Great horned owls are one of the earliest nesting birds in North America. Their nesting season begins in late winter and runs through mid-spring.
When do great horned owls lay eggs?
Great horned owls lay their eggs in late winter to early spring. The exact timing depends on location, but they typically start laying eggs in January or February.
In warmer southern regions, great horned owls may begin nesting as early as December. Further north, they usually start in January or February. The earliest documented nest with eggs was found on December 17 in Louisiana.
Egg laying reaches its peak from late January through March across most of the great horned owl’s range. In Canada and northern U.S. states, the peak is February to early April.
Here are some examples of when great horned owls lay eggs in different regions:
- Southern U.S: December to early March
- Midwest: January to March
- Northeast: February to April
- Western U.S: December to April
- Canada: February to April
Why do great horned owls nest so early?
Great horned owls nest early for a few key reasons:
- Take advantage of winter prey: By nesting in winter, great horned owls can take advantage of abundant prey like rabbits and rodents that is easier to catch and see against the snow.
- Allow time to raise multiple broods: Nesting early allows enough time to raise one brood, and sometimes a second brood later in spring.
- Get a head start over competitors: Nesting before other raptors gives great horned owls first access to the best nesting territories and food.
Nesting early is key to great horned owls’ breeding strategy. It helps maximize their reproduction and gives their young a better chance at survival.
What is involved in a great horned owl nest?
Great horned owl nests are large structures built in the tops of tall trees, abandoned buildings, or on cliff ledges. The owls do not build their own nests. They typically take over an existing nest or roost built by hawks, crows, squirrels, or herons.
A typical great horned owl nest includes:
- A deep bowl lined with fresh leaves, bark, moss, feathers, fur, or other soft materials.
- A nest diameter of 2-3 feet on average.
- Situated 20-60 feet high in a large tree, snag, or rocky ledge.
- Often includes old droppings, pellets, prey remains from previous owners.
In winter, the female owl will make some minor repairs to the nest and create the soft inner lining. She does most of this work in January and February before laying eggs.
How many eggs do great horned owls lay?
A typical great horned owl clutch contains 2-3 eggs. The female owl lays one egg every 1-3 days until the clutch is complete. So a full clutch takes 2-6 days to lay.
Here are some details on great horned owl egg clutches:
- Average clutch size is 2-3 eggs
- Range is 1 to 6 eggs
- Larger clutches occur in areas with abundant prey
- Eggs are dull white and about 2 inches long
- The female owl incubates them for 30-35 days
Having multiple eggs helps ensure at least one chick survives. More eggs may be laid when prey is plentiful to support larger broods.
How long do great horned owls incubate eggs?
After the female great horned owl lays her full clutch, she begins incubating the eggs. The incubation period lasts about 30-35 days.
The female sits tightly on the eggs and rarely leaves the nest. She is fed by the male who hunts for food. The male will also help incubate the eggs for brief periods so the female can take short breaks.
Thanks to the early nesting season, most great horned owl eggs hatch from late February through April. The earliest hatchlings emerge in January and February in southern regions.
Do great horned owls use the same nest each year?
Great horned owls frequently reuse the same nest over multiple years. A good nest in a suitable tree or cliff may be used for 5-10 years or more.
Reusing a nest allows the owls to save energy. They spend less time repairing and rebuilding. It also gets use out of a proven nest in a good territory.
In some cases though, they will switch nests. Reasons great horned owls may use a new nest include:
- Old nest blew down in storm
- Tree died and nest collapsed
- Territory boundaries changed
- Parasites built up in old nest
- Better nest site became available
On average, a great horned owl pair may use a particular nest for 3-5 years in a row. But they will readily move to an alternate site if a good opportunity arises.
When do great horned owl chicks hatch?
Great horned owl chicks start hatching in February through April, after about 30 days of incubation. The eggs hatch over several days, usually 1-2 days apart.
The hatching sequence is:
- First egg hatches
- Second egg hatches a day or two later
- Any additional eggs hatch after another 1-2 days
This staggered hatching creates a size disparity between siblings. The first chick is 5-10 days older and larger than the last hatchling. This leads to a dominance hierarchy where the oldest chick has first access to food brought by the parents.
How fast do great horned owl chicks grow?
Great horned owl chicks grow incredibly fast. They are able to fly and leave the nest by about 7 weeks old. Here is a timeline of their rapid development:
- 0-3 weeks: Chicks are covered in white down. Parents constantly brood and feed them.
- 3-5 weeks: Feathers begin growing. Chicks stand, flap wings, and tear food.
- 5-7 weeks: Full set of flight and body feathers. Chicks hop to branches and take short flights.
- 7 weeks: Fully fledged and able to leave nest.
This swift growth allows young owls to become independent while prey is still abundant. It coincides with the spring boom of baby rabbits, squirrels, and other prey.
When do great horned owl fledglings leave the nest?
Great horned owl chicks typically fledge at around 7 weeks old. However, departure from the nest can range from 6 to 10 weeks of age. Slower growing chicks or those from large broods may fledge closer to 10 weeks.
Fledging often occurs in April or May, but is earlier in southern regions. In Florida, chicks may fledge as early as February. In northern regions, they may not leave the nest until June.
Upon leaving the nest, the young owls can fly clumsily and start dispersing around their parents’ territory. They depend on their parents for food for several more weeks as they learn to hunt.
Can great horned owls have two broods in one year?
It is possible but not guaranteed for great horned owls to raise two broods in one breeding season. The likelihood depends on timing and ample food resources.
Key factors include:
- Nesting started extra early (December/January)
- First brood fledged by early April
- Prey abundance is high
- Female regained enough strength after first brood
With the right conditions, the female may lay a second clutch in late March or April. The second brood then fledges in June or July.
Successfully raising two broods in one year is an impressive feat. It demonstrates the reproductive capacity of great horned owls when circumstances permit.
How many great horned owl babies survive to adulthood?
Even under normal conditions, only about 1-3 great horned owls per nest actually survive to adulthood on average.
Here are typical survival rates:
- Eggs: 75% hatch successfully
- Nestlings: 50% survive to fledge
- Fledglings: 50% survive first year
This works out to a total survival rate of about 19%. So for every 10 eggs laid, only around 2 owls live to breed.
The low survival rate is normal and does not indicate problems. It keeps the population in balance with the habitat and food resources.
What factors affect great horned owl nesting success?
Many factors influence whether great horned owls successfully raise young each season. Key ones include:
- Weather: Extended cold, rain, or snow can reduce survival of eggs and nestlings.
- Prey availability: Lack of food affects parents’ ability to feed chicks.
- Age: Younger, inexperienced parents have lower success.
- Disturbance: Nest disruption by humans or predators reduces success.
- Habitat quality: Nests in poor habitat have fewer young survive.
In peak years with ideal conditions, owls may fledge 3-4 chicks per nest. In poor years, they may fledge none. The average is around 1-2 chicks per successful nest.
Do great horned owls use man-made nest platforms?
Great horned owls will readily use artificial nest platforms provided for them. Platforms are often erected to encourage the owls to nest in a specific location.
Advantages of artificial platforms include:
- Provides nest sites in areas lacking natural sites
- Elevates nests to reduce threats from ground predators
- Allows nests to be monitored easily
- Reduces nest electrocutions on power poles
Platform designs vary, but are often a wooden box filled with substrate secured to a pole, tree, or building. Perches and guard rails help keep eggs and chicks contained.
With some assistance, great horned owls will adapt to nesting on artificial structures quite well.
Conclusion
Great horned owls begin nesting very early in the year – starting as early as December in southern regions. They lay eggs in late winter, incubate them for about a month, and the chicks hatch out in February and March before most other birds.
This unusual strategy helps great horned owls get a head start on breeding. Their young hatch out just in time to take advantage of spring’s peak in rodents, rabbits, and other prey. It’s a reproductive advantage that has served this powerful owl well and allowed it to thrive across North America.