Dear all -
At about 22.45 hours on 17 February 2006 at the closed forest gully that
adjoins our house at Vincentia on Jervis Bay, south coast of New South
Wales I heard juvenile Powerful Owl /Ninox strenua/ calls from the trees
at the front of our house.
To the north and west of the house is a small gully of tall closed
forest falling away to the sea 150 metres to the east at Blenheim Beach,
to the south-west is an open banksia and eucalypt-forested hill crowned
by a large area of lower open forest and heath connected to the south
with a tall closed forest around the creek system leading to Greenfields
Beach gully. To the south and south-east is a residential neighbourhood
with typical house gardens and shrubs and scattered tall Bloodwood,
Stringy-bark and Turpentine trees.
I have been hearing these calls from about Christmas 2005 and being
unable to identify them I posted a request for information on the
Birding-Aus listserver in early January. One reply directed me to “The
Owl Pages website (http://www.owlpages.com/index.php) and I was able to
confirm the calls as the begging call of juvenile Powerful Owls,
supported by the descriptions in HANZAB at Vol. 4, pp. 826-828.
I have heard these juvenile begging calls on most nights since that time
with occasional breaks of a day or two at most. Calling usually
commences late in the evening by about 2200 hours and has been heard as
late as between 0400 and 0430 hours. I have only heard adult “Woo-hoos”
on one occasion, early in the evening. I am loath to draw conclusions
from this data as it has not been collected systematically, though I
think it is fair to say that the regularity and frequency of calling
indicates that these birds have come from a nearby nest. On most
occasions the calls have been within c.50-70 metres of our house. I had
suspected that there was more than one juvenile in the area as on
several occasions I have heard two birds making the begging call, though
each time the second bird’s call was faint and apparently some distance
away. On two occasions that I had been able to see the calling bird in
torchlight I had not seen another bird, juvenile or adult, in the area.
On one occasion the bird was partly obscured by foliage and facing away
and had a dark, chocolatey plumage on its back and feathers and a dark
face when it’s face was turned towards me, on the other occasion I was
only able to see the calling bird by torch-light eyeshine.
On the night of 17 February at about 22.45 hours I was attracted to the
sound of juvenile begging calls close to the front, (eastern) side of
the house. Initially I was unable to locate any bird but soon saw one
bird fly from a tree within 15 metres of the house to perch on a branch
c. 20 metres high in a large stringybark about 50 metres away to the
south-east. This bird perched facing away from me and its wing and back
plumage was a deep chocolate and would have been difficult to see except
that the rising moon (Moonrise was at 21.41 hours) was behind the bird
and I found a position where I could see it in profile against the
lighter sky behind. Soon after perching it began it’s (now) familiar
rattling, metallic trill.
It soon became clear that there was another bird calling nearby, now
responding to the visible bird’s calls and calling of its own accord
when the visible bird was silent. After about ten minutes the second
bird flew to perch facing me a branch c. 15 metres high in another
stringybark tree about 30 metres directly in front of the house. I was
only able to see this bird from front-on. The leading edges of the wings
appeared to be a similar dark shade to the back and wings of the first
bird. It’s chest was a dirty, yellow-grey with sparse fine, dark
streaks. There was a distinct line, at about the same level as that of
an adult bird’s, below which the plumage was a creamy-yellow with no
visible barring. It looked distinctly different to the pictures of
juvenile Powerful Owls facing p. 832 of HANZB Vol. 4.
I now had two Powerful Owls, both presumably juveniles, within sight.
For the next twenty minutes I was able to record a series of short duets
(duration between 30 seconds to about 1 minutes) between the birds. In
between these duets both birds would call individually. The calls of
both birds were of the same duration and tone. The volume of the call of
the first bird seemed marginally greater than that of the second bird,
particularly when it turned to face me.
Since this record I’ve heard (0430 hours 20/02/06) the PO ‘bleating’
call (HANZAB, p. 827) which has been described as “Used by pairs in
greeting; as a food-begging call by both sexes …”
POs have been recorded in the immediate area in the past (Dave Coombes,
pers. comm.) and in the region (Chafer, 1992, Debus, 1997, HANZAB etc).
Some questions that come to mind are:
1. Might the ‘first’ (dark-backed) bird be an adult and is it using the
juvenile “begging” call as a contact call for the obviously
juvenile/sub-adult ‘second’ bird?
2. Has anyone any records on the age to which juvenile/sub-adults use
the begging call? Or any records of adult POs using the begging call?
3. Re the plumage characteristics (‘chest-band’) on the second bird is
quite at odds with juvenile plumage images in HANZAB and any of my field
guides – has anyone seen a similar plumage on a juvenile PO – might it
be characteristic of a sub-adult bird?
4. All occasions I’ve heard to POs calling here have been later in the
evening. On the night in question they started about one hour after
moon-rise, which was about one and a half hours after dark. Might the
birds have been hunting after dark but prior to moon-rise, and only
started calling, and hence advertising their presence to all and sundry,
when they have no advantage over the small arboreal marsupials they
hunt? I have heard Sugar Gliders 'yelping' on the same hillside from
which a PO was giving the begging call.
--
Robert Gosford
M Phil Candidate
CRES
Australian National University
Email:
Email2:
Ph: (02) 4441 8717
Mob: 0419483760
Web: http://uk.groups.yahoo.com/group/ethnoornithology/
Web email:
--------------------------------------------
Birding-Aus is on the Web at
www.birding-aus.org
birding-aus.blogspot.com
--------------------------------------------
To unsubscribe from this mailing list, send the message:
'unsubscribe birding-aus' (no quotes, no Subject line)
to
|
