Preliminary Population estimates of the critically endangered Yellow-crested Cockatoo Cacatua sulphurea on Komodo Island, Indonesia

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Population estimates and breeding of the critically endangered Yellow-crested Cockatoo Cacatua sulphurea on Komodo Island, Lesser Sundas, Indonesia

 

M. JERI IMANSYAH, DENI PURWANDANA, ACHMAD ARIEFIANDY, Y. JACKSON BENU, TIM S. JESSOP and COLIN R. TRAINOR   

Introduction

Although the parvula race occurs on the largest islands in the Lesser Sundas, populations on Timor, Flores and Sumbawa have been decimated by captures for trade (BirdLife 2001). The single largest population is considered to persist on Komodo Island (311 km2) in Komodo National Park. Flocks of 20-30 birds were seen during brief observations from 1989 to 1995, and in 1999 an estimated 100 birds were seen by I. Mauro (BirdLife 2001). During a 30 day population count of Yellow-crested Cockatoo on Komodo in 2000, a total of 366 birds were directly observed, and a further 160 birds were estimated from unsurveyed sites (Agista and Rubyanto 2001).  Our study was done at five key valley areas, which included 320 (87%) of the Yellow-crested Cockatoo’s observed by Agista and Rubyanto (2001). The aim was to establish a new population estimate and compare with the baseline from the 2000 survey. We also noted aspects of nest biology, which may be a key aspect limiting population size (Walker et al. 2005). This study is part of conservation and research project on the Komodo Dragon Varanus komodoensis and terrestrial biodiversity in the Komodo National Park including other flagship terrestrial species, such as Timor Deer Cervus timorensis and Orange-footed Scrubfowl Megapodius reindwardt. These studies are vital to assist the Komodo National Park management to develop conservation strategies and implement site management.  

 

Method 

Komodo Island (311 km2; 8°35’40” S; 119°25’51” E, figure 1) is the largest of five major islands in the Komodo National Park that is dedicated primarily to the preservation of intact savanna landscapes, the Komodo Dragon Varanus komodoensis, and a rich and diverse marine fauna (PHKA 2000). The island has rugged topography with coastal valleys in the lowlands (below 50m) with the highest peak of is 790 m. The main habitat types on the island are savanna, open deciudous forest (tropical dry forest) and quasi cloud (or tropical evergreen) forest (Auffenberg 1981). Komodo Islands has a tropical dry climate and is influenced by monsoons and trade winds. Mean annual rainfall varies with the elevation, but averages less than 700 mm a year, with 948 mm at nearby Labuanbajo, Flores (RePPProT 1989).

This study primarily took place in the following five valleys: Loh Sebita, Loh Liang, Loh Pinda, Loh Wau, and Loh Wenci. The sites were selected because they maintain the largest Yellow-crested Cockatoo populations on the island (Agista and Rubyanto 2001).  The Yellow-crested Cockatoo population was estimated using direct counting from vantage point in each valley (Bibby et al. 2000). The census was carried out during September and October 2005 prior to the beginning of breeding season (Agista and Rubyanto 2001). Direct counting was carried out from hills, which provided observers with a suitable observation point overlooking whole valleys to allow all individuals sighted to be counted. Agista and Rubyanto (2001) used the same method in 2000. Birds were counted each morning (06h00-08h00) for three consecutive days, when they fledging from roosting sites to their feeding areas, resulting a total of three observations for each valley. The results presented within this paper are the highest counts to represent the current population of the Yellow-crested obtained during the population assessment. To assess the density of this species within each valley we divided the highest number of the birds counted by valley area.  Results During the study, 137 individuals of Yellow crested Cockatoo were counted from the five major valleys. The largest population was counted at Loh Liang (62 birds) while the lowest was at Loh Pinda (three birds) (Table 2). The overall mean density of Yellow-crested Cockatoo was 11.43±2.47 individuals km-2 (Table 2) with the highest was found in Loh Wau (18.6 km-2) and the lowest at Loh Pinda (1.67 km-2). There was a significant decline in the counts of Yellow-crested Cockatoo at the five valleys in 2005 compared with the results of the 2000 study (Table 2, Chi square test= 12.41, df = 4, p = 0.01). Population declines per valley was varied from 0-80%.  

Table 1. Past (2000) and Current (2005) population of Cacatua sulphurea on Komodo Island 

Site

Population (2000) Population (2005) Density /km-2 (2000) Density /km-2  (2005) Population decline
Loh Wenci 6 6 14.29 14.29 0%
Loh Sebita 82 50 19.20 11.71 -39%
Loh Liang 190 62 30.45 9.94 -67%
Loh Pinda 18 3 10.00 1.67 -83%
Loh Wau 44 16 51.16 18.60 -64%
Total 340 137 25.02 11.24 -60%

 

Discussion 

The current population (2005 survey) was only 137 birds, compared to the 340 birds in 2000 (Agista and Rubyanto 2001), which represents a major decline over a period of 5 years. The Yellow-crested Cockatoo population on Komodo Island is largely immune from forest loss and captures for trade, yet we report a population decline of 60% between 2000 and 2005. Our ability to interpret the cause of the decline is hampered by the general lack of ecological information on the population. For example, there is no information on the extent to which fledgling birds disperse to nearby ‘mainland’ areas such as Flores or Sumbawa, and if they do, in what numbers?; and, on such an arid island, is the availability of free water limiting during the annual dry season, following unusually dry wet seasons? Our data suggests that nest success on Komodo may be limited by a lack of nest holes. On other islands this might be caused by loss of large trees in selective logging or agriculture, but on Komodo (where large hollow bearing trees are probably naturally limited) it might be caused by older trees senescing, and regular wildfires (M. J. Imansyah, unpublished data) that might have a greater impact on mature rotten and hollow bearing trees.  Populations of the Yellow-crested Cockatoo throughout its range have been in decline since the 1970s primarily because of trapping for trade (PHPA/LIPI/BirdLife International-IP 1998; BirdLife 2001; Setiawan et al. 2001). Only on Sumba has an increased population density been reported, apparently in response to a ban on captures (Cahill et al. 2007).  Komodo Island presents a different context to the other Indonesian islands: cockatoo harvesting is effectively zero because of surveillance and enforcement (Pet and Subijanto 2001) and there is negligible loss of mature trees or forest loss through illegal logging (Pet and Subijanto 2001; Ciofi and de Boer 2004). Captures for trade and loss of mature hollow-bearing trees is undoubtedly driving the decline of other populations, but in the absence of these threats on Komodo it is unclear why the Komodo Island population may have declined.

Note: To get more evidence that yellow crested cockatoo on Komodo island is suffering a severe declines within theis last decades, thus we would like to conduct another survey in September 2008. Donation and volunteers are welcome. please contact Jeri via mjimansyah@yahoo.co.id for more detail.

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~ oleh ekologi pada April, 1, 2008.

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