April 2024 – Discover-Nature

Rodentia are the largest order of mammals in the world, encompassing over 40% of mammal species. A rodent is characterized by having two pairs of large front teeth, one pair in each of the upper and lower jaws. These are called incisors and are used for gnawing vegetation. They have no canine teeth, leaving a large gap between the four front teeth and their molars in the back of the mouth. Rodents can be found in all types of habitat everywhere in the world except Antarctica, New Zealand and a few oceanic islands.

Capybara, Hydrochoerus hydrochaeris, use calls to warn others of danger and to find their young including purring, barking, cackling, whistling, whining, grunting, and chattering.

^{Capybara by Dick Culbert, Gibsons, B.C. Canada, May 2014}

The largest rodent is the capybara, Hydrochoerus hydrochaeris, growing up to 140 pounds. But a majority of species are small animals, under 4 ounces, with bulky bodies, short limbs, and long tails. Compared to their overall size, the body’s surface area is large and contributes to a greater loss of heat than larger animals. To combat this, rodents create more body heat by being constantly active. They consume large quantities of food to meet high energy needs. Many species are active year-round, coming out during early morning and late evening hours to feed. Animals living in habitats with extreme temperatures may hibernate to escape the cold or estivate to escape the heat. These species conserve energy by adjusting their body temperatures to within a few degrees of the air temperature and slow other bodily functions, requiring less food and more rest.

North American beaver, Castor canadensis, hone their upper teeth into efficient biting tools and defensive weaponry.

North American beaver, *Castor canadensis,* by Steve, Washington D.C., Jul 2008

Incisors grow constantly their entire lives. The front surface is protected by a hard enamel shell. The back surface of the upper pair is soft and easily wears away from the constant rubbing of the lower teeth as vegetation is bitten off and chewed. This creates a chisel like edge on the top teeth that is an excellent cutting surface. Teeth are used to gnaw vegetation, dig burrows, and for defense, if attacked. If an animal does not gnaw enough vegetation, the growth rate of the teeth becomes greater than what is being worn away and health problems can develop leading to the inability to eat. This most often occurs in captive animals who are not provided with sufficient quantities of harder vegetation.

Fox squirrels, Sciurus niger, scamper up tree trunks, along branches, and are able to leap to nearby trees, in addition to being fast on the ground and good swimmers.

^{Fox squirrel, Sciurus niger, by Karly Tuminello, Jul 2020}

Food is mainly seeds, leaves, fruit and small invertebrates or insects. A internal structure called a caecum contains bacteria that assists in breaking down plant material into digestible form. Several rodents have eyes that protrude in a half dome from their head allowing them to see both ahead and behind. This wide field of vision allows the animal to easily detect predators. Their daytime eyesight is poor, but they can detect ultra-violet light, allowing excellent vision during twilight hours when they are most often active. Most rodents live in large social groups, but forage individually, using a wide variety of alarm calls to keep others informed when danger is near.

Naked mole-rats, Heterocephalus glaber, have strong jaws that use one-quarter of all the muscle tissue in their body.

^{Naked mole-rats, Heterocephalus glaber, by Roman Klementschitz, Wien, Dec 2003}

Humans often consider rodent species to be harmful pests. While they may carry bacteria and cause nuisance problems, they are also beneficial by eating weed seeds and insects, keeping populations of many pest species in check. Rodents are widely used in human culture as food, clothing, pets, and laboratory animals for research. Visit a museum or nature center to learn about the many fun facts of each family in this amazing group of animals.

Kangaroo rats, Dipodomys sp, hop to move around but can jump 6 to 9 feet, and they get all their water from the seeds they eat.

^{Kangaroo rat, Dipodomys, by U.S. Fish & Wildlife, Sep 2005}

Springtime in the Midwestern United States brings with it everything from light to heavy showers, including tornados. In Illinois, we see an average of 54 tornados a year, with most of them occurring in the month of May. Tornados also occur in other parts of the world during springtime, including Europe, eastern and western China, South Africa, southern Brazil and both the east and west coasts of Australia, but not as frequently as in the U.S.

^{Tornado map by National Oceanic and Atmospheric Administration (NOAA)}

A majority of storm fronts move from southwest to northeast, which is a contributing factor in the Midwest to the formation of violent storms. There are three types of tornados. Non super-cell tornados are small, narrow, and last for only short periods of time, usually only a few minutes. Wind speeds are low, topping out near 80 mph, capable of causing only minor damage. Squall line tornados are generated by smaller thunderstorms traveling one after another forming periods of rain interspersed with calmer conditions. As the end of a squall line bends, small tornados may form with lower wind speeds, usually causing no damage. Super cell thunderstorms are the largest, most powerful storms that can generate tornados ranging from small to great in size and intensity.

^{Upper left: Thunderstorm during VORTEX2 by Sean Waugh, NOAA-NSSL Lower left: Funnel cloud approaching the ground by National Severe Storms Laboratory, NOAA Right: Supercell often associated with violent weather by National Severe Storms Laboratory, NOAA}

Rainstorms form when cool, dry air overlays a layer of warm, moist air. As the warm air rises to higher altitudes, where there is less air pressure, it expands and cools, losing its ability to hold moisture. As water condenses from the cooling air mass, water vapor floating on the air forms clouds. As more warm, moisture laden air moves into the system, the water vapor droplets become heavy enough to fall as rain. As rain falls, it cools the lower air layer, reducing the warm air flow until the rain stops.

^{Photomontage of the evolution of a tornado : Composite of eight images shot in two sequences as a tornado formed north of Minneola, Kansas on May 24, 2016, by Jason Weingart}

Thunderstorms form in the Midwest from warm, moist air moving in from the Gulf of Mexico and cool, dry air blowing in over the Rocky Mountains. A third source of air from the jet stream may wick away enough rain drops so that the lower air mass does not cool, and the warm air keeps feeding and intensifying a storm. As air moves in different directions and at different speeds, the whole storm will start to swirl, tending to pick up speed toward the center of the storm, eventually creating one or more funnels of rotating air.

Tornados are categorized based on the Enhanced Fujita scale from EF-0 to EF-5. This scale gives an estimate of wind speed and severity of damage inflicted. A little more than half of all tornados are found in the EF-0 range where wind speeds do not exceed 85 mph (137 kph) and damage is minor. Less than 1% of all tornados are recorded in the EF-4 (winds 166-200 mph) and EF-5 (winds over 200 mph) ranges. Another recent discovery is that most of the more severe storms tend to produce multiple tornados rotating around each other. Occurrences of multiple small funnels are difficult to observe within a large and often opaque mass of water, wind, and debris. This discovery helps to explain damages where one house may be completely destroyed while the neighbor is almost untouched.

The afternoon is the most likely time of day for these conditions to exist, once the sun has had a chance to heat the earth and air masses in the lower altitudes. In the Midwest, most tornados occur between noon and 8:00pm. Weather services are constantly monitoring conditions to be able to identify when weather patterns exist that may result in the formation of a tornado. Outside warning sirens are used by many municipalities to let people know that dangerous conditions are imminent. If you are hearing a warning siren, move inside and stay away from windows. Tune into radio, television, or internet resources to obtain the most up-to-date information for your area.