How to give validation inside the gridview controls?

<tr>
 <asp:GridView ID="gvWH" runat="server" BorderColor="#BDBDBD" ShowFooter="True"
 CssClass="center" OnRowDataBound="gvWH_RowDataBound"
 GridLines="Horizontal" OnRowDeleting="gvWH_RowDeleting"
AutoGenerateColumns="False">
   <EmptyDataTemplate>
       No Records found
   </EmptyDataTemplate>
        <Columns>
            <asp:TemplateField HeaderText="Type">
                <HeaderStyle HorizontalAlign="Center" />
                     <ItemTemplate>
                     <asp:DropDownList ID="ddlbirdtype" runat="server"
                         AutoPostBack="true">
                      </asp:DropDownList>
                <asp:RequiredFieldValidator ID="RFVbirdtype" runat="server"
                      ControlToValidate="ddlbirdtype"
                  ValidationGroup="GridView1" InitialValue="0" Display="None"
                 ErrorMessage="Please select Bird Type"></asp:RequiredFieldValidator>
              <asp:ValidatorCalloutExtender ID="VCEbirdtype" runat="Server"
              TargetControlID="RFVbirdtype" EnableViewState="false" />
                </ItemTemplate>
            </asp:TemplateField>

            <asp:TemplateField HeaderText="Weight">
           <HeaderStyle HorizontalAlign="Center" />
             <FooterStyle HorizontalAlign="Right" />
               <FooterTemplate>
            <asp:Button ID="BtnAdd" runat="server" Text="Add" OnClick="BtnAdd_Click"
             ValidationGroup="GridView1" CausesValidation="true" />
                </FooterTemplate>
              <ItemStyle Width="100px" />
              </asp:TemplateField>
               <asp:CommandField ShowDeleteButton="True" />
        </Columns>
      </asp:GridView>
  </tr>
  <tr>
     <td align="center">
   <asp:Button ID="btnsave" runat="server" Text="Save" OnClick="btnSave_Click" OnClientClick="return validations1();" ValidationGroup="GridView1" CausesValidation="true"
     Style="height: 26px" />
     </td>
  </tr>