Why is the glossy cockatoo so brainy? part 2
...continued from https://www.inaturalist.org/journal/milewski/67969-why-is-the-glossy-cockatoo-so-brainy-part-1#
The genus Allocasuarina is an extreme example of an organism adapted to Australia. Casuarinas are common in Australia and the genus Allocasuarina – which has serotinous, cone-like seed-capsules adapted to fire – is restricted to Australia. I dominates certain vegetation types as either a tree or a shrub. It has no counterpart in even the nutrient-poorest, more fire-prone ecosystems under similar temperate-zone climates on other continents.
The glossy cockatoo (Calypthorhynchus lathami, body mass ca 425 g) is an extraordinary bird for two reasons. Firstly, it belongs to the family Cacatuidae, which is restricted to Australasia in the broad sense (i.e. south and east of Wallace’s Line). Secondly, it is among the most specialised of birds in diet worldwide, because it eats little but the seeds of casuarinas. Even the juvenile is fed casuarina seeds by its parents from the time of hatching.
In this Post, I think deeply about the ecological niche of C. lathami and what it means for biogeography. Here’s one example of information on C. lathami:
https://www.animalinfo.com.au/fact_sheets/view/4/15/161/fs:An_Experience_with_Glossy_Black_Cockatoos
One cannot really understand the nature of cockatoos without realising that they are, to a large extent, Australasian substitutes for mammals such as rodents and monkeys. I find it remarkable that whole books have been written on the topic of cockatoos without mentioning this context. For example, I’ve just read ‘Cockatoos’ by Matt Cameron, which was published in 2007 as part of the ‘Australian Natural History Series’ of books. The book runs to 220 pages and summarises various aspects of the biology of cockatoos, but nowhere mentions that they are counterparts for e.g. mole rats, woodpeckers, and monkeys. In my view it’s impossible to understand cockatoos without realising this relationship.
This context is particularly relevant to C. lathami, because on any other continent the niche it occupies would likely be occupied by a squirrel. Squirrels are widespread on Earth but have failed to penetrate Australia. Furthermore, the Australasian lineages of rodents have not independently come up with any version of ‘squirrel’, and the marsupials have failed to converge with squirrels. There is simply nothing going on in Australia with something as widespread and taken-for-granted as ‘squirrel’ and it is as an ‘avian squirrel’ that C. lathami can best be understood. I may be the first person ever to point this out, even though it is so obvious.
Please also note that the concept of ‘squirrel’ includes gliding squirrels, and so there is some overlap between ‘bird’ and ‘squirrel’ in the sense of locomotion through the air, from tree to tree. It is remarkable that, although marsupial gliders are common and widespread in Australia, none of these specialises on seeds.
This raises the question: why did Australia come up with a bird instead of a mammal, in a squirrel-like niche, that of specialising on the seeds of casuarinas?
I would argue that this is because casuarinas are so stingy with their seeds that any specialised granivore has to have extreme economies built into its design. Cockatoos are energetically efficient by virtue of their volant flight and their slow growth of the body. They are extremely ‘K-selected’, long-lived, and slow-reproducing, epitomising the adaptation to poor resource-bases. Casuarina seeds are RELIABLE enough to allow virtually complete specialisation, but not LUCRATIVE enough to allow a mammal to exploit this niche.
Casuarinas are stingy casuarinas towards animals, in so many different ways. They support extremely few folivores and no nectarivores, despite being N-fixing plants. They tend to be effectively ‘sterile’ in their relationship to animals generally, as if reserving themselves for fire as their exclusive consumer. What I’d like to show here is that the fact that one species of bird relies on casuarina seed is a case of ‘the exception that proves the rule’.
It is important to realise that C. lathami is economical not only because it is a cockatoo, but also because it is perhaps the species of cockatoo with the slowest pace of life for its body size.
Clutch size in C. lathami is one, in contrast to most other spp. of cockatoos, which lay several eggs at a time. Because each pair attempts to breed in only some years, the average production of eggs per year in C. lathami is <1.
This species, C. lathami, has the smallest rate of bodily growth of all cockatoos. Its nestling period of 90 days is the longest of any psittaciform bird worldwide.
The juveniles of C. lathami remain with their parents for >1 year after fledging, during which time their parents regularly feed them. Contrast this with e.g. the galah (Eolophus roseicapillus), in which the juvenile of only two months old (compared with 15 months in C. lathami) is deserted by its parents.
The slow pace of life of C. lathami perhaps helps to explain the peculiar distribution of this species, which is now restricted to eastern Australia (north of Victoria) except for an outlier on Kangaroo Island in South Australia. Predation by aboriginals was perhaps enough to exterminate the species in most stands of casuarinas. The human species was absent from Kangaroo Island at the time of European arrival. It is thought that the absence of C. lathami in Tasmania is owing to the effects of aboriginal people.
As a footnote, this is how C. lathami uses its specialised beak to process the cones of casuarinas.
According to Cameron (2007), these cones are cylindrical, comprising radially arranged layers of seeds. The lower beak is wide and concave at the end to accommodate the rounded cones. The cones are plucked from the branch with the beak and then transferred to the left foot (that’s right, cockatoos are ‘handed’). With the cone braced against the lower beak, the beak tip is used to dig seeds from each layer. Each seed is held with the tongue against the roughened internal surface of the upper beak and divested of its coat by means of the sharp corners of the lower beak. Once all seeds within a layer have been extracted, remaining cone material is removed to expose a new layer. “Anyone who has observed Glossy Cockatoos feeding in the outermost branches of she-oaks in strong winds, unperturbed by being blown through a 1 m arc, has little doubt of their adaptation to a lifestyle of canopy foraging” (Cameron 2007, page 70). According to Sindel and Lynn: “The unique mandibles of this species which are perfectly designed to hold and extract the seeds from the Casuarina cone, reflect its very specialised feeding habits, and set it aside from all other members of the genus. Both mandibles are particularly broad, the upper protrudes in a balloon like fashion terminating in a small sharp point, while the lower mandible has two well separated, tooth-like protrusions which grip the cone while the upper mandible tears it open to expose the minute seeds. All the birds of this species which I have been able to observe closely when feeding, held the cone in the right claw while removing the seed from the cone. When the seed has been freed from the cone the lower mandible is moved to the bird’s left thus bringing the right side protrusion in line with the point of the upper mandible enabling the seed to be split and the kernel extracted.”
Calyptorhynchus lathami:
http://www.graemechapman.com.au/catalogue/ausbirds3274/b/265225.jpg
http://www.glossyblack.org.au/all%20images/GBClogo.jpg
http://leilajeffreys.com/wp-content/uploads/2014/08/GlossyBlack_Map.png
Allocasuarina verticillata:
http://www.dn.com.au/Arboriculture_Urban_Trees_gallery/Pictures/Allocasuarina-verticillata-drooping-sheoak-street-tree-South-Australia-biodiversity.jpg
to be continued in https://www.inaturalist.org/journal/milewski/67971-why-is-the-glossy-cockatoo-so-brainy-part-3#...
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Most people with a good general knowledge of birds may not realise that parrots were widespread in the USA when the first Europeans arrived there.
Please see the distribution map below for the northernmost species, the now-extinct Carolina parakeet, Conuropsis carolinensis (https://en.wikipedia.org/wiki/Carolina_parakeet):
http://sdakotabirds.com/species/maps/carolina_parakeet_map_large.jpg.
The Carolina parakeet was not some odd tropical bird penetrating aberrant pockets of habitat far north of the Neotropics. Instead it was a ‘mainstream’ bird living in ‘mainstream’ deciduous forests, and eating the seeds of typically North American plants such as oak, elm and pine. It reached nearly to Canada.
Another genus from which it took seeds is Celtis, which penetrates temperate climates on several continents.
The Carolina parakeet foraged in large flocks, and was so common and so responsive to farming that it achieved the status of farm pest in the century before it was completely exterminated.
I have come to suspect that China, too, had at least one indigenous species of parrot. This became extinct at the hands of the human species so long ago that – given the obscurity of Chinese literature to western readers – its existence has now been forgotten. Since much of the deciduous forest belt in China is actually closer to the tropics than that of North America, it seems unlikely to me that the entire order Psittaciformes would have been naturally absent from central China.
The surviving genus Rhynchopsitta still occurs in Mexico, although lost to its former range in the coniferous forests of Arizona and New Mexico.
Judging from its relatedness to the genus Conurus, I suspect that the Carolina parakeet was above-average brainy for a member of the parrot-like birds.
Psittaciform birds are vulnerable to extinction despite their intelligence, versatility, and adaptability, and because of the limited rate of reproduction associated with extremely long-lived birds.
What the extinction of the Carolina parakeet in the nineteenth century means is the loss in the USA of the only widespread species of animal, in this vast country, that was probably capable of speaking human languages to humans.
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