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Eastern Grass Owl

Did you know?

The female Grass Owl is larger than the male.

Calls
Usually silent. A harsh rasping screech perhaps used when a threat present. During courtship there is soft twittering and chirruping; also uttered by the male in flight returning to the nest with food.
Facts and Figures
Research Species: 
No
Minimum Size: 
32cm
Maximum Size: 
38cm
Average size: 
35cm
Average weight: 
130g
Breeding season: 
March to June
Clutch Size: 
3 to 8
Incubation: 
28 days
Nestling Period: 
21 days
Conservation Status
Federal: 
Secure
NSW: 
Vulnerable
NT: 
Secure
QLD: 
Secure
SA: 
Rare
TAS: 
Not present
VIC: 
Not present
WA: 
Secure
Basic Information
Scientific Name: 
Tyto longimembris
Featured bird groups: 
Birds under threat
Nocturnal Birds
Atlas Number: 
252
What does it look like?
Description: 

The Grass Owl is a medium-sized, rather slim owl with long slender legs that are sparsely feathered. The heart-shaped facial disc is white in the male and pale orange buff with dark speckles in the female. It is outlined by a narrow pale ruff with dark edging at the bottom. The eyes are relatively small (for an owl) and have buff and black 'tear' marks below them. The upper parts of the owl are chocolate and buff while the underparts are pale, flushed orange-buff and highly spotted. The wings are rather long and broad, barred dark brown and buff with silvery spots. The underwing is white with fine dark spotting and darkish wing tips. The undertail is white with several narrow dark grey bars. The Grass Owl has a slow flapping and gliding flight with the legs trailing behind or dangling low to catch prey with the feet.

Similar species: 

The Grass Owl is most often confused with the Barn Owl, T. alba, which has much paler, soft grey and pale buff upper parts with small white tipped black markings. The Grass Owl's eyes are proportionately smaller and the facial disc has a characteristic long-faced apppearance. It also stands taller with longer legs which project beyong the tip of the tail when in direct flight and held flush with undertail. The larger Masked Owl, T. novaehollandiae, has more powerful feet which are more densely feathered and its upper parts have a more finely mottled appearance with less distinct and and less prominent dark markings.

Where does it live?
Distribution: 

There are two distinct populations of the Grass Owl. One is found on the flood plains of large rivers from Cape York to Manning River New South Wales. The other is found on grasslands of the Barkly Tableland and Channel country of Western Australia. This species undergoes irruptions (abrupt increases in numbers) when prey is plentiful (mainly the Long-haired Rat, Rattus villosissimus). When the rat populations decline, starving owls disperse widely to suitable habitats.

Habitat: 

Grass Owls are found in open tussock grasslands, coastal heath, lignum, swamps and agricultural land (mainly sugar cane and sorghum, and rice fields in fallow).

Seasonal movements: 

There is no evidence of migration and it is not known whether there is any interchange between the two main populations. The species is dispersive and irruptions occur (sudden increases in numbers) when food is plentiful.

What does it do?
Feeding: 

Grass Owls hunt at night, often in association with other owls in the same area. They search from 4 m to 5 m above the ground, gliding and hovering frequently. The prey is mostly located by the owl's acute hearing. When located, the owls twist and plunge almost vertically, head first, the talons lunging down at the prey at the last moment. Prey items include small mammals, particularly rodents, as well as insects and birds. On capturing the prey the owl usually remains on the ground eating.

Breeding: 

Grass Owl nests are usually in open grassy areas under dense tussocks of grass or sedges. The nest consists of a scraped hollow or a flimsy platform of trampled plant stems. There are usually at least three approach tunnels up to 10 m in length. Only the female incubates the eggs. The male brings food during the night and roosts with her during the day. The young are brooded by the female for several weeks after hatching. After four to five weeks both adults hunt. After two months the young are fully fledged and ready to fly.

Living with us

Grass Owls are affected by the conversion of grass lands to cultivation, burning of cane fields and mustering of cattle. Habitat is also destroyed by drainage of swamps, urban development or sand mining.

References: 
Field guide to Australian Birds.
Field guide to the birds of Australia, 6th Edition
Field Guide to the Birds of Australia.
Handbook of Australian, New Zealand and Antarctic Birds, Volume 4 {(Parrots} to Dollarbird)
Reader's Digest Complete Book of Australian Birds
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