Birds need green feed every day, and Australian grass finches do best with green grass seeds every day during the breeding season. If there is development in your area, then avoid collecting grass seeds from there due to the possibility of herbicide contamination. Also beware of any areas that councils maintain because they regularly spray these too.
You should also watch for dust coming off nearby vacant blocks. The dust can make you and the birds sick.
Your best bet is to grow your own grass seeds. The following link has information on how to do this.
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The birds need cuttlefish skeleton (cuttlebone), mineral grit and clean water at all times.
A vitamin supplement is also useful and should be given to the birds every day or at least a couple of times a week. Try to use a dry powder vitamin supplement because they last longer than the bottles of liquid vitamins. Check the expiry date on anything you buy.
Keep the vitamin supplement cool and dry and out of sunlight. Heat, moisture and sunlight will cause the vitamins to break down really quickly.
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You can try feeding them on fruits like apple, orange, mandarin, banana. Cut these into thin slices and remove uneaten food each day. Green leafy vegetables like spinach, kale, broccoli are also good foods to try, just wash them well before use and make sure they are free of chemicals.
The old fruit can be put into a bucket with a wire lid made from bird wire. Fruit flies will lay their eggs in the rotting fruit in the bucket and the birds can catch the flies as they come and go, and any baby flies that crawl out will be taken too. If you have a few buckets/ containers with fruit in, you will get more fruit flies.
You can get wingless fruit flies from most universities and these don't have wings. You culture them in containers or bottles with bits of fruit in and the flies crawl up the sides and wander around until they get eaten. Keep wingless fruit flies away from normal fruit flies because they will breed together and you lose the ones without wings.
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Aphids can be found on roses in most gardens. Put a plastic container under the flower with the aphids and give it a gentle tap. The aphids drop into the bucket and you can feed them to the birds.
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You can culture mealworms in plastic storage containers. Have about 4 inches of sawdust in a plastic storage container and add a few hundred mealworms. Feed them on pieces/ slices of fruit. Keep the lid on the plastic storage container and over a few months the worms will change into adults and start breeding. The baby mealworms can be used for food. If you have several cultures going it will provide more food and there will be less chance of both cultures crashing. Start new cultures every few months and dump the old ones on the garden when they smell bad.
You can culture earwigs in the same way but you add lots of small boxes (match boxes are ideal) or scrunched up newspaper for them to hide in. Use a pair of tweezers to pick up earwigs by the pincers on the tail or they sting you with them. Quails love earwigs.
Cockroaches and Indian crickets can be cultured in the same way but have a flywire cover on them to stop them escaping. Leave the adults to breed and feed the baby bugs to the birds. There are numerous types of cockroach too and some are quite small (10-15mm long) and make better food than the typical American roach commonly found in houses.
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Get a couple more plastic storage containers and put about 4 inches of flour in them. Put a lid on them but don't have it on too tightly. Leave the flour for a few months and it should become infested with flour weevils. These produce small caterpillar like larvae about 10mm long. You use a flour sieve to go through the flour and separate the larvae, which are fed to the birds.
You can use rice or any other seed too and sometimes you might find a bag of old seed which has cobwebs in. These are from the weevil larvae and you can use this old seed to start cultures simply by adding them to containers of seed.
*NB* keep these cultures away from your normal bird seed so they don't contaminate the seed you feed your birds.
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Get an earthworm farm going. You can feed it food scraps and the worms can be fed to the birds. Quails eat any earthworms, finches prefer the smaller ones. The liquid from the worm farm can be used on the garden (including the green grass seeds you grow).
The most commonly available earthworms are reds, blues and tiger worms. These all grow to about 4-6 inches long. There are small varieties that are more suited to smaller birds but you have to look around for them.
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White worms are sometimes sold as fish food for aquarium fish and these worms are small (around 10-20mm long), and can be cultured in plastic containers with peat moss or potting mix in. You feed them with a dry baby cereal ("Farex" or something similar) and give them an occasional spray with dechlorinated water so the potting mix is a little moist but not wet.
You put some food on the potting mix and put a piece of Perspex on top of the food. The worms eat the food and crawl over the Perspex. You put the piece of Perspex in the aviary and let the birds eat the worms. When all the worms have been eaten, you wash the Perspex and put it back in the worm container.
Have multiple cultures going because they can crash any time and if you lose one, you can use the others to start more cultures.