A very unique species of rodent can be found on the island of Hawai’i. These animals are called rock pocket mice, and they live in crevices in volcanic rock.
These mice have a dark gray to black fur covering their body, paired with a white belly. This is an excellent adaptation for living in the rocks, as they blend in with the dark lava flow rock.
Rock pocket mice are endemic to Hawai’i, which means they are native and exclusive to the islands. Although there are several subspecies of rock pocket mice, all of them live in the same environment and have similar traits.
Because these small rodents feed on seeds and fruits that fall from trees, they are considered frugivores. Like most animals, mating season is a busy time for rock pocket mice. Males will compete for females by wrestling each other.
Why dark-colored rock pocket mice have white bellies
A recent study on micro mammals was conducted by researchers at the University of New Hampshire. The team took samples from dark-colored rock pocket mice living in lava fields in eastern Oregon.
They found that these little creatures had white bellies, and they speculated that this might have something to do with camouflage. While their darker colored backs might help them hide from predators, their light colored bellies might help them hide in their rocky habitat.
The team also found that these mice were all male, which is unusual. It is believed that the gender bias is a result of environmental pressures such as limited food supply and/or limited shelter availability. This leads to increased competition among individuals of the same sex, which results in one individual surviving.
Dark lava produces dark surfaces
The rock pocket mice that live in the lava fields of the Columbia Basin in southern Washington state have a unique and adaptive feature — their dark-colored bellies.
Most varieties of these mice have black or very dark grayish-brown fur all over their bodies. This helps them camouflage in their natural habitat — the dark lava fields.
Since most of the land in this area is made of hardened lava, the soil is rocky and sparse. These little rodents need to hide out during the day to avoid predators, so they dig tunnels under the loose rock where they live. At night, they come out to forage for food.
Their white undersides help them stay cool by reflecting heat.
White belly rock pocket mice are better camouflaged
A series of brown and white patterns on the rock pocket mouse’s belly match the pattern of fresh lava as it flows down the hill. This camouflage helps these little rodents avoid being spotted by predators.
Because these mice live in the volcano crater, their habitat is constantly being changed by volcanic activity. As lava flows down the mountain, new soil is created and old soil is removed, changing the landscape.
As a result, rock pocket mice need to adapt their camouflage to match the new landscape. A white belly would no longer match the new background, so they developed this adaptation to continue surviving.
This is a phenomenon called physiological coloration, which refers to an animal’s coloration due to factors related to its physiology, or internal functions.
Lighter colored bellies reflect light better
As lava flows cool, pocket mice can hide in the dark cavities formed in the rock. A white belly makes it more difficult for predators to spot the mouse hiding in its hiding place.
Because lava flows take a long time to cool, this evolutionary adaptation may prove to be beneficial to the mouse. As lava flows are typically very thick, it takes a while for them to cool down completely.
As they cool, they form solid rock that mice can run and hide in. Since there is no need for a thick layer of fat under the skin, the mouse is not as fat as other types of rodents. This makes them faster and able to escape from predators!
Both of these traits help prevent extinction of the species.
Melanin in the body affects the belly coloration
A beautiful example of camouflage in the natural world is seen in the rock pocket mice that live on dark lava flows. These mice have dark fur, which helps them hide on the dark lava rock.
They also have white bellies, which helps them match the color of the dusty lava rock surface.
When these mice move, their white belly fur shows and then hides their dark fur underneath. This helps them stay hidden from predators as they scamper around the lava rocks.
How does this work? Melanin is a chemical that produces skin and hair color. It is found in most tissues of the body, including the skin and liver.
Whether it is found in the body internally or externally, it can act as a camouflage. Internal melanin can mask blood cells from visual predators.
White bellied rock pocket mice have an advantage
Dark-colored rock pocket mice living on the black lava flows have a harder time surviving and reproducing. A white belly allows these mice to hide in the white powder, making it easier for them to avoid predators and find food.
Because these rodents feed on fungi, they rely on rain to bring water and hence, nutrition to the dry lava flows. When there is no rainfall, their food source is scarce.
The researchers also found evidence of herbivore grazing on the vegetation. When there is less vegetation due to drought, herbivores eat more which can lead to population declines.
These findings show how important access to water and vegetation are for small mammals living in deserts. When conditions are dry or harsh, not all species survive or reproduce which can change an entire population.
Evolutionary adaptation occurs over time
As environments change, species must also evolve to survive. This can be due to environmental changes or as a result of other species evolving. As predators and prey adapt to each other, one of them may have to change in order to keep up the survival of the group.
The rock pocket mice that live on the dark lava flows have white bellies so they can camouflage themselves. The dark lava rock blends in with their white fur, making it harder for predators to see them.
Although they are small, they are very aggressive and will attack if threatened. This is a defensive mechanism that helps protect them from being eaten.
They live in underground tunnels and reproduce frequently. Some females may have up to five litters per year with two to five offspring per litter.
Rock pocket mice are nocturnal creatures
As adorable as rock pocket mice are, they have a very important ecological role. These little rodents eat seeds and help disperse them across the landscape.
Because they only come out at night, they hunt for food then as well. During the day, they hide in crevices in the lava rock where they make their homes.
Their smooth, brownish gray fur helps them blend into the rocks, making it hard for predators to spot them. Their large ears also help them detect predators and escape before being caught.
Unfortunately, due to climate change, the length of the night is getting shorter. This is causing some problems for the rock pocket mice as well as other nocturnal creatures. Fortunately, there are organizations that are working to help solve this problem.