- Island systems and species are susceptible to extinction because of their small population size and an ecological naiveté from an evolutionary past lacking strong competition and predation. For example, only one-fifth of the world’s bird species occur on islands, yet more than 90% of the avian extinctions witnessed during historic times were island forms. Introduced predators and competitor species are among the major conservation issues facing insular systems. On the island of Guam, brown tree snakes (Boiga irregularis) are responsible for the local extinction of twelve native forest birds. The endangered Guam Micronesian Kingfisher (Todiramphus cinnamominus cinnamominus) is one of the species affected by the introduced snake, as the bird remains only in captive breeding institutions on the U.S. mainland. In addition to Guam, the islands of Pohnpei and Palau host endemic subspecies of Micronesian Kingfisher (T. c. reichenbachii and T. c. pelewensis respectively) that are similarly threatened with extinction.
Previous investigations into the behavioral ecology of the Pohnpei subspecies of Micronesian Kingfisher yielded observations of cooperative social behaviors. Over the past three decades, much research has focused on cooperatively breeding species, which are commonly characterized by non-breeding individuals that delay dispersal and assist others with reproduction. Research addressing cooperative breeding suggests that the behavior is a complex response to interacting factors including life history characteristics, demography, resources, movement, and behavior.
The dearth of information available about critically endangered Micronesian Kingfishers, combined with their potential to provide new insights into cooperative social behaviors, inspired the research presented in this dissertation. The aims were two-fold; results were intended to bolster our understanding of cooperative social behaviors while simultaneously providing vital information to conservation practitioners. Methodology for determining the sex of study individuals is presented in chapter two, which facilitated investigations that followed.
Chapter three addressed the interaction between kingfishers and resources at both the landscape and home range scale. Higher population densities are associated with lowland mangrove, marsh forested habitats, and open vegetation types at the landscape scale. Results further indicated that at the home range scale, birds selectively used late succession forested habitats in higher proportions than their availability, and forest areas were entirely utilized in study areas where territories were packed boundary-to-boundary. Together these suggested that forested areas and the resources they contain might be limited for Micronesian Kingfishers.
Movement and space use in Micronesian Kingfishers were the focus of chapter four. Within territories, the home ranges of birds overlapped, although not entirely. Birds of all ages and social classes made extraterritorial prospecting movements, but they appear to serve different functions. Juveniles and helpers were observed dispersing from natal areas, but only after repeated extraterritorial homesteading movements. The timing and destinations of adult prospecting suggested that the behavior might provide opportunities for covert reproduction.
Population demography was addressed in chapters five and six, which concluded with the development of a population projection model that will be useful in kingfisher conservation efforts throughout the Pacific. Nestlings on cooperative territories had higher estimated survival rates than those on pair territories. Further, the timing of nestling disappearances and a modified nestling mandible suggested that mortalities were caused by siblicidal nest-mates. In chapter six, post-fledging vital rates were estimated for Micronesian Kingfishers and a population projection matrix model was developed. Vital rate parameters were then varied, and the model was used in a simulation analysis to evaluate the apparent influence of each parameter on population dynamics across a range of potential values. The exercise was intended to lend insight into the dynamics of Micronesian Kingfisher populations and to form a base model for management of the other eleven endangered Pacific Todiramphus species.
In summary, information presented in this dissertation lends insight into factors important to understanding population demography, resource use, and movement in cooperatively breeding Micronesian Kingfishers. Results illustrate that, like other cooperatively breeding species, the birds on Pohnpei are highly territorial and dispersal options may be limited by territory vacancies and forest resources. Extraterritorial prospecting movements have been observed in many cooperative species, and these results illustrate that they may serve multiple purposes. Siblicide is also a phenomenon present in resource-limited species and its occurrence in Pohnpei Micronesian Kingfishers underscores the importance of resources to the evolutionary history of the birds. Results from demographic analyses and modeling suggest that conservation efforts for Micronesian Kingfishers, and the other eleven Todiramphus species, should be broadly focused on all life history stages.