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 >

Distraction

Colors and patterns for distraction and escape:

Animals put a lot of time and energy trying to avoid being preyed upon, as examples they can camouflage themselves, or trying to make themselves less interesting, or advertise that they are distasteful or poisonous. But we all know that there are predators in these world, they live and they thrive, which means they must get food somehow. So what happens, if in despite of camouflage or other strategies to avoid attack, a predator spots something and decides to attack? Does this mean there is no escape? Of course there might be. Everyone knows that lots of animals have claws, teeth, and other defense mechanisms to fight of a predator physically, and some also chemically, like a bombarding beetle or a skunk. But did you also know that some animals rely on special colors and patterns as a distraction maneuver? Well, here are some ways animals can actually escape an attack without going into physical interactions and without being dangerous.

One of the most famous strategies is startle display(Wilson 2009). This means that an animal being attacked, suddenly show off some powerful and strong colors or patterns that will cause some kind of reaction in the predators behavior. Usually the flashing of color patterns causes the predator to hesitate for a moment, giving the prey some extra time, although maybe just a second or two, but enough to make an escape. Imagine that you are walking past a door, and someone is hiding behind it, and then suddenly jumps out in front of you shouting, the person doesn't need to be dangerous or be a treat to you at all, but you still will display some kind of reaction like freeze for a second or jump to the side to avoid that person. Basically, when something happens fast, which you don't see coming, your brain needs time to adjust and think about what happens and how you should react. This is kind of the same thing that happens when an animal suddenly goes from for example cryptic colors matching the background, til showing of all sorts of colors in a second. This is likely to be extra useful for animals that are slow or clumsy fliers, such as mantises and stick insects, because they need time to prepare for flight(Langridge 2009)

The peacock butterfly has cryptic colors when in a resting position, but if a threat appears, it will open its wings and flash its amazing colors.
From: <http://en.wikipedia.org/wiki/File:Inachis_io_bottom_side.jpg>, viewed 3 April 2014

 From: <http://www.warrenphotographic.co.uk/26028-peacock-butterfly>, viewed 3 April 2014.

Some patterns are proved to be especially good when it comes to creating a hesitation, and can even make the predator retreat. Eye spots are such patterns(Wilson 2009), they seem to be working great, and the pattern is found among many different animals, but is especially abundant among butterflies and moths. These eye spots are found on the wings, and is usually not visible when the butterfly or moth rests. But if in danger, the wings will be spread out, and suddenly a set of 'eyes' appear. The predator, in these cases often birds, will be very surprised and hesitate and might also pull back for a second. Sometimes the predator actually go for a retreat, and this is thought to be because the spots look like the eyes of an owl. And since owls are predators, many smaller animals then back off. Not only moths and butterflies display this pattern, also frogs, octopuses, stick insects, mantises and caterpillars display it, which seems to strengthen the theory of this strategy as being a successful one. It is obviously a feature that has convergently appeared in different groups of animals, and usually if something like this happens, it is because it has an advantage somehow.

This picture shows a Lo moth with eyespots similar to a big animal like an owl.
Picture from: < http://lepcurious.blogspot.com.au/2011/03/defenses-of-butterflies-eyespots.html > viewed 3 April 2014

Another trick some animals use, is displaying some kind of pattern or colors that look similar to a head or at least something that confuses the predator when it comes to which end is which(Wilson 2009). They might also conceal their real eyes in colors or stripes that makes the eyes less visible and this can create more confusion. Butterflies can for example have eyespots, something that looks like antenna, and a shape that may appear as a head on distance. The prinsiple behind this is to make the predator attack the side that is less vulnerable, and it also makes it possible to get away, because the predator will misjudge the direction the prey might be heading for an escape. Lots of animals can survive another day with a lost peace of their tail, but injuries on their anterior side will often be fatal(if they don't get eaten). Butterflies, fishes and centipedes are some animals that uses this technic to confuse predators. An animal that also uses this technic is a caterpillar that has eyespots making it look like a snakes head, fooling a predator in to believing that it is something entirely different than it actually is, which might scare a predator and make it retreat.

This picture show two caterpillars that has patterns on their head making them similar in appearance to a snake.
Picture from: < http://lepcurious.blogspot.com.au/2011/03/defenses-of-butterflies-eyespots.html > viewed 3 April 2014

This fish show a deflection display, drawing attention away from its head towards it's posterior end. Notice how the real eyes are goes almost unnoticed.
Picture from: <http://www.eplantscience.com/index/general_zoology/deflecting_an_attack.php>, viewed 3 April 2014

Although these technics mentioned seem to work in many cases, there are some drawbacks as well(Langridge 2009). If a predator don't use visual cues, like if the predator have bad/no vision or don't see all colors, it might not have any effect at all, so it comes down to which predator that actually hunts a particular prey.

Another effect you can find, is habituation, which means the predator is exposed to the flashing or the pattern several times and over time learn that this doesn't mean anything, or after a while learn to attack the real anterior end after several times of trial and failures. They get used to the display the prey puts up, and then the startling and frightening effect wears off. This means that it probably works best if the predator is a generalist.

Biography:

Wilson, C 2009, Animal behavior: Animal Defenses, Chelsea House, Infobase Publishing, United States.

Langridge, KV 2009, 'Cuttlefish use startle displays, but not against large predators',

Animal Behaviour, Vol.77, No.4, pp. 847-856, viewed 2 April 2014, < http://www.sciencedirect.com.elibrary.jcu.edu.au/ >.

Motion dazzle markings:

Animals have several strategies to avoid predation, and mimicry and camouflage are widely used, and seem to work well for lots of animals. There is one downside using these strategies though, and it is related to movement. When an animal moves, it is exposing itself, making it easy for a predator to spot it. This creates a huge challenge for animals that are moving around to find food sources, and is even more challenging as the animal increases in size, because it is then harder to hide, or make the body blend in with the background. To cope with this, it has been proposed that a good strategy to avoid predation might be something called motion dazzling. So what is this exactly?

Motion dazzle patterns are very bold and visible patterns, that are assumed to create confusion and mislead the predator. During experiments(Stevens, M, Yule, DH, Ruxton, GD 2008) scientists have proved such patterns to be efficient because they make it difficult for the predator to estimate speed, distance and direction. Patterns are proved to be more efficient if the speed increases, so it is likely to be more present in fast moving animals. If a predator- a lion, misjudges the distance to a zebra for example, this might lead to an attack ending in disaster. If a predator misjudges a distance, it might miss the target by centimeters to meters, depending on target, the patterns and the speed, but as long as misjudging is present, there is opportunities for the prey to escape, and this is likely the reason for why these patterns have evolved.

There hasn't been a lot of research on this subject, but there were a couple of researchers that worked with this and got supporting results for motion dazzling being efficient(Stevens, M, Yule, DH, Ruxton, GD 2008). They used a computer program to test if people were more or less likely to hit a target when the target wore stripes and zig- zag patterns, and they found that such patterns made it more difficult to succeed. Since human and vertebrate eyes work pretty much in the same fashion, it is likely that this can be transfered to nature as well.

There are found animals with these dazzling patterns among several taxa, including vertebrates, fishes, reptiles and some insects.

A highly debated animal within this area is the zebra. It has been believed for a long time that the stripes the zebra possesses are a good example of a motion dazzle pattern. Zebras are big animals, that are mostly found on grassland areas with open landscape where there is no place to hide. They have to move a lot during the day, which makes it even easier to detect them. Because camouflage is not really an option for these animals, it would make sense that the stripes would protect them against predators, making it harder to catch them due to misjudging as explained earlier. When they live in a herd, the stripes could even create more confusion. Focusing on one individual will be hard when all zebras have striped patterns that seem to blend in and mix with each other, the outline of an individual will then be hard to see. But one research project found little evidence for this being the case(Caro et al. 2014) when they looked at the distribution of zebras and big predators, and how efficiently the predators were at catching prey.

In general there is a lot of assumptions regarding this area, and little research done. It is hard to conclude if patterns we see are a result of evolution related to motion dazzling, or if there are entirely other reasons for the patterns we see. But it is obvious that some patterns can create confusion and misjugdgment, but if the bold stripes and zig-zag patterns are due to motion dazzle or not, is hard to tell.

The pictures below show examples of animals with bold or high contrast patterns:

Picture from <http://www.youtube.com/watch?v=cgdVVU8tBTQ>, viewed 8 April 2014.

Picture from <http://www.nytimes.com/2008/08/19/science/19obdazz.html?partner=rssnyt&emc=rss&_r=0>, viewed 8 April 2014  

Picture from <http://news.asiantown.net/r/33698/why-do-zebras-have-stripes-distinctive-markings-create-an-optical-illusion-that-dazzles-predators-and-masks-movement > viewed 8 April 2014

Biography:

Stevens, M, Yule, DH, Ruxton, GD 2008, 'Dazzle coloration and prey movement', Proceedings of the Royal Society: Biological science,vol. 275, no. 1651, pp 2639 – 2643, viewed 8 April 2014, <http://rspb.royalsocietypublishing.org/content/275/1651/2639.full >

Caro, T, Izzo, A, Reiner, AC, Walker, H, Stankowich, T 2014, 'The function of zebra stripes', Nature communications, vol. 5, no. 3535, viewed 8 April 2014 <http://www.nature.com/ncomms/2014/140401/ncomms4535/full/ncomms4535.html>