Territorial behaviour is exhibited in cooperative breeders. The quality of defended territories can vary, and high-quality sites, which enhance fitness, should be used preferentially over poorer-quality sites. This study was intended to address issues of territory quality within the plural breeding, joint-nesting, smooth-billed ani (Crotophaga ani). I tested the communal joint-nesting threshold hypothesis, which posits that independent pairs will pay the price of group living if compensated by acquiring a superior territory. My results quantified differences in territory quality in terms of time of first breeding and chances for re-nesting or second-brooding. Per capita territory quality correlated negatively with group size, in conflict with the communal joint-nesting threshold hypothesis. Another hypothesis to explain communal behaviour is the habitat saturation hypothesis. This postulates that offspring remain in their natal territory and delay reproduction because of a local absence of suitable breeding habitat. I tested the habitat saturation hypothesis, which was developed to explain the evolution of group living in cooperatively breeding birds. I compared occupied ani territories with vacant sites, using eight ecological variables that may be important to the fitness of a group. In addition, I compared occupied territories with sites that were occasionally occupied. I did not find the habitat of our population of smooth-billed anis to be saturated. Some sites were never occupied because there are territory characteristics that presumably limit breeding. In contrast with expectations of habitat saturation, there were suitable sites available for breeding that were not in use. Results from both hypotheses presented suggest that there are not obvious group-living benefits and that one must consider other explanations for the evolution and maintenance of this system. / Thesis / Master of Science (MS)

In this thesis, I describe the behavioural ecology of an Australian passerine, the Southern Emuwren Stipiturus malachurus (Maluridae). The southern emu-wren is threatened in several parts of its range, and yet information on the species’ breeding biology, habitat use and mating system is lacking. These data are fundamental to effective conservation management. My research investigated the breeding behaviour and habitat ecology of a population of southern emu-wrens in Portland, Victoria, Australia, over three breeding seasons (2000/01, 2001/02 and 2002/03). also collected data pertaining to habitat use from populations located in Anglesea and Lower Glenelg National Park (Victoria, Australia). Southern emu-wrens commonly formed socially monogamous pair bonds, although cooperative breeding was observed for the first time in this species, where male offspring within several families delayed breeding to help raise younger siblings. Successful nests produced 1.8 fledglings on average, however, a nest had only a 56% chance of success during incubation and nestling phases. Nest failure was mainly attributed to depredation and snakes were identified as major nest predators. The slow breeding rate of the southern emu-wren is typical of a small passerine in the Southern Hemisphere. Nevertheless, adult mortality was unusually high. In one breeding season the adult population was reduced by 50%. The population recovered when individuals dispersed from the adjacent coastal heathland to fill territory vacancies. This highlights the vulnerability of populations to local catastrophe, and potential extinction if spatial separation of populations exceeds the species’ dispersal capacity.

In nature, environments are often variable and heterogeneous influencing ecological and evolutionary processes. This thesis focus on how animals interact with their environment and how that affects the reproductive decisions they make. Using empirical data collected from wild collared flycatcher populations, experiments and molecular approaches I try to unveil some of these relationships and the evolutionary, ecological and conservation implications of these findings are discussed. Firstly, collared flycatchers were shown to use breeding densities of their own and other species using similar resources when assessing costs and benefits associated to breeding in specific habitats. However, species will vary in how informative they are, and the worst competitor – with whom you overlap most in resources needs – also provides the best source of information. Collared flycatcher parents will also benefit differentially from investments in sons and daughters due to habitat characteristics and dispersal differences between the sexes. Here, I show that they will produce more of the sex that will give the highest expected fitness return given the environment they are in. These results also provide a reciprocal scenario to Clark's (1978) classical study of sex ratio adjustment in relation to local resource competition (LRC), as more of the natal philopatric sex is produced when LRC is low. Secondly, the effect of elaborated ornaments on paternity in the socially monogamous collared flycatcher was shown to be of more importance in areas where the intensity of intra- and intersexual conflicts are expected to be elevated. Hence, ornamentation by environmental interactions determines paternity, illustrating that sexual selection through extra-pair paternity is context dependent. Finally, even though the collared flycatcher populations that this thesis is based on have been studied on their breeding grounds for more then 25 years, we know little of where they are when they are not breeding. Here, stable isotope signatures in winter-grown feathers suggests that they may spend their winter with their breeding ground neighbours and do so repeatedly over years. Differences between breeding populations at this small scale should have many impactions for evolutionary and ecological processes as it will, for example, determine with whom individuals interact throughout their life.