The behavioural ecology of the thick-billed grasswren Marina (Maria Carolina Johanna) Louter (MSc Biology) A thesis submitted in fulfilment of the requirements for the Degree of Doctor of Philosophy School of Biological Sciences Faculty of Science and Engineering Flinders University of South Australia Cover image: Typical thick-billed grasswren habitat with chenopod shrubs at Witchelina Nature Reserve in South Australia, and (inset) a thick-billed grasswren (Amytornis modestus raglessi) in the hand. Photos by Marina Louter. ii Table of Contents List of Tables ................................................................................................................... vii List of Figures ................................................................................................................... ix List of Supplementary Material ..................................................................................... xi Thesis Summary .............................................................................................................. xii Declaration...................................................................................................................... xiv Acknowledgements ......................................................................................................... xv Statement of Authorship/Contribution and Acknowledgment ............................... xviii Chapter 1 General introduction ................................................................ 1 Behavioural conservation framework .................................................................... 1 Maluridae as conservation models ........................................................................ 1 Conservation status of grasswrens (Amytornis) .................................................... 3 Reproductive behaviour of grasswrens Amytornis ................................................ 4 Thesis scope and objective ................................................................................... 12 Organization of this thesis ................................................................................... 12 Chapter 2 Habitat recovery from grazing predicts presence but not home range size in thick-billed grasswrens (Amytornis modestus raglessi). ...................................................................................................... 13 Introduction ..................................................................................................................... 14 Methods ............................................................................................................................ 18 Study area ............................................................................................................ 18 TBGW occurrence ................................................................................................ 19 Grazing impact – distance to dam ....................................................................... 20 Vegetation sampling – Jessup transects .............................................................. 20 Arthropod sampling Pitfalls ................................................................................. 22 Radio tracking of grasswrens .............................................................................. 22 Home Range Estimation ...................................................................................... 24 Group size, habitat use and foraging behaviour of grasswrens .......................... 25 Statistical analysis ............................................................................................... 26 Results .............................................................................................................................. 27 Grazing impact and ecological predictor variables ............................................ 27 TBGW occurrence ................................................................................................ 27 Home range size and ecological predictor variables .......................................... 29 Discussion......................................................................................................................... 29 Summary of results ............................................................................................... 29 Impacts of grazing on vegetation ......................................................................... 30 iii Impact of grazing on TBGWs ............................................................................... 31 Conclusions .......................................................................................................... 33 Chapter 3 What predicts nest predation in thick-billed grasswrens (Amytornis modestus raglessi)? ................................................................. 40 Introduction ..................................................................................................................... 41 Methods ............................................................................................................................ 45 Study site .............................................................................................................. 45 Study species ........................................................................................................ 46 Natural nest searching, nest monitoring, and nesting outcome .......................... 47 Nest-predation experiment ................................................................................... 48 Rodent predator activity ...................................................................................... 49 Avian predator activity ........................................................................................ 50 Nesting site characteristics (natural and artificial)............................................. 50 Statistics ............................................................................................................... 51 Results .............................................................................................................................. 52 Nesting biology .................................................................................................... 52 Predation outcome grasswren nests .................................................................... 53 Predator identity natural grasswren nests ........................................................... 53 Nest-predation experiment ................................................................................... 53 Rodent activity and rodent nest predation ........................................................... 54 Avian predator activity and avian nest predation................................................ 54 Nesting site characteristics and nest predation at artificial and natural nests ... 55 Discussion......................................................................................................................... 56 Thick-billed grasswren nesting biology ............................................................... 56 Predation outcome thick-billed grasswren .......................................................... 57 Brood parasitism .................................................................................................. 57 Predator type at grasswren nests ......................................................................... 58 Nest-predation experiment ................................................................................... 59 Nest predation in other grasswren species .......................................................... 60 Conclusion and management implications .......................................................... 61 Chapter 4 Vegetation cover predicts parental feeding rates in thick- billed grasswrens (Amytornis modestus raglessi) .................................... 72 Introduction ..................................................................................................................... 73 Methods ............................................................................................................................ 77 Study site .............................................................................................................. 77 Vegetation cover, shrub abundance and grazing ................................................ 77 Arthropod sampling ............................................................................................. 78 Group size and composition................................................................................. 78 Nest monitoring and nestling measuring ............................................................. 79 Digital video recording (DVR) system design ..................................................... 80 iv Effects of cameras on nest survival ...................................................................... 81 Prey size and prey items ...................................................................................... 82 Feeding rate with nestling age and time of day ................................................... 82 Parental care behaviour ...................................................................................... 83 Statistical Analysis ............................................................................................... 84 Results .............................................................................................................................