---
title: "What the sources say about the Reindeer (Caribou) | AnimalTracks.wiki"
description: "61 claims from the Reindeer (Caribou) profile, each beside the words of the source that backs it."
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---

# What the sources say about the Reindeer (Caribou) (*Rangifer tarandus*)

> 61 claims from the Reindeer (Caribou) profile, each beside the words of the source that backs it. A "..." marks a cut in a quote and [brackets] an insertion.

Profile: [Reindeer (Caribou)](https://animaltracks.wiki/animals/reindeer/)

## Caribou (Wildlife Notebook Series). Alaska Department of Fish and Game, 2025.

https://www.adfg.alaska.gov/static/education/wns/caribou.pdf

| The page says | The source says |
| :--- | :--- |
| the only deer where cows grow antlers too | Caribou are the only member of the deer family (Cervidae) in which both sexes grow antlers. (note: tagline phrasing; moved from ADW (2000) to the ADF&G notebook (revised 2025)) |
| is the only member of the deer family in which both sexes grow antlers | Caribou are the only member of the deer family (Cervidae) in which both sexes grow antlers. |
| In Alaska, adult bulls average 350 to 400 pounds (159 to 182 kg) | Weights of adult bulls average 350-400 pounds (159-182 kg). (note: scoped to Alaska: the notebook describes Alaska's caribou ('Alaska has only the barren-ground subspecies') and follows the weights with how they vary across Alaska) |
| though weights of 700 pounds (318 kg) have been recorded | However, weights of 700 pounds (318 kg) have been recorded. |
| while mature cows average 175 to 225 pounds (80 to 120 kg) | Mature females average 175-225 pounds (80-120 kg). |
| pregnant cows usually keep theirs until their calves are born in late spring | Pregnant females usually retain their antlers until calves are born in late May or early June. |
| In summer they eat the leaves of willows, sedges, flowering tundra plants, and mushrooms | In summer (May-September), caribou eat the leaves of willows, sedges, flowering tundra plants, and mushrooms. |
| Their large, concave hooves spread wide to hold them up on snow and soft tundra, like snowshoes, and work as paddles when they swim | Caribou have large, concave hoofs that spread widely to support the animal in snow and soft tundra. The feet also function as paddles when caribou swim. (note: 'like snowshoes' is a simile for the source's own mechanism (hooves that spread widely to support the animal in snow)) |
| In Alaska, large herds often migrate up to 400 miles between summer and winter ranges | Large herds often migrate long distances (up to 400 miles/640 km) between summer and winter ranges. (note: scoped to Alaska: the notebook describes Alaska's herds, and FDA (2023) gives up to 1,000 miles for herds elsewhere, so 400 is not a species maximum) |
| covering up to 50 miles a day once they set off | Once they decide to migrate, caribou can travel up to 50 miles a day. |
| though smaller herds may not migrate at all | Smaller herds may not migrate at all. |
| Willow leaves, sedges, flowering tundra plants, and mushrooms in summer | In summer (May-September), caribou eat the leaves of willows, sedges, flowering tundra plants, and mushrooms. (note: stats.diet) |

## Caribou. Alaska Department of Fish and Game.

https://www.adfg.alaska.gov/index.cfm?adfg=caribou.main

| The page says | The source says |
| :--- | :--- |
| Caribou live on Arctic tundra, mountain tundra, and in the northern forests of North America, Russia, and Scandinavia | Caribou live in the arctic tundra, mountain tundra, and northern forests of North America, Russia, and Scandinavia. |
| In some areas, wolves, grizzly bears, and golden eagles kill large numbers of newborn calves | In some areas, wolves, grizzly bears, and golden eagles kill large numbers of newborn calves. |
| Caribou swamp them: the cows in a herd give birth to a lot of calves in a very short time, more food than nearby predators can eat | Caribou “swamp” predators – the cows in a herd give birth to a lot of calves in a very short period of time, essentially overwhelming predators in the area with an overabundance of food. |
| Arctic tundra, mountain tundra, and northern forests of North America, Russia, and Scandinavia | Caribou live in the arctic tundra, mountain tundra, and northern forests of North America, Russia, and Scandinavia. (note: stats.habitat) |

## Fun Facts about Reindeer and Caribou. U.S. Food and Drug Administration, Animal Health Literacy, 2023.

https://www.fda.gov/animal-veterinary/animal-health-literacy/fun-facts-about-reindeer-and-caribou

| The page says | The source says |
| :--- | :--- |
| Compared to body size, their antlers are the largest and heaviest of any living deer species | Compared to their body size, reindeer have the largest and heaviest antlers of all living deer species. |
| a bull's can be up to 51 inches long, and a cow's can reach 20 | A male's antlers can be up to 51 inches long, and a female's antlers can reach 20 inches. |

## Caribou. Hinterland Who's Who, Canadian Wildlife Federation.

https://www.hww.ca/en/wildlife/mammals/caribou.html

| The page says | The source says |
| :--- | :--- |
| most cows carry a set | This animal is unusual among deer family members in that most females, as well as males, carry antlers |
| The large bulls lose theirs after the autumn mating season | The large bulls lose their antlers after the autumn mating season |
| Using lichens as their primary winter food sets them apart from all other large mammals and has let them survive on harsh northern range | The ability of caribou to use lichens as a primary winter food distinguishes them from all other large mammals and has enabled them to survive on harsh northern rangeland. |
| Wolves are the caribou's primary predator | which as prey species of the wolf, attract this primary predator of caribou |
| a wolf eats a variety of prey but needs food equal to 11 to 14 caribou a year | A wolf eats a variety of prey but requires food equivalent to 11 to 14 caribou a year. |
| Grizzly and black bears, cougars, wolverines, lynx, coyotes, and golden eagles also prey on caribou | Other predators of caribou include grizzly and black bears, cougars, wolverines, lynx, coyotes, and golden eagles. |
| In danger, a caribou rears up on its hind legs and leaves a scent from glands at the base of its ankles that alerts other caribou | Scent glands located at the base of the ankles are used when the caribou is in danger: the animal rears up on its hind legs and deposits a scent that alerts other caribou to the menace. |
| Antlers Mean Dominance | In the deer family, antler size means dominance. (note: blockquote lead-in) |
| By late winter, when conditions are harshest, pregnant cows still carry their antlers long after the large bulls have dropped theirs | By late winter when conditions are most severe, pregnant females are the dominant members of the herd, because they are the only ones to have retained their antlers. The large bulls lose their antlers after the autumn mating season (note: HWW's 'only ones to have retained their antlers' is not repeated: the ADF&G notebook (2025) says small bulls and non-pregnant cows keep theirs until April) |
| That makes them the dominant members of the herd, able to defend their feeding craters and even push larger caribou off favoured spots | pregnant females are the dominant members of the herd ... The females' dominance allows them to defend their feeding craters from larger caribou and even displace larger caribou from favoured sites. |
| lichens are the primary winter food | Ground and tree lichens are the primary winter food of caribou (note: stats.diet) |
| Most female caribou carry antlers, which is unusual among deer | This animal is unusual among deer family members in that most females, as well as males, carry antlers (note: FAQ 3) |
| in the deer family antler size means dominance | In the deer family, antler size means dominance. (note: FAQ 3) |
| The large bulls lose their antlers after the autumn mating season | The large bulls lose their antlers after the autumn mating season (note: FAQ 3) |
| By late winter, when conditions are harshest, pregnant cows are the dominant members of the herd because they still carry theirs | By late winter when conditions are most severe, pregnant females are the dominant members of the herd, because they are the only ones to have retained their antlers. (note: FAQ 3; HWW's 'only ones to have retained their antlers' softened to 'still carry theirs', because the ADF&G notebook (2025) says small bulls and non-pregnant cows keep theirs until April) |
| That lets them defend their feeding craters from larger caribou and even push larger caribou off favoured spots | The females' dominance allows them to defend their feeding craters from larger caribou and even displace larger caribou from favoured sites. (note: FAQ 3) |
| most pregnant cows keep their antlers until after they give birth in June | Most pregnant females will keep their antlers until after they give birth in June. (note: FAQ 3) |

## Caribou. Denali National Park & Preserve, National Park Service.

https://www.nps.gov/dena/learn/nature/caribou.htm

| The page says | The source says |
| :--- | :--- |
| feet that click when it walks | Caribou produce a characteristic clicking sound as they walk due to tendons snapping past the sesamoid bones in their foot. (note: tagline phrasing) |
| Walking comes with a click, the sound of tendons snapping past sesamoid bones in the foot | Caribou produce a characteristic clicking sound as they walk due to tendons snapping past the sesamoid bones in their foot. |
| the click a caribou makes as it walks, from tendons snapping past the sesamoid bones in its foot | Caribou produce a characteristic clicking sound as they walk due to tendons snapping past the sesamoid bones in their foot. (note: vibe.reason, settled in #182: replaces 'vast subarctic tundra resonance', which argued from geography; the frame-drum beat now rests on the walking click) |

## Rangifer tarandus. AnAge: The Animal Ageing and Longevity Database, Build 15, 2023.

https://genomics.senescence.info/species/entry.php?species=Rangifer_tarandus

| The page says | The source says |
| :--- | :--- |
| On average a reindeer lives 10 to 11 years, in the wild or in captivity | Average lifespan in captivity is similar to what is observed in wild populations (10-11 years). |
| the record in captivity is 21.8 years | Record longevity in captivity is 21.8 years |

## Fosbury & Jeffery (2022). Reindeer eyes seasonally adapt to ozone-blue Arctic twilight by tuning a photonic tapetum lucidum. Proceedings of the Royal Society B: Biological Sciences.

https://doi.org/10.1098/rspb.2022.1002

| The page says | The source says |
| :--- | :--- |
| Eyes that shine deep blue in the Arctic winter | During the long Arctic winter, with the sun below the horizon, the reflection transforms to a deep blue. (note: tagline; 'shine' is the tapetum's reflection (eyeshine), not the iris) |
| Reindeer are the only mammal known to seasonally adapt their eyes to the extremely blue Arctic twilight | Reindeer are the only mammal known to seasonally adapt their eyes to the extremely blue colour of the extended twilight that occupies a large part of the winter 24 h cycle in their Arctic habitat. |
| Behind the retina sits a tapetum lucidum, a mirror-like layer that sends light back through the light-sensing cells for a second pass | a layer directly behind the retina that acts as a mirror ... to redirect incoming light back through the photoreceptors for a second pass |
| In summer it reflects gold and turquoise, like many other mammals' eyes | During the extended exposure to summer daylight, the tapetum reflection shows a gold-turquoise colour similar to many other mammals. |
| In the long Arctic winter it turns deep blue | During the long Arctic winter, with the sun below the horizon, the reflection transforms to a deep blue. |
| its peak matching the color of twilight | While the first-order peak in winter matches the spectral distribution of twilight |
| Researchers propose how: the fluid between its collagen fibers shrinks, letting the fibers pack closer together | We propose that this happens by a decrease of the spacing of the parallel rod-shaped fibrils in the crystal when the volume of the inter-fibril fluid decreases (note: the paper frames the mechanism as a proposed, tested model; the fibrils are collagen ('photonic crystal of parallel collagen fibrils')) |
| mirror layer behind the retina | a layer directly behind the retina that acts as a mirror (note: stats.superpower) |
| shifts from gold-turquoise in summer to deep blue in winter | During the extended exposure to summer daylight, the tapetum reflection shows a gold-turquoise colour ... During the long Arctic winter, with the sun below the horizon, the reflection transforms to a deep blue. (note: stats.superpower) |
| to match Arctic twilight | While the first-order peak in winter matches the spectral distribution of twilight (note: stats.superpower) |
| Behind a reindeer's retina sits a tapetum lucidum, a mirror-like layer of collagen fibers that sends light back through the retina's light-sensing cells for a second pass | a layer directly behind the retina that acts as a mirror ... to redirect incoming light back through the photoreceptors for a second pass (note: FAQ 1; collagen from the abstract's 'photonic crystal of parallel collagen fibrils') |
| In summer it reflects gold and turquoise | During the extended exposure to summer daylight, the tapetum reflection shows a gold-turquoise colour similar to many other mammals. (note: FAQ 1) |
| with a peak that matches the color of twilight | While the first-order peak in winter matches the spectral distribution of twilight (note: FAQ 1) |
| The researchers who measured it propose how: the fluid between the fibers shrinks, letting them pack closer together | We propose that this happens by a decrease of the spacing of the parallel rod-shaped fibrils in the crystal when the volume of the inter-fibril fluid decreases (note: FAQ 1) |

## Hogg et al. (2011). Arctic reindeer extend their visual range into the ultraviolet. Journal of Experimental Biology.

https://doi.org/10.1242/jeb.053553

| The page says | The source says |
| :--- | :--- |
| In Arctic reindeer the cornea and lens also let some ultraviolet light through, and the retina's rod and cone cells both respond to it | the cornea and lens in Arctic reindeer do not block all UV and that the retina responds electrophysiologically to these wavelengths. Both rod and cone photoreceptors respond to UV at low-intensity stimulation. |
| That may help them pick out differences in how Arctic vegetation and types of snow reflect it | A specific advantage of this short-wavelength vision is the use of potential information caused by differential UV reflections known to occur in both Arctic vegetation and different types of snow. |
| paired with a retina that also responds to ultraviolet light | the retina responds electrophysiologically to these wavelengths (note: stats.superpower; 'these wavelengths' are the UV named earlier in the sentence) |
| Arctic reindeer extend their visual range into ultraviolet wavelengths | the retina responds electrophysiologically to these wavelengths. Both rod and cone photoreceptors respond to UV at low-intensity stimulation. ... Reindeer thus extend their visual range into the short wavelengths characteristic of the winter environment (note: FAQ 2; the abstract's 'short wavelengths' are the UV of its preceding sentences, and the paper's title says 'into the ultraviolet') |
| their cornea and lens do not block all ultraviolet light, and the retina's rod and cone cells both respond to it | the cornea and lens in Arctic reindeer do not block all UV and that the retina responds electrophysiologically to these wavelengths. Both rod and cone photoreceptors respond to UV at low-intensity stimulation. (note: FAQ 2) |
| That may help them pick out differences in how Arctic vegetation and different types of snow reflect ultraviolet light | A specific advantage of this short-wavelength vision is the use of potential information caused by differential UV reflections known to occur in both Arctic vegetation and different types of snow. (note: FAQ 2) |

## Holand & Mizin (2025). Rangifer tarandus. The IUCN Red List of Threatened Species 2025: e.T29742A224359765.

https://doi.org/10.2305/iucn.uk.2025-1.rlts.t29742a224359765.en

| The page says | The source says |
| :--- | :--- |
| Vulnerable | IUCN Red List category: Vulnerable (VU). (note: stats.conservationStatus, 2025 assessment) |