest boxes attracted kestrels near them. The most commonly used nest boxes were near artificial trails with urine and feces. The kestrels avoided the other two nest box areas: the one with trails, but no urine, and one with no trails and no urine. This showed that the trails weren’t used as hunting cues. Paired or hunting kestrels preferred to spend time hunting near trails with urine or feces, and resting kestrels were seen evenly in all three areas. Also, four rough-legged hawks were seen hunting near the trails with urine and feces.

Both experiments showed kestrels using trails with markings from voles suggesting that the vole markings may be used to select hunting and nest sites. The researchers propose that the kestrels, in fact, use vole scent markings as visual cues. Kestrels and other predatory birds may use the ultraviolet light from vole markings to scan over large areas new to them before deciding to hunt or nest in the area. The next raptor you see out of your car window could be tracking its prey’s markings using ultraviolet light.


References
Olson, V. (n.d.). Raptor Vision. Retrieved December 10, 2014, from http://www.moremesa.org/wordpress/raptor-vision/

Q & A: Why does a black light make objects glow? (2007, October 22). Retrieved January 21, 2015, from https://van.physics.illinois.edu/qa/listing.php?id=1913

Viitala, J., Korplmäki, E., Palokangas, P., & Koivula, M. (1995). Attraction of kestrels to vole scent marks visible in ultraviolet light Nature, 373 (6513), 425-427 DOI: 10.1038/373425a0

Metabolism and Body Size Influence the Perception of Movement and Time

Zoetropes like this one have been used
for almost 2000 years. If you look in the
slits from the side, the image appears to
be animated. Image by Andrew Dunn
at Wikimedia Commons.

When we watch TV or a movie, we are essentially watching a series of still images presented in rapid succession… so rapid, in fact, that we perceive them to be a single moving image. The ability of movie-makers to convince us that still images are fluid in time is based on our physiology. Specifically, moving-pictures, as they were once called, rely on our critical flicker fusion frequency (CFF), the lowest speed at which we perceive a flashing light source to be a constant light. But we don't have our CFF so we can enjoy movies and TV; it came about from our need to identify and track moving objects.

The ability to identify and track moving objects is critically important for finding and catching prey, avoiding predators, and finding mates. It is these visual abilities that rely on an animal’s CFF. An animal with a low CFF will miss many visual details, like watching your TV with a fast-forward function that jumps ahead 15 seconds at a time. An animal with a high CFF will see all the details that happen in between with a fine-time-scale resolution. But if having a high CFF conveys such an advantage, why don’t all animals have a high CFF?

This week at Accumulating Glitches I talk about how an animal's size and metabolism can influence how it sees the world. Check it out here.

And to learn more, check this out:

Healy, K., McNally, L., Ruxton, G.D., Cooper, N., & Jackson, A.L. (2013). Metabolic rate and body size are linked with perception of temporal information Animal Behaviour, 86, 685-696 DOI: 10.1016/j.anbehav.2013.06.018

Caught in My Web: Food vs. Sex, Recording Vibrations, Genital Distractions, Singing Dogs and Extreme Vision

Image by Luc Viatour at Wikimedia

This week will be the first of a new feature: Caught in My Web, a collection of recent articles, blog posts, videos and more that shed light on interesting aspects of animal physiology and behavior.

 

1. There is often a tradeoff between food and sex. The Schneider Lab talks about the physiology of at what point a male will leave a meal to search for sex in Should I Stay or Should I Go? on the blog Sexandfoodand. To make things more interesting, the critters discussed are the nematode worms, C. elegans, and males are not seeking sex with females, but rather with hermaphrodites. And as a bonus, this article includes the best Harlem Shake video of all time!



2. If you liked my article, Interrupting Insects, on how male treehoppers use vibrations to court females, you’ll love this first-hand account of what it is like to do this kind of research! In his blog Missouri Historian, Micah Fletcher, Micah recounts his experience studying these critters in Eavesdropping on a Silent Symphony.



3. In ScienceNow, Helen Fields tells us how hawk moths giggle their genitals to prevent bats from catching and eating them in ScienceShot: Vibrating Genitals may Ward off Predators. A word of caution: If you are being chased by a hungry predator, try this at your own risk!



4. In Expedition to Find the New Guinea Singing Dog: The Rarest Dog in the World in Running Ponies at Scientific American Blogs, Becky Crew interviews James ‘Mac’ McIntyre, a field zoologist planning an expedition to find and study the world’s most elusive dog species.



5. And just for fun, here’s a video on extreme animal vision by Steve Rotfield Productions.