Friday, July 19, 2024

A great horned owl rests in a tree in Cambridge in May 2015. (Photo: Tom Murray)

Although great horned owls (Bubo virginianus) are among the largest and most common owls in Massachusetts, they are not often seen, because they are nocturnal. These aggressive, well-camouflaged brown birds blend into the trees in which they rest during the day. Great horned owls have two tufts of feathers resembling horns on each side of the head – hence the name. The feathers are neither horns nor ears, though. The owls may use the tufts of feathers for territorial displays.

Great horned owls, like all birds, do not have teeth. They eat their prey whole if it is small enough – like a mouse or vole. Six to 10 hours later, the owl regurgitates sausage-shaped pellets that contain the fur, teeth and bones that cannot be digested. Great horned owls are large birds and therefore their pellets are large too – 3 to 4 inches long and 1.5 inches wide. When these owls capture large prey such as rabbits, they may decapitate the head so they can swallow or carry away the rest of the body. 

A pair of juvenile great horned owls at Cambridge’s Fresh Pond on April 9. (Photo: Aisha Yousuf)

This owl uses the immense crushing power of its talons to sever the spine of prey when it attacks. A strong person can squeeze your hand with about 70 pounds of force per square inch; the crushing power of a great horned owl’s talons is 200 to 500 pounds per square inch! Once the talons squeeze, the prey is killed almost instantly.

These owls sometimes store extra food in a cache near the nest. In winter, the food in the cache freezes, so the owl sits on the frozen meal to thaw it out before eating. Great horned owls have been documented preying on more than 500 species of animals though they feed mainly on four species: mice, rabbits, voles, and rats.

A great horned owl and a chick in a stick nest in Groton in April 2018. (Photo: Tom Murray)

Great horned owls have a fabulous sense of hearing. You cannot see the outer ears because they are simple holes in the head concealed beneath feathers. As on most nocturnal species, one ear is higher on the head than the other. This placement causes sounds to reach one ear a fraction of a second before the other. The owl tilts its head until the sounds are received in each ear at the same time. At this moment, the owl is staring directly at the location of its prey! Even in the dark or under snow, the owl knows exactly where to attack and can hear a moving mouse from 75 feet away.

The eyes, meanwhile, are extremely large – almost the same size as human eyes. If our eyes were as proportional to our bodies as an owl’s, they would be the size of grapefruits. Owls need large pupils so they can collect what little light is available at night. Each of their pupils reacts to light independently. Because their eyes are fixed firmly in the sockets, owls cannot roll their eyes the way people do. Instead, they swivel their head 270 degrees to peer in different directions.

A great horned owl peers from a tree in Bolton in April 2022. (Photo: Tom Murray)

Red-tailed hawks and great horned owls live in similar habitats, hunt for similar prey and nest in similar nests. They live peacefully together because red-tailed hawks are active during the day and the owls at night.

Great horned owls nest earlier than other birds, beginning their courtship rituals in December. They do not build nests; instead, they most often take over an abandoned stick nest of a red-tailed hawk or a great blue heron. The female lays two or three eggs and keeps them warm until they hatch in about a month. While the female incubates the eggs, the male brings her prey that he catches each night. The female sits on her eggs through all types of winter weather – rain, wind, blizzards. Even when air temperatures reach 25 degrees below zero, the female successfully incubates her eggs.

A juvenile great horned owl finds a perch in May 2016. (Photo: Tom Murray)

Fear not: The feathers of great horned owls are extremely soft, which insulates them during cold winter weather. They also allow silently flight and surprise swoops down on unsuspecting prey. Owls fly silently because they have comblike teeth on the leading edge of their flight feathers. These teeth break up the air turbulence that would otherwise make a whooshing sound as they fly. In addition, these owls also have soft feathers and fringe on the trailing edge of their wing feathers. Both help absorb sound. 

Newborn owl chicks are covered in white down. At about six weeks of age, they crawl out of the nest onto nearby branches – a behavior called branching. They use their talons to keep a grip and try their wings. Because they are not fully developed, however, they may end up in embarrassing positions, such as hanging upside down from a tree branch or fluttering to the ground, where they clack their bills in frustration. (The call of this owl is three to eight deep hoots with an increase in tempo in the middle, like a hoo hoohoo hoo. It is the only owl in Massachusetts that hoots. Young owls make hissing or screeching sounds.)

A great horned owl looks down from its nest in Fresh Pond in March 2021. (Photo: Richard George)

The parents are nearby, keeping an eye on the situation and coming to the rescue if needed. The parents keep the chicks warm and protect the chicks for a couple of months, until they have enough feathers to fly and fend for themselves.

When it is not nesting season, great horned owls roost wherever their foraging path ends at dawn. I once spotted a great horned owl in my Somerville backyard. It stayed around unharassed for only a day, however: On the second day, agitated crows mobbed it and chased it noisily away. Great horned owls are a predator of night-nesting crows, so when crows spot one during the day, they call their brethren from near and far to chase the owl from the territory.

Adult great horned owls do not have many enemies. Once they reach a year old, they can live about 15 more years. Their greatest enemy is the human kind. Great horned owls who live near areas where garbage abounds may subsist mostly on rats. For this reason, it is important not to put out rodenticides, which bioaccumulate in an owl’s body and kill it. Great horned owls are also killed by cars or by flying into power lines or buildings – poor ends for a sentinel of the night skies and nocturnal hunter that has captured the imagination of nature enthusiasts and scientists alike.

Reader photo

Mark Seamans observed this red admiral butterfly – with a beak-shaped bite taken out of its wing – in Biloxi, Mississippi, on Nov. 20.

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Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.

This post was updated Dec. 3, 2023, to correct the spelling of Aisha Yousuf’s name.