Oddbills 4

Another in a sporadic series on more-than-usually remarkable bird bills; here's the link to the previous one in the series (and through it to earlier ones). As on that occasion, you get a special offer today - two for the price of one; both are parrots, and both are endemic to the south-west corner of Australia, long isolated from the rest of the continent by aridity and limestone plains. Quite independently, these two species have developed a highly specialised upper mandible, extremely slender and protruding - and both have done so for the same reason, to exploit a remarkably rich food resource, available all year round, provided by just one of the hundreds of species of eucalypts found in the south-west. 

This species is Marri, Eucalyptus calophylla, found (most often in association with Jarrah, E. marginata) as a defining species in huge areas of dry eucalypt forest that dominate the south-west hinterland.

Marri-Jarrah dry forest near Bannister; the Jarrah has fibrous bark, the Marri's (see also below) is in little plates.

 

The food source that our (still anonymous) stars today are after however is found in the distinctive big fruits, in which hundreds of seeds are produced. The fruits can form all year round, and within them seeds continually ripen over a long period; each seed is tiny, but the overall resource is huge and is particularly important in winter when other food is scarcer.

Marri fruit, John Forrest National Park.
These impressive seed-producers can be 50mm long and 35mm wide; when ripe, they are also formidably tough.

A very few birds - notably Carnaby's Cockatoo Calyptorhynchus latirostris - have the tools to simply crush the fruit walls, but our subjects for today are more subtle than that.

Red-capped Parrot Purpureicephalus spurius, Albany,
a truly glorious bird, fairly large and the sole member of its genus.

The key feature of the Red-capped Parrot from our perspective however is the extended upper bill, fairly clear in this picture. Experienced older birds show great dexterity in nipping off the hard ripe Marri fruit, holding it in one claw, testing it and, if it is of good enough quality, rotating it while inserting the upper bill to extract the fruit. (Green fruit are simply chewed apart.) An earlier study found that 54% of Red-capped Parrots in winter had been eating Marri seed. 

Today's second Oddbill is a very close relative of Carnaby's Cockatoo mentioned earlier; indeed Baudin's Cockatoo is virtually indistinguishable in the field - unless you can get close enough see the bill. The long-used names of Short-billed and Long-billed Black-Cockatoo in fact seem eminently more useful. Baudin's has a long slim upper mandible like the Red-capped's, and for exactly the same purpose.

Baudin's Cockatoos Calyptorhynchus baudinii (named for French commander Nicolas Baudin, leader of one the most splendid exporatory expeditions ever to visit Australia, in the first years of the 19th century),
Stirling Ranges National Park.
The special mandible is not as clear as it is in the Red-capped, largely because the bill is part-hidden in feathers; in this pair it can best be seen in the female on the left.

Baudin's Cockies are even more dependent on Marri than the Red-Capped Parrot, with wood-boring grubs comprising most of the rest of the diet. Like the Red-cappeds, they are experts at extracting the seeds without damaging the fruits. Unlike the Red-cappeds though, they are listed as Endangered, both by the IUCN and the Western Australian government. The single population is estimated to comprise between 10,000 and 15,000 birds; the main threat formerly was habitat clearance, while now it is regarded as a mix of loss of mature Marri trees (the key food source), competition for nesting hollows with feral Honeybee colonies, and illegal shooting (primarily by orchadists).

We can only hope that this superb product of evolution can survive our assaults on it.

TOMORROW I LEAVE TO ACCOMPANY A GROUP OF NATURALISTS TO ECUADOR; PLEASE DON'T FORGET ME - I'LL BE BACK HERE WITH ANOTHER POSTING ON FRIDAY 15 NOVEMBER