In In re Bridget R. (1996) 41 Cal. App. 4th 1483, the biological parents of twin girls had initially voluntarily relinquished the girls to an adoption agency, but later sought to invalidate the relinquishments on the basis the relinquishments had not been executed in the manner required by the Indian Child Welfare Act (25 U.S.C. 1901 et seq.) The court reasoned: "A biological parent's constitutional rights, like other constitutional rights, may be waived, provided only that the waiver is knowingly and intelligently made, and the counselling which is required by California law before a parent may relinquish a child for adoption has been held to be sufficient to assume that any waiver of parental rights is knowing and intelligent." (Bridget R., at p. 1506.)