Below is a lot of gathered information over time for Western Screech owls. The information has been gathered by an avid owl watcher (Grandad) for many years. All credit for gathering this information goes to Grandad. He gathered most of this information from All About Birds or Birds of the World. If not from these two sources the sources are noted throughout the document.
NESTING FACTS
Clutch Size: 2-7 eggs
Egg Length: 1.3-1.6 in (3.2-4.2 cm)
Egg Width: 1.1-1.4 in (2.7-3.6 cm)
Incubation Period: 26-34 days
Egg Description: White.
Condition at Hatching: Covered in white down; eyes closed.
The male provides almost all the food for the female and young during nesting, while the female incubates eggs and broods the baby owls. She stays with her young constantly for the first 3 weeks, then takes increasingly long breaks to help the male hunt. Owlets leave the nest before they can fly well. They remain with their parents for about 5 weeks after leaving the nest site.
Fledgling Stage
At 7–10 days before actually leaving the nest, the young climb to cavity entrance to begin peeking out during day and throughout evening hours.
An adult is often close at this time, as the nestlings are vulnerable.
Fledging always occurs at night with adults in attendance, and young birds flying from cavity to nearby branches.
Usually entire brood fledges in 1 night. Once out of the cavity, young remain out, but routinely stay close to nest for 2–4 nights while their flying abilities improve.
Initially they can only flutter awkwardly from branch to branch.
If dislodged from their perch, fledglings reach up into a low bush and pull themselves up onto branches with a foot-over-foot motion accompanied by vigorous wing-flapping.
They can then jump and hop to higher, more secure perches.
Immature Stage
Juveniles remain in close association with their parents for the first 5 wk following fledging. They then begin to wander more and more outside the ranges of their parents and roost farther away (Belthoff and Dufty 1997).
These dispersal movements last only 1–2 wk for most individuals.
Main Foods Taken
Western Screech-Owls consume a wide variety of small animals, especially mammals, birds, annelid worms, insects, and crayfish.
Generally more insectivorous than Eastern Screech-Owl (Ross 1969).
Populations in southwestern deserts seem to take a higher proportion of invertebrates than northern populations do, though insects are still an important part of summer diet at northern edge of range.
Microhabitat for Foraging
Perches on twigs projecting slightly from foliage at the side of a tree or beneath canopy, where it is inconspicuous in silhouette but has a clear view of the ground (Marshall 1957c). As well as capturing prey on ground, gleans arthropods from foliage, captures fish in shallow water, and hawks flying insects in midair.
Food Capture and Consumption
A sit-and-wait predator. Individuals leave roosts for foraging bouts between 12 min before sunset to 27 min after sunset (n = 7) (Hayward and Garton 1988). This hunting technique may predispose Western Screech-Owl to hunt mice in northern parts of its range (Hayward and Garton 1988).
Individuals observed perched above a creek waiting for crayfish to emerge to the shallows, whereupon the owl flies down and grabs one by dipping only its legs into the water (TA).
Behavior
Western Screech-Owls are nocturnal. They usually leave their roosts around sunset to forage, returning within a half-hour of sunrise. You may glimpse them perching at the entrances of their roost cavities on sunny winter days. They are "socially monogamous," meaning that pairs raise young together, although both sexes may also mate outside the pair. The male and female in a pair often preen each other. During courtship and mating, they sing duets, and the male presents food to the female. In breeding season, the male roosts near the nest cavity.
During the last weeks of the nestling period, the female also leaves the nest, often roosting close enough to the male that their bodies touch. Both adults guard the entrance from crows, jays, and other predators.
The male provides almost all the food for the female and young during nesting, while the female incubates eggs and broods the baby owls.
She stays with her young constantly for the first 3 weeks, then takes increasingly long breaks to help the male hunt.
Owlets leave the nest before they can fly well. They remain with their parents for about 5 weeks after leaving the nest site.
Gular Fluttering:
A cooling behavior in which birds rapidly flap membranes in the throat to increase evaporation (Source: Sibley)
Owl eyes are fixed, so they can’t roll their eyes to different positions, like humans can. In order to see a new field of vision, they’ve got to move their whole head.
Bobbing essentially allows them to focus on an object while taking in the bigger picture - judging its distance and position to things around it. This is often called triangulating and will be relied upon throughout their life to hunt successfully (along with their incredible hearing).
An Owl's eyes contribute one to five percent of the owl's body weight.
Even in a Starling the eyes account for more than a tenth of the head weight.
Digestive System
http://people.eku.edu/ritchisong/birddigestion.html and http://www.annemariesmith.net/RVI/PDFs/Digestion.pdf
Tongue facts (Tongue facts)
A raptor's tongue is triangular in shape with two rearward pointing projections which give it the look of a somewhat elongated arrow head.
Those projections, along with a covering of tiny rough projections called papillae, help birds of prey hold and move food around.
Birds have 3 holes in their mouths - one in the roof of their mouth, one in the middle of their tongue and one in the back of the throat on the left hand side (as you look at them).
The holes in the roof of the mouth and the tongue are for breathing - the one into the roof of the mouth goes into the upper respiratory tract (snares, upper sinuses).
The hole in the tongue goes into the lower respiratory tract - lungs.
Normally, while eating, these holes are closed.
The hole in the rear left hand (the bird's right) side is the esophagus and leads to the crop and intestinal system.
Unlike mammals, birds don't urinate. Their kidneys extract nitrogenous wastes from the bloodstream, but instead of excreting it as urea dissolved in urine as we do, they excrete it in the form of uric acid, which has a very low solubility in water, so it emerges as a white paste.
Voice
It is interesting to note that a bird's voice does not originate in the larynx as ours does. Birds have a larynx, but, unlike ours it has no vocal chords. It is used primarily to regulate the amount of air coming into the trachea. Bird sounds are produced in an organ unique to birds called the syrinx.
For most birds, the syrinx is located where the trachea joins the bronchi. Some birds including certain species of owls have two syringes located in the bronchi.
However, where the syrinx is located doesn't seem to matter, for the real sound producers are the muscles that surround the syringeal membranes.
As air passes over these membranes they begin to vibrate, and while they are vibrating, the surrounding muscles apply controlled tension which results in sounds of varying pitches much like a violinist applying pressure to the vibrating strings of his instrument to create different notes.
Owls' head turning ability
An owl cannot turn its head full circle from a forward facing position as is the common belief. An owl can turn its head up to 270 degrees left or right from the forward facing position.
There are several adaptations that allow this:
1) An owl's neck has 14 vertebrae, which is twice as many as humans.
2) Owls have only one occipital articulation with the cervical vertebrae. (There is only one bone situated on top of the backbone.)
Humans have two articulations. This allows the owl to pivot on the vertebrae column much like your body can pivot on one foot. Their muscle structure is arranged in a manner that allows this movement as well.
3) Owls have a special arrangement of the jugular veins with associated bypass connector blood vessels, to ensure that blood supply (and return) are not impeded as the neck is rotated.
Perching
Source
The Achille’s tendon in birds extends from the gastrocnemius muscle from above the ankle. The tendon runs down to the back of the foot and then along the bottom of the toes. When a bird lands on a branch, the ankle bends, stretching the Achilles’ tendon.
The tendons, flexor digitorum longus and flexor halluciss longus, are connected to flexor muscles in the leg. The hallucis works the back toe, known as the hallux, while the digitorum works the three toes in the front. Both tendons stretch over the ankle and these allow a strong grip without the birds having to use their muscles. Some birds also have ridges that lock the toe tendons in place to stop the bird from falling.
When the bird wants to unlock their toes, they stand up, and their legs straighten. This allows the tendons to relax, and the toes become straight again, allowing the bird to fly away.
SourceClutching the branch – Automatic Perching Mechanism To fall asleep, a bird’s body goes through a series of physiological changes. One of these changes is that the muscles lose their stiffness. This happens as a result of reduced brain control of muscle movement, along with various other physiological changes.
To stand perfectly balanced on a branch while the muscles become limp isn’t easy. Anyone who has tried to sleep standing on a train would know this. Birds manage to combat this limpness by locking their legs.
When a bird squats, its talons automatically bend and clutch tightly to the branch, for example. Until the leg is straightened, the talons will not release. The lock occurs because of how the flexor tendons, the tissue that connects to muscles and helps the limb bend, are placed in the legs. As the knee and ankle of the bird bend, the flexor tendon stretches, thus bending the talons.
The locking mechanism also happens because the tissue covering the tendon has a rough surface, although it is smooth in most other animals. The rough surface creates friction between the tendon and the sheath around it, which helps to lock the leg in place.
This so-called ‘automatic perching mechanism’ is a feature in most birds, allowing them to clutch to a branch without worrying about losing their grip and falling off. It isn’t only birds perched upright that benefit from this nifty trait. Parrots actually sleep hanging upside-down!
The locking mechanism comes in handy in other ways too. For predatory birds, for example, being able to firmly clutch their prey while flying to a safe place to feed is the difference between a full belly and starvation. It also helps birds to climb, swim, wade through water, and hang.
Exception to the Automatic Perching Mechanism Dozens of papers found such a mechanism in different avian species, and the case seemed shut, but a paper published in 2012 found that sleeping European Starlings don’t use the locking mechanism when they sleep. The researchers observed that the birds bent their knees only slightly, not enough for the locking mechanism to kick into action.
The toes, as a result, were largely unbent, and the bird balanced on the central pad of its feet while it slept. Additionally, they found that when the birds were anesthetized, they could not balance on the branch.
These results imply that there is more to how a bird balances as it sleeps than a simple brute-force grasp.
Preening
All birds frequently clean and groom their feathers in order to remove dust, dirt and parasites. Owls, like most other birds, use their beak and talons to do this.
The two outer talons on the owls feet are the "feather combs". The sharp medial edge of these outer talons enables them to clean their heads.
Flight feather barbs have tiny barbules that lock the barbs together, making the feather into a single continuous surface.
These barbules often become unhooked during harsh flying conditions or collisions. A bird will use its beak to realign the unhooked barbs and restore the feather to peak condition.
There is small gland called the uropygial, located at the base of the tail that produces a thin oily liquid. This gland is stimulated by the beak, which is then used to transfer the liquid to the feathers to provide them with a protective coating.
Source: The Owl Pages
Allopreening (AL-low-preen-ing)
Mutual preening between two birds, the main purpose of which is to reduce the instinctive aggression when birds are in close contact. In the breeding season, allopreening helps to strengthen the pair bond between the male and female.
Source: Allopreening