Night Hunters

Nocturnal animals are most active at night.  These animals have developed senses, abilities, and hunting strategies over millennia to exploit the nighttime hours, living and hunting in the same habitats as daytime species.  Many nocturnal hunters are more energy efficient in cooler temperatures; some have darker coloration to more easily blend in; and some have jagged silhouettes making them harder to spot.

^{_{Gaboon Viper, Bitis gabonica, showing pit by DonArnold; Copperhead, Agkistrodon contortrix, showing pit by DonArnold; Spider at night by Masse-j, Jul 2015}}

There are advantages to living at a time of day when there is less general activity.  Predators may become more active at night if their prey is nocturnal.  Ambush hunters may find prey is not as nimble in the dark and cannot escape as easily.  Nighttime hunters have less competition for the same species hunted in the daytime.  No animal can see in complete darkness, but let’s take a look at some of the adaptations that allow nocturnal species to distinguish detail and overall clarity as light levels ebb.

Strategies and senses involved in detecting prey are numerous, whether an animal is a daytime or nighttime hunter.  One of the most often recognized is vision – the ability to see prey.  Eyes have two types of cells, rod cells and cone cells, that convert light into nerve signals to the brain.  Cone cells, clustered in the center of the retina, work best in bright light to reveal detail and color.  Rod cells surround the outside of the retina and can detect motion in black-and-white or low-light.  Some species have an additional reflective layer, the tapetum lucidum, located behind the retina.  It acts as a mirror to reflect any light coming through the eye back into the eye, effectively making any image brighter.

_{Barn Owl, Tyto alba, by DonArnold; American Alligator, Alligator mississippiensis, by DonArnold}

Owls have large, forward-facing eyes with binocular vision and depth perception.  Their eyes can pick up light 100 times dimmer than what humans can see.  Big cats, such as leopards, can see 6 to 8 times better than people can and use stealth to take down prey bigger than themselves.  The American alligator and Nile crocodile are ambush hunters with excellent low light level eyesight, being able to detect slight movements and silhouettes on shorelines.  All of these animals use the extra rods in their large eyes to detect movement within short striking distances.

Hearing involves the ability to pick up noise from soft to loud levels.  Fox and coyote can hear sound up to two miles away.  Their ears can move independently to almost any angle and are used to triangulate sound so they can pinpoint the source.  They are especially attuned to higher frequency noise that is often made by smaller rodents or noises made from prey located under snow, dirt, or brush.  Owl ears are asymmetrical, meaning they are not balanced on either side of the head.  Sounds are heard by each ear at slightly different times, again allowing the bird to triangulate and identify the exact location of their quarry.

Hearing also involves the ability to mask sounds so others cannot locate the predator.  For owls, flight feathers have ragged edges and velvety surfaces, both adaptations making the air flow through and over their feathers with little or no noise.  This makes the owl hard to detect by the prey they are hunting.  Large, well-padded paws on big cats provide them with the ability to make slow, quiet approaches to their prey.

Many predators have senses that work any time of day, but choose nighttime hours due to cooler temperatures and less competition.  Sharks have ampullae, organs that detect electric fields which are produced anytime a muscle is contracted by an animal.  Cat’s whiskers and body hair on scorpions detect vibrations in the ground or the air created by other creatures’ movements.  Pit vipers, pythons, and boas all have heat sensing abilities that can detect minute temperature changes close by as prey comes within striking range.  Crocodiles have pressure sensitive scales to detect water disturbances such as prey coming to drink at the water’s edge.  Bats use echolocation, sending out their own sound waves that bounce back to them after hitting an object, identifying size, shape, and distance to that object.  Forest bats use higher frequencies with shorter wavelengths that provide detail at short range, while open grassland bats use longer wavelengths that provide detail at farther distances.

Many species have abilities to navigate, hunt, and avoid danger themselves in the darker hours.  However, light pollution makes these natural abilities harder or impossible to use.  We can respect the nighttime species by turning off any unnecessary outside lights at night, so we can enjoy observing more of those same nighttime wonders.  Learn more at the Jurica-Suchy Nature museum, or a nature center close to you.