Time for action – adding more birds

We are going to add more Bird objects to fly around. To do this, we're going to replace our _bird variable with an array and write some code to spawn the birds:

1. Open the GameScene.m file and remove the _bird variable. Instead, add two new instance variables to the GameScene class, as shown in the following code:

   @implementation GameScene
   {
       CCSpriteBatchNode *_batchNode;
       
       Hunter  *_hunter;
   
       float _timeUntilNextBird;
       NSMutableArray *_birds;
   }

2. Add following method somewhere below the update: method:

   -(void)spawnBird
   {
       //1
       CGSize viewSize = [CCDirector sharedDirector].viewSize;
       
       //2
       int maxY = viewSize.height * 0.9f;
       int minY = viewSize.height * 0.6f;
       int birdY = minY + arc4random_uniform(maxY - minY);
       int birdX = viewSize.width * 1.3f;
       CGPoint birdStart = ccp(birdX, birdY);
       
       //3
       BirdType birdType = (BirdType)(arc4random_uniform(3));
       
       //4
       Bird* bird = [[Bird alloc] initWithBirdType...