While migrating birds are on the horizon, rushing back to the Arboretum to begin building nests and raising young, the young owlets in our resident great horned owl family have already hatched. Unlike most other bird species in New England, which wait until spring and summer to breed, great horned owls mate and lay their eggs during the first and second weeks of February. Keen eyed Arboretum birders found the nest of a mating pair earlier this winter, and with any luck we may see healthy owlets sometime in the next few weeks.
Despite being year-round residents, most Arboretum visitors only see or hear great horned owl during the late fall and winter months. This may in part be because the longer nights provide more time for these birds of prey to hunt, which also makes it an ideal time to raise hungry chicks. Starting around October, male owls begin competing for territories with both good hunting grounds and protected nest sites. Females respond to the males’ territorial hooting and the ensuing “duet” is the sound most people associate with owls as whole (hoo–hoo-hoo-hoo).
Like all owl species, great horned owls do not build their own nests; unlike most other owls, however, they display remarkable flexibility with nest site selection. Although our pair this year seems to like their old red-tailed hawk nest, in other locations these owls are known to fight with and steal nests from bald eagles, nest on top of squirrel drays, inside large tree cavities, on top of large pot planters, on buildings, and even on the ground. This past fall, our arborists even installed several artificial nesting platforms to try and encourage more great horned owl nesting. Although we had no takers this year, the goal of these installations is to help us consistently monitor breeding populations, as well as take advantage of the free rodent control nesting owls provide.
Female owls (hens), typically lay 3 or 4 eggs a year. Once laid, the hen uses a bare patch of skin on her chest (a brood patch) to incubate them. Although eggs can survive exposure to temperatures as low as -20 degrees, long-term cooling can be fatal. As a result, the hen remains on her eggs, unless forced to move, for over a month until they hatch. The male brings food every evening and often stores surplus for her in adjacent trees. However, in order to prevent nest predators from trailing him to the eggs, the male roosts well away from the female during the day.
At this point in March, it is safe to say that the eggs have hatched, but the nest is so high up that we will not know for sure until they fledge and the entire family departs. Born blind and covered in thin downy feathers, the owlets will stay in the nest under the watchful eye of their parents for another month. After a few weeks, they will be large enough to waddle from the nest to the surrounding branches, a life stage fittingly called “branching out”. If all goes well, they will be fit to fly soon after that. After they fledge,the female will continue watching over them, feeding them, and teaching them how to hunt for several weeks more.
If you’d like to learn more about great horned owls, as well as identify other urban birds, join our next monthly bird walk on April 14, from 8:00-9:30am (meets at the Arborway Gate). Although more spring migrants should have arrived by then, we’ll continue keeping an eye on our resident owl family. For more information on nesting activities, keep an eye on this blog as we track the early life stages of tree swallows, black-capped chickadees, and hopefully some Eastern bluebirds using our nest boxes. Spring is here and young owlets are yet another sign of emerging life, albeit high up in the barren trees.