There are two kinds of bands visible in these photos: for larger birds, and for hummingbirds. When laid on their backs, the birds become inert. In one photo below, a hummingbird has been laid in a band for a larger bird. The bands used for hummers are barely big enough to fit around a pencil lead. The bottom photo shows a hummingbird sporting his (or her) new band.
(Ana Loves Hummingbirds, part 1)