White-shouldered Ibis Pseudibis davisoni and Giant Ibis Thaumatibis gigantea are two of the most threatened yet poorly known birds of South-East Asia's dry forests. Anecdotal evidence suggests these species have an intriguing combination of ecological similarities and differences, and as they occur sympatrically there may be an opportunity to safeguard them through joint conservation measures. We compared their foraging ecology and proximity to people in an attempt to unravel their ecological differences and better inform conservation. Landscape-scale habitat use was assessed by recording ibis sightings on journeys through a 75,000 ha dry forest landscape; White-shouldered Ibises were surveyed over 526 journeys (totalling 17,032 km) and Giant Ibises over 349 journeys (11,402 km). The ibises showed broadly similar habitat selection, using a range of wetland and terrestrial habitats. Giant Ibises were more often sighted further from settlements than White-shouldered Ibises, with maximum sighting frequency predicted at 9.9 km from villages for the former and 8.3 km for the latter. Giant Ibis may be less tolerant of human disturbance and/or White-shouldered Ibis may be more dependent on traditional land management practices, but the species' differing use of abandoned paddyfield (a habitat typically near settlements) could also be a contributing factor. At waterholes in the dry season foraging Giant Ibis used wetter microhabitats than White-shouldered, suggesting the species occupy different foraging niches. We make preliminary observations regarding Giant Ibis breeding strategy and discuss potential habitat management actions, concluding that, although conservation could address these species simultaneously in dry dipterocarp forest landscapes, their ecological differences must also be taken into account.
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|Published - 1 Aug 2012