jQuery-UI datepicker default date

I have a problem with the jQuery-UI datepicker, I have searched and searched but I didn't find the answer. I have the following code:

<script type="text/javascript">
$(function() {               
    $("#birthdate" ).datepicker({
        changeMonth: true,
        changeYear: true,
        yearRange: '1920:2010',
        dateFormat : 'dd-mm-yy',
        defaultDate: '01-01-1985'
    });
});
</script>

I want that when the user click in the #birthdate input that the current date selected to be 01-01-1985, now it's setting the current date.