Food of the forest red-tailed Black Cockatoo, Calyptorhynchus banksii naso in south-west Western Australia

11 Pages·1999·2.5 MB·

by  R E Johnstone

FOOD OF THE FOREST RED-TAILED BLACK COCKATOO
CALYPTORHYNCHUSBANKSII NASO IN SOUTH-WEST
WESTERN AUSTRALIA
By R.E. JOHNSTONE
Western Australian Museum, Francis Street, Perth W.A. 6000
and T. KIRKBY
49 Canning Mills Road, Kelmscott, W.A. 6111
ABSTRACT
The principal foods of the Forest Red-tailed Black Cockatoo
Calyptorhynchus banksii naso in south Western Australia arc the seeds
of Marri Corymbia calophylla and Jarrah Eucalyptus marginata. Of
these, Marri is the most important especially during the breeding
season in October-February. Other less important foods in northern
forests include Snottygobble Persoonta longifolia, Common Sheoak
AUocasuarina fraseriarui, Blackbutt Eucalyptus patens and in southern
forests, Albany Blackbutt E. staeri and Karri E. diversicolor. Although
some Marri and Jarrah seed is available all year, the flowering and
subsequent fruiting of both species varies between years on about a
4-6 year cycle. Preliminary results from this study suggest that
variations in the extent of flowering and nutting may detennine the
numbers of birds which attempt to breed
INTRODUCTION The Kimberley subspecies macrorhynchus
is generally common occurring in pairs
The Red-tailed Black Cockatoo
and family parties and small flocks in
Calyptorhynchus banksii is widely
distributed within Australia. Five forests and woodlands. Its range and
subspecies are currently recognised three status have not altered greatly in the
of which occur in Western Australia Kimberley since European settlement.
(Figure 1) namely*. C. b. macrorhynchus The mid-western subspecies samueli has
occurring throughout the Kimberley; C. greatly expanded its range south into
b. samueli found in the arid and semi- the northern wheatbelt in the past 60
arid northern and north-eastern interior years. Whereas it was originally
(i.e. Pilbara, Gascoyne, northern confined to northern watercourses
Wheatbelt and Goldfields); and C. b. including the Murchison, Irwin and
naso inhabiting the south-western Lockier Rivers, it is now most numerous
humid and sub-humid zones (mainly the in the northern and north-eastern
tall eucalypt forests). Ford (1980) and wheatbelt especially the Eurardy, East
Johnstone and Storr (1998). Yuna, Three Springs / Perenjori,
167
Figure 1. Distribution of Red-tailed Black Cockatoo in Western Australia
168
Jibberding and Trayning / Mukinbudin west to near Gingin (casually),
districts, occurring in pairs, small flocks Guildford (resident in colonial times
and occasionally large flocks up to 500. but now rare or absent), Mundijong,
The introduced South African weed the Coolup, Lake McLarty and Goodale
Double-gee Emex australis has become a Sanctuary (16 km S\V of Pinjarra)
major food source for samueli in the (presumably visitors from adjacent
Darling Scarp), Wokalup, Big Brook (23
wheatbelt. This together with the
km west of Nannup), formerly to Vasse
provision of watering points for
River, and Margaret River; and east to
livestock has enabled samueli to increase
Mt Helena (formerly to Toodyay),
in numbers and spread south into what
Christmas Tree Well, North Bannister
was previously unsuitable habitat:
(formerly to Wandering), Mt
Conversely the arboreal forest Saddleback, formerly to the Kojonup
inhabiting subspecies naso has district (where now only casual), Rocky
experienced a severe decline since Gully and upper King River (Figure 2).
European colonisation. Formerly it This forest cockatoo was formerly
occurred north to Dandaragan (where common throughout this historic range
there were once large stands of Marri); but is now rare to uncommon and
in* ii6* us® i2o® 122-
Figure 2 Distribution of C. b. naso in south-western Australia (showing present and former
ranges).
169
JoZ patchily distributed within its current
8 range that has become markedly reduced
c
o through clearing for agriculture. It
CxO
c occurs mainly in pairs or small family
groups (3-5) and occasionally large
flocks up to 200 have been recorded.
It is perhaps noteworthy that although
this large cockatoo is one of the most
conspicuous birds in the southern
forests its fundamental biology is still
poorly understood. Most of the
information concerning the diet is
£
anecdotal Storr (1991), Abbott (1998),
e
D Johnstone and Storr (1998). Since 1996
C
73 we have been studying the distribution,
o status, conservation and breeding
4—>
T3 biology of ruiso in south-western forests.
C
03 The aim of this paper is to identify its
JS
main foods and feeding techniques.
to
c
_o
*4a—I MATERIALS AND METHODS
>
io—
23 The cockatoos were studied at two main
o
&£ sites namely Bungendore Park -
c
(including Wungong Brook) and
1
Jarrahdale (including the Serpentine
,<V
area). Visits were also made to other
areas in the south-west including Collie,
Albany, Denmark, Manjimup, Nannup
and Margaret River to gather
information on distribution, status, diet
and breeding etc The vegetation at the
two main study sites at Bungendore Park
and Jarrahdale is similar being
predominantly Jarrah Eucalyptus
margimta and Marri Corymbia callophylla
with an understorey of Bull Banksia
Banksia grandis, Snottygobble Persoonia
longifolia, Allocasuarina fraseriana and
Dryandra spp. Both sites also contain
scattered stands of Blackbutt Eucalyptus
>-
-C patens and Wandoo Eucalyptus ivandoo.
4c—'
Fieldwork was conducted mostly on a
weekly basis commencing in 1996 and
continuing to early 1999. Flocks were
located in the study sites usually in late
afternoon or early morning and, once
170
located, we recorded the locality, time, population in the Bungendore area is 70
number of birds and flock composition, birds and at Jarrahdale 100 birds. A
habitat and behaviour including feeding total of 219 feeding observations were
behaviour. The estimated total made in the main study sites (each
Table 2.
Forest Red-tailed Black Cockatoo (C. b. tiaso) Observations of food taken compared with
S'
1. Mam Cycle. 2. Jarrali Cycle. 3. Breeding Cycle
% of total feeding records (monthly basis), birds feeding on Marri
m
SIS
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ill
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00L 06 08 0^ 09 OS Ot' OS 05 0L 0
% of total feeding records (monthly basis), birds feeding on Jarrah |;;; |
171
observation ranging from several birds They are methodical feeders returning
to the majority of the flock) (see Table each day to the same tree until the food
1) . Food trees were noted, food samples supply is exhausted It was frequently
including discarded nuts were collected noted that adjacent trees of the same
and in some cases photographed. species were untouched throughout this
feeding activity, even after the
'favoured' tree was depleted. It is also
RESULTS
noteworthy that Marri provides both a
FOOD AND FOOD AVAILABILITY much larger seed and a heavier seed
crop when compared to Jarrah and other
The principal food in both study sites
foods. For example Marri nuts contain
was Marri and Jarrah (see Table 1)
approx 5-6 times the seed mass
comprising almost 90% of the diet. We
compared to Jarrah. The seed weight in
made % observations with a total of
Marri is 0.113g v Jarrah 0.020g; seed
960 birds feeding on Marri and 87
length Marri 12.9 mm v Jarrah 4.5 mm;
observations with a total of 712 birds
and seed width in Marri 7.2 mm v 3.0
feeding on Jarrah. Other less important
mm (Abbott 1984). Additionally fewer
foods include Eucalyptus patens,
Marri nuts contain no seed than is the
Allocasuarina and Persoonia. There were
case of Jarrah. Thus the work effort
two observations of two birds feeding on
needed to open a Marri nut is justified.
dead Banksia grandis, two observations
The abundances of the various foods
with a total of 36 birds feeding on the
and feeding location, technique and
seeds of the introduced Spotted Gum
timing highlighted the importance of
Eucalyptus maculata and one observation
Marri and the birds’ knowledge of their
of 9 birds feeding on the seeds of the
territory.
introduced Cape Lilac Melia azederach.
All food was taken from the tree canopy
with the Persoonia and Banksia being FEEDING TECHNIQUES
small understorey trees.
The method of feeding on Marri and
Birds were recorded feeding on Marri Jarrah was distinctive and of use in
throughout the year (see Tables 1 and plotting the occurrence of these
2) ,however there was a strong seasonal cockatoos after they have fed in an area.
shift between March and June from A bird either nips off a nut within range
Marri to Jarrah and other foods. Flower of one position or nips off a branch (up
and subsequent fruit production of both to 300 mm long and 9 mm thick) with
Marri and Jarrah varies between years several nuts and then, while still
on about a four to five year cycle (see holding the branch breaks off individual
tree ecology below and Table 2). nuts. In either case it extracts and husks
Preliminary results indicate that the the seed from the nut with its bill.
extent of flowering and nut production Leaves and other small stems are often
may determine the numbers of nesting also nipped off to allow easier access to
birds in the subsequent breeding season. nuts. On finishing, the branch is
Although some seed of Marri and Jarrah dropped to the ground. The ground
is available all year, the cockatoos are beneath the tree becomes littered with
extremely selective with respect to chewed nuts, leaves and small branches
which trees they feed in and there may with up to 70% of the ground beneath
be large differences in seed quality, the canopy covered in nuts and leaves.
nutrient value, seed size and seed fill. Attention is often drawn to a feeding
172
party by the sound of hard nuts being manoeuvred in the bill (Figure 5) and
cracked open and the continual stream the seed capsule is split open by the bill
of debris falling to the ground. When and the seeds extracted and husked at a
feeding in the outer foliage birds often rate of 2-5 nuts per minute (see Figure
pulled thin branches together for more 6). One adult extracted seeds from 30
secure footing and one female was seen nuts in 8.20 minutes. In some cases
to wedge herself into a fork with a spray however only half the seeds from each
of nuts in windy conditions. nut are extracted.
A llocasuarina
Marri
Allocasuarina cones are held in the foot,
Usually a bird bites off a tough woody
split down the centre with the bill then
nut and transfers it to the foot, almost
rotated with the foot in order to extract
invariably the left foot (but some birds
and husk the seeds. Times recorded to
are right footed). Marri nuts are large,
extract and husk the seeds from
thick and woody with measurements
Allocasuarina cones range from 30-36
ranging from 25-45mm long and 20 x
seconds. The seeds of Allocasuarina are
40mm in width and birds will feed on
retained in the mature cones for only 1-
green to hardened ripe nuts. The Marri
2 months (January-February) and after
nuts are opened in a number of ways
this time very little seed remains for the
(Figures 3 and 4) with individuals using
cockatoos to harvest
one of the following techniques.-
The fruits of the Snottygobble
1. Holding the nut by the pedicel and
(Persoonia) are split down the centre
chopping their way into the bowl
and the tiny seed extracted. Birds feed
(or hypanthium) from the rim
very slowly on Snottygobble at the rate
2. Holding the rim of the nut and
of about 2 fruits per minute and not all
chopping in at the base of the
fruits are eaten. Often adults spending
hypanthium
time pruning the outer branches as well
3. Holding the nut at the rim or base as feeding. Spotted gum nuts are
and chopping in at the centre and handled the same way as jarrah nuts.
rotating the nut in the foot anti¬
Cape Lilac fruits are sometimes held in
clockwise.
the foot but mostly sliced in half and
Depending on the individual skill of the seeds extracted with just the bill and
bird it takes about one-two minutes tongue
(0.38 - 2.45 minutes) to extract and
husk the seed from a Marri nut. One
DAILY ACTIVITY PATTERNS
adult male extracted seeds from five
In both study areas the flocks spend the
green nuts in 3.12 minutes. On one
night roosting in tall straight trunked
occasion an adult female was also
isolated stands of Jarrah-Marri-
observed taking (grabbing) opened nuts
Blackbutt growing in a road side verge,
from her mate feeding alongside, taking
edge of a paddock or at the edge of a
them from his foot just as the seeds were
forest block. The birds usually leave
exposed.
their night roosts at sunrise (ca. 05:00
Western Standard time) split into
Jarrah smaller family groups and move into
Jarrah nuts are held firmly in the foot or adjacent forest. Our study flocks (with
173
Figure 3. Discarded green Marri nuts from one tree showing range of opening methods.
Figure 4. Discarded Marri nuts eaten by naso showing both base (top row) and rim (bottom
rows) opening methods.
174
Figure 5. Female C. b. naso with Jarrah nut in bill.
Figure 6. Discarded Jarrah nuts eaten by naso.
175
some banded birds) were usually located into nuts in March-December and the
within 1-4 km of the roost. After a seeds dehisce from mature nuts in
short period of preening and sometimes January-February of the third year.
basking in morning sunlight they began Overall taking about 17 months
feeding, usually in Marri or Jarrah trees. between initiation of buds and the
shedding of seeds At the end of this
Feeding continued for up to 10-12
cycle trees which produce a heavy
hours sometimes with short breaks to
flowering and crop of nuts, are in poor
move to another tree, preen or clean the
condition with reduced leaves in the
bill. Bill cleaning involves wiping the
canopy and few new leaves. The
bill on dead branches or chewing into
resources used in producing such large
dead wood especially Jarrah and
flowers and nuts are so great that the
Banksia. At around 16:00 to 17:00 hrs
tree requires another three years to
birds would stop feeding, begin bill
recover enough to repeat the process. In
cleaning and preening, become more
any one year only about 20-50 percent
vocal and move off in small groups to
of the trees produce a large nut crop. It
drink at water in tree hollows, creeks,
is also noteworthy that a small
puddles, dams and troughs. Overall they
proportion of Marri trees produce only
have a preference for drinking at tree
male flowers and seedless fruits (Carr et
hollows and appear quite uncomfortable
al. 1981).
on the ground. On dark, the birds would
return to the roost area. In Jarrah, flowering occurs every 4-6
years (Abbott and Loneragan 1986).
This behaviour was repeated each day
Buds are initiated in December-January
unless there was a marked change in the
each year and if conditions are
weather especially with heavy rain and
favourable they are retained and
strong winds. Under these conditions
develop further, flowering between
birds foraged less and remained more
September and December. These flowers
subdued in their behaviour. When
develop into nuts during the next year
breeding the female leaves the nest
and mature in September. Seed is shed
hollow once or twice a day to be fed by
three months later in December-March
the male (by pump regurgitation). It
taking overall 24-27 months from bud
takes immatures over a year to develop
initiation to shedding seed.
the skills necessary to extract seeds from
Marri nuts and during this period they
are constantly attended by both parent
CONCLUSIONS
birds. Young birds must also learn which
trees produce nuts with seed in order Habitat destruction has clearly caused
not to waste effort on seedless nuts. the Forest Red-tailed Black Cockatoos
marked decline in south-western
Australia. The extensive clearing of the
ECOLOGY OF MARRI AND JARRAH
Jarrah-Marri and Wandoo forest and
The flowering and subsequent nutting of woodland, largely for agriculture, has led
Marri and Jarrah varies significantly to a loss of over one third of its original
from one year to the next. Marri flowers range. Land clearing has slowed greatly
heavily on a five year cycle (R Mawson in recent years. Cockatoos are however
pers. comm.). Buds are initiated in long-lived and it is not clear whether
August or September, mature by January this factor is masking a continuing
when flowering commences, develop decline in their overall populations.
176