Earlier, Derek Parker, in a comment, noted
Community churches in the UUA have a single membership role, a single board, but (as in a UUA/UCC set-up) report membership using one of two methods...
(a) half the membership is reported to the UUA, and dues payed accordingly
(b) members are asked which denomination they want to support with their dues, and so membership is paid accordingly (at Sycamore a small minority vote to pay their share to the UUA, and the majority to the UCC)
I think that's right, but what I intuit from the UCC website is that community and interdenominational churches report their whole membership to the UCC, and it seems a few did to the UUA last year, the forgoing notwithstanding.
A drop of hundreds of members in the UUA can be accounted this way, and I'll see if I can cook up those numbers later, at least for the "missing" UCC part.
Of course, why the "lack of brand loyalty" to the UUA, or the greater loyality to the UCC. Are their dues lower? Or, as I suspect, do they provide the services (meaning principly, can they settle a minister) over the long haul.
The UCC -- and the rest -- being larger, can be more local, and will usually beat out a Unitarian Universalist ministerial candidate. (I think there are some calendar issues, too.)
Indeed, my new minister, Adam Tierney-Eliot is one of the few Unitarian Universalist (Christian) ministers to serve one of these jointly-affiliated congregations.
Perhaps the Christian ministers in the UUA need to put pressure on the Settlement Office to make sure we're given every chance of serving these blended congregations. It would certainly make staying with the UUA easier.
After all, "do they provide the services (meaning principly, can they settle a minister) over the long haul" can mean a minister's relationship to a denomination, too.