Dispersal and population dynamics of the blue-breasted fairy-wren, Malurus pulcherrimus, in fragmented habitat in the Western Australian wheatbelt

The blue-breasted fairy-wren, Malurus pulcherrimus, is a small, permanently sedentary, socially monogamous, co-operatively breeding, long-lived Australian passerine, whose core distribution is contained within the Western Australian wheatbelt. Little is known of their dispersal capabilities and population dynamics, knowledge of which are urgently needed as their preferred habitat becomes increasingly fragmented and degraded, due to clearing for agriculture. From 1993 to 1998, we studied a colour-banded population of blue-breasted fairy-wrens living in 13 small, 3 medium-sized and one large habitat remnant in an agricultural landscape at Wyalkatchem. Wrens in small remnants were more likely to disperse between remnants than were those in larger remnants. Females were likely to travel further and were more likely to disperse between remnants than were males. Dispersing females in the largest remnant moved a median straight-line distance of 400 m compared with 3 km for females in the smaller remnants. The furthest recorded movement was 9 km (straight-line distance) or about 14 km by the nearest corridor route. Females living in fragmented habitat may have to travel many times the distances travelled by females in unfragmented habitat. Demographic modelling shows that, over an average run of seasons, the wrens in the study population will produce sufficient yearlings to fill all breeding vacancies, provided none are lost during dispersal. However, in our study landscape, an estimated 11% of dispersers were lost to the population (i.e. either dispersed outside the study area or died during dispersal). We show that the remnants in the study landscape can be divided into neighbourhoods based on their relative connectivity. About 14% more potential dispersers were lost from the poorly-connected areas than from a core 'well connected' neighbourhood. This difference would be sufficient to cause population decline in a poorly connected neighbourhood. We conclude that, for species with poor dispersal capacity living in fragmented habitat, failure to maintain an adequate corridor network could be one of the most important factors contributing to a species' decline.