THE ANIMAL FILES

Arctic fox

Vulpes lagopus

Winter white is one coat strategy, not the only one.

Arctic foxes combine a compact body with dense seasonal fur and flexible food use. White and blue colour morphs change differently through the year. Cached food and stored fat provide two ways to carry energy from plentiful periods into scarcity.[1]

Follow the evidence ↓
Arctic fox
Image: Hobboto4ek (Ольга Яковлевна Куликова / Olga Y. Kulikova) · Commons · CC BY-SA 4.0
Two colour routes
The blue morph remains dark in winter.[1]
A compact heat budget
Short ears and muzzle limit exposed area.[1]
Storing in two places
Food caches and body fat bridge shortages.[1]

Two colour routes

The white morph changes from a brownish summer coat to white in winter. The blue morph remains grey, brown or dark, becoming only somewhat lighter. Both have insulating fur despite their different colours.[1]

A compact heat budget

A compact shape and short extremities reduce surface area relative to body volume. Dense underfur contributes insulation, and countercurrent exchange in the legs helps conserve heat. These features work alongside behaviour rather than eliminating the need for food.[1]

Storing in two places

Lemmings and other rodents are important where available, while coastal populations can rely heavily on birds. Foxes also scavenge and cache eggs or other foods. Energy can remain outside the body in a cache or inside it as fat.[1]

A COMMON MIX-UP

Must every Arctic fox turn pure white in winter?

No. The blue morph remains darker and changes less dramatically.[1]

TRY A LITTLE REASONING

How does a cached egg differ from stored body fat as an energy reserve?

Reveal the explanation

The egg remains food outside the fox until retrieved, while fat is energy already stored within its body.[1]

Sources & editorial notes

Adapted and translated from the cited Wikipedia revisions, with source-linked reasoning. Image credit and licence are listed separately above.

Adapted and translated from Wikipedia contributors; exact revisions are linked below. CC BY-SA 4.0

  1. Wikipedia contributors — Arctic fox (cited revision)
  2. NCBI Taxonomy — Vulpes lagopus

Last fact check:

One discovery leads to another

WolfA pack is a social family, not just a contest for a title.Canis lupus ↗CoyoteA pounce, a den and a chorus are three different clues.Canis latrans ↗Brown bear“Brown” is a species name, not a reliable colour swatch.Ursus arctos ↗