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A comparison of foodplant utilization by nectar-feeding marsupials and birds in the Fitzgerald River National Park, Western Australia

Saffer, V.M. (1998) A comparison of foodplant utilization by nectar-feeding marsupials and birds in the Fitzgerald River National Park, Western Australia. PhD thesis, Murdoch University.

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In heathlands at the western end of the Fitzgerald River National Park, Western Australia, Honey Possums Tarsipes rostratus were the most abundant mammal and meliphagid honeyeaters the most abundant birds. These heathlands contain many plant species in the families Proteaceae and Myrtaceae, whose protracted and asynchronous, yet overlapping, patterns of flowering result in nectar and pollen available all year. This continual food resource supports vertebrate populations that are predominantly nectarivorous. This thesis examines inter-relationships between nectar-feeding mammals and birds, and floral assemblages that supported them, at the western end of the Park between June 1994 and March 1997. The characteristics of the flowers visited most often were assessed in relation to the different pollination syndromes suggested as associated with small mammals or birds.

Honey Possums are tiny (8-12g) diprotodont marsupials that feed exclusively upon nectar and pollen, mainly at night. They were caught in four grids, in a line 42-72m apart, each grid containing 10x10 pitfall traps 5m apart. Five box traps were also used in each grid. Twenty trapping sessions, each of three consecutive nights, resulted in 1,371 captures of Honey Possums from 24,000 trapnights (5.7% trap success). Honey Possums accounted for 91% of all mammals caught; the Grey-bellied Dunnart Sminthopsis griseoventer, the Southern Bush Rat Rattus fuscipes, the House Mouse Mus musculus and the Ashy-grey Mouse Pseudomys albocinereus comprised the remainder. Overall, there appeared to be some correspondence between the capture rates of Honey Possums and the flowering patterns of some of their favoured plants, whereas temporal differences in the abundances of the five species of honeyeaters were not related in any simple manner to the magnitude of floral food resources (nectar and pollen), nor to invertebrate abundance.

Birds were censused using instantaneous point counts in each trapping grid and six 12m long mist-nets operated regularly adjacent to the grids. During twenty trapping sessions, 2972 birds were recorded and 94% of these were honeyeaters. White-cheeked Honeyeaters Phylidonyris nigra and New Holland Honeyeaters Phylidonyris novaehollandiae accounted for 83% of all honeyeaters; Tawny-crowned Honeyeaters Phylidonyris melanops. Little Wattlebirds Anthochaera chrysoptera and Western Spinebills Acanthorhynchus superciliosis made up most of the remainder.

More Honey Possums were caught and their condition indices were highest in winter, when up to six of their favoured food plants were in flower. Fewest Honey Possums were caught and condition indices were lowest in autumn, when fewest plants were in flower. In contrast, more honeyeater birds were present over summer and fewest during winter.

Eight plant species within the Proteaceae were studied in detail. Three species, Banksia baueri, Banksia nutans and Dryandra plumosa, had floral characteristics typical of plants thought to be visited more frequently by mammals than birds. The remaining five species, Banksia baxteri, Banksia coccinea, Dryandra cuneata, Lambertia inermis and Adenanthos cuneatus displayed floral traits associated more with plants thought to be favoured by birds. However, temporal differences in the presentation of pollen (anthesis) and nectar, and amounts of nectar produced by these eight species did not conform to the predictions of separate mammals and bird pollination syndromes.

Nonetheless, direct observations of foraging by Honey Possums and honeyeaters indicated preferences for flowers with two different suites of characteristics. Samples of pollen carried externally by 1218 Honey Possums and 1001 honeyeaters, and voided in faeces by 107 mammals and 225 birds, confirmed marked preferences for these different types of flowers. Flowers visited mostly by Honey Possums tended to occur low or on the ground, to be inconspicuous or hidden in foliage, drably coloured but with a distinctive odour. In contrast, flowers visited by honeyeaters were brightly coloured (red or yellow), exposed on the plant, often in a terminal position, and higher above the ground.

Despite these clear preferences, especially evident when food from their favoured flowers was abundant, both Honey Possums and honeyeaters commonly visited flowers in both categories. Thus, although a degree of specialisation was apparent in the relationships between these nectarivorous vertebrates and their food plants, there was also opportunistic generalisation in flower usage. Honey Possums were highly sedentary, whereas most honeyeaters were transient in the area studied. Honey Possums are entirely dependent upon pollen grains for protein whereas honeyeaters also eat invertebrates. In consequence, Honey Possums appear more reliant than honeyeaters upon the floral products of a small suite of plants, but the dependence of these plants upon Honey Possums for pollination remains to be resolved.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): Division of Science
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Wooller, Ron, Bradley, Stuart and Richardson, Ken
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