Survival ecology for the Yellow-crested Cockatoo

Posted by Anna Reuleaux

Two years ago we attended a workshop on Yellow-crested Cockatoo conservation on Sumba which quickly resulted in several research projects on the species. These research projects funded by Loro Parque Fundación (LPF) and Zoologische Gesellschaft für Arten- und Populationsschutz (ZGAP) were combined into a PhD project for Anna. Here she reports on the first full year of work.

Cockatoos on Sumba inspecting cavity (Photo: Anna Reuleaux)

Yellow-crested Cockatoo Cacatua sulphurea is endemic to Indonesia and Timor Leste, and Critically Endangered. They used to be common throughout the Lesser Sundas and Sulawesi - so common that most older villagers remember being sent to the fields to kill cockatoos in their childhood to protect the corn harvest. Now the cockatoos are so rare that the majority of children have never seen one. Anna’s PhD research aims to provide the knowledge base for urgently needed conservation action for this charismatic species. This includes finding out which of the former cockatoo populations on the Lesser Sundas and Sulawesi still prevail, estimating their numbers, and, most importantly, understanding why the species survived in some locations and died out in others. Examining the productivity of the species and its limiting factors is also essential for understanding viability, or lack of it, within the populations. 

Climbing ladders to access cockatoo nests were still evident on Pantar (Photo: Anna Reuleaux)

Dynamics of the Sumba population

The largest remaining population is found on Sumba with remaining population numbers of the orange-crested sub-species C. s. citrinocristata thought, at the last count, to be in the thousands (Cahill et al. 2005). Burung Indonesia (the Birdlife Partner) and the Fund for Endangered Parrots (a working group of ZGAP) have been working together in a successful long-term public awareness campaign on the island, which has resulted in the creation of a National Park, and poaching coming to a virtual halt on Sumba.

Cockatoo roost on Sumba (Photo: Anna Reuleaux)

In order to judge viability of the population it is essential to understand the demographic parameters and limiting factors for reproduction. Therefore Anna and the cockatoo team of Burung Indonesia have set out to monitor nests during the core breeding season from October to March. Finding active nests has proven difficult, but with increased search efforts in the 2015/16 season, the team found 19 sites that were prospected by cockatoos. Unfortunately only five had eggs laid in them and only one chick fledged. A second single chick was already sticking its head out of the cavity entrance which indicated nearing fledging but on the next visit it looked like this (see Figure below). This cockatoo chick died shortly before fledging, probably due to predation. The skeletonised remains were found in the cavity without the skull.

This cockatoo chick died shortly before fledging, probably due to predation (Photo: Ana Reuleaux)

Cockatoo chicks very much alive and looking forward to contributing to viability of the Sumba population (Photo: Anna Reuleaux)

Frustrated with the unknown causes for nest failures in the first season, the team installed camera traps above the entrances of prospected cavities for the 2016/17 season. Although there was no lack of cockatoo activity around the monitored cavities, only two active nests were found, both late in the breeding cycle, and in previously unmonitored cavities. One of the pairs even fledged two chicks, which is a first in documented nest attempts on Sumba.
Camera trap footage from cavities provided ample evidence of competitors and potential predators. A Long-tailed macaque Macaca fascicularis and an Asian Palm Civet Paradoxurus hermaphroditus were caught looking into a cockatoo cavity, which was luckily empty at the time. Two species of owls used the cavities at night on a regular basis, Short-tailed Starlings Aplonis minor, Great-billed Parrots Tanygnathus megalorynchos and Eclectus Parrots Eclectus roratus occupied sites that were abandoned by cockatoos.

Sumba has an inordinate number of birds species interested in holes in trees - here, the endemic hornbill inspects (Photo: Anna Reuleaux)

Where do other populations remain, and why?

There are six other C. sulphurea subspecies in the Lesser Sundas, on Sulawesi and on three small island groups in the Sulawesi and Java Sea. From March to May this year, Anna went on a ‘road trip’ to survey the populations of C. s. occidentalis on the island chain between Sumbawa and Alor. The largest remaining population of this subspecies is in Komodo National Park and will be surveyed later this year. Between Sumbawa and Alor there are about 70 locations with Yellow-crested Cockatoo records of the past (Threatened birds of Asia and other reports), most of which are certain to be free of cockatoos today. Anna and field assistant Romy from Burung’s Sumba programme set out to survey the most promising of these locations, estimate approximate numbers and find likely sets of conditions allowing populations to survive.

The team found surviving populations in fifteen locations varying in (minimum) size between four and 46 individuals. Evidence for capture of cockatoos was almost universal in all populations: captive birds in the villages, ‘harvested’ numbers reported by locals, or climbing setups still visible on the nest trees. The reasons why these populations are still clinging on are very varied and each place has its own story, but what all have in common is some sort of protection from capture for the pet trade. This may be remoteness, difficult access, a formally protected area, sacred land, exclusive and perhaps sustainable harvesting by one trapper, a climbing accident, and awareness work by NGOs. The amount and normality of trapping still happening was shocking and will surely lead to the extinction of populations in the near future, if nothing is done about it.

Cockatoos survive in areas that are difficult to access, like here on Alor (Photo: Anna Reuleaux)

From July to September Anna will survey the population on Sumba to obtain a much needed new population estimate. This distance sampling survey will try to match previous surveys as closely as possible, and will include other key bird species and habitat parameters. In October, Burung’s Ecologist Benny and Anna will estimate the cockatoo population of Komodo National Park. They will spend 4-6 weeks on the islands of Komodo and Rinca and use distance sampling methods similar to those applied on Sumba.

The Rinca-Robong-Flores daily cockatoo commute (Photo: Anna Reuleaux)

 The Sumba cockatoo breeding season will already have started when Anna and Benny get back to Sumba. The trail cameras will remain in place on the nest trees year round. Hopefully more of the monitored cavities will become active and additional ones can be found. Once the breeding season calms down with chicks starting to fledge, it will be time for Anna to survey the rest of the species’ range for remaining populations: West Timor and Timor Leste, Sulawesi and the islands of Tanahjampea and Wakatobi. The remote population of C. s. abbotti on Masalembo may not need a visit as it is tiny and closely monitored by other organisations.
 

Romy scanning for cockatoos on Pulau Adonara (Photo: Anna Reuleaux)

When the results of all these surveys come together, we will have a much better understanding of the Yellow-crested Cockatoo’s status and be able to identify key areas for immediate conservation interventions and for more long term work. Anna’s PhD, supervised by Stu, along with Martin Jones (MMU), Nigel Collar (BirdLife), and Ani Mardiastuti (Agricultural University Bogor), is due in 2019.

This project is funded by Loro Parque Fundación, Zoologische Gesellschaft für Arten-und Populationsschutz, Fond für bedrohte Papageien and Strunden Papageienstiftung. Currently Anna is supported by a scholarship of the German Academic Exchange Service (DAAD). The work is a close cooperation with Burung Indonesia, particularly with the team on Sumba. Further counterparts in Indonesia are Agricultural University Bogor (IPB, Prof. Ani Mardiastuti) and Universitas Nusa Cendana, Kupang. We are grateful that the Indonesian Government (Ristekdikti and KLHK) gave permission for this research. 

 
References

Cahill, A. J., Walker, J. S. and Marsden, S. J. (2006). Recovery within a population of the Critically Endangered citron-crested cockatoo Cacatua sulphurea citrinocristata in Indonesia after 10 years of international trade control. Oryx 40: 161–167.