Abbott’s booby is an Endangered seabird in the Sulidae family, which includes boobies and the closely related gannets. Christmas Island is home to three Booby species; the brown booby, red-footed booby and Abbott’s booby. Abbott’s booby (Papasula abbotti) is genetically distinct from other boobies which belong to the Sula genus. It is thought to have diverged from other members of the family early in its evolutionary history (Department of the Environment and Energy 2017).
Abbott’s booby was first described from a specimen collected near Madagascar in the 1800s, but populations declined and it now breeds exclusively on Christmas Island. Abbott’s booby was listed as Critically Endangered by the IUCN Red List in 2000 but with the protection of critical nesting habitats their listing was downgraded to Endangered in 2005 (Birdlife International 2016).
PRL acknowledges the importance of this species, and are committed to ensuring that mining does not negatively impact this species. PRL has a strict policy commitment to ensure mining does not result in loss or damage to Abbott’s booby nest trees. We are also committed to minimising any potential indirect impacts of mining on this species. Historically this has not been the case, with the former Government-owned Phosphate Company clearing extensive areas in the centre of the Island in the 1960s and 1970s resulting in loss of important breeding habitat.
The population appears to have stabilised since the establishment of the Christmas Island National Park in 1980, and habitat loss due to clearing is no longer considered a threat to the species (Yorkston and Green 1997, Birdlife International 2016, Department of the Environment and Heritage 2004). A conservation levy generated by present day mining is now used to rehabilitate historic mining areas which occurred in Abbott’s booby habitat.
Studies from the early 1900s indicate that Abbott’s booby has probably always nested principally in the west and south west of the Island (Reville, et al. 1990, Yorkston and Green 1997) within what is now the Christmas Island National Park. Island Wide Survey records indicate that 91% of recent Abbott’s booby records are protected within the National Park, with the remainder mostly occurring in Unallocated Crown Land (Department of National Parks 2016). Few Abbott’s boobies have been recorded in PRL mining tenements, which have all been cleared by previous mining companies and generally lack mature canopy trees suitable for nesting.
Though graceful in the air, the Abbott’s booby is clumsy on land and finds it difficult to regain the air after landing. In calm conditions Nelson (1971) observed that Abbott’s boobies may fall 30 feet (9.1 m) or more after taking off, and their choice of habitat is probably due largely to the need for safe entry and departure from nesting trees.
Abbott’s booby nests almost exclusively in emergent canopy trees, preferring nest sites with a clear area below, from which it can take off on the leeward side. Christmas Island receives south-easterly trade winds for much of the year (Yorkston and Green 1997, Bureau of Meteorology 2017) so most nests occur on the protected north-western side of trees in areas of uneven canopy, where emergent trees, clearings or topography allow easy take offs. This often includes nests on the eastern side of clearings and roads which provide an edge that the boobies can launch into.
Naturally, wind and turbulence affects Abbott’s booby’s ability to access nest trees. Fledglings making their first flight attempt are particularly vulnerable as a failed attempt will cause them to fall between the trees where there is little prospect of regaining the canopy and nowhere to launch from. Affected fledglings typically starve to death or are eaten by robber crabs (Reville, et al. 1990). For this reason, wind gusts and eddies caused by turbulence can impact upon breeding success. Cyclones are also a significant threat to Abbott’s boobies, with a severe storm in 1988 causing the deaths of a third of monitored fledglings (Reville, et al. 1990).
Clearing of forest downwind of clearings can create additional turbulence which may affect birds accessing nesting trees. Wind tunnel studies and observations of bird nesting behaviour and success have demonstrated that this effect is dependent on canopy height (typically around 30 m), with the downwind area of effect being ten times the average canopy height. The most vulnerable area is from five to ten canopy heights from the edge of the clearing (Raupach, et al. 1987). Clearings of less than 50 m width, such as those made for roads or exploration, do not seem to cause turbulence (Raupach, et al. 1987, Reville, et al. 1990). Planting of wind breaks up wind of the boundary of clearing areas has been suggested as a mitigation measure to ameliorate the effect of forest clearing (Raupach, et al. 1987, Reville, et al. 1990).
Abbott’s booby feeds mainly on tropical flying fish found within a day’s flight of the island though they may travel hundreds of kilometres to feed (Hennicke and Weimerskirch 2014). Their foraging behaviour is influenced by ocean temperature. Flying fish size decreases as sea surface temperatures rise. Warmer, less productive ocean waters result in longer foraging trips by the Abbott’s booby, while cooler oceans result in shorter foraging trips (Hennicke and Weimerskirch 2014). This relationship between foraging behaviour and ocean temperature indicates that climate change may be a significant threat to the Abbott’s booby, and global warming is considered a key threatening process in the Abbott’s booby recovery plan (Department of the Environment and Heritage 2004). Climate change may also increase the frequency or severity of storms and cyclones which also pose a significant threat to this seabird (Department of the Environment and Heritage 2004, Director of National Parks 2011).
The Abbott’s booby Recovery Plan lists six threats affecting the Abbott’s booby (Department of the Environment and Heritage 2004). Some of these threats are no longer relevant. For example, the Asia Pacific Space Centre project which was previously considered a threat has since been abandoned. The 2014 Draft Biodiversity Conservation Plan for Christmas Island lists four key threatening processes for Christmas Island (Director of National Parks 2014):
There are a range of measures in place to ensure mining does not impact on the Abbott’s booby. All clearing must be assessed and approved, and this requires field surveys to ensure there are no nest trees within or close to the proposed clearing area. Potential impacts of turbulence are also included in this risk assessments in liaison with Government regulators and buffers are implemented around nest trees to reduce turbulence affects. PRL are currently investigating the possibility of a small mining lease extension to extend the life of the Christmas Island mine (refer blog post 24/11/2016). A risk assessment process for these areas included a field survey of surrounding trees for Abbott’s boobies so that critical habitat is avoided and the downwind effect of turbulence may be factored in, and avoidance or mitigation planned.