December 2022 – Discover-Nature

Snake Defense

Snakes, with over 3,000 species worldwide, are one of the largest groups of reptiles. They are found on every continent except Antarctica and live in every type of habitat including freshwater and saltwater. They have numerous enemies and have developed defensive strategies enabling them to survive and prosper.

^{Catching a snake on the wing by CuriousLog, Jun 2007}

^{Red-shouldered hawk with snake by Don Loarie, Mar 2018}

^{Great Blue Heron eating snake by C Watts, Jan 202}2

Snakes must deal with threats from a wide range of animals. Bird species that prey on snakes include raptors, ravens, egrets , and storks. Nocturnal hunters, including owls, have excellent sight in low-light conditions and often hunt by spotting movement among foliage. Likewise, during daytime hours, red-tailed hawks and eagles can spot movement on the ground while soaring. Snakes are normally line-of-sight hunters, and are often unaware of threats from above, giving avian predators a distinct advantage.

_{^{American crocodile, Crocodylus acutus by Florida Fish and Wildlife, Feb 2021; Wolverine by Maia C, Aug 2012; Skunk by D Fletcher, May 2016}}

Most mammal predators are larger, more agile, and faster. Badger, wolverine, and racoon are all excellent climbers and may hunt from an elevated perch. Wolverine and skunk are also burrowers that will dig out their prey from underground. Snakes living in saltwater and freshwater environments are eaten by predators such as crocodiles and snapping turtles. In addition, some larger snake species regularly hunt smaller snakes.

^{Copperhead on dead leaves by Abbott Handerson Thayer, Mar 2022}

Snakes use a number of non-aggressive strategies to avoid confrontation and escape. Their best defense is to remain hidden, using colors and patterns to break up the outline of their body, allowing the snake to blend with the background foliage and be overlooked by any predators. Another passive strategy is balling, involving compressing their body into a tight coil or ball, typically with the head tucked in to protect this most vulnerable area. Playing dead is often an effective means to escape predation, honed to perfection by the Western hognose snake. This snake convulses its body, rolls onto its back, and lets its tongue loll out of its mouth. It may vomit or spew blood, release fecal matter or musk, all in its attempt to convince a potential predator that it is already dead and no longer appetizing.

^{Timber rattlesnake balled and hidden by Peter Paplanus, Apr 2022}

Mimicry is a development that has taken place in some species over long periods of time. Batesian mimicry is when a harmless species has evolved the coloration of a more dangerous species to fool a predator into leaving it alone. Scarlet kingsnakes of the southeastern United States are quite harmless but look very much like Eastern coral snakes, a venomous species in that same area. Auditory mimicry involves creating sounds used by more dangerous snakes. Fox snakes, found in deciduous forests, often vibrate their tails in leaf litter, making a buzzing noise very similar to the sounds made by rattlesnakes living in the same area.

^{Scarlet kingsnake by FWC Fish & Wildlife Research Institute, May 2015}

^{Eastern coral snake by FWC Fish & Wildlife Research Institute, Sep 2014}

Snakes often use one or more methods of intimidation. Bright display colors are found among many venomous species and serve as a warning to potential predators that this snake is dangerous. Another form of intimidation involves a snake inflating its body or a body part to make it look bigger. The puff adder inflates its whole body by filling its lung with air. Cobras hold their heads high and flare out an extra fold of skin on either side of their heads, commonly called “hooding.” Intimidation may also involve auditory cues including the rattling of a snake’s tail and the hiss emitted by cobras as they bring up their heads.

When the above strategies do not allow the snake to escape, most species will not hesitate to strike. Several species do not bite, striking with the nose or an open mouth; however, all venomous snakes will bite in self-defense, although they may not inject venom. A few species are able to spit venom, used purely as an act of self-defense, although if the venom targets an eye or nasal passage, the results can be extremely painful.

Snakes are some of the most interesting species with a lifestyle very different from our own. They have many strategies for keeping themselves safe from wild predators, and will be around for us to observe, learn about, and be fascinated by.

Sloths

Sloth, a word used in English for over 400 years to mean slow, was used in the 17th century to name six species of slow-moving mammals native to the tropical rainforests of Central America and northern South America. Those in the genus Choloepus have two toes on their forelimbs and include Linnaeus’s two-toed sloth, Choloepus didactylus, and Hoffman’s two-toed sloth, Choloepus hoffmanni. In a second genus, Bradypus, they have three toes on their forelimbs and include the pygmy three-toed sloth, Bradypus pygmaeus, the maned sloth, Bradypus torquatus, the pale-throated sloth, Bradypus tridactylus, and the brown-throated sloth, Bradypus variegatus.

^{Hoffmann’s two-toed sloth, Choloepus hoffmanni, by Leyo, Jul 2008}

^{Linnaeus’s two-toed sloth, Choloepus didactylus, at London Zoo by Dick Culbert, Nov 2007}

Sloths are 24″ to 30″ in length, weighing 8-17 pounds. They have rounded heads with tiny ears, and their forelimbs are almost twice as long as their hind limbs. Three-toed species have a small, stubby tail. Limbs are adapted for hanging and grasping, while strong claws help to support the weight of the animal. About half their body weight is from the undigested food in their stomach, which is constantly filled. Sloths have an unusual number of vertebrae in their necks, either six or nine compared to most mammal species that have seven. This allows them to almost look backwards, being able to turn through a 270˚ arc.

^{The most common sloth is the Brown-throated sloth, Bradypus variegatus, shown here in its native habitat at Cahuita National Park in southeast Costa Rica… by Christian Mehlführer, Feb 2007}

Everything about the sloth is slow: their daily routine, their feeding, their movements, and their metabolism. They are nocturnal, eating at night and spending most of the day hanging motionless, while sleeping. Their low-energy, leaf-based diet supports a slow-paced lifestyle. Sloths are primarily folivores, feeding on leaves and fruit of several tree species. They have a multi-chambered stomach with symbiotic bacteria to help digest fibrous vegetation in a slow process that can take several weeks to fully process a single meal.

^{Pale-throated sloth, Bradypus tridactylus, by Fernando Flores, Apr 2013}

^{Pygmy three-toed sloth, Bradypus pygmaeus, by Bernal Saborio, Jan 2017}

Sloths move very slowly, even when threatened, averaging just 13′ a minute. They rarely leave their arboreal habitat, except to defecate. This happens only once every eight days, when they go down to the ground. They are extremely awkward and exposed during these short periods. However, sloths are agile swimmers and often use this ability to move between locations. Having a low metabolism allows them to hold their breath underwater for up to 40 minutes. Slow movements also provide protection from predators that hunt by sight, looking for movement among the trees, including ocelots, jaguars, and harpy eagles.

^{Observe the tint of the green algae in the hair of this three-toed sloth, genus Bradypus, by HenryAlien, Aug 2008}

Sloths have long, shaggy hair that is home to a host of other organisms. Each strand is grooved, able to retain rain water, and hosts a symbiotic green algae. The algae gets shelter and water from the hair and provides nutrients to its host by absorption through the sloth’s skin. The algae is also a source of food for several other species including mosquitos, ticks, mites, beetles, and several moth species whose entire lifecycle depends on sloths. When a sloth goes down to the forest floor to defecate, female moths lay their eggs in the dung. Moth larvae feed and pupate in the dung, leaving several months later to fly up into the trees to find a mate in the sloth’s hair and begin a new cycle of life.

^{It is easy to imagine the grasping and defensive possibilities presented by these claws of Linnaeus’s two-toed sloth, Choloepus didactylus, by Andy, Dec 2018}

Sloths have several predators, but their long, sharp claws make formidable weapons if they are attacked. However, their biggest threats come from poaching, deforestation, and electric wires as more forest acreage is being opened to development. Habitat destruction is a serious threat to the world’s rainforests, and supporting efforts to slow down or stop this process provides the best assistance for sloths and other rainforest species. You can observe these unique and interesting animals at many zoos, or learn more at your local natural history museum, including the South American display at the Jurica-Suchy Nature Museum at Benedictine University.

Arctic Adaptations

The Arctic circle will experience its coldest time of year this month, as the sun does not rise in the visible sky between October and March. Animals that live in this part of the world have developed many adaptations for living easily and comfortably in these extreme conditions.

Most arctic animals are either very small or very large. Small animals, like arctic foxes and arctic hares, easily burrow under snow and ice to create comfortable dens. Tight entrances and long passages help keep air trapped under a thick layer of snow that acts as insulation, minimizing contact with the much colder external air. Body heat from the den’s occupants warms the temperature even further. Large animals also use dens including ringed seals and polar bears.

_{Polar bear on ice pack by Christopher Michel, Jul 2015; Musk Ox by Malcolm Manner, Mar 2013; Moose & frozen sagebrush by Steven Robinson, Oct 2017}

Larger animals have a high body volume to surface area ratio, as is found in the shape of a ball. Internal heat is generated relative to body volume, and it is lost relative to surface area. Large, tubby animals including polar bears, musk oxen, and moose generate lots of heat while losing very little. Other adaptations help maintain this balance of heat and loss.

Shaking polar bear by TambakoTheJaguar, Mar 2016

Thick, hollow fur/hair traps air inside each strand as well as underneath its heavy layers. Paws are covered in thick fur for stability, grip, and warmth. Long, furry tails can be used as blankets to wrap around bodies and noses. Oil secreted from special glands coat outer layers of fur, hair, feathers, and skin protecting the animal from direct contact with freezing waters. In addition, oil repels water so that it quickly runs off when the animal is on land, keeping them dryer and less exposed to cold air wicking away body heat.

Huddling fur seals by Michael Sale, Nov 2006

Huddling reindeer by Ben Townsend, Nov 2005

Polar bears, arctic foxes, walruses, seals, and musk oxen all have blubber, a thick accumulation of body fat just below the skin layer. This prevents cold from penetrating the body cavities that contain vital organs. It can also be utilized for energy for movement or to create additional body heat. Huddling is another method used to prevent cold from getting to the center of a mass. Used by musk oxen, arctic foxes, walruses, seals, and arctic hares, staying close with a large group is warm and comfortable.

Reindeer, also known as caribou, are known by their long noses. Air follows a twisty route through the nasal passage before reaching the lungs. Interior walls contain many blood vessels close to the surface that warm the passing air up to seventy degrees before it enters the lungs. Warm blood running through arteries from the heart distributes body heat. By the time it reaches an animal’s extremities, it has cooled and not much body heat can be lost. Reindeer have countercurrent vascular systems where veins containing cool blood returning to the body’s core run adjacent to arteries with warm blood. The colder veins absorb heat so the body core stays warmer.

Arctic fox staying warm by Marc Dumont, Feb 2015

Polar bear portrait by Peter Kaminski, Jan 2005

Extremities are one body area where heat is easily lost and exposure to cold can be damaging or deadly. Arctic foxes and arctic hares have shorter ears, noses, limbs, and snouts than species in the same families living in temperate weather zones. Ringed seals lack any external ears. Musk oxen have short legs and tiny ears, as do polar bears. Many of these adaptations can be viewed in the wild, or at your local zoo. Natural history museums also have displays where we can learn about many cold-adapted species.

Why Do Woodpeckers Peck Wood?

Some central North America bird species, including chickadees, woodpeckers, nuthatches, and sapsuckers chisel cavities in dead or dying trees to create shelter and to find food. Many of these birds are year-round inhabitants, and their efforts are easier to observe during late autumn and winter when there are few leaves to obscure our view. Today we will investigate how beak sizes, beak shapes, and several other adaptations contribute to woodpecker woodworking skills.

^{_{Pictures above clockwise from top left: Yellow-bellied sapsucker by Keith Williams, May 2015; White-breasted nuthatch by Canopic, Feb 2021; Red-Breasted nuthatch by Doug Greenberg, Sep 2018; Black-capped chickadee by CCPoor, Mar 2012}}

Woodpecker beaks are thick and sturdy, with a chisel-like tip to cut away wood in small chips. The hard-hitting tip exerts about 1200 Gs of force up to twenty times each second. This amount of force is equivalent to a human hitting their head against a brick wall at 16mph. A human brain floats inside the skull surrounded by cerebrospinal fluid. When our head stops suddenly the brain continues moving forward until it is stopped by the skull. If the force is hard enough, this may result in a concussion. A woodpecker’s brain fits snugly inside its skull and moves and stops in conjunction with skull movement. Inside the skull, the bone is spongy, absorbing energy from the brain moving after the skull stops, managing the impact without harm.

Pileated woodpecker started a new cavity by Peter Stevens, Jan 2020

Other bodily adaptations also help to control and dissipate the energy resulting from pecking activities. A woodpeckers top beak overhangs the bottom beak, forcing pecking vibrations downward, away from the skull and through the muscles to the rib cage. Additional ribs are present at the top of the rib cage, attaching strong muscles to the skull that assist in managing the vibrations.

Hairy woodpecker by Jerry McFarland, Jun 2014

A woodpecker’s body is held very steady by feet that are adapted to gripping in a vertical position, pulling the body tight to the trunk. At the same time, the pygostyle, a set of fused bones located at the base of the backbone with strong muscles running the length of the tail, allow the bird to stiffen the tail and wedge it against the tree trunk. Claws, feet, and tail provide strong structural support as the bird works to chisel out a cavity from solid wood.

Red-bellied woodpecker gripping tree with braced tail by Jim Mullhaupt, Jul 2014

A woodpecker’s eyes contain two additional organs not usually found in other bird species. The pecten and choroid surround the sides and back of the eye socket. They are filled with fluid right before pecking is started to compress the eyeball into the socket and minimize all vibrations affecting the eyes as the bill strikes wood. Additionally, an extra thick nictating membrane, the clear, third eyelid present in all birds, helps protect the eyes from flying chips.

Smaller woodpecker species, including the downy woodpecker, have beaks with less of a chisel shape and more of a point. The beak is used to punch through thin bark layers and pick out small insects from tunnels running under the tree bark. Insects living inside grass, weed stems, and galls can be easily extracted by a finely pointed beak.

Downy woodpecker on grass by Adam Buzzo, Feb 2018

Woodpeckers provide a vital role in forest habitats. Whether a species migrates or not, most will likely change locations for better food sources, warmer weather, or breeding at one or more times during the year. Each time they move, they create a new nesting cavity. As old cavities are abandoned, there are 40 or more other species waiting to use these cavities for shelter, protection, or hunting. As you take your winter walks, be on the lookout for active cavities among the woodland trees in your area – and the species that are actually using them!