Thank you Gumby and Ozzie!
For Gumby (this is taken from a book I'm writing on waxbills, small finches from Africa and Asia):
BEHAVIOUR
GRASS DEPENDENCY
Although the vast majority of waxbills are primarily seedeaters not every species relies on grass seed for its subsistence diet, eating other plant seeds instead. Nevertheless, almost all will partake of it some of the time and the majority will eat it most of the time. Only the aberrant allies, the antpeckers, nigritas and olivebacks, with one exception, are truly independent of any plant seeds (though the seeds found in fruit are consumed by some species), as these have developed specialised feeding habits more akin to insectivores and frugivores. The exception is the White-collared Oliveback Nesocharis ansorgei, which is believed to feed entirely on the seeds of the composite Melanthera scandens.
Those waxbills that are heavily dependent on grass for food lead lives inextricably linked to it in other ways. Besides the provision of seeds the grass yields up succulent young shoots and abounds with tiny insects. The grass also affords the waxbills protection, as foraging for seeds that have fallen to the ground means they are often at liberty to eat while, at the same time, being hidden from view to many predators. Finally, its long leaves and inflorescences are gratefully accepted for use in nest construction.
The grass family is one of the largest in the plant kingdom and contains about 10,000 different species. Fundamental to the grass’ growth is good light; it cannot survive in the deep shade of a forest. Some species of waxbill live and breed on the forest edge and so are able to quickly dart into the bushes and trees at the first sign of danger. For sustenance, however, like their cousins who prefer or have to feed in the open, they, too, rely on the grass’ seeds and its harboured community of tiny inhabitants: aphids, bugs and beetles.
To survive, the grass and its insect community need water and this comes with the rains. During and after rainfall the grass immediately undergoes a remarkable transition. Green leaves are produced in only a day or so, followed by fresh ripe and half-ripe seeds. The insects, taking advantage of this succulent fresh vegetation to munch and sap to suck, are fast stirred into action. So, too, are the waxbills. With food of the right kind now available in abundance, they are stimulated to breed.
Hard seeds, which are unlikely ever to be as hard as the commercially available type, are overlooked in favour of the ripe and half-ripe ones, while the infinite number of insects makes easy pickings for any birds with a growing family of hungry nestlings. Protein is essential for the rapid healthy growth of the young and that found in seeds is augmented in the quick and easily assimilated form that only a soft-bodied insect can provide, and which the parents are able to regurgitate to their offspring quickly for optimum results. Of additional benefit to the chicks is that they are, in fact, getting two meals for the price of one, because the insect’s innards will inevitably contain some nutritious undigested plant matter.
FEEDING POSITIONS
Skead (1975) describes the feeding postures of four different species of waxbill he studied in the wild and which can be applied to the group as a whole. While not every individual species performs every posture they all undertake some of them, and the Estrilda species, in particular, are able to perform most. The feeding methods are classified as:
a) Grass seeds
- Feeding from substrate.
- Digging into substrate with bill-sweeping movement.
- Taking grass culm (stem) in beak then placing under foot.
- Taking seeds directly from inflorescence.
- Flying up and landing on culm, then bearing it down to ground under weight and shuffling up to inflorescence.
(f) Flying up, taking inflorescence tip in bill and bearing it down to ground then perching on it.
(g) Jumping up and taking seeds off one by one from inflorescence.
- Perched on grass inflorescences
- Perching on mass of inflorescence which remain upright.
- Grasses bending but not reaching ground so bird remains in upright position.
- Grasses bending double so bird hangs with head pointing downwards.
- Perched on bush or wire fence
- Leaning forwards and pecking at seeds
- Taking culm in beak and placing under foot (as in 1 (c)).
- Invertebrate Food
Newton (1973), in his classic work on the true finches, the Fringillidae, illustrates six different feeding positions undertaken by species in this family. These are: a) standing; b) in a normal perching position on a plant-stem; c) leaning forwards; d) perching on a bent plant-stem, so that the bird’s centre of gravity lies over one of its feet; e) clinging to a vertical stem; f) hanging upside down. In addition, he states that the Chaffinch Fringilla coelebs and Brambling F. montifringilla sometimes chase and catch flying insects, and the Bullfinch Pyrrhula pyrrhula sometimes hovers to obtain seeds and insects from the ends of branches. I have personally witnessed blue-headed cordon-bleus and black-rumped waxbills perform these actions, so overall waxbills are very similar to the true finches in their feeding postures. Where there is a wide overlap in food items, the manner in which it is collected probably serves to separate the different species ecologically.