$(document).ready(function() {

    $("#countrydropdown").bind("change", selectCountry);

    function selectCountry(e) {

        var country = $("#countrydropdown option:selected").attr("value");
        if (country == "Mexico") {
            $("#selectZip").hide();
        } else if (country == "Canada") {
            $("#selectZip").hide();
        } else {
            $("#selectZip").show();
        }
    }

    $("#countrydropdown").change();

}
);