function toggleDiv( DIV ){
	var tDiv = document.getElementById( DIV );
    if(tDiv.style.display == "none"){
    	tDiv.style.display = "block";
    } else {
    	tDiv.style.display = "none";
    }
}

function init () {
    if ( document.getElementById("bird") ) {
        var bird = document.getElementById("bird");
        bird.onmouseover = function () {
           toggleDiv("bubble_default");
           toggleDiv("bubble_mm");
        }
        bird.onmouseout = function () {
           toggleDiv("bubble_default");
           toggleDiv("bubble_mm");
        }
    }
}

addLoadListener(init);