Date of Award
Master of Science
School of Natural Sciences
Faculty of Health, Engineering and Science
Professor Will Stock
Dr Peter Mawson
Dr Robert Davis
To achieve a balance between sustainable development and conservation of threatened species, management depends on understanding the predicted response and interaction of that species with their environment in order to develop appropriate mitigating solutions. The Carnaby’s cockatoo Calyptorhynchus latirostris is declining across much of its range due to the detrimental effect of habitat degradation and loss. Since the decline of food resource availability in non-breeding areas is believed to be contributing to the reduction in the number of Carnaby’s cockatoos knowledge of the birds’ foraging ecology and the influence of external factors on food resource availability is essential for effective management. Despite extensive studies and conservation work on the Carnaby’s cockatoos, there remain many gaps in our understanding of the birds’ foraging behaviour. The aim of this thesis is to fill some of those gaps.
Carnaby’s cockatoos are destructive feeders, removing plant parts with strong beaks by holding them while extracting seed and insect larvae. Surveys of the birds feeding preferences were analysed by recording feeding residues of the number of eaten and uneaten infructescences left behind on the ground following foraging bouts. It was noted that Carnaby’s cockatoo diets were highly variable in terms of plant structures and species manipulated and consumed. Twenty-four species of food plants were manipulated by Carnaby’s cockatoo. Of these, 15 species of plant were consumed for seeds, with 53% of the total being made up of proteaceous species. Six of the 15 species (all Banksia species) were also manipulated as inflorescences. Grubbing for insects that were living in or on the woody stem tissue was observed in 63% of the food resource plant species collected. Carnaby’s cockatoo displayed a strong preference for food resources of the Banksia and Hakea genera.
The relationship between Carnaby’s cockatoos and Banksia species was further examined to understand infructescence availability and variability in seasonal and total annual counts to determine the amount of potential food available to Carnaby’s cockatoos. Banksia attenuata, B. grandis, B. ilicifolia, B. menziesii, B. prionotes and B. sessilis were targeted in this study. Infructescence availability was determined through examination of Carnaby’s cockatoo feeding residues and numbers of mature infructescences that make up the standing crop of infructescences containing seeds. Banksia infructescences were available throughout the study for five out of the six species, although seasonal and annual amounts available varied. The numbers of infructescences available were not significantly (P > 0.05) influenced by soil type. However, infructescence numbers were significantly (P < 0.05) reduced by the presence of Phytophthora cinnamomi. In general the number of infructescences significantly (P < 0.05) increased as post-fire age increased.
Plant allometric relationships between morphological characteristics and number of infructescences were investigated to help identify factors which best predict infructescence numbers. For B. attenuata, canopy volume, canopy area and girth emerged as the best individual predictive models for explaining the variability of the number of infructescences. Multiple linear regression of all B. attenuata plant morphological variables accounted for 29% of the variability in the number of infructescences. Canopy volume, canopy area, girth and foliage height were the best individual predictive models for determining the number of infructescences for B. menziesii. The combination of all B menziesii plant morphological characteristics explained 44% of the variability in the number of infructescences. All the models tested for B. sessilis revealed significant (P < 0.05) relationships with correlation coefficients > 53%. Canopy area was the best individual predictive factor for B. sessilis, accounting for around 90% of the variation. Multiple linear regression analysis combining all B. sessilis plant morphological variables revealed a correlation coefficient of 92%. In comparison to B. attenuata and B. menziesii (resprouters), B. sessilis is an obligate reseeder which is killed by fire. As a consequence of reseeding post-fire, B. Sessilis commonly occurs in dense thickets and are often more uniform in plant size, age and infructescence availability than resprouters and therefore displays stronger allometric relationships. Determining the influence of external factors on infructescence numbers helps in establishing the amount of food resources available for Carnaby’s cockatoos and in turn highlights the importance of various food resource habitats.
Banksia species investigated as part of the food resource availability study were further examined to determine temporal variability of infructescence use by Carnaby’s cockatoo. Carnaby’s cockatoos showed themselves to be tolerant of changing resource availability which allowed them to effectively utilise food resources across the landscape throughout all seasons. Approximately 50% of resources available were utilised by Carnaby’s cockatoo throughout the year, with around 80% of handled infructescences consumed. Carnaby’s cockatoos showed flexibility in diet, with temporal variability in food resource use throughout the year. Infructescence resource use was highest between April and September. Level of consumption was a direct result of infructescence availability with no significant differences recorded in infructescence use in the presence of P. cinnamomi and different post-fire age stands.
Seed energetics and proportion of seeds and follicles available and consumed were investigated to determine the number of infructescences required to meet daily metabolic requirements of Carnaby’s cockatoo. Over 65% of infructescences handled were consumed for seed for each Banksia species. B. sessilis recorded the largest number of infructescences and follicles manipulated by Carnaby’s cockatoos. The energy content of Banksia seeds ranged from 20-23 kJ g-1. Seed weight varied from 0.075g ± SE 0.016 for B. attenuata to 0.007g ± SE 0.002 for B. sessilis. The number of infructescences required to meet the birds’ daily energy intake ranged from 14 for B. grandis to 3821 for B. sessilis, based on mean number of follicles manipulated for seed and one-hundred percent seed availability. Incorporation of the potential number of seeds per follicle increased the number of infructescences required: B. attenuata, B. ilicifolia, B. menziesii and B. sessilis increased by almost 200%, while B. prionotes and B. grandis increased by 200% and 300%, respectively.
Information collected on plant morphology, structure and infructescence availability combined with infructescence consumption and seed energy reward by Carnaby’s cockatoos allowed the development of food resource algorithms to guide habitat quality assessment. Establishment of quantitative criteria for assessing habitat quality for Carnaby’s cockatoo, such as methods for determining food resource availability, allows for effective integration of biodiversity issues into planning and impact assessment processes. The research undertaken for this thesis will add to the understanding and conservation of Carnaby’s cockatoo, an iconic South Western Australian species.
Johnston, T. (2013). Food resource availability for Carnaby's cockatoo Calyptorhynchus latirostris on the Swan Coast Plain. Retrieved from https://ro.ecu.edu.au/theses/595