The Flammulated Owl (Psiloscops flammeolus) is a small, secretive owl found in western North America. These owls are highly migratory, breeding in western mountains and foothills and wintering in Mexico and Central America. Flammulated Owls nest in cavities in trees, often old woodpecker holes or natural cavities. Their specific nesting habits and habitat preferences have been the subject of research by ornithologists seeking to learn more about this elusive species.
What kind of habitat do Flammulated Owls prefer?
Flammulated Owls are strongly associated with ponderosa pine and mixed conifer forests. They prefer open, mature forests with large diameter trees and an open understory. The owls avoid dense, even-aged stands. Specific nesting habitat preferences include:
- Mature pine and mixed conifer forests
- Open understory with little mid-level vegetation
- Presence of snags and dead/dying trees for nesting cavities
- Higher abundance of arthropod prey in open forests
- Dry forests, as wetter areas may have more predators
- Higher elevations from 4,000-7,900 ft (1,200-2,400 m)
Research in Oregon found that Flammulated Owls strongly selected large-diameter (>53 cm DBH) ponderosa pines and snags for nesting. Nests were typically in areas with lower shrub cover and higher maturity pines. The owls avoid dense, young forests and prefer the open understory of mature, open canopy stands.
What kinds of cavities do they nest in?
Flammulated Owls are secondary cavity nesters, meaning they do not excavate their own nest cavities. Instead, they rely on existing holes, cracks, or cavities in trees that are formed naturally or created by primary cavity nesting birds like woodpeckers.
Specific cavity characteristics include:
- Cavities are typically in large, mature pine or aspen trees.
- Average nest height around 16 feet above the ground.
- Entrance holes average 2.7 inches wide.
- Depth of nest cavities ranges from 8-36 inches deep.
- Owls prefer cavities with small entrances to deter predators.
- Will also use nest boxes designed for American Kestrels.
- Have been found nesting in old woodpecker cavities, natural branch holes, split trunks, and broken tops of snags.
The owls line the cavity with soft material like bark flakes, wood chips, or feathers. Cavities provide a protected space for the female to lay her eggs and raise the young owlets. The male will roost nearby to help defend the nest site.
What trees do they nest in?
Flammulated Owls most commonly nest in cavities in large, mature pine trees. Favored nest trees include:
- Ponderosa pine
- Douglas-fir
- Western larch
- Grand fir
- Aspen
- Cottonwood
Ponderosa pine seems to be the most preferred nesting substrate overall. Mature pines tend to have more natural cavities, decay, and are frequently used by nesting woodpeckers. However, any large, mature tree with suitable cavities may be used.
The owls have also been recorded nesting in small tree species like juniper where larger nest trees were scarce. Tree condition and cavity availability is more important than tree species. The owls will readily use nest boxes placed in appropriate habitat.
What is their nesting phenology?
The breeding season and nesting timeline for Flammulated Owls follows a typical pattern each year:
- March-April: Owls arrive on breeding grounds and males establish territories
- May: Females arrive and pairs bond, copulation occurs
- May-July: Egg laying peaks in June, incubation 25-30 days
- June-July: Owlets hatch, fledge at 4 weeks old
- August: Owls finish nesting season and depart for winter grounds
The owls are single brooded, meaning they only have one clutch per breeding season. Average clutch size is 2-3 eggs. Incubation starts when the first egg is laid, so owlets hatch asynchronously. Parents care for fledglings for several weeks before migration.
Nest initiation and egg laying dates can vary across the owl’s range depending on latitude and elevation. For example, Colorado owls nest earlier from May-July compared to Oregon owls that nest later from June-August.
How many broods do they have?
Flammulated Owls are single brooded, having just one clutch per breeding season. They do not lay multiple broods in a year like some songbird species.
Several factors contribute to their single brooded nesting strategy:
- Owls are physiologically adapted for small clutches and slow reproduction.
- The male provisions the female and owlets with food, which limits resources.
- It takes about 3 months from nest building to fledging young.
- They have a short breeding season at higher elevations.
- Single broods allow more time for the young to develop flying skills.
Having one brood ensures the parents can adequately care for and feed the few owlets. It also gives the young time to grow and fledge before the adults and juveniles migrate in late summer. This conservative reproductive strategy is common in many raptor species.
How many eggs do they lay?
Typical Flammulated Owl clutch sizes range from 2-4 eggs, with 3 eggs being the most common. According to breeding records:
- 52% of clutches had 3 eggs
- 24% had 2 eggs
- 20% had 4 eggs
- 4% had 5 eggs
Larger clutches are associated with years of high prey abundance. Small clutches of 1-2 eggs may be from younger females breeding for the first time.
Flammulated Owl eggs are round and white. They measure about 1.3 inches long by 1.1 inches wide. The female does all the incubating and cares for the owlets once they hatch.
The small clutch size allows the female to effectively incubate the eggs and facilitates the male provisioning the family with enough food. It also compensates for the higher mortality risk from predators in small cavity nests.
How many times do they nest per year?
Flammulated Owls nest just once per year. They are not capable of having more than one brood per breeding season.
Some key reasons why they nest only once a year:
- Their clutch size and reproduction rate is low compared to songbirds.
- It takes over 2 months to complete one nesting cycle.
- Energetically costly for the small owls to lay multiple clutches.
- Short breeding season at higher mountain elevations.
- Late summer is needed to develop juveniles before fall migration.
With only one brood, the owls can focus their energy on successfully fledging their few owlets. The long nesting process from cavity selection, egg-laying, incubating, brooding, and provisioning young means they cannot complete multiple nests in one season. Their reproductive strategy favors quality over quantity for the best chance of juvenile survival.
Do they reuse nest sites?
Flammulated Owls frequently reuse the same nest sites in successive years, provided the habitat remains suitable. There are several advantages to nest site fidelity:
- Returning to a proven site saves time and energy.
- Familiar cavity and surroundings may offer better protection.
- Prior experience hunting on established territory.
- Old nests are lined with soft material that deters parasites.
However, nest reuse depends on nest availability each year. Some factors that may force owls to find new sites include:
- Old cavities deteriorate or collapse between seasons.
- Predation may cause site abandonment.
- Fledglings dispersing to establish new territories.
- Forest fires may alter habitat conditions.
- Competition from other cavity nesters for limited sites.
On average, a given nest may be reused for 2-3 years before the owls are forced to find a new cavity. Females show stronger nest site fidelity than males. Ultimately nest site selection is based on cavity availability and habitat suitability annually.
How often do they successfully raise young?
Flammulated Owl reproductive success varies annually. On average, 65-85% of nesting attempts successfully fledge at least 1 young owl. However, complete nest failure may occur 30-40% of the time.
Some factors influencing nest success:
- Age and experience level of breeding pair.
- Prey abundance and weather patterns during nesting.
- Nest cavity susceptibility to predators.
- Human disturbance near the nest site.
- Parasitism by insects like fleas, mites.
- Chance events like treefall that damage nests.
Nesting success tends to be higher in prime habitat with adequate prey availability. Younger owls breeding for the first time are more prone to failure. With such high variability, long-term nest monitoring is needed to discern population-level trends.
How do they defend their nests?
Flammulated Owls use several strategies to defend their cavity nest sites from predators and perceived threats:
- Aggressive mobbing of intruders with loud calls, swooping flights.
- Camouflage – cryptic plumage hides incubating females.
- Small cavity entrances prevent entry by larger predators.
- Lining nests with aromatic greenery may mask scent.
- Nesting on north-facing slopes may avoid overheating.
- Remote cavities in upper branches deter climbing predators.
- Will feign injury to distract predators from nest.
The male owl stays nearby while the female incubates and broods, helping drive off intruders. Adults will fiercely attack potential threats, but may abandon compromised nests to try again the next year. Their small size prevents direct confrontation, so stealth and concealment are their main defenses.
Do both parents help raise the young?
Yes, both the male and female Flammulated Owl play important roles in raising their young:
Female:
- Selects the nest cavity
- Lays and incubates the eggs
- Broods newly hatched owlets
- Feeds owlets by tearing prey into small pieces
- Protects nest from predators and threats
- Keeps nest clean and removes fecal sacs
Male:
- Helps feed female before egg-laying
- Delivers food to female and owlets
- Stands guard near the nest
- Defends territory and attacks intruders
- Roosts nearby and alerts family to danger
The female does the majority of direct care while the male provisions food. Both will continue caring for the fledglings as they learn to hunt. This biparental care is essential for the owlets to grow and develop properly.
How long do the young stay in the nest?
Flammulated Owl owlets fledge from the nest cavity at around 4 weeks of age. The nestling period timeline is:
- 0-2 weeks – Owlets hatch and are brooded by the female.
- 2-3 weeks – Owlets grow flight feathers and become more active.
- 3-4 weeks – Owlets near adult size and practice wing flapping.
- 4 weeks – Owlets fully feathered and ready to fledge.
The owlets hatch asynchronously over several days as each egg is laid. This results in some size variation, but most are ready to leave the nest around 28-34 days post-hatching.
Fledging ends the nesting stage, but juveniles will still be dependent on the parents for several more weeks. The family group remains together on the breeding grounds until fall migration in August-September.
Do juveniles return to their place of birth?
There is limited data on natal dispersal and philopatry in Flammulated Owls after fledging. However, observations of banded birds indicate:
- Juveniles likely disperse from natal areas prior to first breeding season.
- Natal dispersal distances of 15-25 miles have been recorded.
- Males disperse further than females on average.
- Dispersal allows colonization of areas beyond saturated high-quality habitat.
- Reduces risks like inbreeding and nest site competition with parents.
This dispersal tendency means most juveniles do not return precisely to where they were born to establish their own territories. However, they may settle in nearby suitable habitat. More banding studies tracking individuals are needed to better understand Flammulated Owl dispersal behavior and distances.
Conclusion
In summary, Flammulated Owls exhibit some key nesting behaviors and preferences:
- Cavity nesters dependent on mature pine or aspen forests.
- Favor open understory with large snags and dying trees.
- Prefer old woodpecker cavities in large diameter pines and aspens.
- Clutch size averages 2-3 eggs, 1 brood per year.
- Nest April-August, peaking in June.
- Owlets fledge at 4 weeks old.
- Exhibit nest site fidelity but may be forced to relocate.
- Bi-parental care is essential for owlet survival.
- Juveniles likely disperse away from natal site.
Understanding details of their breeding ecology aids conservation efforts for the species. Protecting mature montane forests with suitable nesting trees and cavities remains critical to safeguard Flammulated Owl populations. Continued field research and monitoring is needed to track nesting success over time, especially in response to factors like climate change and habitat loss.
References
McCallum, D.A. (1994). Flammulated Owl (Psiloscops flammeolus). In A. Poole and F. Gill (Eds.), The Birds of North America. Philadelphia, PA: The Academy of Natural Sciences and Washington DC: The American Ornithologists’ Union.
Siders, M.S. and Kennedy, P.L. (1996). Forest structural characteristics of Accipiter nesting habitat: Is there an allometric relationship? Condor 98:123-132
| Location | Habitat Description | Nest Tree Species |
|---|---|---|
| Central Oregon | Mature ponderosa pine forest | Ponderosa pine |
| Southwest Idaho | Mixed pine-fir forest | Douglas-fir |
| Northern Colorado | Open ponderosa pine woodland | Ponderosa pine, Aspen |
| Southern British Columbia | Interior Douglas-fir forest | Ponderosa pine, Douglas-fir |
Key Facts on Flammulated Owl Nesting
- Cavity nesters dependent on mature pine or aspen forests.
- Favor open understory with large snags and dying trees.
- Prefer old woodpecker cavities in large diameter pines and aspens.
- Clutch size averages 2-3 eggs, 1 brood per year.
- Nest April-August, peaking in June.
- Owlets fledge at 4 weeks old.
- Exhibit nest site fidelity but may be forced to relocate.
- Bi-parental care is essential for owlet survival.
- Juveniles likely disperse away from natal site.
Understanding details of their breeding ecology aids conservation efforts for the species. Protecting mature montane forests with suitable nesting trees and cavities remains critical to safeguard Flammulated Owl populations. Continued field research and monitoring is needed to track nesting success over time, especially in response to factors like climate change and habitat loss.
References
McCallum, D.A. (1994). Flammulated Owl (Psiloscops flammeolus). In A. Poole and F. Gill (Eds.), The Birds of North America. Philadelphia, PA: The Academy of Natural Sciences and Washington DC: The American Ornithologists’ Union.
Siders, M.S. and Kennedy, P.L. (1996). Forest structural characteristics of Accipiter nesting habitat: Is there an allometric relationship? Condor 98:123-132
| Location | Habitat Description | Nest Tree Species |
|---|---|---|
| Central Oregon | Mature ponderosa pine forest | Ponderosa pine |
| Southwest Idaho | Mixed pine-fir forest | Douglas-fir |
| Northern Colorado | Open ponderosa pine woodland | Ponderosa pine, Aspen |
| Southern British Columbia | Interior Douglas-fir forest | Ponderosa pine, Douglas-fir |
