Palm cockatoo info is taken from the “AZA Palm cockatoo Studbook – 2007”.
Palm Cockatoo “Quick Facts”
Range: New Guinea, Aru Islands, & Cape York Peninsula, Australia
In New Guinea - forest and dense savannah woodland up to about 1,300 m.
In Australia - the fringe zone between dense rainforest and Eucalyptus woodland.
Male Weight: 545 to 1092 g
Female Weight: 503 to 950 g
Length: 49 to 68 cm, measured from the top of the head to the tip of the tail
Wild Breeding Season: Every month of the year, with peak egg laying in September (Murphy et al, 2003).
Captive Breeding Season: Every month of the year, generally winter and spring seasons
Eggs: One white egg
Incubation: 31 - 36 Days
Wild Nest Type and Size: Tree Cavity, generally open topped hollow trees or limbs with internal dimensions ranging from 18.5 x 20.5 cm to 35.0 x 80.0 cm (Murphy et al, 2003)
Captivity Nest Box: 16"x16"x36" or hollow log with sufficiently large cavity
Subspecies and Range
Systematically, the palm cockatoo is thought to be the most distantly related of the cockatoo species, being the first to split from the group according to a molecular study by Brown and Toft, 1999 and is found in the monotypic subfamily Microglossinae (Igag, 2002). Murphy, 2005, states that “A diverse array of unique physical and behavioral attributes reflects this deep phylogenetic divergence from the other cockatoos and supports their monospecific status”.
The palm cockatoo is considered one of the largest cockatoo species and one of the largest parrots in Australasia (Forshaw, 1969; Gordon, 1978). It was first noted by Van der Meulen in 1707 and formally described in 1788 by Gmelin as Psittacus aterrimus (Storch, 1996). In 1820, Kuhl put it into the monotypic genus Probosciger. Forshaw (1973) describes three subspecies; Probosciger aterrimus aterrimus, P. a. goliath, and P. a. stenolophus. In the January/February 2001 issue of the AFA’s Watchbird, Forshaw names four subspecies, adding P. a. macgillivrayi to the afore mentioned three subspecies. Upon examination of the range of these four subspecies, Forshaw appears to have split P. a. aterrimus into P. a. aterrimus and P. a. macgillivrayi with P. a. macgillivrayi designated as the Australian population. Other publications have included the subspecies P. a. alecto and P. a. intermedius (Bates & Busenbark, 1969) which may have been earlier synonyms for the more recently recognized subspecies. The following sub-specific locations are derived from Forshaw's "Parrots of the World", 1973.
P. a. aterrimus occurs on the Aru Islands, Misool in the western Papuan Islands, West Irian, southern New Guinea from about Merauke east to the Gulf of Papua, and on Cape York Peninsula, northern Australia. The Australian population seems to have a very sparse and patchy, but widespread, distribution (Storch, 1996).
P. a. goliath is found on the western Papuan Islands except Misool, and in New Guinea from the Vogelkop, West Irian, east through the central regions to south-eastern Papua. This subspecies may not be separable taxonomically from P. a. aterrimus (Forshaw, 1973). P. a. aterrimus and P. a. goliath are quite similar in appearance other than size with P. a. goliath being the larger of the two.
P. a. stenolophus is confined to Japen Island in Geelvink Bay, West Irian, and northern New Guinea from the river of Mamberamo, West Irian east to about Collingwood Bay in Eastern Papua. Poor documentation has caused some confusion in geographic variation of the palm cockatoo. P. a. stenolophus is reportedly as large as or larger than P. a. goliath but has much narrower crest feathers (Forshaw, 1973).
A recent study by Murphy, et al, (2007) puts forth a theory that palm cockatoos are only split into two sup-species, P. a. aterrimus and P. a. goliath. They looked at the DNA of 71 palm cockatoos from 17 locations across their range. The DNA was taken from museum skins and nestlings. Their study clearly showed that the birds found on Vogelkop Peninsula, New Guinea and the islands west of there were separate enough from the rest of the population to be considered a separate sub-species, P. a. goliath. They found that the rest of the population (everywhere east of the peninsula including Aru islands and Australia) was too closely related to be split as indicated by the above authors and should all be classified as P. a. aterrimus. They go on to explore a possible reason for this split by looking at the geography of the region and its historical sea level changes in the past 250 thousand years. They suggest that “the occurrence of two deep marine troughs maintained a narrow mountainous barrier between eastern and western birds throughout much of the Pleistocene (era) at a time when extensive land bridges formed elsewhere in the species’ range and that this has maintained their genetic distinctiveness” (Murphy, 2005; Murphy, et al, 2007). The Volgelkop Peninsula is attached to the rest of New Guinea by this narrow mountainous piece of land called “Bird’s Neck” and Murphy, et al, suggests that with the receding sea level, the higher elevation plant species (which are not suitable for palm cockatoos) dominated most of the Bird’s Neck and cut off any exchange of genetics between the two populations. The land bridges that formed during this time kept the eastern New Guinea, Aru islands, and Australian populations connected and allowed enough exchanged of genetic material to keep them closely related. Murphy goes on to say that their ability to expand across these land bridges “gives some hope that anthropogenically driven extinction (e.g. along parts of New Guinea’s north coast, P. Igag pers. comm.) may be counteracted by migration over time”. But Murphy (2005) also shows that palm cockatoos have a very slow life-history strategy that would make any re-colonization a very slow process.
The palm cockatoo’s name is possibly derived from their fondness for the fruit of the Pandanus or Screw palm Pandanus sp. (Young, 1986). The adaptation of their unique beak, however, makes them one of the few birds that are capable of removing the meat from the nut of the Kanari tree, Canarium australasicum. In season, this nut makes up a large portion of their diet (Young, 1986). They have also been observed eating fruit buds from Darwin Stringy-bark Eucalyptus tetradonta, seeds from Cocky apple Planchonia careya, Beach almond Terminalia catappa, T. australis, Elaeocarpus arnhemicus, (Storch, 1996), the black bean tree Castanospermum australe, the fruit of the nonda tree Parinari nonda (Forshaw, 1973), pandanus such as Pandanus spiralis, bushman’s clothes peg Grevillea glauca, Persoonia falcate, and from the quandong Elaeocarpus sp. (Igag, 2002). Murphy (2005) notes that they predominately eat from the Canarium australasicum and Parinari nonda trees on Cape York Peninsula. Igag (2002) lists the following trees in New Guinea that palm cockatoos eat the seeds from; Semecarpus curtissii, Buchanania macrocarpa, Goniothalamus sp, Cerbera floribunda, Canarium acutifolium, C. asperum, Garcinia maluensis, Terminalia impediens, Okari nut T. kaernbachii, T. crassifolia, T. canaliculata, T. capitulata, Sloenea paradiseanum, S. aberrans, S. sogerensis, Elaeocarpus sepikanus, Lithorcapus celebicus, Lithocarpus lauterbachii, Nebergia celebica, Aglaia sp, Pandanus pseudopapuanus, Finschia chloroxantha. Geophagy, the consumption of soil, by palm cockatoos was first documented in 2006. The theory is that “soil is ingested to counterbalance the effects of toxic compounds in fruit” (Symes et al, 2006).
This species is not normally sighted in large groups and are not considered "flock-feeders" as are many of the white cockatoo species. Usually only one to six individuals are observed in the tree tops or on feeding limbs (Forshaw, 1973). The birds sometime congregate in open woodland after sunrise and feed there or along the rainforest edge before finally returning to individual roosting trees just before sunset (Forshaw, 1973). Palm cockatoos in Australia have been observed foraging the first couple hours of daylight, then perching in the rainforest, often over a stream, during the hot part of the day, and then returning to the woodlands late afternoon before roosting for the night (Storch, 1996). They have been found to forage in woodlands during the dry season and to forage in the rainforest in the wet season, which could be related to the availability of food resources (Storch, 1996). Palm cockatoos in Cape York Peninsula, Australia are primarily found to inhabit the areas between rainforest and dense savannah (Murphy, 2005) and in New Guinea are primarily found in the rainforest (Igag, 2002). This difference might be due to their most limiting resource, the nest tree, being more readily available in the dense savannah. As with many other cockatoo species, their fondness for fruits and nuts has contributed to their demise in agricultural areas of New Guinea.
The breeding season for palm cockatoos in Cape York Peninsula, Australia begins in July and runs through the end of May (Forshaw, 1973, Murphy et al, 2003; Murphy, 2005) and in New Guinea it begins in May and runs through February (Igag, 2002). The peak egg-laying month in Cape York Peninsula, Australia was found to be September (Murphy et al, 2003).
Their nests are usually found in hollow limbs and holes in trees, but are predominately found in broken off trunks of trees with the opening facing skyward. They have been found to use both dead (majority of nests in New Guinea) and live trees (majority of nests in Australia) of Melaleuca sp., Lophostemon suaveolens Eucalyptus sp., Corymbia sp., and Blepharocarya involucrigera, Sloenea forbbesii, Nubergia celebica, Elmerilla tsiampacca, Dysoxlum sp., Pometia pinnata, Pandanus pseudopapuanus for nesting (Storch, 1996; Igag, 2002; Murphy et al, 2003; Murphy, 2005). The pairs attend their nests year round which the males defend and display on or near with vocalizations, drumming, and with crest and wing extending (Heinsohn, 2003). They line the bottom of the hollow with a platform of splintered twigs which is unique to all the parrots. The platform starts out with sticks dropped in by the male which either land on the internal ‘mud gut’ of the hollow or get caught on the inside of the hollow and act as the platform’s foundation. The male then carries more sticks to the nest and chews them into progressively shorter lengths ending up with splinters about the size of toothpicks. It is with this last layer that the female assists with the nest platform construction (Murphy et al, 2003; Murphy, 2005). The platform may be as deep as a few inches to several feet (Forshaw, 1973; Igag, 2002; Murphy, 2005). The male will maintain three or four nest trees (with inactive and active nests) year round (Murphy, 2005). Most active nests were found in live trees and the size of the hollows ranged from 18.5 cm x 20.5 cm to 35.0 cm x 80.0 cm (Igag, 2002; Murphy, 2005). Nest trees are one of the most limiting factors for palm cockatoos and a very important resource. Murphy, 2005, notes that the destruction of nest trees (in Cape York Peninsula, Australia) is mainly due to fire and wind and most of these were the inactive nests. He speculates that the palm cockatoo’s drumming and calling from inside the hollow (Murphy et al. 2003) could allow the birds to figure out the “density and durability of the nest tree”.
The normal clutch size is one egg. Both the male and female share the incubation duties with the male’s turn usually happening during the day and the female’s during the night (Murphy, 2005). Murphy’s (2005) theory for this is that rival males are more likely to attempt a nest takeover during the day, so the incubating male will be there to defend the nest. The single egg is laid on the platform the pair spent so much time building and maintaining. Since they have such a long egg laying season, the nests can become flooded during the rainy season and the platform of twigs keeps the egg above water unlike other parrot species who can have their breeding seasons cut short because of flooding in the nest (Forshaw, 1969; Igag, 2002; Murphy et al, 2003; Murphy, 2005). The platform also allows feces to be washed through and not foul the nest (Forshaw, 1969; Igag, 2002; Heinsohn et al, 2003; Murphy et al, 2003). Another behavior observed by Murphy is the raking of the toothpick size twigs with the bird’s beak, which is done by the incubating bird and probably helps to keep the platform from packing down. Incubation takes 31 to 36 days and the chick fledges between 65 to 85 days (Low, 1980; Shubot, 1990; Murphy, 2005). It has been noted that chicks are generally fed late in the day and usually occur between one and three days apart (Igag, 2002). A six year study in Cape York Peninsula, Australia found that 63.4% of eggs laid hatched, which is a similar rate to other parrots but that 81% of nesting attempts “failed to produce a fledgling, thereby ranking the breeding success of palm cockatoos among the lowest reported for any species of parrot” (Murphy et al, 2003; Murphy, 2005). Although Igag’s, 2002, two year study had about a 60% failure rate. Predation is probably the largest factor in failed attempts with “small varanids Varanus spp., large rodents, and black butcherbirds Cracticus quoyii” being the most likely cause of egg disappearance and “amethystine pythons Morelia amethistina and large varanids like Varanus panoptes” being responsible for the disappearance of chicks older than 30 days, in New Guinea this includes humans (Igag, 2002; Murphy, 2005). Igag, 2002, saw chick starvation in other large parrots in New Guinea, but not in palm cockatoos even though they are a specialist feeder. He speculates that “since palm cockatoo food is probably the most energy-rich, they may be less affected by the absolute availability of fruit in the environment than the other two species. In addition fallen nuts last a longer time on the forest floor and can be eaten when the storey supply is out of season.” Murphy’s observations suggest that palm cockatoos breed, on average, once every 2.2 years.
Murphy, 2005, describes courtship display as follows;
“On three occasions where pairs were observed courting at the nest, the males positioned themselves at the entrance of the hollow. The males were usually observed wing-spreading, stamping and drumming without making any calls other than soft clicks. Males invariably had their cheeks blushed during this period, and would often chew the rim of the entrance and overtly “act out” dropping the splinters into the hollow. Male palm cockatoos also bobbed their heads into the hollow as if they were feeding, despite the fact that nothing was in their beaks. Sometimes males were observed adapting a static posture whereby they sat at the entrance, and held their body in a rigid position roughly parallel to the hollow. The reaction of the female during these displays presumably depended on her level of interest in breeding at the time. If “uninterested”, the female sat nearby with her cheek patches concealed by her lower cheek feathers, and would often preen. If “interested”, the female blushed and brought sticks to the nest to be added to the nesting platform.”
Males usually do most of the displays, including courtship displays as seen above. Displays by palm cockatoos both in the wild and in captivity include wing-spreading, head-turning, cheek blushing, crest raising and lowering, foot stamping, swinging, and numerous calls such as “disyllabic whistles, harsh ‘crac’ calls, and ‘hello’ calls” (Murphy, 2005; M. Taylor, pers. obs.).
Palm cockatoos differ from the other cockatoos physically with their thin crest feathers and naked cheek patches and they are the only black cockatoo with solid black tails (Murphy, 2005). In addition to the above mentioned habit of making and dropping splintered twigs into their nest log, the palm cockatoo has other unique behaviors. Another example of this is territorial drumming by the male. This is done with either the balled up foot or a short stick being pounded on the top of a hollow stump (Wood, 1984; Murphy, 2005). This is one of the rare instances of tool use by a bird species. This behavior is illustrated in the Palm Cockatoo print by Steve Hein at the front of this studbook.
The palm cockatoo is protected by the countries throughout its range; Indonesia, West Irian, Australia, and Papua New Guinea. Exportation for commercial purposes has been prohibited since they were listed on Appendix II to the Convention of International Trade in Endangered Species (CITES) on 1 July 1975 (Young, 1991). This status was upgraded to Appendix I in July 1987 (Young, 1991). Storch (1996) states that in Australia “the species is currently classified as ‘Vulnerable’ under the Queensland Nature Conservation Act 1992 and as ‘Insufficiently Known’ under the federal Endangered Species Act.”