Getting a bunch of errors

private bool gameStarted = false;
[SerializeField]
private Texture gameStateText;
[SerializeField]
private GameObject player;
[SerializeField]
private BirdMovement birdMovement;
[SerializeField]
private FollowCamera followCamera;
private float restartDelay = 3f;
private float restartTimer;
private PlayerMovement playerMovement;
private PlayerHealth playerHealth;



// Use this for initialization
void Start () {
        Cursor.visible = false;

        playerMovement = player.GetComponent<PlayerMovement> ();
        playerHealth = player.GetComponent<PlayerHealth> ();

        // Prevent the player from moving at the start of the game
        playerMovement.enabled = false;

        //Prevent bird from moving at the start of the game
        birdMovement.enabled = false;

        //prevent the follow camera from moving to its game position
        followCamera.enabled = false;
}

// Update is called once per frame
void Update () {

    // If the game is not started and the player presses the spave bar...
    if (gameStarted == false && Input.GetKeyUp (KeyCode.Space)) {

        //...Start the game.
        StartGame ();
    }

    // If the player is no longer alive...
    if (PlayerHealth.alive == false) {

        //... end the game
        EndGame ();

        //...incremement a timer to count up to restarting...
        restartTimer = restartTimer + Time.deltaTime;

        //...and if it reaches the restart delay...
        if (restartTimer >= restartDelay) {

            //...then reload the currently loaded level.
            Application.LoadLevel (Application.loadedLevel);

        }
    }
}
private void StartGame() {

    // Set the game state
    gameStarted = true;

    //Removing the start text
    gameStateText.color = Color.clear;

    //Alow the player to move
    playerMovement.enabled = true;

    //Allow bird to move
    birdMovement.enabled = true;

    //Allow the camera to move
    followCamera.enabled = true;

}

    private void EndGame(){

    // Set the game state
    gameStarted = false;

    // Show the game over text
    gameStateText.color = Color.white;
    gameStateText.text = "Game Over!";

    //Remove the player from the game
    player.SetActive (false);

    }