The Great Horned Owl (Bubo virginianus)

Feb 24, 2019 Features / Columnists, Interesting Creatures in Guyana

---

The great horned owl (Bubo virginianus), also known as the tiger owl (originally derived from early naturalists’ description as the “winged tiger” or “tiger of the air”) or the hoot owl, is a large owl native to the Americas.
It is an extremely adaptable bird with a vast range and is the most widely distributed true owl in the Americas. Its primary diet is rabbits and hares, rats and mice, and voles, although it freely hunts any animal it can overtake, including rodents and other small mammals, larger mid-sized mammals, birds, reptiles, amphibians, and invertebrates.
In ornithological study, the great horned owl is often compared to the Eurasian eagle-owl (Bubo bubo), a closely related species, which despite the latter’s notably larger size, occupies the same ecological niche in Eurasia, and the red-tailed hawk (Buteo jamaicensis), with which it often shares similar habitat, prey, and nesting habits by day, thus is something of a diurnal ecological equivalent. It is one of the earliest nesting birds in North America, often laying eggs weeks or even months before other raptorial birds
The great horned owl is generally coloured for camouflage. The underparts of the species are usually light with some brown horizontal barring; the upper parts and upper wings are generally a mottled brown usually bearing heavy, complex, darker markings. All subspecies are darkly barred to some extent along the sides, as well.
A variable-sized white patch is seen on the throat. The white throat may continue as a streak running down the middle of the breast even when the birds are not displaying, which in particularly pale individuals, can widen at the belly into a large white area.
South American horned owls typically have a smaller white throat patch, often unseen unless actively displaying, and rarely display the white area on the chest. Individual and regional variations in overall colour occur, with birds from the subarctic showing a washed-out, light-buff color, while those from the Pacific Coast of North America, Central America, and much of South America can be a dark brownish color overlaid with blackish blotching.
The skin of the feet and legs, though almost entirely obscured by feathers, is black. Even tropical great horned owls have feathered legs and feet. The feathers on the feet of the great horned owl are the second-longest known in any owl (after the snowy owl). The bill is dark gunmetal-grey, as are the talons.
All great horned owls have a facial disc. This can be reddish, brown, or grey in colour (depending on geographical and racial variation) and is demarked by a dark rim culminating in bold, blackish side brackets. This species’ “horns” are tufts of feathers, called plumicorns. The purpose of plumicorns is not fully understood, but the theory that they serve as a visual cue in territorial and socio-sexual interactions with other owls is generally accepted.
The great horned owl’s song is normally a low-pitched but loud ho-ho-hoo hoo hoo (or also transcribed as bu-bubu booh, who-hoo-ho-oo or who-ho-o-o, whoo-hoo-o-o, whoo) and can last for four or five syllables.
One transliteration is You still up? Me too. The call is resonant and has warranted descriptions as varied as “solemn” and “terrifying”. The female’s call is higher and rises in pitch at the end of the call. Female vocalizations are higher in pitch because of a smaller syrinx in the larger sex. Calling seems to peak after rather than before midnight.
Usually, territorial hooting decreases in February or March at the onset of egg laying. On occasion, this species exhibits “an indescribable assemblage of hoots, chuckles, screeches, and squawks, given so rapidly and disconnectedly that the effect is both startling and amusing”.
Descriptions of some of these odd sounds including a growling krrooo-ooo note pair, a laughing Whar, whah, wha-a-a-a-ah, a high-pitched ank, ank, ank; a weak, soft erk, erk, a cat-like meee-owwwwww, a hawk-like note of ke-yah, ke-yah, and a nighthawk-like peent.
These vocalizations may be variously uttered when the birds are disturbed and angered at the nest (frequently preceding an attack on an interloping human or other animal), represent the vocal development of young owls, or are given during courtship and during territorial disputes with other owls.
Young owls still in the care of their parents make loud, persistent hissing or loud, piercing screeching sounds that are often confused with the calls of the barn owl
Occasionally, these owls may prey on threatened species. Following the devastation to its populations from DDT, the reintroduction of the peregrine falcon to the Mississippi and Hudson Rivers was hampered by great horned owls killing both young and adult peregrines at night.
Similarly, as mainly recorded in New England, attempts to reintroduce ospreys, after they were also hit hard by DDT, were effected by heavy owl predation on nestlings, and the owls were also recorded to take a large toll locally on the threatened colonies of roseate terns.
Where clear-cutting occurs in old-growth areas of the Pacific Northwest, spotted owls have been badly affected by considerable great horned owl predation. While at least the ospreys and peregrines have rebounded admirably nonetheless, bird and mammal species that are much rarer overall sometimes fall prey to great horned owls, many in which even sporadic losses can be devastating.
Among the species considered threatened, endangered or critically endangered by the IUCN which are also known to be killed by great horned owls are Townsend’s ground squirrels (Urocitellus townsendii), Pacific pocket mice (Perognathus pacificus), giant kangaroo rats, Stephens’ kangaroo rat (Dipodomys stephensi), black-footed ferrets, greater and lesser prairie chickens, marbled murrelets (Brachyramphus marmoratus), ivory-billed woodpeckers, Florida scrub jays (Aphelocoma coerulescens), pinyon jays, Kirtland’s warblers (Setophaga kirtlandii) and rusty blackbirds (Euphagus carolinus).
The American Bird Conservancy’s “green list” includes birds with considerable population declines (many classed as near threatened by the IUCN) or other immediate threats and/or restricted populations. Altogether, great horned owls hunt 50 different species from that list. [Source: Wikipedia]

---

---