The raven cull – a dangerous syllogism

Syllogism: a deductive scheme of a formal argument consisting of a major and a minor premise and a conclusion (as in “every virtue is laudable; kindness is a virtue; therefore kindness is laudable”)

Sounds logical right?

But here’s how it can go wrong:

“Something must be done; this is something; therefore we must do this.”

And sadly this appears to be exactly how Scottish Natural Heritage (SNH) has got itself in a tangle with their misguided (and comprehensively criticised) authorisation of a raven cull in Perthshire.

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The problem in this instance is the decline in some of our native wader species. This is a significant problem and something must indeed be done. For example, the UK may hold 25% of the global breeding population of Eurasian curlews but numbers are declining rapidly. In recent years the curlew has has good reason to sound so melodiously melancholy, sounding its once familiar fluting call over fewer and fewer of its former haunts. Between 1995 and 2011 alone, curlews suffered a 45% decline in breeding abundance across the UK. In Ireland breeding curlew populations have declined by over 90% in the past 40 years.

And so, the fact that curlews are in trouble is clear. That ravens are to blame however is very far from being equally clear.

Indeed, the scientific consensus is that a host of factors have contributed to the curlew’s decline, amongst them commercial afforestation of marginal hill land, changes in farming practice reducing habitat quality (e.g. cutting reeds in pasture land in Spring when curlews are nesting) and climate change (this year’s remarkable hot weather will have done the bog-loving curlew no good at all).

It is also true that there is clear evidence that predation by generalist predators such as crows and foxes have contributed to curlew declines, most significantly through nest predation.

So why the outcry about the raven cull?

Firstly it does not appear to be science-led. We know from Fletcher et al. (2010) that curlews (and golden plover, and red grouse) are more abundant on keepered moorland where predator control is executed, but this study did not explicitly examine the impact of ravens. When Amar et al. (2010) did explicitly investigate the associations between wading birds and ravens in the uplands, they concluded that:

“Our study found no significant negative associations between raven abundance and population changes in upland waders, and so does not provide support to justify granting of licences for the lethal control of ravens in the interest of population-level conservation of these upland wader species.”

SNH appear to have ignored this scientific analysis in favour of the anecdotal stories of a group with vested interests in predator control, giving the green light to the Perthshire raven cull simply “to see what happens.” Ravens are worshipped in some cultures, but they have long been the target of ire from sheep farmers (who claim the birds attack their lambs) and gamekeepers (concerned about raven predation reducing the shootable numbers of their carefully managed red grouse). Strikingly the majority of the cull area extends across several grouse moors, leading many to question the true motives of this “experimental” cull.

This is not good science and it sets a dangerous precedent.

Is the raven simply another victim of our own complex prejudices?

Ravenous: very eager or greedy for food. Synonyms: voracious, insatiable, ravening, wolfish.

Furthermore, what conclusion will we safely be able to draw if, after the raven cull is carried out, curlew numbers do increase? There has been no detail released about experimental design and it appears that there are no scientific controls set up. Any observed uptick future in curlew numbers might therefore be a result of their release from raven predation, or it might be that some other variable has changed – perhaps an increased effort in predation control generally or perhaps simply a change in the weather! The Countryside Alliance has thrown its support behind SNH, praising them for prioritising science over emotion“, but the Countryside Alliance have never had a strong grasp of science, appearing instead to be caught up in emotional vilification themselves.

Others have criticised the anti-cull campaigners for their selective support of the raven, using “whataboutism” to decry an apparent lack of interest in culls of other “pests” such as rats (another intelligent species which might be imagined to garner more public sympathy). But this argument is flawed. Rats have not been absent for centuries from much of the UK, as have ravens. Rats have not recently recovered so much of their native range, as have ravens, returning to much of lowland England and Scotland after centuries of absence, a return attributed to a combination of decreased persecution (at least until now) and an increase in sheep carrion. To threaten that recovery so soon after it is achieved seems to many to be reckless as well as misguided.

And this brings us to another important point. Conservationists increasingly agree that lethal control is a poor management tool. When it is delivered piecemeal it can be disruptive to predator populations with the result that surviving predators actually cause more harm (splintered wolf packs may have killed more livestock than intact packs prior to limited culls in America) and thus lethal control is likely only effective if predators are virtually eliminated over wide areas.

This is what happens on grouse moors where a suite of predators are ruthlessly removed, but is this the management model we want across our countryside, in our areas of outstanding natural beauty and throughout our national parks? Are we prepared to persecute ravens so heavily?

Instead conservationists are increasingly promoting the exploration of non-lethal methods of control, resorting to lethal control only as a last resort.

And remember, we don’t yet even have any scientific evidence that ravens are limiting curlew numbers in the first place! In Iceland there are estimated to be about 2,500 nesting pairs of ravens with other non-breeding birds occurring in large flocks up to one hundred strong, and yet Iceland also supports some of the greatest wader populations in the world. Even within Scotland, Orkney supports large numbers of ravens and an exceptionally high density of curlews.

So here’s a suggestion for SNH. Set up a proper scientific trial to explore a variety of management options related to raven abundance and curlew breeding success, but also to habitat management and farming practices.

Amongst those options, priority should be given to testing the effect of experimental removal of sheep carrion from the hill. If sheep carrion is supporting inflated numbers of generalist predators and scavengers including foxes and crows, then wader predation is a problem of our own making. Additionally, if upland forestry plantations are providing a refuge for foxes, should we not explore the possibility of fencing them in, especially when they are adjacent to critical wader breeding areas, much as we fence deer out?

In the meantime, the pointless Perthshire cull continues, but a crowdfunded legal challenge is underway. Watch this space!

 

 

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