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Possum on the Menu – Powerful Owls

Powerful Owl in tree

Powerful Owl

Powerful Owls (Ninox strenua) belong to the hawk owl group whose face is more hawk-like than the broad, rounded face traditionally associated with owls. It is large at 60-65 cm in length and adorned by stripped feathers. This species is an uncommon resident in eucalypt forests from the Dawson River in Queensland to southeast South Australia.

At night the Powerful Owl preys on birds and mammals. The list of mammals includes species of glider possums, Ring Tailed Possums, young Brush Tailed Possums and less commonly rats and rabbits. This species rightly earns the name Powerful Owl not only for its size but also for the size of the animals on which it preys. Cat owners should be pleased that this Owl’s preferred feeding habit is to take its prey from trees.

Over the last two years (2012-13) our district has been blessed by the presence of a Powerful Owl. We were initially altered to its presence by its distinctive loud call, a mournful, slow Woo Hooo and by the sound of its feeding habits, which are disturbingly distinctive – details later.

The sound of possums in distress came not long after we heard the Powerful Owl calls, confirming that we had a Powerful Owl in residence. The first was the sudden wheezing sound of the life being squeezed out of a possum as the Owls’ powerful claws gripped it. The second was very loud screaming by an obviously terrified possum that went on for a time before the screaming rapidly faded in the distance as the Owl carried off its meal.

When feeding the Owl generally starts by ripping the head off its prey and swallowing it whole.  Feeding continues as the owl tears pieces from the body and devours them.  Powerful Owls have been observed sleeping in their roosts with the lower half  of the prey’s body clenched in its claws to be devoured later in the day.  Estimates are that each owl needs to eat the equivalent of a large possum every 2-3 days. Powerful by name powerful by nature!

The sounds of nature in the raw so close to the house were very disturbing especially the prolonged screaming. A friend mentioned that he observed a baby Koala being taken by a Powerful Owl with the same disturbing noises.

In the last month (July 2013) we were alerted to a Powerful Owl’s presence in trees on our property by the discordant sound of mobbing birds. Crows en mass, mickies, currawongs and butcher birds all mobbing a large striped form huddled in one of the tall trees by the house.

On the first occasion when Judy investigated the racket she looked up to see this massive bird in flight. She was more than impressed by its huge wingspan. On the second occasion we were able to see the large striped form in the trees and with some waving of our arms scared off the crows. After the crows left the other birds eventually lost interest and we had the Owl with us for most of the day. It disappeared about mid afternoon, probably sick of us perving at it. We still hear its voice occasionally at night or early morning. A pleasant sound for us, but not so for the possums.

There are many sites on the web for this wonderful but uncommon owl, both photos and calls.

UPDATE

(July 2013)

Powerful Owls occupy a home range of 800 to 1000 hectares. Although they occur as pairs they roost separately in a number of favoured roosting trees in their territory.

Today (12 July 2013) and for the third time this month we have been blessed by an Owl roosting in a large tree near our house. This time it has a large Ring Tailed Possum corpse in its claws. The size of the possum is an indication of the strength of this Owl – the common name Powerful Owl is certainly apt.

The Owl is holding the possum body by the head end with the remainder of the body hanging free below the roosting branch.  The head, pectoral girdle and fore legs of the possum are missing, but the Owl has made no effort to feed on the remains throughout the day. According to reports it will do this before it departs for the night.

UPDATE

(24 September 2013)

Since my last update the Powerful Owl has more or less taken up our rainforest patch as a daytime roosting post. The denser canopy of the rainforest seems to deter the mobbing birds and they rarely bother him now. The frequent appearance of the Owl in our rainforest patch allowed me to get some nice action shots of the Owl preening.


Note the short tail, broad wings and strong feet with large claws, the latter well adapted to taking large prey such as possums. Note also in the shot of the spread wing, the frayed appearance of the trailing edges of the primary feathers. This provides the silent flight common to owls.

The face does not have a typical owl-like conformation, but is more hawk-shaped leading to its alternate common name, Great Hawk Owl. At 60-65 cm in length they are, with the exception of two eagles, the most impressive raptorial bird in Australia.

A Chick Arrives

Powerful Owl family

Powerful Owl family

Recently we have been finding owl feathers on our front footpath and occasionally the Owl has roosted in our property near a large Scribbly Gum on our footpath. This led us to believe that that the Owl we see is a male and that he and his mate might be nesting in a large hole in the trunk of  an old Scribbly Gum on our footpath.

Our suspicion was confirmed two days ago when much to our delight a chick appeared with its parents. I managed to get some shots of the three together. They are amongst branches of a Black Bean tree and it took some maneuvering and awkward positioning to get the shots but perseverance paid off.

The female is the lower owl and slightly smaller than the male who is visible from the underneath on the left.  Note the large feet and claws of the fledgling.

I haven’t noticed the Owl holding any more possum bodies lately and feel the Owls are resorting to larger birds such as crows for food. Certainly as time went on the possum kills were getting smaller and we assumed the Owl was down to juveniles.

The chick trills at dusk just outside Judy’s study widow. We are thrilled to have them here and hope they stick around for a while longer – although the possums may disagree.

UPDATE

Brush Tailed Possum with juvenile on back

Mother possum with juvenile on back

(December 2013)

The digestive system of owls cannot process feathers, bone or fur from their prey. These items are consolidated in their second stomach (gizzard) to be later regurgitated as pellets. Examination of these pellets reveals details of an owls’ prey.

Judy and I kept a lookout for pellets from the adult Powerful Owl but were unrewarded. Fortunately the fledgling owl provided a daily supply of pellets, which contained a lot of small bones embedded in fine, grey fur.

We sent pellet samples to Dr Steven Van Dyke at the Queensland Museum who identified the prey as juvenile Brush Tailed Possums (Trichosurus vulpecula). From the size of the bones the possums must have been taken from their mother’s back shortly after emergence from the pouch.  There appeared to have been at least one possum per night, which represents a serious depletion of Brush Tailed Possum progeny in our district. This level of predation and that of the adults is no doubt the reason for this Owls’ large territorial range of 800-1000 hectares.

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