Here's two pictures of a couple of bourkes.... the female on the left, male on the right. They were brother/sister, however sadly I lost the male (due to one of my budgies and I realised it too late)
I tried selecting a soft violet fabric to use as a background to try and bring out their colors...
I like to refer to bourkes as finches in a parrot body... they aren't quite as flighty as finches, but they are just gorgeous, calm little birds who love to twirp throughout the day! They don't sound like other birds of course!
Grass parakeets are any parakeet under the scientific name of Neophema, however bourkes have been 'reclassified', so technically they aren't grass keets.. but are still considered ones. Occasonally, psephotus and platycercus (rosellas) are also considered grass parakeets.
Neophema Grass Parakeets (the real ones!)
Elegant
Blue Winged
Orange Bellied
Rock
Turquise
Splendid aka Scarlet Chested
Neopsephotus Grass Parakeet
Bourke
Psephotus Parakeets
Red rumped
Mulga aka Many Colored
Paradise
Golden Shouldered
Blue Bonnet
Here's a good site for grass keets...
http://www.grassparakeet.com
Here's a video of two redrumps, with somebody whistling in the back.... the male redrump (the one on right) does make a sound part way through...
http://www.youtube.com/watch?v=EdFlUSREC9U
In this video you may hear some of the different grass keets that this owner has... among other birds.
http://www.youtube.com/watch?v=e35_iBPzTGo
Heres that redrump again showing off.... although he sounds similar to a cockatiel to me... lol
http://www.youtube.com/watch?v=CJy4PCAaTJo
What I've noticed though, is that some grass parakeets tend to be so laid back that they would do well with cockatiels finches and canaries... where-as budgies tend to be too hyper and tend bully others. They are easy to tame, primarily speaking, however most people tend to keep them more as aviary birds than pets. I'd actually recommend a grass parakeet (such as a bourke) to a child rather than a budgie, they just tend to be that calm...