Monitoring population change in the cryptic and threatened Western Ground Parrot in relation to fire

Abstract

Measures of abundance and population trends are necessary for informed management of rare species, but obtaining reliable estimates of sparsely occurring species is an ongoing challenge in conservation biology. It is even more difficult when the species of interest is also cryptic. We censused a population of one such species, the Western Ground Parrot (Pezoporus wallicus flaviventris), over several years to develop a monitoring protocol to assist in future management, extend understanding of its response to fire, and provide a model that could be used with other cryptic bird species. Abundance of Western Ground Parrots, monitored by means of calling frequencies, varied from year to year at a study site in Fitzgerald River National Park, south-western Australia. Frequency of calling increased significantly from 1996 to 2000. During this time, frequency of calling peaked in 1998 in part of the study site that had been unburnt for more than 40 years, and remained high in 2000. Frequency of calling was similar in a more recently burnt part of the study area except in May 1998, when frequency was lower following a fire that burnt part of this area five months previously. Frequency of calling dropped significantly in both the long unburnt and recently burnt areas between 2000 and 2004; exact reasons for this are unknown. Western Ground Parrots can use recently burnt vegetation where it is immediately adjacent to an established population, but do not need fire to create habitat, at least in the timescale of 40 years. The current monitoring protocol, where eight listening posts are counted approximately three times each, is capable of detecting an annual change in frequency of calling of ∼13%. The number of listening posts would need to be increased to 14 in order to detect an annual change of 10%, and would need to be increased to 40 in order to detect an annual change of 5%.