The screech owl (Megascops asio) is a small owl native to North and Central America. This nocturnal bird comes in a variety of color morphs, which refer to the different color variations within the same species. Screech owls exhibit color polymorphism, meaning their plumage can vary between individuals of the same species. There are three main color morphs of the screech owl: gray, red, and brown.
Gray Morph
The gray morph, sometimes called the “classic” screech owl, is the most common color variety. As the name suggests, gray morph screech owls have predominantly gray plumage. Their underparts are lightly barred and they have dark streaking on the breast. The feathers on the back and wings are mottled with black, brown, white, and grays. Gray morphs have yellow eyes and grayish facial disks (the circles of feather around the eyes).
This coloration provides great camouflage when the owl is roosting during the day amid tree bark and branches. The barred patterns break up the owl’s outline, helping it blend into the background. The yellow eyes are thought to improve night vision. Overall, the gray morph is likely the ancestral and original coloration of screech owls before other color variants evolved.
Distinguishing Features
- Gray and black mottled back and wings
- Yellow eyes
- Light barring on underparts
- Streaking on breast
- Gray facial disk
Red Morph
The red or rufous color morph has reddish-brown plumage instead of gray. The back and wing feathers are a rusty brown color with fine dark barring. The underparts are boldly streaked with black lines on a reddish-brown background. The facial disk is also a rusty red-brown. But like the gray morph, the red screech owl has yellow irises.
The red hue is produced by a higher concentration of the pigment phaeomelanin in the feathers. This morph was once thought to be a separate species, called the red owl. But it is now known to be genetically the same species as the gray morph screech owl. The red coloration may provide an alternative camouflage strategy amid the colors of tree bark and dead leaves.
Distinguishing Features
- Rusty red-brown back and wings with dark barring
- Reddish facial disk
- Bold streaking on underparts
- Yellow eyes
Brown Morph
The brown color variant of the screech owl is also sometimes referred to as the chocolate morph. As the name indicates, this morph has dark brown plumage instead of gray. The feathers of the back, wings, and breast are saturated with blackish-brown pigmentation. Like the other morphs, the underparts have streaking and barring, but in brown and black. The facial disk is also chocolate brown.
Interestingly, the brown morph screech owl has dark brown eyes instead of the yellow irises other color morphs display. The brown morph is produced by higher levels of the melanin pigment eumelanin. This gives the rich dark brown coloration. The brown morph is less common than the gray and red varieties.
Distinguishing Features
- Chocolate brown back, wings, and facial disk
- Brown streaking and barring on underparts
- Dark brown eyes
What Causes the Color Morphs?
The different colorations of the screech owl are caused by genetic differences influencing the production and distribution of pigments in the feathers. The various morphs are inherited according to simple Mendelian genetics:
- The allele for gray coloration is dominant.
- The allele for red coloration is incompletely dominant.
- The allele for brown coloration is recessive.
This means:
- Individuals with two copies of the gray allele (homozygous) will be gray morph.
- Individuals with one copy of the gray allele and one of the red allele (heterozygous) will be red morph.
- Only individuals with two copies of the recessive brown allele (homozygous) will exhibit the chocolate brown morph.
The gray morph is the most common because its genetic allele is dominant. The red and brown morphs are controlled by recessive alleles and therefore rarer. But all three variants can occur in the same screech owl population because of their heterozygosity.
Gender Differences in Color Morphs
There are some subtle but noticeable differences in plumage coloration between male and female screech owls:
- Males have more heavily saturated gray, red, or brown coloration overall.
- Females have slightly more distinct barring and streaking patterns.
- Females may show more white spots on the shoulders.
- Females are on average larger than males.
However, there is considerable individual variation. The sexes show more differences in size than in color. Color morph alone is generally not a reliable indicator of gender in screech owls.
Geographic Distribution of Color Morphs
The relative frequencies of screech owl color morphs vary in different parts of their geographic range. Some patterns include:
- Gray morphs predominate along the Pacific Coast and in eastern regions.
- Red morphs are more common in the Rocky Mountains and southwestern deserts.
- Brown morphs are rarely the majority but occur in scattered populations.
In areas where two color morphs co-occur, the gray morph typically outnumbers the red or brown variants. The environmental factors influencing this geographic distribution are not fully understood but may relate to camouflage advantages in different habitats.
Can Screech Owls Change Color?
Individual screech owls cannot change their coloration. Each owl inherits genes coding for a specific morph and retains that coloration throughout its life. However, the relative abundance of certain color morphs within a population can shift over generations if mating and survival patterns change:
- If a certain morph experiences lower mating success or survival rates, it may decline in the population.
- Morph frequencies could change if owls with certain coloration are more likely to disperse and reproduce.
- Environmental changes like fire or deforestation could favor one morph over others.
So while individual owls are stuck with their morph, the overall makeup of morphs in a screech owl population can evolve over time.
Do the Morphs Represent Separate Subspecies?
At one time, ornithologists debated whether the different color morphs of screech owls warranted delineation as separate subspecies. However, research in genetics, physiology, anatomy and behavior has shown the morphs to be:
- Capable of interbreeding and producing viable offspring.
- Genetically similar and sharing a recent common ancestor.
- Identical in proportions, size, bone structure, and calls.
This indicates the color variants are all polymorphisms within the single species Megascops asio. Different subspecies are recognized for screech owls east and west of the Rocky Mountains based on characteristics like size and vocalizations. But color alone does not define distinct subspecies of screech owls.
Are Some Morphs Better Camouflaged?
The variation in screech owl coloration does likely confer different degrees of camouflage against certain backgrounds. This may explain the geographic distribution of morphs:
- Gray morphs – Excellent camouflage against lichen-covered tree bark and shadowed branches. Widespread as ancestral coloration.
- Red morphs – More cryptic in areas with reddish rock and clay backgrounds. Provides alternative to gray in some habitats.
- Brown morphs – Probable better camouflage in habitats with dark tree bark.
This variation in camouflage ability may influence relative survival and reproductive success. It could account for local distributions and shifts in morph frequencies over time.
Do the Morphs Have Different Behaviors?
Most research to date has found little evidence for differences in behavior among screech owl color morphs. Studies comparing morphs have found:
- No significant differences in diet, prey capture ability, or feeding rates.
- No differences in nest site selection, nest success, or number of offspring.
- No variation in perch heights, roost sites, or mobbing behaviors.
Morphs produce similar vocalizations and respond equally to owl calls. There is also no evidence female screech owls preferentially choose males of a certain color when choosing mates.
These results suggest color morphs exhibit essentially identical behavior in most respects. Differences in local adaptation are more likely to arise from geographic variation than coloration itself.
How to Identify the Color Morphs
Distinguishing between screech owl color morphs simply requires comparing key plumage traits:
- Gray morphs – Gray and black mottled feathers with yellow eyes.
- Red morphs – Rusty red-brown coloration with yellow eyes.
- Brown morphs – Chocolate brown feathers with brown eyes.
The morphs overlap somewhat in size, so this is not a reliable identification feature. Immature owls may be duller in color before attaining their full adult plumage. But the relative coloration patterns will be apparent. Understanding the common traits of each morph makes identifying them straightforward.
Conclusion
In summary, the screech owl exhibits three distinct color morphs: gray, red, and brown. These morphs are produced by different inherited pigmentation genes and patterns. The relative camouflage advantages of each morph likely explain their varied geographic distributions and population frequencies. However, the color variants are simply polymorphisms of the same species as they show no behavioral differences and freely interbreed. Their unique coloration provides an interesting example of how variation within a species can adapt it to new environments and habitats.
