Web Forms :: Getting Values Of Month In A Control?

<form id="form1" runat="server">
<input type="hidden" id="hdnDay" runat="server" />
<asp:DropDownList ID="ddlMonth" runat="server" onchange="populateDatesForMonth(this.value);">
<asp:ListItem Text="Jan" Value="1"></asp:ListItem>
<asp:ListItem Text="Feb" Value="2"></asp:ListItem>
<asp:ListItem Text="Mar" Value="3"></asp:ListItem>
<asp:ListItem Text="Apr" Value="4"></asp:ListItem>
<asp:ListItem Text="May" Value="5"></asp:ListItem>
<asp:ListItem Text="Jun" Value="6"></asp:ListItem>
<asp:ListItem Text="July" Value="7"></asp:ListItem>
<asp:ListItem Text="Aug" Value="8"></asp:ListItem>
<asp:ListItem Text="Sep" Value="9"></asp:ListItem>
<asp:ListItem Text="Oct" Value="10"></asp:ListItem>
<asp:ListItem Text="Nov" Value="11"></asp:ListItem>
<asp:ListItem Text="Dec" Value="12"></asp:ListItem>
</asp:DropDownList>
<asp:DropDownList ID="ddlDay" runat="server" onchange="setDay(this.value);">
</asp:DropDownList>
</form>

when i chnage the month or slecte th emonth i need to get the value in a cariable or a hiiden field