Seed-predation of Calyptorhynchus banksii naso on Melia azedarach

@deans_beaver

A remarkable event is taking place in and near my garden at the moment.

The species involved are:

• Melia azedarach (https://www.inaturalist.org/taxa/53720-Melia-azedarach),
• Calyptorhynchus banksii naso (https://www.inaturalist.org/observations?taxon_id=557759), and
• Leptocneria reducta (https://www.inaturalist.org/taxa/208624-Leptocneria-reducta and https://matthewkeighery.com/white-cedar-tree-and-the-caterpillar-attack/)

Melia azedarach has long been a common suburban tree in the Perth metropolitan area, to which it is not indigenous. It thrives on neglect (https://www.bushlandperth.org.au/weeds/cape-lilac-or-white-cedar/).

Each autumn it produces fleshy fruits, containing hard kernels.

This tree is subject to obvious damage by two types of animals, in this suburban setting.

Each summer and autumn, M. azedarach risks defoliation by L. reducta. This caterpillar can strip the tree of all its leaves, although most individuals are only partly defoliated in a given season. This process has occurred in the Perth metropolitan area for decades.

Each autumn, the same species of tree is damaged grossly by C. b. naso.

This cockatoo arrives in autumn, attracted by the still unripe, green fruits (https://www.dreamstime.com/melia-azedarach-branch-fruit-branch-fruit-melia-azedarach-tree-image141022501 and https://erikaroper.com/blog/cocky-notes-return-of-the-karak).

The bird spends hours splitting the unripe fruits, including their single woody seed, in its beak, in order to eat the kernels. During the same foraging sessions, it - for some unknown reason - wantonly snips off leafy branches, so that the ground under the tree is littered daily with large amounts of foliage attached to twigs of diameter up to 1 cm.

What I have described so far is familiar to any suburban gardener who pays any attention to the trees and their attendant animals. And such attention is usually paid, because

• the caterpillars of L. reducta are reviled by all as a pest, owing to their itch-producing hairs and their habit of crawling into houses in large numbers to pupate,
• the cockatoo is such a conspicuous and loud bird that its presence is obvious even to those usually uninterested in birds, and
• the profuse litter, of two types, created by the cockatoo cannot be ignored by any householder wishing to keep some semblance of neatness in the garden or on the road-verge.

https://www.inaturalist.org/observations/51569282

My own attitude to the cockatoo is one of delighted indulgence, because

• this is a taxon threatened with extinction (https://www.dpaw.wa.gov.au/images/documents/plants-animals/animals/animal_profiles/frtb_cockatoo_fauna_profile.pdf),
• the utilisation of M. azedarach by the cockatoo is relatively recent, having become common in my suburb only in the last decade (https://erikaroper.com/blog/cockynotes-article and https://blackcockatoorecovery.com/cockatoos-and-animals/black-cockatoos/forest-red-tail-cockatoo/ and https://museum.wa.gov.au/explore/online-exhibitions/cockatoo-care/forest-red-tailed-black-cockatoo) - testimony to the intelligent versatility of the bird (https://www.inaturalist.org/journal/milewski/60822-new-intelligence-on-australasian-parrots#), as its natural habitat has been reduced.

The bird and the insect are, in a sense, competitors for the tree. This is because stripping by the caterpillars reduces the capacity of the plant to produce its fruits.

Given a choice, I would prefer for the individuals of M. azedarach in my garden to be damaged by C. banksii naso, rather than L. reducta. This has been the case this season.

The mature specimen (more than 15 metres high) of M. azedarach in my front yard has been only lightly defoliated by the caterpillar this year. This has allowed an ample crop of the unripe fruits, and a good opportunity for the cockatoo to forage right here at my home, within metres of where I sit typing this Post.

On the ground, where I daily sweep up and remove the gross litter of foliage and foliage-bearing twigs, is the green fruit-halves dropped by the cockatoo. These halves consist only of the split woody seed-coat and its still-adhering green (unripe) flesh, neither of which is edible to doves.

The cockatoo seems extremely painstaking and patient in its processing of the fruits, and the kernels are so small (imagine the size of a flattened match-head) that it takes hours to fill their stomachs.

Posted on April 23, 2023 02:23 AM by milewski