Building the Tree of Life begins with the goal Make the Tree of Life Flourish! The in-game menu that allows collecting birds is called Grow the Tree of Life!
When collected from, Nature buildings have a chance of dropping the birds needed for upgrades. You can also request a (random) bird every 2 hours, and get them from friends off the wall feed. A related goal For The Birds! gives you a Bird Sanctuary that helps collect birds every 18 hours.
The tree of life is unusual in that he has a payout boost radius of 7 tiles. He can therefore be added to an otherwise fully optimised business setup for an additional boost of up to 100%. All Nature Buildings can receive 3x the listed percentage boost from the Tree, for a maximum of 300% at Level 6.
Removal returns it to your Inventory, but you'd likely have to rebuild the whole thing. Note that every time you upgrade your tree, your bird collection will be reset. (If you have three flamingos and you only need two, you will also lose the third.)
HINT: Make sure you have the rarest 3 birds on your Wishlist at all times. This gives you much better odds through clicking your neighbor's feed items. Be certain you have all 3 on your Wishlist right before you go up a level, or you will lose time getting them back on it.
Also visit Zynga's Tree of Life Guide
According to Zynga this goal will end in 31 days, starting from April 28, 2012.
|+3% payout to Businesses, Residences and Community Buildings|
|Level 2||Building Materials||Bonus|
2x Blue Jay
|10 Energy, +15% payout to Businesses, Residences and Community Buildings|
|Level 3||Building Materials||Bonus|
4x Blue Jay
|15 Energy, +24% payout to Businesses, Residences and Community Buildings|
|Level 4||Building Materials||Bonus|
8x Blue Jay
|25 Energy, +36% payout to Businesses, Residences and Community Buildings|
|Level 5||Building Materials||Bonus|
16x Blue Jay
|50 Energy, +76% payout to Businesses, Residences and Community Buildings|
|Level 6||Building Materials||Bonus|
32x Blue Jay
|100 Energy, +100% payout to payout to Businesses, Residences and Community Buildings|