Polar bears are one of the most iconic animals in the world. Their beautiful white fur coats allow them to camouflage in the Arctic snow and ice. However, at times polar bears can appear more yellow or cream colored. This has led many people to wonder – why do polar bears look yellow sometimes?
The Structure and Color of Polar Bear Fur
Polar bear fur consists of two layers – a dense undercoat and longer guard hairs. The underfur is made up of fine, soft hairs that provide insulation. This undercoat is typically not visible. The guard hairs are longer, coarser hairs that protect the undercoat and repel water. These outer guard hairs are hollow and translucent, which allows light to pass through and give polar bears their white appearance.
While the guard hairs appear white, they actually have no pigment. Polar bears look white because the hairs refract and scatter all visible wavelengths of light equally. This complete scattering of visible light makes the fur appear white to our eyes. However, the individual hairs are transparent at their tips, allowing the color of the skin and underfur to influence the bear’s overall color.
Why Do Polar Bears Sometimes Look Yellow or Cream?
There are a few reasons why polar bears may temporarily appear more yellow or cream in color:
- Age and fur condition – Cubs and juveniles have thinner, more sparse fur that can take on a yellowish hue. Older bears with more worn or damaged fur may also lose their bright whiteness.
- Dirty or wet fur – Polar bear fur that becomes dirty or stained from algae, mud, oil, etc can make the bears appear more yellow. Wet fur also tends to look darker.
- Sunlight effects – Intense sunlight can sometimes give polar bear fur a more yellow cast, especially if the fur is thin or damaged.
- Molting season – Polar bears molt once per year, replacing their entire coat. During molting their fur may become stained, matted, and yellowed.
- Skin tone showing through – The skin and underfur of polar bears can range from pink to yellow. As bears age and their guard hairs thin, more skin tone shows through.
However, these color changes are usually only temporary. Once the bear molts, cleans its fur, returns to shade, or restores fur density, the bright white color will return.
How Does Fur Color Help Polar Bears Survive?
Polar bears’ white fur provides crucial camouflage when hunting on the sea ice. By blending in with their snowy surroundings, the bears can stalk closer to prey without being seen. This helps them successfully hunt seals, their favorite prey. The whiteness also reflects heat and keeps the bears warm.
However, the Arctic sea ice is rapidly declining due to climate change. This forces polar bears to spend more time on land instead of on their ice hunting grounds. On land, the bears’ white coats stand out starkly against dark soils, vegetation, and rocks. This makes hunting on land much more difficult for polar bears compared to camouflaging on ice.
How Does Fur Color Change Throughout the Year?
Polar bears undergo an annual molt each spring and summer to replace their entire fur coat. This begins around late April to early May and lasts through August or September. Polar bear fur is at its whitest and fullest during winter months after completing the molt.
During the molt, polar bears may rub on snow and ice to help shed their old, worn fur. They also spend more time in the water during this period. Their fur gradually takes on a yellowish, dingy cast as it wears. By late summer, bears emerge from the molt with a fresh, full white coat just in time for the return of winter ice.
| Month | Fur Condition |
|---|---|
| January-March | Thickest and whitest fur after completing molt |
| April-May | Molting begins, fur may start yellowing |
| June-August | Molting peaks, fur at its thinnest, yellowest, and dirtiest |
| September-October | Molt wrapping up, fur improving and whitening |
| November-December | Freshly molted thick white coat as winter returns |
How Does Diet Affect Fur Color?
Polar bear fur gets its bright white color from dietary amino acids. In particular, the amino acid tyrosine has been found to be crucial for depositing white pigment into mammal fur. When animals do not get enough tyrosine in their diets, it can result in paler fur colors.
Polar bears get most of their tyrosine from the high protein diets they eat while hunting and feeding on seals. During times where seals are less available, such as summer months when sea ice recedes, bears may not get enough tyrosine in their diets. This nutritional deficiency can contribute to molting fur turning more yellow until their diet improves.
Do Populations Have Different Fur Colors?
There are 19 different polar bear subpopulations across the Arctic. While their fur may show temporary variations in color, there are no distinct color differences across populations. All healthy polar bears maintain bright white fur throughout adulthood.
However, one exception was a lone female bear that lived in the Beaufort Sea region. Dubbed “the Golden Bear”, this bear had golden-tinged fur due to a leucistic condition. Leucism prevents full pigmentation, resulting in white or patchy color. The golden bear was not an albino as she had some pigmentation in her eyes and skin.
Threats to Polar Bears Related to Fur Color
Climate change poses the biggest threat to polar bears’ survival, especially the decline of sea ice. As sea ice shrinks, polar bears are forced to spend more time on land and wait longer for the ice to refreeze so they can hunt seals. Spending more time on land leads to polar bears’ white fur becoming more stained and matted from dirt and algae.
This darker fur color makes it much harder for the bears to successfully hunt while on land. And if the bears cannot hunt enough seals, they cannot replenish the protein and amino acids in their diets needed to regenerate bright white fur. This creates a negative cycle threatening the bears’ survival.
Oil spills are another threat, as contact with oil damages and yellows polar bear fur. One study of polar bears affected by oil found it took over 3.5 years for bears to fully recover normal fur colors after an oil spill exposure.
Conclusion
In conclusion, polar bears’ beautiful white coats sometimes take on a temporary yellowish hue due to age, molting, dirt, oil, sunlight, and nutritional deficiencies. But across populations, healthy adult polar bears maintain snowy white fur year-round thanks to their hidden skin tone and translucent guard hairs. This camouflage helps them expertly hunt seals on the ice. However, threats from climate change and oil spills may make it harder for polar bears to keep their iconic fur looking bright white.
