The western jewel butterfly ( Hypochrysops halyaetus): factors affecting adult butterfly distribution within native Banksia bushland in an urban setting

Abstract

Adult western jewel butterflies Hypochrysops halyaetus Hewitson were studied in the Koondoola Regional Bushland Reserve on the northern outskirts of the Perth metropolitan area, Australia, in 1999. The butterfly is myrmecophilous, and the southern (Perth) form is considered to be ‘Vulnerable’. Butterfly dispersal, distribution, population size and habitat preferences were estimated using mark-recapture techniques. Butterflies were capable of moving large distances, and were widespread within the reserve but with a low density; however, one small physical area (80 × 20 m) contained a colony with large numbers of individuals. This colony, and an adjacent area of bush, was subject to a detailed microdistribution study: 1158 butterflies were marked within it over a 25-day period. The small size of the microdistribution study area compromised statistical independence assumptions: spatial autocorrelation was tested for and corrected, where appropriate, using a Markov-chain Monte-Carlo approach. Sex differences were evident in spatial autocorrelation: female data were not spatially autocorrelated, whilst male data was. The latter probably reflects the impact of the perching mode of mate location employed by males. Butterflies appeared to prefer rather degraded bush typical of a post fire/disturbance regime with high densities of the host plant Jacksonia sternbergiana. Males were positively correlated with the proportion of bare ground, again probably relating to preferred perching sites for mate location. Females were negatively correlated with Conospremum stoechadis probably indicating dense ground cover in degraded areas and Xanthorrhoea preissii probably an indicator at the site of more mature vegetation. Reserve management to improve vegetation quality may threaten the persistence of the butterfly within the reserve, whilst controlled burning to create even quite small new areas of habitat in an urban situation may be difficult to achieve. The creation of suitable habitat may be possible using mechanical means, provided the action of fire is not an essential component of habitat creation. As the western jewel appears to prefer degraded vegetation, it is possible that there may be opportunities for this species’ expansion within the urban environment provided that its mutualistic ant partner is also present.