NT
Waterfall Swift Hydrochous gigas



Justification

Justification of Red List Category
This poorly known species has a disjunct and probably small population, which is thought to be in decline owing to the loss and degradation of forests within its range. It is currently considered Near Threatened, although more detailed surveys are urgently needed to clarify its status.

Population justification
The global population size has not been quantified, but the species is described as rare and local (del Hoyo et al. 1999).

Trend justification
This species is extremely poorly known, but several colonies have apparently declined or disappeared in recent years, suggesting that population size may be falling. This is likely to be related to forest loss in areas surrounding breeding colonies. A slow decline is suspected overall.

Distribution and population

Hydrochous gigas occurs highly sporadically in the Main Range, Peninsular Malaysia, the mountains of Sumatra and West Java, Indonesia, and appears to be numerous on Gunung Kinabalu, Borneo (Collar et al. 2000, D. Bakewell in litt. 2016). All individual populations appear to be small, although one, at Gede-Pangrango, Java, was once fairly large but has seemingly now vanished, and surveys of three Javan volcanoes only reported it from Gunung Salak where it was described as rare (seen <1 time per day) (Mittermeier et al. 2014, J. Mittermeier in litt. 2016).

Ecology

This species occurs over steeply mountainous rainforest, being largely dependent on waterfalls as breeding sites. Altitudinal limits are poorly known, but there are records from 800 m in Peninsular Malaysia, 440 m on Sumatra and 300-1500 m on Java (del Hoyo et al. 1999). Although this species lacks echolocation, it has acute poor-light vision and may be a crepuscular feeder, potentially contributing to the paucity of records.

Threats

This species may be dependent on areas of forest cover surrounding breeding sites, and therefore be susceptible to the effects of logging and landscape conversion for agriculture. The restricted nature of their waterfall breeding sites may pose an inherent limitation to population size, increasing their susceptibility to disturbance.

Conservation actions

Conservation Actions Underway
No targeted conservation actions are known for this species.

Conservation Actions Proposed
Conduct surveys throughout the known range in order to determine current status and population size. In particular, clarify its presence, abundance and distribution on Borneo. Conduct ecological studies to explore habitat requirements, particularly the link to rainforest cover surrounding breeding sites. Protect areas of suitable habitat from clearance, degradation and disturbance.

Acknowledgements

Text account compilers
Westrip, J., Benstead, P., Gilroy, J., Taylor, J.

Contributors
Bakewell, D., Mittermeier, J.


Recommended citation
BirdLife International (2021) Species factsheet: Hydrochous gigas. Downloaded from http://www.birdlife.org on 18/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 18/10/2021.