I just used and tested it using Try It. I tested it with all of the different scopes.
https://www.googleapis.com/auth/plus.login Know your basic profile
info and list of people in your circles.
https://www.googleapis.com/auth/plus.me Know who you are on Google
https://www.googleapis.com/auth/userinfo.email View your email address
https://www.googleapis.com/auth/userinfo.profile View basic
information about your account
It doesn't appear to matter you get back the birthday in all of the scopes. But what does matter is that the Users Birthday must be set to public
in the Account. If it's set to anything else, your circles, only you, it's not listed. This appears to be true even when you are trying to see your own information. (Sending Me.)
Update and the year is 2018
The People api now returns the birthday of the current user
People.get However i suspect its linked to google+ so if the user hasn't filled it out you probably wont get info.
GET https://people.googleapis.com/v1/{resourceName=people/*}
Send Resournce name of people/me
and birthdays personFields
{
"resourceName": "people/117200475532672775346",
"etag": "%EgQBBzcuGgwBAgMEBQYHCAkKCwwiDDQwaGhWYzc3cXJBPQ==",
"birthdays": [
{
"metadata": {
"primary": true,
"source": {
"type": "PROFILE",
"id": "117200475532672775346"
}
},
"date": {
"month": 1,
"day": 6
}
},
{
"metadata": {
"source": {
"type": "ACCOUNT",
"id": "117200475532672775346"
}
},
"date": {
"year": 1971,
"month": 1,
"day": 6
}
}
]