European animal rescue charities are appealing for the release of a vulture called Nelson that has been captured by a militia in Yemen, stands accused of being a spy and is being held hostage amid the country’s civil war.

Nelson, a Bulgarian griffon, was tagged as part of an attempt by a wildlife protection group to reintroduce the species into the wild in its original homeland. The breed lives in large numbers in Spain but is threatened elsewhere in Europe.

However, on his annual migration south from Bulgaria, he appears to have become separated from other vultures and come to ground exhausted near Yemen’s third city, Taiz.

The pro-government force that runs Taiz and has defended it from the Iranian-backed Houthi rebels decided that the