Great Horned Owl Species Notes, Development Photos and Case Histories

The most powerful and aggressive of North American owls, the Great Horned Owl dominates the wildlife community in which it lives. This highly adaptable species is equally at home in deep forest, open country, or in city parks and golf courses. Prey species include mammals, birds, and reptiles, and range from small rodents to animals as large as foxes, opossums, geese and herons. The young, however, are rarely aggressive towards each other. Because of the size and strength of their prey, young Horned Owls take much longer to develop and reach independence later than small species such as kestrels and screech owls. To enable their offspring to have the entire summer to develop their hunting skills, and also to ensure the availability of prey during the peak of their nesting season, Great Horned Owls begin nesting in January. Thus, young Horned Owls are usually the first to be seen by wildlife rehabilitators.  Because of their long dependence on their parents after fledging, it is extremely desirable to reunite or foster these young owls if at all possible, so that they can develop their hunting skills while still protected and supported by experienced adults.

These owls appear to be thriving in developed areas, and they often nest in suburban backyards and on golf courses. In Alabama, although they occasionally make use of ledges on rocky cliffs for their nests, they show a marked preference for nesting in the crowns of mature pines, frequently occupying nests that were built by crows, hawks, or even squirrels.   Since the owls do little or nothing to improve their nests, it is quite common for the nest to disintegrate, especially as the young put on weight and begin to move around. Incubation is 30 to 37 days, and the mother bird stays on the nest brooding and guarding the young nestlings until they develop their thick coat of down and their eyes open.  At about 3 to 4 weeks of age, the juveniles are able to feed themselves and keep themselves warm, and the female no longer stays on the nest.   However, she joins the male in keeping watch from concealment in a nearby tree.  Once you spot a nest, or a brancher, it is usually fairly easy to spot at least one adult on guard in a nearby pine tree. The species account in Birds of North America documents three instances in which a single Great Horned Owl was able to fledge owlets after the death of its mate.

Great Horned Owls readily accept the laundry basket nest in cases where the original nest has been destroyed. If at all possible, the nest basket should be situated close to easy perching for the adults, or the edge of the basket should be reinforced with at least one large branch lashed firmly in place to provide perching for the adult.  A Great Horned Owl family used one of our laundry basket nests every year until it disintegrated 9 years later.  (See page 27)

It is routine for branchers to tumble to the ground, and to remain grounded for up to four weeks.   The adults feed them on the ground, and the young birds stay concealed in low cover until they gain the strength and agility to hop and flap to perches above the ground.  By this time the birds are quite large, and can defend themselves from most predators.   As long as the branchers are in an area where they will not be threatened by human activity, it is unnecessary to interfere. Case 4 describes one of several cases where grounded branchers on golf courses returned to the ground after being placed in a tree, and even moved considerable distances on the ground.  However, on many other occasions, branchers have accepted a boost back up into the trees, and have made their way up into the canopy when thus assisted.

The determining factor may be the availability of smaller trees with plenty of low, interlocking branches that make it easy for juveniles to hop and flap their way up into the canopy.  Many golf courses in our area have eliminated much of the understory, leaving only very tall trees with no low branches.

In several cases, I have taken custody of a brancher that was in an unsafe location and held it in a flight cage furnished with branches and other perches, with a thick substrate of clean pinestraw. As soon as the brancher could get up to the perch and stay there, it was returned to its family. An absence of one to two weeks made no difference, since another juvenile was still being tended.

 

Great Horned Owl (Bubo virginianus)

Development Photos

Hatchling

 

Young Nestling

 

Brancher

 

Fledglings

 

Talons

 

Case Histories

Case #1

Case #2

Case #3

Case #4

Case #5

Case #6

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