FACING EXTINCTION? THE SWORDGRASS BROWN; A CASE-HISTORY AND A PRELIMINARY SURVEY ON THE SUNSHINE COAST, QUEENSLAND
The Varied Swordgrass Brown (Tisiphone abeona Donovan)is a butterfly living on the edge of survival. This is a remarkable endemic species. It occurs scattered along the eastern Australian coastline and wet hinterlands from South Australia to South-eastern Queensland. All the populations have now become greatly fragmented since the arrival of Europeans.
The ‘grand-father’ of Australian butterfly research, Gustavus Athol Waterhouse (in 1914 and 1928) noted the remarkably different colour forms of this pretty butterfly which varied from orange to white on a ground colour of brown, These forms varied geographically, depending on the their occurrence- from south to north in Eastern Australia. The colonies were found to be restricted to discrete coastal or sub-mountain habitats. In his biological studies, Waterhouse considered these varieties to be distinct subspecies, naming them abeona, albifascia, Joanna, aurelia, morrissi, regalis and rawnsleyi. A second species Tisiphone helena (Olliff) was described from North Queensland. In both species the sexes were very similar.
Tisiphone abeona rawnsleyi is a beautiful dark, northern subspecies restricted to bush-land from about Frazer Island to the Caloundra region. It is a medium-sized butterfly, mostly chocolate brown in colour, and decorated by six ‘alarming’ eyespot markings on the wings (male illustrated). As its name implies the caterpillars feed only on Sword-grass (Gahnia) that grows in wet woodland habitats from sea to approximately 400m elevation.
Adults fly low and slowly within small, sunny clearings, and when disturbed, escape with a remarkable ability to dodge within the sharp Gahnia leaves. Adults have been observed feeding on Melaleuca, Leptospermun and Parsonsia flowers. On the Sunshine Coast the eggs are laid near the base of the sedge tussocks or often on the leaves of nearby small dicotyledon shrubs. The long, thin pale green larvae of the Sword-grass Brown are specialist feeders on the tall, slender Gahnia clarkei, which usually grows near riverulet swamps and upland swales, often close to wet sclerophyll forests that contain Paperbark trees, Fan-palms and Flooded Gum.In some areas they may occasionally eat G. aspera, G. subaequiglumis and G. sieberiana, although these plants prefer more sandy (‘Wallum’) heaths and open shrub lands. The pupae are found singularly in shaded areas attached to vegetation near the base of their food-plants.
The butterfly is bi-voltine, flying during the morning and late afternoon on sunny days in September to late November and again from late January to late April. In some areas males fly to the summit of hills, but generally both sexes remain close to their wetland habitats. Its feeble flight provides a vulnerable target for traffic. The colonies of rawnsleyi were probably always scattered and limited to discrete biomes.
Preliminary Survey
In the last 10 years I have kept watch on several colonies of rawnsleyi , mostly from localities in the southern half off its range along the coastal areas between Booreen Point (north of Noosa) and south to Landsborough, and also in the upland hinterlands at Mt. Coodoo- Mt. Wolvi area (south of Gympie) and the Blackall Range near Mapleton (above 300m). All populations studied have suffered gradual habitat reduction in their wetland localities, probably due to habitat disturbance and food plant reduction. In the last 5 years most colonies have dramatically decreased, with small to moderate numbers of this butterfly found only in limited, isolated patches of wetlands.
Tisiphone abeona rawnsleyi now mostly occurs in undeveloped areas on the Sunshine Coast that normally contain large numbers of G. clarkei.. It appears that the butterfly has suffered greatly from land disturbance particularly in areas of rapid human population growth of the Sunshine Coast. The draining of swamp-lands has undoubtedly been a major cause, and frequent bush fires have also taken their toll. More alarmingly there appears to have been a reduction of the Sword-grass Brown in the protective areas of National Parks and Nature Reserves, suggesting more momentous climate fluctuations. or specific ecological disturbance of an unknown nature. This year (2019) the general area has experienced exceptional wild fires, north of Coolum, especially impacting north of the Noosa River.
Results
Most selected areas visited contained over 100 tussocks of Gahnia clarkei (note that individual plants are difficult to identify as mature growth can reach to over 3m. high which, unless supported by trees, collapses to produce ground-level ‘pups’ that take root in spreading lateral communities (few young ‘seed’ plants were observed except in disturbed and fired soils). The butterflies were rarely found in abundance, and discrete colonies were initially found to contain no more than 20 specimens within areas less than 1000 square meters during each visit. It was estimated that each season contained no more than 100 specimens in any of the study areas, but a lot less in small stands of Gahnia.
Each of the largest areas (locality list in ‘Appendix’) Ba, Ea, Ia, Jc. Ka, La and Ma, initially averaged about twenty observations of probable individual butterflies [not tagged]. However each year the count appeared to diminish, with a reduction in 2019 to less than a dozen individuals at these ‘good’ sites. At most of the other listed sites only one or two specimens were observed and at some the butterfly was absent (adults and juveniles). Between 2012 and 2017, six or seven Sword-grass Browns (adults and larvae) were collected from a variety of ‘good’ locations and released in my garden, now containing small colonies of both young and mature food plants of 3 species of Gahnia. None of the butterflies or their progeny survived beyond the second season. It is possible that the exact natural habitat was not reciprocated in my garden. Some recent (August 2020) controlled burns (in area Ka) have seriously damaged colonies.
The good news is that there is some evidence of small colonies moving into re-establishment areas of G. clarkei planted within new housing developments, particularly those located near natural swampy bush-land. This last season (late 2019) only seven localities were observed to contain rawnsleyi, and only two of these harbored more than a dozen adult specimens. Throughout the year very few larvae or larval ‘eats’ were found, although the larvae of the Painted Sedge-skipper butterfly (Hesperilla picta) that feeds exclusively on Gahnia clarkei were not uncommon.
The future
Undoubtedly there are other suitable areas for the Swordgrass Brown in more inaccessible areas of forest north of Noosa, surrounding Cooroy and east of Pomona. Clumps of Ghania clarkei are still reasonably common in and around parklands, large gardens, golf courses and sports grounds of suburban districts, but these may not be sufficient for the butterfly.
The extensive bushlands of the Great Sandy National Park/Cooloola Recreation Area was not studied in this survey and could enclose suitable stands of Gahnia.
Many years ago large areas of Gahnia habitat south of Landsborough (eg. surrounding Australia Zoo and east of Beerwah) were reclaimed for pine tree plantations, but Gahnia survive (marginally) for at least one harvest of this softwood. I have not recorded Tisiphone eitherin these areas or south of the Glasshouse Mountains or at Bribie Island, and the extent of its range south towards the Brisbane River has not been sufficiently studied. Further molecular research could reveal interesting results in terms of the speciation and gene-flow of Tisiphone.
More thorough searches are needed to study the vulnerable or endangered status for this endemic Sunshine Coast butterfly. So far I have not seen Swordgrass Browns on Fraser Island and the species is surprisingly absent further inland on the Conondale Ranges, which shares many of the Sunshine Coast butterfly species. A drone survey would very likely be very effective in pin-pointing further habitat localities!
As an ‘indicator species’, the Swordgrass Brown is an ideal study subject. It is a relatively low-mobile, ground flying butterfly, and their large (rhomboid) larval eats are quite visible. So far I have not been able to establish a viable colony in my garden. It is probable that this butterfly has very specific survival requirements within micro-habitats that need a more detailed study.
Summary
The reduction both of species and numbers of most butterflies on the Sunshine Coast has been significant. It is likely that the reason for this is habitat loss. In the past ten years there has been acceleration in human population throughout. However some of the localities studied are adjacent to or within National Parks. These areas, if not all, are also vulnerable to wild-fires. At this stage the endemic Tisiphone abeona rawnsleyi is not assured of extinction protection, but is still an excellent study species for the Sunshine Coast.
Andrew F. Atkins, PO Box 42, Eudlo, Queensland 4554.
(see our Places page for the locations appendix to this study)