The case put forward for it to be a genuine vagrant consists of timing and location. Its after breeding season so the birds are moving further afield, at this time of year in Spain their traditional ponds and lakes are drying up.
The bird is a western race, so its range is closer to Britain than other forms of swamp-hen which have been known to escape into the wild from captivity. Also there are other westerns swamphens way out of their range in France at the moment. All of which may makes the Minsmere bird more credible.
Other highlights included Bittern over the reedbeds close to where the Swamphen was loafing and two adult Stone Curlew accompanying a single chick just past the visitor centre on the grassland.