Editing Arctic fox (section)

===Reproduction===
In the spring, the Arctic fox's attention switches to reproduction and a home for their potential offspring. They live in large dens in frost-free, slightly raised ground. These are complex systems of tunnels covering as much as {{cvt|1000|m2}} and are often in [[esker]]s, long ridges of sedimentary material deposited in formerly [[Glacier|glaciated]] regions. These dens may be in existence for many decades and are used by many generations of foxes.<ref name="NOAA" />

[[File:Fox pups animals.jpg|thumb|Pups of Arctic fox with summer morph]]
Arctic foxes tend to select dens that are easily accessible with many entrances, and that are clear from snow and ice making it easier to burrow in. The Arctic fox builds and chooses dens that face southward towards the sun, which makes the den warmer. Arctic foxes prefer large, maze-like dens for predator evasion and a quick escape especially when red foxes are in the area. Natal dens are typically found in rugged terrain, which may provide more protection for the pups. But, the parents will also relocate litters to nearby dens to avoid predators. When red foxes are not in the region, Arctic foxes will use dens that the red fox previously occupied. Shelter quality is more important to the Arctic fox than the proximity of spring prey to a den.<ref name="ReferenceB" />

The main prey of the Arctic fox in the tundra are lemmings, which is why the white fox is often called the "lemming fox". The white fox's reproduction rates reflect the lemming population density, which cyclically fluctuates every 3–5 years.<ref name="dx.doi.org">{{cite journal|last1=Pagh|first1=S. |last2=Hersteinsson|first2=P. |name-list-style=amp|title=Difference in diet and age structure of blue and white Arctic foxes (''Vulpes lagopus'') in the Disko Bay area, West Greenland|journal=Polar Research|date=2008|volume=27|issue=1|pages=44–51 |doi=10.1111/j.1751-8369.2008.00042.x|bibcode=2008PolRe..27...44P|s2cid=129105385|doi-access=free}}</ref><ref name="doi.org" /> When lemmings are abundant, the white fox can give birth to 18 pups, but they often do not reproduce when food is scarce. The "coastal fox" or blue fox lives in an environment where food availability is relatively consistent, and they will have up to 5 pups every year.<ref name="doi.org" />

Breeding usually takes place in April and May, and the [[gestation period]] is about 52 days. Litters may contain as many as 25 (the largest litter size in the [[Order (biology)|order]] [[Carnivora]]).<ref>{{cite book|last=MacDonald|first=David W.|title=Biology and Conservation of Wild Canids|year=2004|publisher=Oxford University Press|isbn=978-0-19-851556-2}}</ref> The young emerge from the den when 3 to 4 weeks old and are weaned by 9 weeks of age.<ref name="NOAA" />

Arctic foxes are primarily [[Monogamy in animals|monogamous]] and both parents will care for the offspring. When predators and prey are abundant, Arctic foxes are more likely to be promiscuous (exhibited in both males and females) and display more complex social structures. Larger packs of foxes consisting of breeding or non-breeding males or females can guard a single territory more proficiently to increase pup survival. When resources are scarce, competition increases and the number of foxes in a territory decreases. On the coasts of [[Svalbard]], the frequency of complex social structures is larger than inland foxes that remain monogamous due to food availability. In Scandinavia, there are more complex social structures compared to other populations due to the presence of the red fox. Also, conservationists are supplying the declining population with supplemental food. One unique case, however, is [[Iceland]] where monogamy is the most prevalent. The older offspring (1-year-olds) often remain within their parent's territory even though predators are absent and there are fewer resources, which may indicate [[kin selection]] in the fox.<ref name="doi.org" />