Tawny owls (Strix aluco) are medium-sized owls found throughout much of Europe and parts of Asia. They get their name from their prominent reddish-brown or “tawny” plumage. But while tawny is the predominant color, their feathers can range from various shades of brown to gray. Their coloration provides excellent camouflage amongst the bark and branches of trees. In this article, we’ll take a closer look at the range of colors exhibited by tawny owls and what functions they serve.
Tawny Owl Feather Colors
The feathers of tawny owls can vary considerably between individuals. However, some general patterns emerge:
- Back and wings – These are covered in mottled brown, tawny and gray feathers. They provide camouflage against tree bark.
- Face – Facial discs are a lighter brown/tawny color framed by a thin darker border. The contrast helps owls locate prey.
- Underparts – The chest and belly feathers are pale with dark streaks. This helps break up the owl’s outline when viewed from below.
- Legs – Long feathers called tarsal bristles are brown flecked with white and cover the legs and toes.
- Eyes – The eyes are black. They are surrounded by black and white spectacles of short, stiff feathers.
Males and females have identical plumage. Juveniles start out slightly grayer but gain their rufous plumage after their first molt. Color can vary somewhat by geographic region, with northern populations being generally darker and redder.
Functions of Tawny Owl Feather Colors
The feathers of tawny owls are specially adapted to suit their nocturnal, predatory lifestyle:
Camouflage
Perhaps the most important function of a tawny owl’s coloration is camouflage. Their mottled brown, gray, and rufous plumage provides excellent concealment against tree bark and in the dappled light of wooded environments. This enables them to roost invisibly during the day and stealthily ambush prey at night. Lighter underparts help break up the owl’s outline when viewed from below.
Silent flight
An owl’s feathers have evolved for silent flight. The frayed, soft edges of the flight feathers muffle noise, allowing the owl to swoop down on prey undetected. The velvety down feathers further dampen sound.
Water resistance
The feathers are structured to repel water, keeping the owl dry and well insulated in damp conditions. The barbicels on each feather have tiny hooks that zip them together into a waterproof barrier. Oil from the preen gland provides additional water resistance.
Temperature regulation
The loose structure of the feathers traps air and provides excellent insulation. Paired with a dense layer of down, this helps tawny owls retain body heat. The legs are protected by long bristly feathers, while facial discs regulate blood flow to prevent overheating.
Communication
While tawny owls are cryptically colored for camouflage, some markings play a role in communication. For example, the white “eyebrows” allow owls to express emotions and signal intent to other owls. The black eyes are thought to camouflage stare direction, giving owls an advantage when hunting.
Differences Between Male and Female Tawny Owls
Identifying the sex of a tawny owl by sight alone is extremely difficult. Males and females have identical plumage, a phenomenon known as monomorphism. Even trained ornithologists cannot reliably distinguish males from females without measuring them. Here are some subtle differences:
- Females are slightly larger than males on average.
- Females tend to have more delicate markings compared to males.
- Male flight feathers may be more evenly barred.
However, there is considerable overlap between the sexes in terms of size and color. Plumage characteristics also vary geographically, making sexing by sight subjective at best. The most reliable method to sex tawny owls is to measure wing length, with females averaging 5 to 10% larger than males.
Plumage Changes Between Juveniles and Adults
Juvenile tawny owls undergo a molt into adult plumage in their first autumn/winter after hatching. The sequence of changes is as follows:
Natal down
Hatchlings are covered in white or yellowish down. This keeps them warm in the nest but provides no camouflage outside of it.
Mesoptile plumage
The owl’s first true feathers start growing at around 2 weeks old. These “mesoptile” feathers are pale gray with little to no barring. The owlet is still vulnerable at this stage.
First juvenile plumage
By 5-6 weeks the mesoptile feathers are replaced by the barred and mottled juvenile plumage. The young owls are now able to leave the nest. Their plumage provides camouflage amongst branches.
Second juvenile plumage
This is acquired through a partial molt in early autumn. The new feathers are slightly more rufous than the first set. Markings are coarser and streaking more pronounced.
First adult plumage
The full adult plumage emerges after a complete molt over winter. This produces the rufous, brown, and gray feathers with fine speckles and vermiculations that provide the best camouflage and mute communication signals.
Geographic Variation in Tawny Owl Coloration
While broadly similar across their range, the coloration of tawny owls does vary between different geographic regions:
Britain and western Europe
Tawny owls here tend towards rich rufous-brown upperparts and pale underparts heavily streaked with dark brown. They generally appear more richly colored than populations further east.
Central Europe and Scandinavia
More subdued gray-brown and tawny plumage prevails in these areas. Underparts are lighter with sparser streaking. Overall the owls match the duller, colder environments.
Eastern Europe and Asia
Here the upperparts become paler gray-brown. Less rufous tinges are present and markings are finer. The underparts appear almost unstreaked whitish. This pale coloration matches the bleak, snowy winters.
Iberia and North Africa
Tawny owls from Spain and northern Africa tend to be darker sooty-brown above with heavy dark streaking below. This provides excellent camouflage against darker woodlands and scrubby vegetation.
The drivers of these geographic shifts in color are likely linked to differences in climate, habitat, and available prey between regions. Where tawnier plumage prevails, the environment is often warmer and woodier.
Albino and Melanistic Tawny Owls
While uncommon, aberrant color morphs do occasionally arise in tawny owl populations:
Albino tawny owls
Albinism is caused by inherited recessive genes and results in a complete lack of melanin pigment. Albino owls are pure white with pink eyes, legs, and bill. Without camouflaging coloration, survival in the wild is challenging.
Melanistic tawny owls
Melanism is an excess of melanin. Melanistic owls are very dark sooty-brown or black, often with faint ghostly vermiculations. They are sometimes referred to as “black tawny owls.” Their dark color may improve camouflage at night.
How Scientists Study Tawny Owl Color
Ornithologists use several techniques to quantitatively study tawny owl plumage:
Spectrometry
Reflectance spectrometry measures the precise wavelength of light reflected by feathers. This allows researchers to characterize colors independent of human perception.
Digital photography
Under controlled lighting conditions, digital photos can be used to analyze colors. Software measures RGB values, hue, saturation, and brightness of selected pixels.
Microscopy
Examining feather structure under a microscope reveals how the microscopic arrangement of melanin granules and air pockets creates different colors via scattering and diffraction.
Molecular genetics
Sequencing genes involved in melanin production like MC1R reveals genetic determinants of plumage traits. Comparisons between populations can show how color evolves.
Role of Tawny Owl Color in Bird Identification
For birders, the rufous-brown plumage provides a handy clue in identifying tawny owls:
- Eliminates similarly-sized owls like barn owls and long-eared owls that lack brown coloration.
- Distinguishes tawny owls from brown-plumaged tawnier relatives like short-eared owls which have darker underparts.
- Separates tawny owls from mottled brown wood owls that lack streaking below and have yellow eyes.
Knowing the variations in geographic color can aid identification of subspecies. However, caution is required as the color tone can vary under different lighting conditions. Definitive ID may require examination of subtle markings in the hand.
Conclusion
Tawny owls exhibit a varied palette of brown, rufous, tawny, and gray feathers that provides excellent camouflage in wooded environments. Plumage characteristics are specially adapted for the owl’s nocturnal habits and vary between sexes, juveniles, and across the owl’s widespread geographic range. Understanding these color patterns aids birdwatchers in identifying tawny owls in the field while also providing insight into the selective pressures driving evolution of camouflage in birds.