Seasonal color change in animals

What do Arctic foxes, hares and ptarmigans have in common?

These animals are found up north in Europe and America/Canada, and they have adapted to a life in an environment that is highly affected by changes in weather from one season to another. During summer the sun can be hot, and the environment is composed of green vegetation, soil and rocky layers in between. In winter, the temperatures can go really low over long periods of time, especially in alpine areas. The winter can last for 6 to 8 months and with it comes great amounts of snow that paints the environment in white colors. For an animal living under such changing conditions, having one color throughout the year will make them really vulnerable. These animals mentioned, have together with several other species adapted two types of coats, one for winter and one for summer.

Winter coat is thick, long and white, and gives good protection and isolation against low temperatures and cold arctic winds. It also matches the background perfectly and provides a good camouflage. During summer the environment changes, and the coat also changes to match the background, and to make the animal more comfortable when the temperature rises. This time of year the coat gets more grey or brown depending on the species, and the coat gets shorter(if fur) and not so dense and warm(Harris 2009).

The obvious strategy behind this color change is camouflage and background matching. For example, a brown hare against a white background of snow would be a very easy target for an eagle soaring in the sky. Natural selection seems to favor the animals that match the background best. Animals that have the ability to match the changing background by producing different colors of fur or feathers, have a higher probability of surviving, and will through time reach a higher fitness level because they are less preyed upon. There is a reason why you in arctic climates can find the same color patterns in several very unrelated species of animals. They have all been shaped by the same harsh environment and faced the same challenges when it comes to blending in, so the white winter coat is a result of convergent evolution, an adaption to better fit in.

How and when do the animals change their coat? A research from 1970 on mountain hare in Scotland, gave researchers a clue about which mechanisms that lies beneath the color change. The shedding of fur is thought to be triggered by change in daylight – in other words daylengt(Flux 2009). When the days grow shorter, this will trigger release of hormones(Harris 2001) in the animal that leads to changes in colors and composition of the coat. Temperatures on the other hand will decide how fast this change will occur(Flux 2009). When days grow shorter during fall, the change of color can be postponed if the temperatures are high, and same can happen in spring if the weather are very cold, then the white fur might be shed later. On the other hand, if spring arrives early one year and it is really hot, they can shed their fur in a couple of days, compared to other times where they can use 2-3 weeks. (Flux 2009)

There are several animals that are found in the northern hemisphere that displays distinct winter and summer coats, some examples are: Species of hare and mouse, the barren ground caribou(not fully white winter coat though), the weasel(the ermine), the arctic fox, and the ptarmigan(grouse, bird).

This is a ptarmigan that you can find up in alpine areas in Norway. During winter this bird is displaying a wonderful winter coat. Photo: Per Ivar Somby.

Viewed 30 April 2014, <http://nrksuper.no/super/blog/dyr-i-vinterdrakt/ >

Same bird in summer coat:

Photo: Terje Kolaas

viewed 30 April 2014, <http://www.birdlife.no/naturforvaltning/nyheter/?id=1231 >

The weasel, also found in Norway, have a brown and white summer coat, but entirely white winter coat. Photo: Anne Elliott.

Viewed 30 April 2014, <http://nrksuper.no/super/blog/dyr-i-vinterdrakt/ >

Biography:

Flux, JEC 2009(date of publishing on internet- first ever published 1970), 'Colour change of Mountain hares (Lepus timidus scoticus) in north-east Scotland', Journal of Zoology, vol.162, no 3, pp. 345-358, viewed 30 April 2014, <http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1970.tb01270.x/pdf >

Harris, T 2001, HowStuffWorks.com(Discovery communications), Atlanta, US,viewed 30 April 2014,<http://animals.howstuffworks.com/animal-facts/animal-camouflage2.htm >