After you defeat Parasite and save the Ra Tree, you revive plants and can reach Great Cliff, also known as Grecliff, where the birds lived.
Go east and enter the cave. There is a dead end to the north where you can fight a Stone Golem. Otherwise, go east, being careful of the Parionton that swoops down to attack you. From there, go north and jump up the ledges. Get past the Stone Golem at the top, then go up the stairs.
Follow the winding path, killing the Stone Golem on the way. Eventually you reach a boulder blocking your path. Push it to the left to get rid of it. Go south. You can't push this boulder because there are two small rocks behind it. Pick up those rocks to get rid of them, then push the boulder down. It comes to life as a Stone Golem, so kill it and continue going south to exit this area.
You will be outside. First, climb up the vine, then go east and into the cave. You're on a ledge in 2F. Go north and open the chest to get a STR potion. Use it right away to permanently increase your STR by 1 point. Go south again and exit the cave, then go west again and go down the vine. Then go east and you'll encounter some Mudmen. Keep going east, and go into the cave door.
This is another part of 2F. Make your way to the northeast corner of the room, past some Stone Golems. Go up the stairs in the upper-right corner of the room.
There are several Parionton birds that attack you in this room. You need to go to the northwest corner of the room, but you might want to avoid swimming because the Pariontons can attack you more easily if you are in the water. You will see a chest in the bottom right corner of the room, but you can't reach it yet. Go to the northwest corner of the room and go up the stairs.
Go south down the left path. You encounter a Stone Golem, and also a Quaker that drops from the ceiling. When the Quaker lands, it causes a tremor, immobilizing you temporarily. Kill the monsters and go west. Go up the two flights of stairs, but don't go into the stairway at the top, because it just leads to a dead end. Instead, go west and follow the path to the outside.
Go east and climb up the vine, then climb down the vine to the right. Go east past the Mudman and then climb up the vine to the right. Go into the door there.
Inside, there is a Stone Golem. A Quaker falls from the ceiling. When you are done with the monsters, go up the stairs.
Go west and go into the door the wall. Approach the two boulders to wake them up. Kill the two Stone Golems, then open the chest to get RocSpear. A black boulder falls from the ceiling. Equip RocSpear and hit the boulder to get rid of it. Go back outside.
Go all the way back to 4F, where you ignored some stairs because they led to a dead end. Go through that door.
Grecliff 5F, part 2
Run toward the big hole to the south, then jump. You should make it across the gap. A Quaker will fall when you reach the other side, leaving you vulnerable to the Parionton birds. After you deal with those monsters, go south and jump over the next gap. From there, go west and then use the exit.
You're outside again. You can see a treasure chest to the west, but you can't reach it. For now, exit to the east. Go up the vine here. Go eastward, using the vines to proceed. At the east side of the screen, after you have gone up the vines, go past the door to find a Magirock. Take it, then go south and into that door.
Go north and use your RocSpear to get rid of the black boulders that are in the way. Go west past where the boulders were, then go south to go back outside. Go west and jump up the many ledges. At the top, go west to reach the next area.
Go west and you will see some Borfes on the ledges. Kill them and make your way down the ledges. Keep going downward until you see a vine. Go past that vine and you will see another vine south of a cactus. Go down that vine to find a Mudman and a Magirock. Then go back up the vine and use the other vine that goes into the hole. You will fall down a chute. If you don't press any buttons, you will return to the area where you got the Magirock a moment ago. To go to the correct place, hold left on the D-pad. You'll arrive near a chest that you couldn't reach before. Open it to get an S.Bulb.
Now go down the vine near where you just got the S.Bulb. This chute only goes in one path, so just fall and you will reach another area. Go west until you reach a door. Go into it.
Cliff 2, 1F
This is another part of the cliff. In this big room, Mini Quakers will pop out of holes in the ground and spit fireballs at you. If you want to kill these enemies, you have to be quick, because they hide in their holes if you get too close. Run toward the Mini Quakers when they pop up and press the attack button to get rid of them.
Go to the northwest corner of this big room to get a Magirock. Then go to the northeast corner to find the stairs to the next floor.
Cliff 2, 2F
Run across the brown rocks to the left, then kill the Quaker at the end of the path. If you don't hurry, the Quaker will cause a tremor, making all of the brown rocks fall. You will then have no choice but to fall down to the room below, where you encountered all of the Mini Quakers. Carefully make your way through this area, killing the big Quakers as quickly as you can so that they won't knock down all of the brown rocks. The key is to run across the brown rocks and press the attack button at the correct moment so you kill the Quaker before it can cause a tremor. Go to the southeast corner of the room and use the south exit.
Outside, go west and jump up the ledges, but be careful because a bunch of Pariontons will attack you. After you have dealt with these monsters, check on the sparkle in the nest. You'll receive the Sharp Claws. These are automatically equipped, much like the Giant Leaves that allow you to swim. The Sharp Claws allow you to climb bumpy walls. There is a bumpy wall to the right of the nest, so climb up it. Keep going up, being careful of the Pariontons along the way, and open the chest at the top to get an M.Bulb.
Now, go down all of the bumpy walls and ledges in this area until you have reached the bottom. Go east past the door to exit the area. Go east across the narrow path and keep going east until you find a bumpy wall near some Mudmen. Climb up the bumpy wall. At the top, there is a door. If you don't need an M.Bulb, just go into the door and skip to the next paragraph. Otherwise if you need an M.Bulb, go east, and jump down the bumpy wall there. Exit to the east. Climb the vine in this screen and go north to find a bumpy wall. Go up that wall and go north to find an M.Bulb in a chest. Go back down the bumpy wall and the vine to the left. Go west past the door to reach the previous area. Go up the angled bumpy wall and go into the door at the top.
Grecliff 5F, part 3
If you want some experience, go up the stairs to fight a Quaker and two Pariontons. Otherwise, swim east across the water. After the second set of stairs, go north, then go through the door in the north wall.
Grecliff 6F, part 2
Go south through this room, but be careful of the Quaker that comes falling down near the middle of the room. There are Pariontons in this room as well. Go south to exit the room.
Go up the bumpy wall to the left. Fight the Borfes and go northwest to get a Magirock. Go northeast to get 87gems.
Go back down the bumpy wall, and go down the many ledges on the east side of the screen. When you climb down the vine here, you will roll down another forked path, so hold right on the D-pad to go toward the right. You should end up on a ledge with a Magirock. Climb down the vine and fight the Borfes, then go east to the next area.
Climb up the bumpy walls. When you finally reach the top, you'll enter the boss's area.
Be careful not to fall off of the edge of the screen here or you will have to start the battle over.
Most of the time, the green bird will throw three spikes at you. They move slowly, so they should be pretty easy to avoid. You can also hold R to block the spikes. Usually the green bird is too high up for you to hit with your spear, but sometimes it flies low enough that you can hit it if you stand at the highest edge.
If the green bird doesn't throw any spikes, it is about to swoop downward at you. Hit the green bird when this happens, but avoid letting the bird hit you. Try running past the bird before it swoops down, then hit it. If you don't hit the bird after it swoops down, it will create a tornado that can knock you off of the area, forcing you to climb back up and start over. It's possible to run toward the tornado to avoid getting pushed off.
After you hit the green bird several times, it will summon a purple/brown bird that tries to poop on you. Just avoid the poop and keep attacking the green bird as before.
Resurrection of Birds
After the battle, birds are resurrected. You'll end up in a sanctuary called Sanctuar. Go north and climb up the cliff at the top. You'll reach KingNest. If you climb up the western cliffs, you reach a wandering soul runs a MagiShop. Go to the bottom of KingNest and go east to find a bird running a shop where you can buy a BirdSuit. There is a rock blocking the vine. Pick up the rock and throw it. Climb up the vine here to reach the King Bird. Then go back down the vine and talk to the three birds down below to go to Windvale.
Go into the cave and follow the path north. Throw the three rocks into the hole and you'll hear a voice. After the wind starts blowing, go outside and talk to the gull to go back to the KingNest. Climb the vine and talk to the King to get the WindPin. Be sure to buy the BirdSuit from the salesman bird south of the King. If you can't afford it, go back down to Grecliff and kill monsters until you have enough gold. Then when you have the BirdSuit equipped, go to the three birds that are south of the King, then talk to the bird on the left to go to Safarium and Zue.