Mark-recapture may reveal more about ecology than about population trends:Demography of a threatened ghost bat (Macroderma gigas) population

Since European settlement in Australia, the geographical range of ghost bat s (Macroderma gigas) has contracted northwards. Ghost bats are thought to o ccur in disjunct populations with little interpopulation migration, raising concerns over the current status and future viability of the southernmost colony, which has also been threatened by mining activity. To address these concerns, demographic parameters of the southernmost colony were estimated from a mark-recapture study conducted during 1975-1981. Female bats gave b irth to a single young in late spring, but only 40% (22-70%, 95% CI) of fem ales bred in their second year, increasing to 93% (87-97%, 95% CI) for fema les greater than or equal to 2 years old. Sixty-five percent of juveniles c aught were female. Annual adult survival ranged between 0.57-0.77 for femal es and 0.43-0.66 for males, and was lowest over winter-spring and greatest in autumn-winter. Juvenile survival for the first year ranged between 0.35- 0.46 for females and 0.29-0.42 for males. Adult survival varied among seaso ns, was negatively associated with rainfall, but was not associated with te mperature beyond being lower in late winter. Poor survival may result from the inferior daytime roosts that bats must use if water seepage forces them to leave their normal roosts. Although these age-specific rates of fecundi ty and survival suggested a declining population, mark-recapture estimates of the population trend indicated stability over the study period. Counts a t daytime roosts also suggested a population decline, but were considered u nreliable because of an increasing tendency of bats to avoid detection. It is therefore likely that some assumptions in estimating survival were viola ted. These results provide a caution against the uncritical use of populati on projections derived from mark-recapture estimates of demographic paramet ers, and the use of untested indices as the basis for conservation decision s.