Birds – Owls – Discover-Nature

Sounds of the Season

It is late summer, heading into fall, and now is the time of year that the afternoons and evenings grow noisier. Some of the loudest species we hear throughout the year are currently active, calling to maintain contact with family members, to warn of impending threats, or to seek mates.

Singing insects are out at all times of the day and night. Crickets, katydids, grasshoppers, and cicadas four insect families active from late afternoon through the nighttime hours. These species all produce calls using a process known as stridulation. The edge at the base of a front wing, called a scraper, is rubbed across the base of the opposite wing, which has a bumpy surface called a file. This movement can produce buzzing or chirping sounds as well as melodic tones.

^{Annual cicada, Neotibicen spp., by Tony Cheng, Sep 2013}

Annual cicadas, Neotibicen spp., are a large insect averaging two inches in size with brown, green, or black bodies and white undersides. Adult males find spots among the branches of trees and woody shrubs where they can hang out and call for a mate. Calls can be heard throughout the day as a loud buzzing for several seconds that slowly fades to silence. Cicadas get louder with warmer temperatures towards late afternoon but cease all calling as dusk settles.

^{Common true katydid, Pterophylla camellifolia, male & female by TJWalker, U of FL}

^{Grey bush cricket, Gryllidae spp., by LHG Creative Photography, Jul 2010}

^{Grasshopper by Peter Miller, Nov 2020}

Katydids, Pterophylla camellifolia, are well-camouflaged with long, green wings that look much like the leaves of the plants they hide in. Despite their appearance, katydids along with crickets, from the family Gryllidae, and grasshoppers, from the family Acrididae, cannot fly. Katydids choose to occupy branches in tall trees, while crickets and grasshoppers prefer lower vegetation, including tall ground cover, from which to call for a mate. These insects will call well into the night on warm summer evenings, but quickly fade away once temperatures start to drop.

^{Common true katydid male, Pterophylla camellifolia, Carter County, MO, OSF-online}

^{Jumping bush cricket, Hapithus saltator, two calling by Daniel Parker, Sep 2023}

Many of these calls are among the loudest made by wildlife. A sound chamber, made by bowing out the wings from the body to create a hollow space, serves to amplify the sound. From the high-pitched melodic notes of the katydid to the chirping of crickets and grasshoppers, these calls can resonate and carry long distances.

^{Great Horned Owl, Bubo virginianus, by Frank Lambert, Dec 2016}

^{Eastern Screech Owl, Megascops asio, by Paul Driver, Sep 2023}

Against this background, we may also hear night birds, especially owls. In northern Illinois, great horned owls, Bubo virginianus, produces a series of low-pitched hoots to warn off territorial invader, call to a young one, or attract a mate. Eastern screech owl calls, Megascops asio, utter a long trill, lasting three to six seconds. Owl’s calls are easy to recognize and can be heard over long distances, making them an effective method of communication in the dark.

^{Coyote, Canis latrans, by Paul Marvin, Apr 2012}

^{Northern Raccoon, Procyon lotor, by Paul Driver, Sep 2010}

Other sounds that you may hear at night include coyotes, Canis latrans, using yips and barks to maintain contact with other individuals, or by young when begging for food. Long, drawn out howling is used to mark territorial boundaries and is often heard in response to emergency vehicle sirens, which we think are perceived as threats by coyote populations. Raccoons, Procyon lotor, are another species that is very active during the late nighttime hours approaching dawn. If they are close by, you may hear purring or chittering sounds used between adults and their young. Whether alone or in a group, when they are startled, raccoons will aggressively defend themselves and other family members emitting loud barking noises. Screams and growls between fighting individuals are often heard.

Late summer evenings can be quiet and slow or full of noises and events. Taking time to walk or sit quietly in your own backyards and listen can be a rewarding experience. Come to the Jurica-Suchy Nature Museum or visit your local nature center to learn more about wild nights in your area.

^{Clockwise: Coyote, Canis latrans, by Paul Marvin, Apr 2012; Eastern screech owl-red morph, Megascops asio, by Laura M, Feb 2023; Great-horned owl, Bubo virginianus, by Don Miller, Jul 2016; Raccoon, Procyon lotor, by Alex ONeal, Aug 2010; Raccoon, Procyon lotor, by Ellya Selhub, Jan 2006}

Great Horned Owls

The great-horned owl, Bubo virginianus, is native to much of the Americas, including most of North America and Central America and about half of South America. It is the second heaviest owl in North America, right behind the snowy owl, Bubo scandiacus, weighing up to five-and-a-half pounds with a wingspan between three and five feet.

^{Great-horned owl, Bubo virginianus, by Andy Reago&Chrissy McClareen, Aug 2012}

^{Range and distribution of Great-Horned Owl, Bubo virginianus by BirdLife International, 2014}

Feathers cover the entire body, including their feet, and are varying shades of browns and grays. Their backs and heads are mottled or barred in several patches. This coloration, especially when coupled with mostly nocturnal activities, provides excellent camouflage. Their ‘horns’ are actually feathers sticking upwards on either side of their heads. These are called plumicorns, but their function is not well understood. The feather structure of the wing allows owls to fly silently and includes a serrated leading edge to disrupt turbulence and softer feathers behind to help deaden sound.

^{Great horned owl plumicorns by Jean-pol Grandmont, Aug 2013}

^{Great horned owl wing structure by Peter K. Burian, Aug 2015}

The owl’s ears are covered by feathers, but are not symmetrical with one being higher on the side of the head than the other. This arrangement provides the owl with the ability to triangulate sounds and precisely locate prey in the dark or when prey is hidden, such as when an animal is moving about under a layer of snow. Their flattened face, shaped as a round disc, also helps to direct sound to their ears. Like all owls, their eyes are fixed in the sockets, but the bird can swivel its head almost 180° to either side allowing it to see in all directions.

^{Great horned owl talons by Curtis Bouvier, May 2010}

Great horned owls hunt from a perch, observing the area below them before diving swiftly and silently from far above. Their diet consists of small mammals, birds, amphibians, and a variety of snakes. Their talons are powerful and deadly, with a grip comparable to much larger birds such as golden eagles. Most prey is killed by being pierced or crushed in the talons. Owls may hunt and kill for more than their immediate needs and will cache their kills for future meals.

Great horned owls are not migratory. When an owl is ready to mate, courtship occurs in late fall and pairs mate for life, establishing a territory together in which they will live their entire lives. Most territorial defense is through hooting at a transgressor, but rare physical confrontations have been observed. If an owl cannot establish its own territory, it will live in silence among the fringes of other territories.

^{Great-horned owl juveniles, Bubo virginianus, by Alan Vernon, Jun 2010}

^{Great horned owl female & juvenile on nest by John Kees, Apr 2012}

Males are responsible for picking a nest site, almost always taking over a nest constructed by another species. Mated pairs breed once every two to three years, laying from one to six eggs. Egg laying occurs between late February and early April. The female alone incubates the eggs, never leaving the nest, while the male hunts and brings her food. After about 33 days, the eggs hatch. Young owls will start to fly after seven weeks, but take a full month or more to become proficient.

^{Great horned owl calling, Bubo virginianus, by Michael & Katie LaTour, Jan 2019 (at 0:02, 0:10)}

^{Great-horned owl pair calling by Bushman, Dec 2013 (at 0:18, 0:41, 0:51, 1:22)}

Owls are more often heard than seen. Although the females are larger than males, females have a smaller voice box and thus a higher pitched hooting call ending with a slight rising note. Juveniles can make hissing or screeching sounds and are often misidentified as barn owls, Tyto furcata.

You can learn more about these magnificent birds at the Jurica-Suchy Nature Museum. Make a reservation to come see us by visiting our website at: https://ben.edu/campus-links/jurica-suchy-nature-museum/ (click on Register to Visit the Museum).

Illinois Owls

Owls are found year-round in northern Illinois, and they come in several sizes and shapes and live in various habitats. Owls found near urban areas are often active only in the evening or at night, making them elusive to find and observe their behaviors. Native owl species have a highly varied diet, hunting almost every animal smaller than themselves from insects and crustaceans to small mammals, reptiles, and amphibians. Some of their unique characteristics and places to find them are highlighted below.

^{Barn Owl, Tyto alba pratincola, by DonArnold, JSNM Museum and Great Horned Owl, Bubo virginianus, by DonArnold, JSNM Museum}

Great Horned Owls, Bubo virginianus, live in every habitat across North America, Central America, and parts of South America. Standing two feet tall with mottled brown and gray feathers, they are well camouflaged during nighttime activities. Their ‘horns’ are actually feather tufts sticking out above their ears, which may enhance hearing and make them easy to identify. Look for them at dawn and dusk in tall trees standing on the edges of open spaces. The Barn Owl, Tyto alba, hides in tree hollows or dense vegetation during the day, coming out to hunt at night. They are a foot tall with a distinct white face and chest and pale brown and gray backs. A high energy lifestyle requires them to eat more than other animals their size. They are mostly found in open fields near wooded areas that provide diverse habitat for prey.

^{Barred Owl, Strix varia by DonArnold, JSNM Museum; Northern Saw-whet Owl, Aegolius acadicus by DonArnold, JSNM Museum; Short-eared Owl, Asio flammeus by DonArnold, JSNM Museum}

Three owls are daytime hunters, but not often found in urban areas. Barred Owls, Strix varia, have small territories, covering no more than a few square miles during their lifetime. They are brownish gray with dark stripes on their bellies. They hunt during both daytime and nighttime and have been known to eat carrion if it’s easily available. Look for them in wetlands with mature woodland cover nearby. Another daytime hunter, the Short-eared Owl, Asio flammeus, is an abundant species standing about a foot tall and known by its brown speckles covering a cream colored undercoat, with a barred tail and wings and a light belly. Their diet is similar to other owl species, but they may also hunt rabbit and weasel. Look for them flying low to the ground in open areas including grasslands, meadows, and wetlands. The Northern Saw-whet Owl, Aegolius acadicus, is only six inches tall, with a round, light colored face and belly streaked with brown, and a brown back with light spots. They are highly maneuverable and can easily hunt in small spaces. These owls have incredibly sharp talons and beaks, and they are able to take down prey larger then themselves. They favor dense, mature forests, especially those containing conifers.

^{Eastern Screech Owl, Megascops aslo, by DonArnold, JSNM Museum; Long-eared Owl, Asio otus, by DonArnold, JSNM Museum}

The next two species are smaller, nighttime hunters, often found in urban areas. The Eastern Screech Owl, Megascops aslo, stands eight inches tall and is all grey or slightly reddish-tinged. This owl species has also been observed feeding on fruits and berries. They are found in forests, wetlands, and urban neighborhoods with mature trees. The Long-eared Owl, Asio otus, one of the most abundant owl species world-wide, is a foot tall, with black and brown plumage. They hunt by stealth, waiting on a perch for prey to come close, then pouncing. Look for them in urban settings with large trees and in many state park areas.

Snowy Owl, Bubo scandiacus, by DonArnold, JSNM Museum

A winter only resident, the Snowy Owl, Bubo scandiacus, stands two feet tall with distinctive, almost pure white plumage. They are active both night and day, and can cover large distances in their daily hunts. A large, ferocious hunter, they can take down prey larger than themselves. They are found in a widely diverse set of habitats including open grassland, wetlands, shorelines, and several of our area’s larger airports.

We have many owls on display at the Jurica-Suchy Nature Museum. Come in and learn from our newest Illinois In Winter display or our owl and other raptor displays. We are closed for the holiday break, but consider visiting us as we reopen for the Spring semester in early January. Check out our schedule and make a reservation to come see us at https://ben.edu/campus-links/jurica-suchy-nature-museum/.

Illinois Owls

Owls are a type of raptor, a bird of prey with forward-looking eyes, large talons, and hooked beaks. Raptors are known for having the best vision of any animal, and they are skilled hunters found across all habitats. Other raptors include hawks, eagles, falcons, kites, and vultures. There are nineteen owl species native to North America, and eight of them are regularly found in Illinois.

^{Pictures clockwise above: Black Kite by Martine LIU, Getty Images; Golden Eagle by Timu Abasov, Getty Images; Red-tailed Hawk by BrianEKushner, Getty Images; Turkey Vulture by James Opiyo, Getty Images; Peregrine Falcon by Harry Collins, Getty Images Pro}

Owls have large eyes that look forward and provide a wide angle of view. Their binocular vision helps these birds easily spot prey and accurately judge distances when either stationary or in flight. An owl’s eyes cannot move within the eye socket, so the owl must move its entire head, which is capable of rotating 270 degrees to see completely around itself. Their vision is extremely sensitive to light, and they are capable of hunting when conditions are quite dark.

^{Barn Owl face by QuentinJLang, Getty Images}

^{Great-horned Owl looking back by Celine Bisson, Getty Images}

The feathers on their round faces help to direct sound into their ears, which are located on either side of their head. Their ears are small openings covered by feathers that can enhance and separate sound waves, working like binocular vision, allowing the bird to identify how far and in which direction a sound originates. Their enhanced ability to detect movement around themselves, coupled with excellent vision, makes these birds of prey one of the top hunters in their environment.

^{Owl beak closeup by GrahamH, Pixabay; Snowy Owl talons by WWing, Getty Images; Black fur in owl pellet by Justin Smith, Getty Images}

Sharp beaks and talons are used to capture and hold prey, and to easily tear apart meat. All raptors have eight toes ending in a talon, or sharp claw, made of keratin. Owl talons are long and curved and are used to easily grasp a branch or a prey animal. Their beaks are made of bone covered with keratin, with very sharp edges. They have no teeth to chew food, and they eat their prey whole or in large chunks. Whatever is not digestible, including bones, fur, and feathers, is compressed into a wad in the owl’s mouth and spit back out as a pellet. An Investigation of owl pellet contents can reveal the prey the owl is currently eating.

Fringed ends of owl flight feathers by ElvisCZ, Pixabay

Owls have fringed outer edges to their flight feathers that deaden almost all sound made while flying, making it difficult for prey to detect an owl coming for them. An owl’s large, rounded wings and short tail provide great maneuverability while flying. Their excellent vision, hearing, and flight maneuverability allows them to hunt at night in areas with numerous obstacles including woodland and urban areas.

In the next blog, I will take a closer look at the owls in Illinois. At the Jurica-Suchy Nature Museum, we have several displays that highlight the various characteristics of owls and other raptors. We are closing for the holiday break, but consider visiting us as we reopen for the Spring semester in early January. Check out our schedule and make a reservation to come see us at https://ben.edu/campus-links/jurica-suchy-nature-museum/.

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.

Large eye pupils on Eastern Screech Owl,*Megascops asio* by Greg Hume

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.

Coyote, Yosemite 2009 by Yathin S Krishnappa

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.

Two views of Wellington, New Zealand, taken same night by Science Learning Hub–Pokapū Akoranga Pūtaiao, University of Waikato, http://www.sciencelearn.org.nz

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.