function birdMove() {
  //var pos = Math.random() * 300 + 280;
  var pos = Math.random() * 580;
  $('#bird_head').animate({left: pos}, 500);
  $('#bird_leg').animate({left: pos}, 500);
}

function initRollOverImages() {
  var image_cache = new Object();
  $("img.swap").each(function(i) {
    var imgsrc = this.src;
    var dot = this.src.lastIndexOf('.');
    var imgsrc_on = this.src.substr(0, dot) + '_on' + this.src.substr(dot, 4);
    image_cache[this.src] = new Image();
    image_cache[this.src].src = imgsrc_on;
    $(this).hover(
      function() { this.src = imgsrc_on; },
      function() { this.src = imgsrc; });
  });
}