Density and Total Population Estimates for the Threatened Christmas Island Hawk-Owl Ninox natalis

Abstract

Radio-tracking and territory mapping in plateau primary forests mainly during the dry season revealed that Christmas Island Hawk-Owls Ninox natalis occupied essentially exclusive territories with an average area of c. 18 ha. Estimates of home range size from radio-tracking data collected over a period of 10 to 67 d were smaller (males 13 ha, 10.6 ha, 10.1 ha, 9.5 ha and 5.5 ha; females 6 ha and 7 ha) but in general supported the conclusions from territory mapping data. Christmas Island Hawk-Owls were widespread on the island in both primary and disturbed habitats. Call-playback censusing of 22 sites repeated five times detected no significant difference in the relative abundance of owls between primary forests on the plateau and the surrounding terraces and scree slopes; significantly fewer owls were detected in regrowth forest. These results provide an estimate of 562 105 occupied owl territories on the island. From this we estimate that there may be fewer than 1000 mature Christmas Island Hawk-Owls remaining and recommend that this taxon remain listed as Vulnerable.