Google Contacts API - Updating Birthdays and Anniversaries

I am trying to update my google contacts using the API. I know through php we can send an UPDATE to the contact by posting a XML file.

I am not 100% sure what the xml is supposed to look like to house the birthday element. This what I currently ha开发者_开发问答ve.

<atom:entry xmlns:atom="http://www.w3.org/2005/Atom" xmlns:gd="http://schemas.google.com/g/2005">
  <gd:name>
    <gd:givenname>John</gd:givenname>
    <gd:familyname>Doe</gd:familyname>
  </gd:name>
  <gd:birthday when="2011-09-09"></gd:birthday>
</atom:entry>

And I have NO Clue as to how to format the Anniversary (event). I can't seem to find any documentation on this online. Any help would be appreciated.

When I pull it from Google Contacts it looks like this:

<gContact:event rel="anniversary">
  <gd:when startTime="1981-10-15"/>
</gContact:event>