Resource-Partitioning Between Three Syntopic Thornbills (Acanthizidae: Acanthiza Vigors and Horsfield)
Total Page:16
File Type:pdf, Size:1020Kb
RESOURCE-PARTITIONING BETWEEN THREE SYNTOPIC THORNBILLS (ACANTHIZIDAE: ACANTHIZA VIGORS AND HORSFIELD) HENRY LAWRIE BELL (B.App.Sc., Canberra College of Advanced Education; M.Sc., University of Papua New Guinea) A Thesis submitted for the degree of Doctor of Philosophy of The University of New England January 1983 iii TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF PLATES LIST OF APPENDICES ACKNOWLEDGEMENTS ABSTRACT INTRODUCTION Chapter 1 1-7 PART I Environment, Availability of Food, and the Bird Community Chapter 2 The Environment 8-33 Chapter 3 Availability of Arthropods 33-47 Chapter 4 The Bird Community 48-52 PART II Social Organization of Thornbills Chapter 5 Social and Territorial Organization 53-88 Chapter 6 Mixed-species Flocks of Insectivorous Birds 89-106 PART III Foraging Behaviour Chapter 7 Substrate Foraged Upon by Thornbills 107-125 Chapter 8 Plant Species Foraged Upon by Thornbills 126-153 Chapter 9 Vertical Distribution 154-174 Chapter 10 Foraging Method 175-189 Chapter 11 Diet 190-204 Chapter 12 Morphology 205-220 PART V Chapter 13 Food Limitations in Thornbills 221-241 Chapter 14 General Summary 242-248 REFERENCES 249-272 APPENDICES iv LIST OF TABLES Number Page Table 1. Results of Transect Counts of Vegetation at Wollomombi 18 Showing Percentage of Numbers and Canopy Cover by Plant Species, and the Extent of Defoliation During Drought. Table 2. Mean Density of Plant Species at Study Area, Wollomombi 19 (individuals/ha) (data from point-centred quarter sampling method). Table 3. Proportions, by Height Categories, of Volume of Foliage 20 of Plant Species at Study Area (died or defoliated shown in brackets). Table 4. Proportions, by Eucalypt Species, of Trunk Bark Available 22 to Birds; and of Trunk Sizes by dbh at Wollomombi. Table 5. Seasonal Abundance of Arthropods Inside and on the 46 Surface of Bark of Eucalypts at Wollomombi, 1978/79. (Data supplied by R.A. Noske). Table 6. Distribution, by Months, of Agonistic Displays and 61 Breeding Records of Brown Thornbills at Wollomombi, and Division of Labour at the Nest. Table 7. Distribution, by Months, of Agonistic Displays and 69 Breeding Records of Buff-rumped Thornbills at Wollomombi and Division of Labour at the Nest. Table 8. Distribution, by Months, of Agonistic Displays and 77 Breeding Records of Striated Thornbills at Wollomombi, and Division of Labour at the Nest. Table 9. Interactions (see paragraph 111) in Mixed-species 98 Feeding Flocks, Between Thornbills and Other Species. Table 10. Composition, by Time, of a MSF Following Buff-rumped 101 Thornbills 2 July 1979 (see Figure 32b). v. Number Page Table 11. Differences Between Mean Annual and Seasonal 117 Frequencies of Use of Substrate by Thornbills. Significance Values and Direction of the Seasonal Value from the Mean (+: higher than mean, -: lower than mean) are shown. 2 Table 12. Significance by X Test (d.f.l) for Increases 133 Between Seasonal Use of Plant Species for Foraging by Thornbills Against Mean Values for Each Plant Species Over the Whole Study Period. Table 13. Preferences of Brown Thornbills for Plant Species 134 Compared with Frequency of Plant Species in Study Area. Table 14. Preferences of Buff-rumped Thornbills for Plant 138 Species Compared with Frequency of Plant Species in the Study Area at Wollomombi. Table 15. Preferences of Striated Thornbills for Plant 139 Species Compared with Frequency of Plant Species in the Study Area at Wollomombi. Table 16. Preferences of Brown Thornbills for Different 143 Groups of Eucalypts. Table 17. Preferences of Buff-rumped Thornbills for Different 144 Groups of Eucalypts. Table 18. Preferences of Striated Thornbills for Different 145 Groups of Eucalypts. Table 19. Foraging by Thornbills on Main Groups of Eucalypts, 146 When in MSF and Overall (including MSF). 2 Table 20. Significance, by X Test (d.f. 1) of Foraging by 160 Thornbills, by Seasons, at Heights More Frequently Than Expected, 1978/81. vi Number Page Table 21. Proportions of Foliage at Wollomombi, by Height 165 Categories, Compared to the Frequency of Observat- ion of Thornbills in those Categories. Table 22. Frequency of Foraging by Thornbills on the Foliage 168 of Plant Species Below 2m in Height and the Availability of Foliage at that Level. Table 23. Mean Numbers and Biomass (per 10 ha) by Height 172 Distribution of Insectivorous Birds at Wollomombi, 1978-81. 2 Table 24. Significance, by X Test (d.f. 1) of Foraging Methods 179 Used by Thornbills, by Seasons, at Wollomombi, 1978-81. Table 25. Distribution (%) of Observations of Thornbills at 181 Wollomombi 1978-1981, by Substrate and Foraging Method Used. Table 26. Distribution (%) of Observations of Thornbills at 182 Wollomombi 1978-81, by Plant Species and Foraging Method Used. Table 27. Significance Levels (by Wilcoxsons Sum of Ranks Test) 185 of Differences by Time of Day in Speeds and Distance Covered by Thornbills in Foraging. Table 28. Prey Items of Thornbills at Wollomombi Identified 198 by Direct Observation. Table 29. Behaviour of Thornbills at Wollomombi When Offered 199 Sugared Water. Table 30. Differences in Stomach Contents of Thornbills 201 Between Warmer Months (October-March) and Cooler Months (April-September). vii Number Page Table 31. Results of Comparisons of Morphological Data Between 213 Species Pairs of Thornbills (each pair compared by T-test except where otherwise shown; *: Mann-Whitney U-test; : mere comparison of means for each species). Table 32. Results of Grasping-strength Tests on Thornbills at 214 Wollomombi (value for each individual in g). Table 33. Comparison of the Seasons of 1978/79 in Which Each 227 Thornbill Species Carried out its Specialised Foraging Behaviour Significantly More Than Expected, and the Availability of Arthropods by Seasons. Table 34. Comparisons, by T-test, of Mean Overlaps and S.D. 228 Between Thornbill Species in Months of Scarce and Abundant Resources. Table 35. Percentage Overlaps in Foraging Between Species Pairs 232 of Thornbills Compared When in and When Not in MSF. viii LIST OF FIGURES Page Figure 1. Study Areas at Wollomombi Falls Reserve of R.A. Noske 10 and L. Huddy (Edgaris Spur and Quail Thrush Spur) and H.L. Bell (EdgaA Spur). Figure 2. Mean monthly maximum and minimum temperatures, Monthly 12 and mean monthly rainfall, monthly Plant Growth Index and monthly Leaf Growth Index at Wollomombi Falls Reserve (September 1978 to August 1981). Figure 3. Distribution, by height categories, of foliage present 17 at Wollomombi showing proportions killed or defoliated by drought. Figure 4. Cross-section of bark on trunks, at breast height, 23 of three Eucalyptus spp. (life-size). Figure 5. Leaves of (a) Stringybark Eucalyptus caliginosa, 26 (b) Box, E. sp. aff. cypellocarpa, (c) Gum, E.viminalis, (d) bipinnate Acacia., A. irrorata. Figure 6. Leaves of (a) Cassinia quinquefaria, (b) Olearia viscidula, 27 (c) Jacksonia scoparia, and (d) Exocarpos cupressiformis. Figure 7. Monthly biomass (mg wet weight/1000g foliage) of arthropods38 taken from grass sweeps and foliage sampling at Wollomombi, September 1978-August 1981. Figure 8. Monthly biomass (mg wet weight/1000g of foliage) of 39 arthropod samples taken from eucalypts, bipinnate Acacia, Olearia, Exocarpos, Jacksonia and Cassinia at Wollomombi, September 1978-August 1981 . Figure 9. Monthly biomass (mg wet weight/1000g of foliage) of 41 Coleoptera, Hemiptera, Formicoidea and Araneidea taken in foliage samples at Wollomombi, September 1978-August 19 81 . Figure 10. Monthly biomass (mg wet weight/100 X 2 m grass sweeps) 42 of Araneidea, Hymenoptera, Diptera and Lepidoptera taken in grass sweeps at Wollomombi, September 1978-August 1981 . ix Page Figure 11. Proportions of arthropods, by lengths, taken in foliage 44 samples and grass sweeps at Wollomombi. Figure 12. Monthly mean lengths of arthropods taken on grass sweeps 45 and on foliage samples of eucalypts, bipinnate Acacia, OZearia and Jacksonia at Wollomombi, September 1978- August 1981). Figure 13. Mean monthly biomass of all insectivores at Wollomombi 50 (13a) mean daily energy demand of insectivores compared with arthropod samples (13W-; Resource demand (Kjoules/ 10 ha per mg arthropods/1000 g of foliage) and distribution of breeding records of insectivores at Wollomombi(13c). Figure 14. Percentage occurrences, by months (September 1978-August 56 1981), of Brown Thornbills by size of party (total n: 4656 individuals, monthly range 63-112). Figure 15. Territories of Brown Thornbills at Wollomombi, 1978/79, 58 1979/80, 1980/81 (September-August) and 1981/82 (September-February). Letters denote colour-banded birds. Top bird of each pair is female. (Note: BuR daughter of YY, BuW son of LB). Figure 16. Inverse correlation (r: 0.855, P: < 0.01) between 59 frequency of observed agonistic encounters by Brown Thornbills against colour-banded neighbours and length of territorial boundary. Letters identify females, number in brackets: number of breeding seasons. Figure 17. Sizes of Brown Thornbills territories at Wollomombi, 60 and the proportion of each covered by understorey (Spearman Rank Correlation, smallness of territory with proportion covered in understorey, r: 1.000, P: 0.01). Letters refer to female of each pair. Figure 18. Percentage occurrences, by months (September 1978- 64 August 1981), of Buff-rumped Thornbills by size of party (total n: 4674 individuals, Monthly Range 30-232). Page Figure 19. Territories of clans of Buff-rumped Thornbills at 66 Wollomombi 1978-181. Area to North cleared grazing land, to South gorge country, unoccupied by species. Figure 20. Clan and group territories of Buff-rumped Thornbill 67 at Wollomombi, 1978/79, 1979/80, 1980/81 (September- August) and 1981/82 (September-February). Letters refer to banded birds (paragraph 75) top bird is female. Figure 21. History of individual Buff-rumped Thornbills of Clan A, 68 at Wollomombi 1978/82. Broken edge at left of bar indicates age unknown at banding, at right indicates known to be alive after leaving.