National recovery plan for the Lord Howe Woodhen (Gallirallus sylvestris)
NSW National Parks and Wildlife Service, 2002
3. Distribution and Abundance
The Lord Howe Woodhen occurs only on Lord Howe Island (see Figure 1). It was discovered in 1788 and observed on subsequent visits by mariners who described it as common. It appears always to have been confined to the mainland of the island and there are no records of it on the offshore islands, which lack forest (Fullagar 1985).
The island was settled in 1833-34, at which time the Woodhen was still reported as quite common (Lourie-Fraser 1985). By 1853, however, the species had become almost restricted to the higher and more isolated southern parts of the island (the southern mountains), with a few persisting in lowland areas until the end of the 1930s (Miller and Kingston 1980, Fullagar 1985, Lourie-Fraser 1985).
A bird collector named R. Bell resided on Lord Howe Island just before World War 1. From his shooting records, it was clear that the Woodhen occurred throughout the southern mountains, both in the lower and upper areas (Miller and Kingston 1980). Bell recorded particularly high densities at Little Slope on the south-western part of the island. At the same time, he described population densities on the small (25 ha) plateau on Mount Gower as comparatively low, suggesting that this area was possibly marginal habitat for the species (Miller and Kingston 1980).
By 1940, the species was confined to the upper regions of Mounts Lidgbird and Gower and three isolated pockets on the south-eastern flank of Mount Gower. By the 1970s, most individuals occurred on the Mount Gower plateau, above the cliff line. There is a single record of a Woodhen from the Transit Hill area (Miller and Mullette 1985). The reasons for the contraction in range are discussed in Section 8 of this plan.
Since 1940 the distributions of Woodhens and feral Pigs have mostly been mutually exclusive. It is probable that Pig predation on nesting Woodhens, as well as habitat disturbance and modification from Pig feeding activities, contributed significantly to the disappearance of birds from areas inhabited by Pigs (Miller and Mullette 1985) (see Section 8).
Between 1978 and 1983, Pigs were eliminated from the island and a captive breeding program for the Woodhen was producing birds for release into the wild (see Section 9). The release sites of the captive-bred birds are shown in Table 1.
|Date||No. of Birds||Release Areas|
|May 1981||4||Little Slope (S.W. coast of island)|
|Nov 1981||1||Kings (Salmon Beach on W. coast of island)*|
|Dec 1981||3||Little Slope|
|Feb 1982||7||Little Slope|
|Jun 1982||8||Little Slope|
|Jan 1983||17||Erskine Valley (btw Mts Lidgbird and Gower)|
|Feb 1983||7||Erskine Valley|
|June 1983||12||Erskine Valley|
|Nov 1983||7||'Goat House' (E. of Mt Lidgbird)|
|Nov 1983||3||Boat Harbour (N.E. of Mt Lidgbird)|
|Dec 1983||8||Boat Harbour|
|Mar 1984||5||Boat Harbour|
|Source: Fullagar 1985
* only bird released in the settlement area.
Between 1982 and 1988, Woodhen numbers on Little Slope increased to an estimated 28 birds (1986-88), but by 1989 had declined to six birds (Harden 1990a, see Sections 4 and 8). Surveys conducted in 2001 recorded 13 individuals on Little Slope. Viable breeding populations had established themselves patchily through much of the settlement area in the central and northern lowlands of the island (Harden 1986).
Post release surveys of Erskine Valley and on the east side of Mt Lidgbird showed that the captive released populations did not persist at either locality between 1985 and 1989, and only a handful of birds were recorded in those areas (Harden 1986, 1987, 1990b; Harden and Robertshaw 1988, 1989). A small number of isolated pairs persists in these areas to the present (R. Harden, NPWS, pers. comm., D. Hiscox, LHIB, pers. comm.).
By 1989, it became apparent that the vast majority of territories of released captive bred birds in the lowlands were located in Megaphyllous Broad Sclerophyll Forest (sensu Pickard 1983), particularly the Kentia Palm (Howea forsteriana) association. Territories in other settings have been associated with residences where supplementary food has been available. Within this vegetation type, most territories occurred on or immediately downslope of areas of igneous geology (Harden and Robertshaw 1988, 1989). Similar vegetation with calcarenite geology was unoccupied. Despite the high fecundity of the species and its ability to colonise suitable new areas subsequent to rehabilitation, birds have not colonised such vegetation on other geology to the same degree.
The total number of birds on the island has not increased significantly since the initial captive release program (1981 - 1983) and associated rapid breeding and spread of released birds (1981 - 1985). This suggests that, at least in the lowlands, the population of Woodhen may have reached carrying capacity, as suggested a decade earlier by Harden and Robertshaw (1988).
The total population can be estimated by adding 20-30 birds (10 pairs), to account for areas not surveyed (R. Harden, NPWS, pers. comm.). On this basis, the total population estimate in 1997 was 220-230 individuals and 71-74 breeding pairs. These were distributed approximately as follows:
- c. 70 birds in the settlement area;
- c. 65 birds on Mount Gower summit;
- c. 30 birds on Far Flats;
- c. 15 birds at Grey Face;
- c. 10 birds at Little Slope; and
- c. 20-30 estimated total on the summit and east side of Mount Lidgbird, Thatch Pocket, Little Pocket and Big Pocket on Mount Gower.
The November 1998 survey counted 160 individuals and 44-50 breeding pairs. However, this was considered to be an underestimate as the weather was the most unfavourable of any survey since 1985, and the seas too rough to allow access to Little Slope. Counts recorded for surveys conducted since November 1999 are presented in Table 2. The Lord Howe Island Board (LHIB) staff has conducted the surveys since 1999 (Harden in prep.) and some adjustment in survey results may initially have occurred due to changes in survey personnel.
|Location||November 1999||April 2000||November 2000||April 2001||November 2001||April 2002|
|Little Slope||6||no survey||9||13||13||no survey|
|* Survey undertaken after Providence Petrels (Pterodroma solandri) had arrived making it difficult to hear and locate Woodhens.
# Add 20-30 to total for population estimate as per 1997 estimate.
There has been concern over the apparent lower numbers counted in the April 2001 survey. The drop in numbers appeared to be located primarily in the settlement, Far Flats and Mt Gower. Supplementary feeding of Woodhens at some locations within the settlement has ceased and this may have contributed to the lower numbers of birds in the settlement and Far Flats. In addition, the Providence Petrels had arrived on the top of Mt Gower prior to the survey and the noise generated by the birds impacted on the survey teams ability to locate and record Woodhens. The November 2002 and April 2002 surveys indicate that the numbers on Mt Gower appear relatively stable. Similarly numbers within the settlement have increased since April 2001. Of particular interest is the reappearance of Woodhens at Boat Harbour in April 2001. A database for managing the Woodhen survey data has been developed and will be managed by the LHIB. The database will assist in analysing trends in the survey data and assessing the status of the Woodhen population.