Tawny Owls

Little tawny owl on a branch

Little tawny owl on a branch

Wilden Marsh Nature Reserve and the Lower Stour Valley are owl country. Local names like Hoo Farm, Hoo Brook and Hoo Wood suggest that owls were, perhaps, more in evidence in the past than they are today; however, there are still decent numbers living in the valley. There are many mice and rats living on Wilden Marsh, and these are most likely responsible for attracting owls to this area.

The owl is a nocturnal bird of prey that hunts mainly rodents, usually by dropping from a perch to seize its prey, which it swallows whole; in urban areas its diet includes a higher proportion of birds. Vision and hearing adaptations and silent flight aid its night hunting. The tawny owl is capable of catching smaller owls, but is itself vulnerable to northern goshawks.

The tawny owl is a robust bird, 37–46 cm in length, with an 81–105 cm wingspan. Weight can range from 385 to 800 g (0.849 to 1.764 lb). Its large rounded head lacks ear tufts, and the facial disc surrounding the dark brown eyes is usually rather plain. The nominate race has two morphs which differ in their plumage colour, one form having rufous brown upperparts and the other greyish brown, although intermediates also occur. The underparts of both morphs are whitish and streaked with brown. Feathers are moulted gradually between June and December. This species is sexually dimorphic; the female is much larger than the male, 5% longer and more than 25% heavier.

The tawny owl flies with long glides on rounded wings, less undulating and with fewer wingbeats than other Eurasian owls, and typically at a greater height. The flight of the tawny owl is rather heavy and slow, particularly at takeoff. As with most owls, its flight is silent because of its feathers’ soft, furry upper surfaces and a fringe on the leading edge of the outer primaries. Its size, squat shape and broad wings distinguish it from other owls found within its range; great grey, eagle and Ural owls are similar in shape, but much larger.

An owl’s eyes are placed at the front of the head and have a field overlap of 50–70%, giving it better binocular vision than diurnal birds of prey (overlap 30–50%). The tawny owl’s retina has about 56,000 light-sensitive rod cells per square millimetre (36 million per square inch); although earlier claims that it could see in the infrared part of the spectrum have been dismissed, it is still often said to have eyesight 10 to 100 times better than humans in low-light conditions. However, the experimental basis for this claim is probably inaccurate by at least a factor of 10. The owl’s actual visual acuity is only slightly greater than that of humans, and any increased sensitivity is due to optical factors rather than to greater retinal sensitivity; both humans and owl have reached the limit of resolution for the retinas of terrestrial vertebrates.

The commonly heard female contact call is a shrill, kew-wick but the male has a quavering advertising song hoo…ho, ho, hoo-hoo-hoo-hoo. Tu-whit, Tu-who: this stereotypical call is actually a duet, with the female making the kew-wick sound, and the male responding hooo. The call is easily mimicked by blowing into cupped hands through slightly parted thumbs. Mimicry of the tawny’s call can produced a response from the owl within 30 minutes in 94% of trials. A male’s response to a broadcast song appears to be indicative of his health and vigour; owls with higher blood parasite loads use fewer high frequencies and a more limited range of frequencies in their responses to an apparent intruder.

Broadly speaking, most owls’ mating seasons run from very early Spring until the hottest days of Summer. Many of the larger species begin their courtship in February, though their mating season won’t begin until March. It then lasts through August. Conversely, many smaller species’ mating seasons don’t begin until May, also lasting through August.

One Comment on “Tawny Owls

  1. A good read this! In July and August for the last couple of years I’ve been a volunteer with the local Wildlife Trust following up possible sightings of Barn Owls but have yet to find one although I have seen Long Eared Owls. All our birds of prey here are under real pressure and whilst there are many causes for this I think the greatest threat is ourselves!

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