Nocturnal Animals

I like to get outside every day, but with these really hot days oftentimes I go for a walk late in the evening as things start to cool off.  It is quieter and pleasant – but not too quiet.  There are still lots of sights and sounds of nature at night.  What are all of these animals that are out well into the night?  And why are they not active during the day?  And how do they see in order to do anything?

All animals use their senses to find food and shelter and avoid predators.  Nocturnal (active at night) animals have heightened senses or special adaptations that help them survive in the dark.  Sight is the sense that humans rely on the most, but it is not as useful when there is very little light available.  Structures in the eye called cones allow animals to see color.  Other structures called rods are used to gather light.  The more rods in the eye, the better an animal can see overall, and especially at night.  Some nocturnal animals such as raccoons, bobcats, owls and rabbits have many more rods than daytime animals allowing them to see much clearer in the dark.  And many of those same animals have very large pupils that let in more light.

Owls, opossum, deer and fox have much better hearing than most other animals.  Hearing adaptations include having larger ears, many of which are cup-shaped in order to gather more and fainter sound waves.  A hertz (hz) is a unit of measure for soundwaves.  We can hear between 20hz and 20,000hz, whereas a mouse can hear from 1,000hz to 100,000hz.  This means the mouse can detect an insect moving under the leaves from several yards away.  Another adaptation of many nocturnal species is asymmetrical ears.  They can hear from each ear independently, allowing them to triangulate where the sound is originating.  Triangulation can help identify the direction the sound is coming from – right, left, up or down, as well as how far away the point of origin is.

Echolocation, a specialized version of a hearing adaptation is used by bats in our area.  The bat produces a high-pitched sound wave that is returned to the bat’s ears after it has bounced off another object.  Bats use echolocation to determine an object’s size, shape, distance and whether the object is moving or stationary.  If the object is moving, the bat can also determine the direction.  A bat can emit calls at a slow rate of 15-20 per second up to 200 per second when closing in on prey.

Smell is another sense used for hunting.  Fox, raccoon, coyote, mink and skunk all have enhanced nasal passages and brain centers for detecting and identifying odors.  They have enhanced abilities to detect fainter odors and to be able to identify their origin to a finer degree.  Nighttime air is often still and moist, allowing scent molecules to linger longer, enabling an animal to better locate food as well as detect predators.

All of these differences make life easier at night for nocturnal species. There are fewer predators,  and it is easier to hide in order to avoid becoming a meal.  But there is also less competition with other predators to find food, and enhanced senses to create unique  hunting strategies.  Light pollution can be a huge negative influence on true nocturnal species.  Constant night light sources affect species dependent on day-night triggers for behavioral patterns.  Migration patterns may be disrupted; insects are attracted to light/heat sources only to be trapped and/or killed; reproductive cycles can be altered.  In the green frog, an Illinois native, males will call less and move around more making it much harder for females to find and mate with them. 

You can learn more by spending some time enjoying the nighttime yourself.  Use your senses to detect what is active in your own backyard after dark.  Try observing with and without a flashlight or your porch light.  Give other species time to get comfortable with you being outside by spending 5-7 minutes sitting quietly before moving around.  Use a cell phone to record what you are hearing, and write down your observations and experience as soon as you can after returning indoors.  Consider repeating this activity on a rainy night or a winter night, and keep a journal of your experiences to learn and better understand the habitats where you live.