Background In February 2001, a survey of the south eastern end of Balls Pyramid led to the discovery of a small population of D. australis on a precipitous slope 65 m above sea level. Two adults and one nymph (all females) were located feeding on an endemic tea-tree (Melaleuca howeana).
On the 26 March 2002, a second survey of the ledge was undertaken by D. Hiscox and C. Haselden (Lord Howe Island Board Environmental staff). The results of this survey are detailed below :
Methods The survey basically duplicated the techniques used during the first survey. A nocturnal search of the ledge where D. australis was known to occur was conducted between 0930 h and 1130 h. No attempt was made to obtain morphometric measurements of any specimens observed.
Results The survey commenced at the northern end of the ledge. On the first melaleuca shrub encountered, three adult female D. australis were observed. A pair of Common Noddy terns (Anous stolidus) were nesting on the shrub.
The second shrub was located approximately four metres from the first melaleuca. This melaleuca was by far the largest shrub on the ledge and was also the shrub where three D. australis were observed during the first survey. Grazing on the new leaf tips of this melaleuca, twelve D. australis were observed.
In close proximity to the second shrub, four smaller melaleuca were growing both against the basalt face of the ledge and also towards the edge of the ledge. A number of D. australis were observed feeding on these shrubs. A more precise description of D. australis distribution on the ledge is not possible due to their movements on the melaleuca during the survey and the extremely unstable nature of the scree and soil on the ledge, making access to the outer shrubs potentially hazardous.
In total, twenty four D. australis were observed during the survey. Out of this number ten individuals could be positively sexed, eight females and two males. D. australis were observed grazing over six Melaleuca shrubs, these shrubs were located within an area of approximately thirty metres by six metres.
Prior to the conduct of the survey the Island had received substantial rainfall. As a result of the rain, the vegetation on the survey site was noticeably lusher than was observed during the first survey. Covering the ledge around the melaleuca bushes were observed the following four plant species, Sporobolus virginicus a grass, Acyranthus aspera a herb, Tetragonia tetragonioides a herb and Cyperus lucidus a sedge.
An increase in water seepage through seams in the basalt face was also noted. At least three seeps were observed on the ledge. Growing directly below or in close proximity to these seeps were located the melaleuca bushes on which the D. australis were sighted. A short time prior to the survey a significant rock fall had occurred approximately forty metres to the south of the ledge. No evidence of fresh rock fall was observed on the survey site.
Three of the lowest melaleuca bushes on the ledge were once again being invaded by morning glory Ipomea cairica. Control of the I. Cairica vines adjacent to the melaleuca bushes has been undertaken on one occasion since the first survey. It is apparent that control of I. Cairica vines adjacent to the melaleuca needs to be undertaken on a regular basis. It should be noted that widespread control of I. Cairica below the ledge is not recommended as this vine acts as an important ground cover and helps to consolidate the loose soil on the steep face of the pyramid.
Note : This report should be read as an addendum to the primary survey report, Priddel et al.
References Priddel D, Carlile N, Humphrey M, Fellenberg S, Hiscox D,(2001) Discovery of an extant population of the Lord Howe Island Stick-insect (Dryococelus australis), and recommendations for its conservation.