Yellow-crested Cockatoos protected by dragons

January 8th, 2021 | by David Waugh
Yellow-crested Cockatoos protected by dragons
Conservation projects
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Of Indonesia’s staggering total of 17,508 islands, the name of a relatively small one, Komodo, has been conferred ona formidable species of monitor lizard which lives there. This of course is the Komodo dragon (Varanus komodoensis), the world’s largest lizard, growing up to 3m in length and weighing up to 70kg. Komodo dragons hunt and ambush often large-bodied prey and are known occasionally to attack humans, which adds to their fearsome reputation. The Komodo dragon is listed as ‘Vulnerable’ to extinction in the IUCN Red List of Threatened Species, and Komodo National Park was founded in 1980 to protect Komodo dragon populations on Komodo and neighbouring islands including Rinca, Padar and Bero.

Adult Yellow-crested Cockatoo.

Sharing Komodo Island, but ‘Critically Endangered’ in the same list, is the Yellow-crested Cockatoo (Cacatua sulphurea) of which occidentalis, one of the seven recognised subspecies, inhabits the island. Yellow-crested Cockatoos have been badly affected by over-exploitation for trade, as well as loss of their forest habitat, and they have either disappeared from much of the geographical distribution or exist in small remnant subpopulations. To help guide conservation action for this species, since 2016 a project has been operational to gather crucial information, including surveys of all remaining cockatoo subpopulations to produce accurate estimations of population size, to determine their ecological requirements and identify the need for interventions and re-introductions. With biologist Anna Reuleaux as the principal investigator, the project is a collaboration between Manchester Metropolitan University, UK and Burung Indonesia, the country representative of BirdLife International, supported by the Loro Parque Fundación and the Zoological Society for the Conservation of Species and Populations. 

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Map of Komodo Island and its habitats.

Komodo Island, with an area of 340 km2 and a maximum elevation of 824 m above sea level, is the largest and highest of the islands of the national park. Being situated in one of the driest areas of Indonesia, its natural water sources are scarce and streams do not run for most of the year. Large areas of the island are covered by open grassland interspersed with scrubland, palm savanna, small patches of broadleaved trees, and gallery forests along watercourses. Deciduous monsoon forest occupies valleys of larger streams close to the sea, and at higher altitudes (>500 m) closed-canopy forest can be found, which is referred to as ‘quasi cloud forest’ or ‘mossy forest’, becoming sparse forest and scrubland further downhill. Komodo and the island of Sumba, where C. s. citrinocristata is endemic, have long been suspected as the most important strongholds of the Yellow-crested Cockatoo. A recent scientific publication* reports the result of the survey conducted by Anna and her field team in November and December of 2017 and brings the great news that Komodo Island does indeed hold a large subpopulation.

Komodo Dragons in deciduous monsoon forest.

For parrot species such as the Yellow-crested Cockatoo and other rare, highly mobile birds in fragmented rugged habitats, sampling each inhabited patch is frequently unattainable. Therefore, in Komodo the researchers used, for the first time ever with a critically endangered species, a technique called density surface modelling (DSM). To do this, counts of cockatoos were made from fixed points or stations (called point count distance sampling) in 25 randomly selected areas within habitat assessed as suitable for Yellow-crested Cockatoos. The results from the counts, plus values from an index of wetness and the percentage of palm savanna and deciduous monsoon forest, were incorporated into the DSM,

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Palm savanna, deciduous monsoon forest and grassland habitats.

which in turn allowed the researchers to estimate how many cockatoos remained undetected and to produce a map of predicted cockatoo densities in Komodo. They validated the predictions (93% coincidence) by using three independent sources of cockatoo observations: data from the annual monitoring by the national park staff, citizen science observations from eBird (eBird Basic Dataset 2019, www.ebird.org), and cockatoo records from survey reports.

A pair of Yellow-crested Cockatoos at the nest entrance.

Yellow-crested Cockatoo groups were observed at 48 of the 178 count locations, with an encounter rate of 0.38 groups per (point) count. Encounter rates were highest in deciduous monsoon forest (0.91) and palm savanna (0.62) and lowest in the remaining habitat types (0.19 in grassland and scrubland; 0.06 in sparse forest; 0.00 in quasi cloud forest). The average number of cockatoos in each group seen was 2.61 individuals. Yellow-crested Cockatoos also prefer palm savanna and deciduous monsoon forest on other islands, but their absence from quasi cloud forest in Komodo is surprising, given that they are found in similar habitat types and altitudes on other islands. The overall population estimate from the field survey is of 1,113 (95% Confidence Interval: 587–2,109) individuals on Komodo Island, this being considerably larger than previous conservative estimates. The density surface maps showed cockatoos to be absent over much of the island, but present at high densities in wooded valleys.

Anna Reuleaux (left) with the field team planning the cockatoo surveys.

Direct counts collected annually by experienced national park rangers from vantage points overlooking six coastal valleys in Komodo Island show an increase from 382 cockatoos recorded in 2011 to 733 in 2019 (493 to 883 including the islands of Rinca and Bero). This is evidence that the population has at least been stable and is probably increasing over those recent years. Thus, as well as providing protection to the Komodo dragon, the national park appears to be working as a long-term stronghold for the cockatoo. The remoteness and topography of Komodo Island and its fearsome dragon appear to provide some natural protection from habitat destruction and illegal trapping. However, enforcement of legal protection for the cockatoo by park authorities has been important and made possible due to the resources derived from the many paying visitors (about 180,000 in 2018) attracted by the Komodo dragons. The park has the support of local communities, which largely depend economically on tourism. As such, Komodo National Park provides a successful model of methods and resources that could be applied in other protected areas where formal protection has yet to increase local populations of the Yellow-crested Cockatoo.

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* Anna Reuleaux, Benny A Siregar, Nigel J Collar, Maria R Panggur, Ani Mardiastuti, Martin J Jones, Stuart J Marsden (2020) Protected by dragons: Density surface modeling confirms large population of the critically endangered Yellow-crested Cockatoo on Komodo Island, The Condor 122: 1-15. https://doi.org/10.1093/condor/duaa042

Author: David Waugh, Correspondent, Loro Parque Fundación

Photo: 1,5 – C. Lam-Wiki; 2 – Adapted from Reuleaux et al, 2020; 3 – Bahnfrend-Wiki; 4 – MarkofJohnson-Wiki; 6 – A. Reuleaux

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