Stone the crows

Everything eats something. And when something is cute, vegetarian, or eats creepy crawlies, it’s fine. If it tweets, chirps, and socialises as a charm, a covey, a richness, a trembling, or a pitying, it’s fine.

But when it caws, cronks, squawks, or croaks, and when it hangs out in murders, wakes, parliaments, hordes, mobs, screeches, scolds, mischiefs, clamours, and unkindnesses, it’s better dead than red in tooth and claw. And it’s invariably the antagonist in the avian chapter of our epic saga of the decline and fall of nature on our scepter’d isle.

We are supposedly a nation of animal lovers. But the growing frequency of headlines that scream about the huge and long term loss of biodiversity, and the drastic and wide ranging falls in the populations of many species does, however, contradict our national sense of self righteousness when it comes to nature. You see, we are selective. We croon over the benign, and boo and hiss the villain red in tooth and claw. Quite simply, we root for the underdog and shoot the top dog.

When it comes to birds, we don’t even need an identity parade – we already know who the suspects are… It’s the raptors and, of course, the infamous Crows Gang: Carrion, Raven, and Magpie. Especially Magpie. After all, sorrow comes with every one.

The charge against the accused was lodged in full in the Country pullout of our local paper around the end of May, but then I inadvertently lost it to the council recycling team. But the first witness for the prosecution gave their statement just a week later and was caught in time to capture for posterity…

So these species are clearly out of control. They are implicated as prime offenders responsible for the decline of song birds, farmland birds, and waders from our increasingly manicured and highly managed green and pleasant, deforested, de-wetted, and often monocultural land. Not that i’m subliminally trying to convince you so early in the article that there might be other causes.

The recent legal challenges by Wild Justice to the way that Defra and Natural England had been running an unlawful licensing regime for the control of certain predatory species of birds reminded us that there are armed vigilantes out there effectively acting on circumstantial evidence alone and lynching the suspects without a fair trial. But although some are simply worried about an urban misunderstanding ultimately curtailing their fun, many of these people are acting with the best intents and are genuinely concerned about the decline of songbirds and moorland birds. And of course there are plenty of others, perhaps like Angry From Wherever who, on the face it, potentially align their views with the loudest rural voices and base their understanding of the issues on the premise of who said what about what to whom. And then he said.. And then she said… 

I’m rural born and bred having grown up in, and still live in, farming communities. My relatives were farmers. I worked on farms from time to time as a teenager; mainly with cows, sheep, and cauliflowers. I know how firmly rooted traditional views can be when it comes to predation and the perceived need to control it by lethal force. But I’m also originally trained in a science. Yes, Geography is a science – I have 2 qualifications ending in “Sc.”. So I’m a scientist. Indeed, a fully operational Master. Now Geography’s real value is in providing a framework for organising and relating knowledge from a range of fields. Surely worthy of a capital letter. Geography puts our understanding of natural sciences, physical processes, societies, and economies within the context of place and time and helps us organise, communicate, and understand our world. Ooh, that’s good. I think that may appear in many of my articles!

Science is all about building up knowledge that is based on observation and data, and which produces explanations and predictions that can be tested and re-tested systematically by others. Science lacks emotion. It doesn’t, or shouldn’t, really take an opinion or a view that cannot be supported without facts. And there are no such things as alternative facts. There are emotional and passionate scientists, of course. They are usually human, after all, and have normally taken a path that reflects their personal interests and passions.

Now Wild Justice is not specifically seeking to stop predator control through lethal means, but rather to stop the casual and uncontrolled killing of so-called “pest” species, including the names topping Britain’s Most Wanted, the Crows Gang.

In trying to explain the rationale behind their challenges to a public and media that seems uniquely able to block both ears whilst simultaneously humming loudly and keeping a finger on a trigger, they point out that numerous studies have generally and consistently concluded that there is no evidence-based scientific justification for the rampant killing of our infamous gang of corvid hoodlums for the purpose of conserving other wild birds.  The data collected by decades of research does not show or support any link between the populations of the predatory species and the declining populations of those that are predated.

So is the shooting down of fugitive carrion crows a classic example of a miscarriage of justice? Have we hanged the wrong magpie in a classic case of mistaken identity?

There is plenty of data, and so no doubts, that show there have been rising populations of many predator species, especially raptors and also, to some extent, members of our syndicated Crows Gang over recent decades. However, these rises are considered to be less about over-population and more about the recovery of populations in the decades since we banned some of our least delightful, but sadly most effective, pesticides. Which both directly targeted and indirectly affected a range of species.

Time to consider population dynamics…

Now, it’s a big subject and here I really do run the risk of jumping headfirst into a deep end in which I will struggle to swim and could even hit my head on the hard floor. Beyond basic regression analysis, my statistical methods days are long behind me. But if I delve back into my dim and distant past and, more specifically, my undergraduate studies in biogeography, I know that populations of predators and of prey species generally align over time. They are dynamic with a tendency towards being cyclical with predator populations peaking sometime after those of prey species. The population size of predators is limited by, amongst other things, food availability and breeding habitat availability. If prey species do well, perhaps because of an abundance of food, of habitat cover, and of availability of breeding territories, then their numbers may increase. In response, predator numbers may also follow with increases – after all, their food has just grown in abundance! And plenty of food means that breeding territories can be smaller and, so, there can be more of them.

But there comes a point at which the populations of the prey species are limited in some way from growing any further, perhaps because there is eventually a lack of breeding territories. The knock-on effect is that this then limits the predator populations because their food (our cute and chirpy prey species) is no longer growing in abundance. Which means that the predators too have reached a limit both in terms of food and, consequently, have also probably run out of space for breeding territories. The lag in the population growth of the predators as they head towards their habitat’s “carrying capacity” then starts to impact the now-stable and limited populations of the prey species. Which then declines due to over-predation. And this decline means a reduction in the availability of food for predators, which in turn becomes a limiting factor to the predator population. Which adjusts accordingly.

Are you still with me?

As a geographer, my visual interpretive abilities far outweigh my mathematical and statistical prowess, so i’ll use a picture to help you visualise what I mean and what is more fully explained by Lotka–Volterra equations, also known as the predator–prey equations (a dive into which I am not prepared to take, you’ll be relieved to learn):

So that’s a very, very simple view of how populations of predators and prey species tend to reflect each other, albeit with a time lag, and tend to become limited from exponential growth, falling as they often do into a cycling pattern. In extreme cases, this is a “boom and bust” cycle.

Now this is not to say that there aren’t times and places where predators have a far greater impact on prey species. The boom part of the predators’ population cycle can, and does sometimes, have a disastrous impact on the prey species before the limiting factors come into play.

After reading and getting thoroughly annoyed at the aforementioned and fairly sensationalist article in the paper, resulting in the subsequent follow-up letter a week later from Angry From Wherever, I decided to delve into the scientific paper that the original article was quoting, or perhaps misquoting. Because science, and the raw fuel of science, data, is what should be informing us, and journalists should be articulating it to us properly.

The science in this case, although funded by a charity with, as some commentators might allude to, a greater sympathy for specific groups of species (prey) than others (predators), was undertaken by a university led research team. This team actually found that individuals within a population of a predatory species such as our dandy ringleader, Pica the Magpie, can differ greatly in how likely they predate other bird species compared to others within their own predator population. 

The researchers found, through observations and the data collected and analysed, that there was little evidence supporting a general link between rising numbers of members the Crows Gang and declines in their feathered and shelled snacks. But the data did show that where there are some particularly thuggish individuals in the Gang that have developed a tendency towards more targeted and persistent predatory behaviours, some disproportionate impacts on prey species than would otherwise generally be expected did occur. It found that where such individuals are, er, “removed” from a habitat where they are having a disproportionate impact, this might help vulnerable populations of prey species avoid an overall significant decline. But as with many of the studies into predator-prey relationships and population dynamics, that particular study generally found little evidence of any real link between an increasing populations of the Crow Gang and a subsequent decline in the populations of prey species, specifically songbirds.

So although the science, conducted by scientists, in a science department at a university, and using data collected, processed, analysed, and interpreted using scientific methods, was presented in the newspaper under a pessimistic headline bemoaning how our songbirds are being ever more decimated by the ravenous horde, the science again had actually suggested differently. 

So why are populations of some songbirds, farmland birds, and waders continuing to show long term declines?

Food. Shelter. And the decline in the availability of both. 

Which is a longer way of saying “habitat loss”.

And as we know, species populations are limited by the abundance, or lack of, both food and shelter.

Hedges get cut. Scrub and trees get removed. Pesticides remove insects. Monocultures of arable crops reduce the variety of foods. Native flowers and grasses are replaced with more silage-friendly species. Silage is cut earlier than hay traditionally was. And it’s rolled before it’s cut. Meadows are grazed and compacted to fine lawns and sterilised of flowers and shrubs. Dead wood is removed. Verges are cut. Slurry poisons the water courses with excessive amounts of nitrates and phosphates. Moors are burnt to favour specific vegetation in order to encourage unnaturally high populations of some species over others. And if there is a reduction in the management of an ecosystem, be it from a decline, a loss, or a change in natural or human stewardship, natural succession may, at least in the short term, reduce habitat variety and cover, perhaps favouring a short term boom in predator populations. I could go on.

Any bird is more likely to be weakened, ill, or even starve without enough food. Food comes from the habitat. Which is in long term decline. And when the prey species also declines in response to these diminishing resources, the lower population size in turn becomes increasingly impacted by the effects of that other limiting factor, predation.

With less cover and less food, predators can more easily spot their lunch, especially if it’s a ground nesting bird or a conveniently fast-food takeaway in the form of that bird’s eggs. And less cover means fewer nesting sites. Which might also force prey species to nest closer to the breeding territories of their enemies, which because they are breeding, need to find food for many more hungry mouths.

So, as the science continues to demonstrate with real data over and over again, the decline of many bird species is far more strongly linked to habitat loss that comes with the intensive agricultural uses of our land and other development activities, rather than the inexorable and uncontrolled rise of the Crow Gang.

Conversely, habitat creation creates cover and food. Which in turn support healthy populations of prey species which are far less vulnerable to being predated. And directly removing or fooling (by cunning stunts such as diversionary feeding) delinquent individuals from a predator population probably does help.

But cleansing the fields and moors of Pica and his mates? Surely that’s just identifying a fall guy to take the rap as we continue to intensify agriculture, clean and tidy and develop the land, and generally deflect the blame from our ongoing crimes of habitat destruction.

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