How do you transport a lion's head around the world?

Cecil was a major tourist attraction in Zimbabwe's Hwange National Park

When news emerged of the illegal killing of Cecil the lion in Zimbabwe on 1 July, one detail stood out for many online commentators.

Cecil's head and skin were removed, according to the Zimbabwe Conservation Task Force (ZCTF), a local charity.

Walter Palmer, the US dentist who shot the animal, believed the hunt was legal but could still face charges.

The removal of the head of a hunted animal is not unusual - one wildlife charity says 665 lions are killed as trophies in South Africa alone every year.

In the last day, three US airlines - Delta, United and American Airlines - have said they will no longer transport the trophies of big-game animals such as buffalo, elephants, leopards, lions and rhinos.

All of which leads to one question: how can the remains of some of the world's most valuable animals end up being transported on commercial airlines?

Where is Cecil's head now?

Not so fast - that should become more clear later.

Is it illegal to export a trophy animal?

No - as long as it was not killed illegally, as Cecil allegedly was.

Hunting trophy animals is not illegal in many African countries. In Zimbabwe and South Africa, hunting is regulated, and hunters must obtain permits to kill certain animals in certain places.

Erica Kock, of Trophy Service Tannery in Pretoria, said export of trophy animals was tightly controlled in South Africa.

All legal hunters and hunting farms are registered, and anyone wishing to export a trophy animal needs to submit an export application via the taxidermist to the government.

"If we don't produce all the required documentation, we can't export - it's that simple," Ms Kock said.

What are the other restrictions?

The UK and the US, for example, demand import licences on top of export permits issued by the countries where hunting takes place.

In the UK, all applications must be made to the Animal and Plant Health Agency (Apha) - who can still refuse the application.

A spokesman for Apha said licences to import trophies had been issued to 61 people in the year up to 30 July. Only 16 of those have so far been used, the spokesman said.

But if the animal is classed as endangered, extra permission has to be given by the origin country.

Endangered animals such as some tigers and elephants are listed under Appendix One of the Cites (Convention on International Trade in Endangered Species of Wild Fauna and Flora) index.

If it was classed under the Cites index and killed without the permission of the host country, the animal cannot be exported, and will be seized.

African lions such as Cecil, while said by Cites to be vulnerable, are not classified as endangered and therefore not listed under Appendix One.

Who won't transport trophies?

As well as the three airlines who announced a change in rules on Monday, many others have already said they would not carry trophy animals.

A number, including Lufthansa, Emirates, British Airways and Singapore Airlines, have recently introduced bans, many in the wake of a petition launched on the change.org website.

Wildlife experts told the BBC that recent bans in particular are significant, as they block all trophies - not just protected species or those hunted illegally - from being transported.

Who is left?

Mark Jones, a wildlife policy manager with the Born Free Foundation, said the focus had been on trying to persuade "the big American carriers" not to transport trophies - that has now been achieved, he said.

"But trophy hunters can be very determined people," he said. "They will look for other ways to transport their cargo."

The focus now, Mr Jones said, could be on airlines from developing economies, whose citizens he said are taking more of an interest in hunting.

A spokeswoman for China Airlines, that does not fly to Africa, said cargo managers told her they had never been asked or approached to carry trophy animals.

Courier company FedEx said it did not accept animal carcasses for shipment but "may accept legitimate shipments of parts for taxidermy purposes".

A spokesman for UPS said the delivery company avoids "making judgements" on the contents of shipments but all must comply with the law.

Maersk, a shipping company, said it had strict procedures in place to prevent its ships carrying illegal cargo.

And Cargolux, a cargo airline, said it does not carry ivory or any animal products coming under Cites Appendix One. Other airline cargo companies did not reply.

So where is Cecil's head?

Had anyone tried to export Cecil's head, they would not have obtained the necessary licence for it to leave Zimbabwe. Plus, they would have probably been subject to intense scrutiny "given all the furore around this particular case", said Mark Jones, of the Born Free Foundation.

As it turns out, the head and pelt were seized by police when they raided the house of Theo Bronkhorst, a guide who has since been arrested.

The head and pelt were to be sent to South Africa for export to the US, Jonny Rodrigues, the chairman of the Zimbabwe Conservation Task Force, told the BBC.

He said they were hopeful police would return Cecil's head so it could be mounted at the entrance to Hwange National Park as a memorial to the lost lion.