Effects of ENSO-induced forest fires and habitat disturbance on the abundance and spatial distribution of an endangered riverine bird in Borneo

Effects of ENSO-inducedforest fires and habitat disturbance on the abundance and spatial distributionof an endangered riverine bird in Borneo


published by Animal Conservation 8: 27-31

Resit Sözer and Vincent Nijman, 2005


Droughts induced by the 1997-1998 El Nino Southern Oscillation (ENSO) event sparked large-scale forest fires affecting
millions of hectares on Borneo. We studied the effects of ENSO-induced disturbances on a riverine bird, the critically
endangered white-shouldered ibis, Pseudibis davisoni, along the Mahakam River in East Kalimantan, Indonesian Borneo.
Island-wide fire hotspots were more likely to occur near rivers and part of our study area was indeed affected by fire. Based on
25 boat surveys (2590 km) that yielded 91 records, we recorded significant changes in abundance and spatial distribution of this
bird in our study area. Encounter rates were higher during the pre-ENSO (1992-1996) periods than the post-ENSO
(1997-2000) ones and differed between seasons. No ibises were seen post-ENSO along river sections that were affected by the
fires, whereas pre-ENSO encounter rates were 2.4 birds/102 km. Encounter rates along those sections that were not affected by
the forest fires more than doubled from 2.0 birds/102 km pre-ENSO to 5.6 birds/102 km post-ENSO. This was most probably
due to enhancement of displaced birds. In view of the permanent character of the change in spatial distribution, active protection
of the remaining stretches of riverine forest is of the utmost importance for the survival of white-shouldered ibis.

For more information please contact Vincent Nijman at nijman@science.uva.nl


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