);
        g.append(innerFire);

        fglayer.append(g);

        return g;
      }

      for(let i = 0; i < 10; i++) {
        randomBirds(i);
      }

      const [speedupBtn, slowdownBtn, pauseBtn, playBtn]
        = ['Speed up', 'Slow down', 'Pause', 'Play'].map((type, i) => {
          const button = new Button(type);

          button.attr({
            anchor: [0.5, 0.5],
            pos: [1300, 400 + 150 * i],
            size: [170, 50],
            font: '36px Arial',
            lineHeight: 5