Silvereye huddling and mutual grooming

[Commoncopper]

Hi, I've observed silvereyes huddling and mutually grooming each other several times now.
Does anyone know about this behaviour? I'm interested in the relationship of the pair eg whether they're likely to be siblings etc. Does the temperature affect the likelihood of huddling? Do other birds exhibit this behaviour?
I assumed initially that the eye closing of the bird being groomed indicated relaxation and pleasure. This may be partly true. But the grooming can be quite aggressive and, as in the photo below, the closed eye is likely to be also for protection.
Thanks

[Jan]

Since you haven't had anyone reply yet, this is what I've observed over several years.
They are probably mated pairs, as it mostly occurs late in the winter when they are getting ready to nest. Here in Chch they nest fairly late in spring, maybe when insects are more abundant. I feed sugarwater when it's very cold and observe them mutually preening when perched in pairs on the nearby twigs and branches. I guess they remove mites and other parasites from each other.
You could look to see if there are differences in plumage between the 2 birds. Some people reckon the males have brighter russet colours, but I can't decipher that.

[Neil Fitzgerald]

Like Jan, I see allopreening like that a lot in late winter and had also assumed it is part of pre-breeding but have nothing to back that up. It's very cute.