Passaro não aparece

O aplicativo executa, mas a bola vermelha(passaro) não aparece. Segue as classes Main Activity, Game, Passaro e Cores respectivamente.

public class MainActivity extends Activity {

    private Game game;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        FrameLayout container = findViewById(R.id.container);
        game = new Game(this);
        container.addView(game);
    }

    @Override
    protected void onResume() {
        super.onResume();
        game.inicia();
        new Thread(game);
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        game.pausa();
    }
}

public class Game extends SurfaceView implements Runnable{

    private boolean isRunning;
    private SurfaceHolder holder = getHolder();
    private Passaro passaro;
    private Canvas canvas;

    public Game(Context context) {
        super(context);
        inicializaElementos();
    }

    private void inicializaElementos() {
        this.passaro = new Passaro();
    }

    @Override
    public void run() {
        while (isRunning){
            if (!holder.getSurface().isValid())continue;
            canvas = holder.lockCanvas();

            passaro.desenhaNo(canvas);

            holder.unlockCanvasAndPost(canvas);
        }
    }

    public void inicia() {
        isRunning = true;
    }

    public void pausa() {
        isRunning = false;
    }
}

public class Passaro {

    private static final float X = 100;
    private static final float raio = 50;
    private static final Paint color = Cores.getCorDoPassaro();
    private float altura;

    public Passaro(){
        altura = 100;
    }

    public void desenhaNo(Canvas canvas) {
        canvas.drawCircle(X,altura,raio,color);
    }
}

public class Cores {
    public static Paint getCorDoPassaro(){
        Paint paint = new Paint();
        paint.setColor(0xFFFF0000);
        return paint;
    }
}