JUST to warn you: this story does not have a happy ending. At least, not yet. It’s about two birds of prey called Marlin and Hoolie and what happened to them when they flew into the sky over Scotland. But it’s also about the human beings looking up at them, sometimes through binoculars, sometimes along the barrel of a gun. Do we need to change what we're doing to protect Scotland’s birds of prey?

But before we get into all of that, we should follow the story of Marlin and Hoolie from the beginning – it's a brief story and a sad one. Marlin and Hoolie were hen harriers, that most distant and beautiful of wild birds. We know for a fact, because they were tagged by the RSPB, that they fledged in 2018 – Marlin in Aberdeenshire, and Hoolie from Easter Ross. Marlin then flew south and spent two winters in Yorkshire while Hoolie crossed the sea to Ireland.

Then, earlier this year, both of the birds returned to Scotland. The chances are they were looking for mates to raise chicks. If you’ve ever been lucky enough to see a male hen harrier in the wild, then you may have seen their mating behaviour. The only way to describe it is sky dancing: swoops, curls, loops and dives to attract a female and scare off other males. You may also have seen the acrobatic mid-air drop the male does when he’s delivering prey to the female.

Who knows if Marlin or Hoolie got that far (hen harriers generally start to nest in April) because we learned last week that Hoolie’s tag stopped transmitting on April 5, a month after his return to Scotland. Three days later, the same happened to Marlin. No trace has been found of the birds since. They’ve disappeared. They are not the first.

Here’s what we know about what happened. Both Hoolie and Marlin disappeared in or close to the Cairngorm National Park. Grant Moir, the chief executive of the park authority, said after the disappearances that the evidence showed hen harriers are persecuted in the park and that it was unacceptable. Ian Thomson, the head of investigations for the RSPB in Scotland, also said the birds had disappeared very close to where other similar incidents had occurred and heightened suspicions that they could be added to the very long list of protected birds of prey killed on grouse moors; the birds disappeared in an area managed for grouse.

The Scottish Gamekeepers’ Association was sceptical, however, and said any suggestion that the hen harriers had been killed as a result of criminal behaviour would not stand up in court. A spokesman for the organisation said they had expelled eight members who had been convicted in recent years of wildlife crime and that they would always take a hard line on the issue. However, they also said that the satellite tagging of birds should be independently monitored and verified.

We shouldn’t be surprised that opinion is divided in this way because the hen harrier is a bird that attracts the most extreme views: some people love it, some hate it, and it is contentious because it eats grouse and a grouse that’s eaten by a hen harrier is a grouse that can’t be shot by someone paying lots of money for the right to do so. An article on Highland sports in The Quarterly Review in 1845 said hawks of all sorts destroy game and “the worst of the family, and the most difficult to be destroyed, is the hen harrier”. The 1958 book Grouse Shooting and Moor Management also describes the hen harrier as a “nasty bird of evil habits … it must be got rid of at all costs”. These attitudes linger: for some, the hen harrier is an interloper that will help itself to your grouse.

The view of the conservationists is quite different. In his beautiful book Raptor, the writer James Macdonald Lockhart describes seeing raptors in Orkney where they are relatively thriving. “These birds will astonish you with their beauty,” he says. “I wish others could see what I saw over Orkney, how the harriers made a ballet of the sky.” The conservationist Mark Avery, who has campaigned for a ban on grouse shooting, feels the same way. “Each day I have seen a hen harrier,” he says, “has been enhanced by the sight of this bird.”

The RSPB’s Ian Thomson shares their feelings, but the beauty is mixed with something blacker. He describes being taken to hen harrier nests in Aberdeenshire as a boy only to arrive and find that the chicks and the nests had been destroyed. “That sickening memory has stuck with me for nearly 40 years,” he says, “and that, plus the stuff we experience these days when we see hen harriers shot and illegally poisoned, motivates me to try to get it stopped.”

I have spoken to Ian about this problem – the persecution of birds and how to stop it – and he’s always been clear about what he sees as the reasons for the problem and the disappearance of hen harriers such as Marlin and Hoolie as well as what needs to be done to stop it happening. He says the vast majority of detected incidents and prosecutions are linked to grouse shooting.

"But what’s really important to stress,” he said in a zoom call, “is that the stuff that’s publicised and found is just a sample and more often than not it’s an unknown proportion of what’s going on. It's only when you start looking at populations, in particular the hen harrier, that you start to get an idea of the levels of persecution taking place.” The shooting industry’s view on that is that yes, there is some persecution but that it’s relatively low and is not sanctioned by the estates and landowners. There is no real debate about the fact that it happens.

To understand what is, and isn’t, going on to solve the problem, we need to look at the detection and enforcement, and what, if anything, needs to change to better protect the hen harrier. What no one’s doing is denying there is a problem because the figures show clearly that there is: the latest hen harrier survey in Scotland reveals a Scottish population of around 460 breeding pairs, which is a fall of 27% over the last 12 years.

So first: detection. The hen harrier frequents remote and deserted locations which makes its killing fairly straightforward. The female is also extremely brave in defending her nest so, if by any chance, the first shots miss her, she will return to the nest to mob the intruder, making her despatch fairly easy. And it all happens a long way away from any policeman or investigator.

The shooting community, on the other hand, say it’s not quite so easy. The lawyers for the Scottish Gamekeepers’ Association, for example, have told me that these days it is actually harder, not easier, to commit wildlife crime. The advance of technology, they say, combined with more information on wildlife crime being accessible to the public mean there’s a greater chance of being seen or caught than ever before. Their view is that the chance to commit wildlife crime is nowhere near as great as it was 20 years ago.

Whoever’s right, no one knows what happened to Hoolie and Marlin, although some recent good news on the subject of detection and enforcement is that the penalties for wildlife crime have been increased: earlier this month, the Scottish Parliament passed the Animals and Wildlife Bill which will increase the maximum penalty for the most serious animal and wildlife crimes to five years imprisonment and an unlimited fine. The question is of course: what does it matter if you increase the penalties without increasing the chances of being caught? Some people in animal protection think Scotland needs to have a specialist environmental police force dedicated to wildlife crime, as they have in other countries.

But there's an even bigger question. If the disappearance of birds of prey is linked to driven grouse shooting, then what do you do about it? Could the rules around driven grouse shooting change so that it can be made more sustainable and safer for the hen harrier and other birds? Or do we need to go further and ban driven grouse shooting altogether?

Mark Avery is one of the public voices calling for a complete ban. Subjugating the land to the interests of one species – red grouse – is unnatural, he says, and, not only that, the management regime to deliver the desired populations of grouse depends on the illegal control of wildlife. “There’s nothing like it anywhere else in UK conservation,” he says in his book Inglorious, “and there’s nothing else quite like it anywhere else in the world. The crimes against the hen harrier are a product of our British history, our British class system and our British politics.”

Ian Thomson of the RSPB agrees with Avery about the nature of driven grouse shooting. “When you look at the bigger issue,” he says, “it’s linked to single species management over vast swathes of our uplands that are focused on producing large numbers of grouse. It's actually grouse ‘farming’ that’s going on in some areas and the management is ruthless. Raptor persecution is a symptom of unsustainable land management.”

However, Thomson does not go as far as Avery in calling for a ban and agrees with the conclusion of the recent Scottish Government report that called for a new licensing system. The report, which was chaired by Professor Alan Werritty of Dundee University, recommend a licensing scheme if there is no “marked improvement” in the ecological sustainability of grouse moor management within five years; Thomson believes the system could be used to require shooting estates to come up with business plans that are dependent on sustainable management. "It's not about stopping grouse shooting,” he says, “it's about having a sensible way forward.”

We do not know yet how the Scottish Government is going to respond to the Werritty review, although it was set up with the express instruction to give due regard to the socioeconomic contribution that grouse shooting makes to Scotland’s rural economy even though there is disagreement about what that might be. The estates say the contribution is vital, particularly in areas where there are low rates of employment; the conservationists on the other hand say the economic value of driven grouse shooting is exaggerated. Meanwhile, the momentum does appear to be building for an end to the status quo.

Exactly what shape that will take is still unclear and the disagreements are going to be hard to resolve because there is so much disagreement about the hen harrier itself. But perhaps we can end by looking up at the bird in the sky. In Latin: Circus cyaneus. In Gaelic: Clamhan luch. In the eyes of the conservationist: a thing of beauty. In the eyes of the keeper on a grouse moor: a menace. As for the bird itself, it doesn’t know anything about any of these man-made names and differences or the division it provokes. Instead, it follows its instinct. It swoops and swirls and loops. It dances in the sky.