Journal of the Royal Society of Western Australia, 86(4), December 2003 
We attempted to take the six fruits from different parts of 
each tree. Fruit wet mass, fruit length and diameter, seed 
number and total seed dry mass were recorded for each 
fruit. Seeds were dried to a constant weight at 50-70 °C in 
a Labmaster drying oven. Feed and non-feed 
comparisons were made using nested ANOVA (SPSS 
version 11.5), with year and tree type as fixed factors, 
and site as a random factor nested within year. 
Classificatory discriminant analysis was accomplished 
with statistiXL (v 1.1). Mean (± S.E.) values for feed and 
non-feed trees were calculated from the mean values for 
six fruits from each tree. 
Results 
Feed tree fruits were significantly longer (F, 33g = 14.48, 
p < 0.001) and had a greater diameter (F U3g = 11.65, p = 
0.001); they also had more seeds (F i;}37 = 24.3, p < 0.001), 
larger seeds (F U23 = 10.2, p = 0.002) and a higher total dry 
seed ma£s (F 1333 = 40.4, p < 0.001) than non-feed trees 
(Table 1). The ratio of total seed mass to fruit wet mass 
was also significantly higher for fruits from feed than 
from non-feed trees (F ] 335 = 46.44, p < 0.001). Wet mass of 
the fruits did not differ significantly between feed and 
non-feed trees (F J335 = 3.3, p = 0.070). Year of sampling 
did not affect the "fruit length (F ]29 = 2.80, p = 0.105), the 
seed content of fruits (either seed number, F, 29 = 0.45, p = 
0.506; individual seed mass, Fj ^ = 2.32, p = 0.139; or total 
dry seed mass, F 129 = 1.69, p = 0.204), or the ratio of total 
seed mass to fruit wet mass (F ]29 = 1.89, p = 0.180), but 
the wet mass of whole fruits (F U9 = 7.97, p = 0.009) and 
fruit diameter (F 129 = 9.58, p = 0.004) were significantly 
greater in 2003. All fruit and seed characteristics showed 
highly significant variation between sites: fruit wet mass 
( p 29,335 = 31 - 7 ' P < 0-001), fruit length (F 2933g = 16.21, p < 
0.001), fruit diameter (F 2933g = 28.63, p < 0.001), seed 
number (F 29337 = 2.64, p < 0.001), individual seed mass 
(F 29323 = 2.31, p < 0.001), total seed mass (F 29333 = 2.92, p < 
0.001), and the ratio between the total seed mass to fruit 
wet mass (F 29335 = 6*18/ p < 0.001). 
Table 1 
Characteristics of Marri fruits from trees that Forest Red-tailed 
Black Cockatoos use (Feed) and ignore (Non-feed). Values are 
mean ± standard error, n = 31, average of 6 fruits per tree. 
* indicates significant difference at p < 0.05. 
Feed 
Non-feed 
Fruit wet mass (g) 
24.1 ± 1.72 
23.2 ± 1.57 
Seed number per fruit* 
3.9 ± 0.18 
3.1 ± 0.20 
Individual seed 
0.10 ± 0.003 
0.09 ± 0.005 
dry mass (g) 
Total seed dry mass (g) * 
0.39 ± 0.018 
0.29 ± 0.020 
Total seed mass to 
0.02 ± 0.001 
0.013 ± 0.001 
fruit mass ratio * 
Discussion 
Characteristics of Marri fruits 
The characteristics of Marri fruits examined in this 
study are generally typical of Marri fruits examined in 
previous studies. Gill et al. (1992) reported that Marri 
fruits contained similar numbers of seeds per fruit (3.1 ± 
1.3) as found in this study (3.5 ± 0.2), while Abbott (1984) 
found an average of 4 seeds per fruit. These slight 
differences in average number of seeds per fruit are 
presumably due to variations in study sites and perhaps 
variation in Marri flowering and fruiting from year to 
year (Mawson 1995), although we found no differences 
in seed characteristics between two years. Gill et al. (1992) 
reported that Marri fruits contained a total seed weight 
of 0.51 ± 0.17 g per fruit compared to 0.34 (± 0.02) g in 
this study. Again, different localised climatic and soil 
conditions, and yearly variations in fruiting may account 
for these differences, although we found no significant 
difference between the two years sampled. 
Two non-feed trees in this study were found to have 
fruits containing no seeds (classified as male fruits), as 
has been described previously for Marri (Carr et al 1971; 
Mawson 1995). Marri varies with respect to the 
proportion of male fruits. Some trees only produce male 
fruits, never female fruits containing seeds (Carr et al. 
1971); male fruits are often withered in appearance, but 
fruits of the male trees from this study were normal in 
appearance. According to Carr et al. (1971) male fruits 
have no seeds because of ovule abortion late in 
development. Mawson (1995) suggested that the presence 
of male trees meant that birds feeding on Marri need to 
be discerning, to avoid wasting time and energy feeding 
on fruits that would give no energetic return. We found 
that Forest Red-tailed Black Cockatoos are even more 
discerning, since feed and non-feed trees differ in fruit 
energy yield. 
Feed and non-feed Marri trees 
Our study supports Johnstone & Kirkby's (1999) 
hypothesis that there is a difference in seed 
characteristics between feed and non-feed Marri trees. 
Feed trees have a higher seed number, individual seed 
mass and total seed dry mass per fruit compared with 
non-feed trees, indicating that cockatoos select Marri 
trees that have fruits with a higher energy content. Marri 
seeds contain 22.9 kj of combustible energy g* 1 (Cooper et 
al. 2002). Therefore, feed trees provide 8.85 k] fruit 1 (0.39 
g x 22.9 kj g 1 ; assuming that all the seeds are eaten), 
which is a 34% greater return than for non-feed trees 
(6.61 kj fruit- 1 ; 0.29 g x 22.9 kj g' 1 ). 
Clout (1989) and Pepper et al. (2000) reported that 
Glossy Black Cockatoos (C. lathami) in New South Wales 
and South Australia also selected feed trees with a greater 
seed return than non-feed trees, when feeding on 
Allocasuarina littoralis and A. verticillata respectively. Feed 
A. verticillata trees for South Australian Glossy Black 
Cockatoos (C. /. halmaturinus) have 23% larger seeds, 21% 
more seed per cone and 13% more energy per cone than 
trees from which the birds did not feed (Pepper et al. 2000). 
In our study, feed Marri trees had 10% larger seeds and 
25% more seeds per fruit than non-feed trees and provided 
Forest Red-tailed Black Cockatoos with 34% more energy 
per fruit than non-feed trees (2.6 times the energy 
difference for A. verticillata). This presumably reflects the 
large size of Marri compared to A. verticillata seed, and 
possibly a greater variation of total seed dry mass in Marri 
compared with A. verticillata. It is also possible that Forest 
Red-tailed Black Cockatoos are more selective feeders than 
South Australian Glossy Black Cockatoos. 
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