Distribution and locationDistribution and location

Distribution and location

The Christmas Island Hawk-Owl is restricted to Christmas Island in the Indian Ocean (10o0'S; 105o40' E), approximately 1400km northwest of Australia. The nearest land is Java in the Republic of Indonesia, 360km to the north. Christmas Island is 135km2 in area and 75% is covered with original vegetation. During 1994-1995, Christmas Island Hawk-Owls were widespread and occurred in all Primary, Marginal and secondary regrowth rainforests. The highest densities were found in Primary rainforests (Hill & Lill 1998a). Hill and Lill (1998a) concluded that the total population size was probably limited primarily by the area of remaining rainforest and that the observed owl densities within available habitat had probably not changed markedly since settlement (Hill & Lill 1998a). The lack of change in density of birds in the habitat available combined with the reduction in 25% of habitat area leads to the conclusion that the population has declined by 25%.

Using data from radio-tracking, territory mapping and census by playback of calls, Hill & Lill (1998a) found that owls were uniformly distributed throughout the two Primary and Marginal of rainforest at a density of 5.5  1.0 territories per square kilometre. They speculated that densities might be lower in some Marginal rainforests because of the more seasonal microclimates in areas exposed to the prevailing southeast winds. In regrowth vegetation they found that owls were present at significantly lower densities (1.7  1.1 territories/km2).

Approximately 75% of Christmas Island is still covered with natural vegetation and 84% of this (63% of the island) is within National Park (Figure 1). “Primary Rainforests” (du Puy 1993) outside the park are currently protected from clearance by a Federal Government moratorium, and Primary rainforest, Marginal rainforest and second-growth rainforest or regrowth vegetation may be removed only within the constraints of the EPBC Act and EPBC Regulations.

Rainforest rehabilitation has been occurring on Christmas Island for several decades. Currently, the main aim is to revegetate mined areas adjacent to Abbott's Booby nesting habitat in an attempt to reduce wind turbulence caused by the clearings and implicated in reduced nesting success of the booby (Reville et al. 1990). There are approximately 70 clearings covering 3200ha or 24% of the island area (Carew-Reid 1987). It is not known how long it will take for rehabilitation plantings to develop into forest which can be used by Christmas Island Hawk-Owls: it would not be long before these areas might be used for foraging, however, it is likely to be centuries before mature trees with nesting holes are available.