Songbird Science

Songbirds and science

The following blog is based partly on the witness statement from Wild Justice (passages in red) which was part of the claim issued to the court on 21 March (and emailed to Natural England although they will not have had a formal sealed document for some time after that due to court delays, but they had this in their email inboxes). The passages not shown in red were not part of the Wild Justice witness statement.

Carrion Crow. Photo: Tim Melling

The scientific evidence from large-scale and exhaustive studies does not support the idea that Magpies, Jackdaws, Jays or Carrion Crows have an impact on songbird numbers. For example the scientific non-governmental organization the British Trust for Ornithology states on its website about Magpies (my emphasis);

For many people the Magpie is a villain, responsible for the widespread decline of songbirds. Research examining the question of whether Magpies have been responsible for songbird decline has failed to find any evidence to support the notion that they are to blame. It is true that while Magpie numbers have tended to increase, those of many of our songbird species have declined. These increases and decreases have occurred over different time periods and in different parts of the country, which suggests that the general patterns are a coincidence and not cause-and-effect.

… and about Carrion Crows;

Carrion Crows are opportunist feeders and have a wide and varied diet. Because they may take gamebird eggs and chicks they have been targeted by gamekeepers. Similarly, sheep farmers sometimes control thse (sic) crows because of the perception that they kill young lambs. However, insects and other invertebrates are the main prey in summer, with carrion and other scavenged food an important addition during the breeding season. Grain becomes important in the autumn and winter. The predation of eggs and young chicks tends to be highly seasonal, with the crows seeking to satisfy the needs of their own growing brood. Since these crows only produce a single brood of chicks each year, their impact as predators is restricted.

… and about Jays;

The Jay’s diet is actually more varied than this. Carrion is readily eaten and road casualties may be taken where a road runs through woodland. In the summer, the eggs and young of other birds may be taken as a source of high protein nourishment for their own chicks.

… and about Jackdaws, nothing at all about any suspicion that they are a cause of songbird decline . 

This is hardly surprising since BTO studies of long-term and voluminous datasets have not unearthed evidence for Carrion Crows, Jays, Magpies or Jackdaws having any impact whatsoever on songbird numbers. A significant paper was published in March 2010 by BTO scientists and co-workers from academic institutions (see here for layperson’s summary ) where the authors state;

In the biggest ever analysis of songbirds and their predators, published today in the Journal of Applied Ecology, scientists look at the role of predators in the decline of species such as Bullfinch and Yellowhammer. Whilst a small number of associations may suggest significant negative effects between predator and prey species, for the majority of the songbird species examined there is no evidence that increases in common avian predators or Grey Squirrels are associated with large-scale population declines.’ and also ‘There were a large number of positive associations between predators and prey, suggesting that predator numbers have largely increased as the amount of prey has increased. This is particularly the case for native avian nest predators (Great Spotted Woodpecker, Magpie, Jay and Carrion Crow). Although this largely exonerates these predators, as driving declines in the numbers of songbird species at a national level, it does not preclude individual predators having local effects.

The mass casual killing of such species as Jay, Carrion Crow and Magpie previously tolerated under the General Licences (now withdrawn after Wild Justice’s legal challenge – ‘ Marian Spain, interim CEO of Natural England, ‘the licences were unlawful’) does not appear to have any scientific basis in being useful for populations of songbirds.

In contrast there is evidence that some ground-nesting birds such as Grey Partridge and breeding waders can be more seriously affected by predation by Carrion Crows – though not to my knowledge by predation by Magpies, Jackdaws or Jays.

No doubt Natural England is carefully considering these matters when it comes to replacing the General Licences and no doubt the Chief Executive of the BTO, Andy Clements, who is also a Natural England Board member and Chair of the Natural England Scientific Advisory Committee, has been pointing out these studies, if Teresa Dent of the GWCT, also a Board member of Natural England, did not get there first with this science.

Jay. Photo: Tim Melling

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46 Replies to “Songbird Science”

  1. The soothing voice of reason. Hopefully, some members of Songbird Survival, many of whom were easily marked out with their hysterical comments relating to the General Licence challenge, will do a bit more 'homework' on their subject.

  2. In each and every case, these species have lived alongside each other for a very, very long as predator and prey. The balance will (and always has) shifted one way then the other. If there is a long-term and serious decline in any 'prey' species but not a corresponding long-term serious increase in 'predator' species, then the reason(s) for the decline lie elsewhere. Killing predators is not the answer, but can only be short-term mitigation. This is why I object to Curlew Country's policy of killing foxes and crows.

    1. Where I live we have zero foxes and guess what - loads of curlews and ground nesters, loads of hen harriers (nearly as many breeding pairs on 8.5K ha as the whole of England). Uncontrolled fox numbers are not good news for these species - SIMPLES.

        1. Coll. And I do appreciate that fox control is not part of the general licence coverage but I was responding to Andy's thread "This is why I object to Curlew Country's policy of killing foxes and crows." General licences have nonetheless proved to be a very useful, effective and much less money and time consuming (departmental wages and farmer's paperwork) answer to the need for control of species such as crows and woodpigeon than farm to farm, field to field specific licences which take forever to administer to no additional advantage. There is an old saying - if it isn't broke don't fix it. Now I could fully understand the objection to any species being on a general licence if it were even remotely in trouble numbers wise. If there were a dearth of crows or woodpigeons then the licences should have to be made more specific to the problem/damage caused to each individual farmer but where is the dearth of crows and woodpigeons? Answer me that please.

          1. Peter - you're telling us all what you would like the law to be - but it ain't so. You can either break the law and suffer the consequences, stick to the law and/or try to change the law. Welcome to the campaigning world. Anyway, NE are now changing things a lot; read this

          2. Thanks for your welcome to the 'campaigning world' Mark. You seem a little blunt in your manner of reply but perhaps that is what the 'campaigning world' has done to you. I am not opposed to any scientifically based, evidence led reassessment of 'pest' species and their category of threat - some of these rethinks should probably have been done years ago - but I am opposed to trouble making for it's own sake and I rather think there is more than a small degree of personal slighting between you and NE. Anything to do with your failure to get them onside in other of your campaigns?

          3. Peter - better not come on here trouble-making for its own sake then...I'll keep an eye on you.

          4. Thanks Mark, I daresay that's exactly what an opportunist carrion crow says to a ewe that's stuck on her back with a spine to spine delivery. I'll keep an eye out for you. Both most likely. Very reassuring and not the slightest bit threatening eh?.

          5. Peter - it would be good if the farmer were keeping an eye open for that ewe...I think that's what is supposed to happen. And I've done a small amount of shepherding in the past.

        2. Agreed Mark, and as a shepherd yourself you'll know that farmers are hard working and stretched and like the rest of us non deities only capable of being in one place at one time. There are some sad and thankfully rare exceptions but all of the farmers I know, and that is plenty, are passionate about the welfare of their reared stock, their breeding lines, the quality of their produce and they care very deeply about the future of what they do to make a living. The old crow has his living to make too but there has to be some balance and a certain amount of priority given to legitimate farming practices and general licences are part of this and will continue to be so , albeit now in a modified form. If it is anything to you I cannot understand the shooting of rooks, jays and other comparatively harmless, indeed beneficial species so some good may well have come of your success. My qualified congratulations in that respect.

          1. Peter - I'd say many rather than all but you may have a very skewed sample of farmers for all I know. Or perhaps a very small sample size?

            Yep, it is difficul;t to see why anyone needs to kill a Jay.

  3. Mark, Looking at the pedigree of the Natural England Board on paper. How come they have not realised or spoke/ done something about the legality of the General Licences over the years. Are they fit for purpose?

  4. I have noted that the Wildlife and Countryside Act in Scotland is markedly different from that elsewhere. The licence conditions are different as well. An example for conservation of wild birds as follows: "GL 01/2019: To kill or take certain birds for the conservation of wild birds General Licences allow authorised people to carry out activities that would otherwise be illegal under the Wildlife & Countryside Act 1981 (as amended). They cover situations where we accept that there may be no other satisfactory solution. However, they should only be used as a last resort. Operators must be able to explain what other alternatives they have tried if challenged."
    SNH has accepted in the General licence that there may be no other satisfactory solution to protecting say songbirds provided that this killing birds that they don't like explain the alternatives they have tried.
    I don't like this but it is markedly different to the case in England.

  5. I recall reading a paper from The Netherlands a few years ago which looked at predation on ground-nesting birds ( waders, ducks, larks) using sophisticated combinations of nest temperature loggers and video surveillance. This seemed to indicate that the bulk of ground nest predation took place at night, predominantly by foxes, rats, hedgehogs and mustelids. The perception had been that Crows were the principal nest predator, but the evidence from this study suggested that it was of a lower order of significance. Throughout my experience as birder, ringer, warden and part-time keeper and ecologist I have always maintained that Brown rats are by far the most significant nest predator of a very wide range of bird species taking eggs, chicks and even adults. On the Calf of Man I even witnessed Rats predating Magpie chicks!! Of course, Crows and Pies are very visible, rats much less so...….!

  6. Norman
    Similar data here from another source

    Nest‐temperature loggers deployed at seven sites indicated that 88% of nest predations occurred during darkness, suggesting nocturnal mammalian predators

    At seven sites predator control had no overall effect on chick survival, monitored by radio‐tracking 459 chicks, but there were differences in the effect of predator control among sites. Densities of predators were low during years without predator control measures at the majority of these sites.

    Worth a look.

    Now my Rat rant ; some years, when my neighbour finally ploughs in his shredded maze game cover along our hedge line it is still fairly full of all cobs. The woods and field around my property are inundated with dozy starving rats, scratching at dandelion roots to get some nourishment, climbing trees and generally wandering about in broad daylight.
    One year I saw one of these rats that did reached our house attacking a feisty Partridge on her nest under the garden. hedge.

  7. Let's not forget that Crows also predate Magpie nests. That fact alone is enough to cause these nitwits to spin round in their own skins! In addition to this blog, the RSPB are on the receiving end of some hilariously stupid comments on FB; many from those who claim to be land "managers" of one sort or another. These positions seem to be the only ones where a complete lack of understanding of relevant issues is seen as a desirable qualification.

  8. So only 12% of nest predation could be down to corvids, that is probably unlikely to affect the overall productivity or long term survival of prey or predator. Then chick survival is NOT affected by predator control. So all those cries of anguish from the likes of Amanda Anderson (MA) or Tom Orde-Powlett ( Castle Bolton Estate) on the TV that the loss of current general licences will result in the EXTINCTION of Curlew Lapwing and Black Grouse to corvid predation was just that--- hysterical nonsense. Then for years if you look at it carefully GWCT research has showed predator control made no significant difference to Black Grouse productivity whatever else is claimed.
    I find it hard to believe that NE can justify a general licence to kill any corvids for preservation of native flora and fauna. It will be interesting to scrutinize any wording of any such licence, it certainly must be different to that which has just be withdrawn.

  9. While we all debate the extent of predation on prey species I feel that not enough attention is being paid to habitat restoration or improvement as a way of restoring more stable food chains to our countryside. Intensive agriculture on low ground and "managed" heather on grouse moors plus huge swathes of sheep cropped hills with the odd patch of native woodland is not a recipe for a stable environment where predation does not adversely affect prey populations.....but that wrecked countryside suits the game shooting industry with its boom and bust economics, huge artificial populations of released or corralled pheasants and red grouse - where the killing of all predators is built into their systems. ...

    1. Aye it's habitat management that's being sidelined by the shooting lot, far more so than predator control is by the real conservation movement. When it was pointed out that capercaillie and black grouse ncreased at Strathspey just with habitat management and no predator control the researcher who announced it got dogs abuse on social media. That wasn't helped when he claimed that returning pine marten and goshawk meant there was more Predation between predators and that helped the two grouse species - the keepers were fuming at that! Same with nightjar, another ground nesting bird, the RSPB and Forest Enterprise really helped it with habitat work in Dumfriesshire, not a jot of predator control. These and other examples are practically impossible if you believe the keepers so the public really need to be told about them.

      1. There is also the data from RSPB Dovestone where waders increased significantly with improved habitat through management and there was no predator control. Then the real reason shoots go on about such predator control is so that they can have an over population of grouse, pheasants or partridge to shoot, protection of ground nesting song birds and waders is how they sell it to the rest of us.

        1. Er, actually RSPB killed 487 carrion crows over 11 reserves in 2015/16 "to protect ground nesting birds". What is good for the goose is surely good for the gander?

          1. Peter - the RSPB killed 487 Carrions Crows over 200+ nature reserves I suspect - an area of 120,000+ha I think - but i may be out of date.

            The reason you know that is that I set up a system of reporting on it publicly. How many game estates do the same? And what would the equivalent number be?

          2. 11 reserves is what it says. Neither here nor there really though is it? It's the principle.
            A perfectly valid question re' game estates Mark. You probably know more about game estates than I do but I'm sure their management varies enormously and their policy toward predator control varies in a similar fashion so very difficult to even guestimate at numbers. Might these estates be rather more encouraged to report the figures of their predator control of they were not so vilified by certain activist groups? I am sure a less aggressive, more open and productive forum for information exchange is long overdue but everyone seems so entrenched. Too many absolutists, self promoters and narcissists involved on both sides. As I asked before though, seeing as corvids and wood pigeons are actually thriving across Britain under the current handling of the general licences what possible reason is there for calling out that way of dealing with those licences? Is this not just trouble making for the sheer sake of it in reality?

          3. Mark. If I had to lay my pathetic life savings on it I'd say the difference between 11 and 200+ is 189+ wouldn't you? My arithmetic is nearly as bad as my spelling but I think I got that one right. To be more specific the entry reads Carrion/Hooded Crows 2015/16 - Number of Reserves 11 - Total Killed 487 - Reason "To protect ground nesting birds". The following years it was Carrion/Hooded Crows 2016/17 Number of reserves 15 - Total killed 528 - Reason "To protect ground nesting birds". Other controlled species were numerous including 'Feral' Barnacle geese and the reason being "To protect ground nesting birds.
            How's my arithmetic doing?

          4. Peter - and those are all the reserves on which those species were controlled by RSPB (as I understand it, and I think I do understand it) and the RSPB has over 200 nature reserves which cover an area greater than the size of Bedfordshire. So the table could read 220 reserves totalling over 110,000ha - have you got the point yet?

        2. I am a bit thick with numbers but I'm trying very hard so bear with me. Is what you are saying that although the 487 crows were shot on a total of 11 specific reserves we don't use the combined hectarage of those 11 reserves where the 487 crows were actually culled, we in fact add all of the nationwide (220) RSPB reserves together, including the irrelevant 209 reserves where no crows were culled, to arrive at our figure of crows per hectare culled for the RSPB in 2015/16?

          Numbers are fascinating and all that but really all I was pointing out was that while farmers control crows to suit their lamb/beef/crop production ends and game estates no doubt control crows to suit their game production ends, it is also the case that bird protection charities like the RSPB control crows to suit their ends as well. I feel these various differing interests have more in common than meets the eye and am not sure the crows culled per hectare is really the main yardstick for comparison. Perhaps something more positive can be achieved by cooperation rather than each party being it's own little secret squirrel club? Have there been any such meetings of minds, constructive talks between farming, game production and conservation interests?

          1. P_eter - by George yu've got it! Yes, if the RSPB bought the rest of the world an continued Crow control only on a double handful or so of its nature reserves that is ecactly what would happen. While youa re here, would you like to buy a finely crafted drawing of a two-headed tadpole sent to Chris Packham recently? If so

        3. Highly original artwork and Chris clearly has a real eye for detail too although it looks like an unfinished masterpiece somehow. Something's missing. I know, I know -- it is all to easy to overwork a painting when you are going for that natural moment but it need a little more heart somehow? Anyway, he could certainly give up the day job and survive as a professional dauber. Going by the scale of the 50p piece that's either a very large tadpole or a small Johnson - which way is it travelling? Yup quality work as ever. If he signs it he might make over £10,000 but out of my reach financially I'm afraid. Tell Ricky Gervais it's up for grabs, he'll give him £10,000 for it.

    2. All that agriculture, forestry, game management etc you so dislike employs people, keeps rural schools, post offices, pubs, hotels, shops, bus services etc open and running. Keeps local communities from dying out. What creates employment and provides similar stability in your alternative vision of rural communities?

      1. Thanks for the dislikes but what is the answer to my perfectly legitimate and I would have thought important question?

        1. Yup, thought so. No vision of rural economy or community structure whatsoever. This is what can easily be ignored and destroyed, cut by cut, by an urban stream of armchair logic. Well for people who live in the countryside these matters are important, all contributory rural activities including nature reserves, game estates, farms, forestry, turbines, dams, etc etc are what maintain rural life. I would have thought that was an important consideration to anyone with progressive views about our countryside. It isn't just a drive-in bird spotting venue, rural Britain is an economically fragile community, it is important because it has a heart, it is people.

          1. "a drive-in bird spotting venue"

            That's eggsactly where it's going - entry-fee kiosk under the big-M arch

  10. It baffles me that woodpigeons are common everywhere, yet their flimsy, conspicuous nests would seem particularly vulnerable to corvids and squirrels. How do they get away with it while songbirds come a cropper?

    1. James, I guess that the fact that woodies can and do have eggs and young in practically every month of the year leads to massive productivity of young,. Were it not for predation as you describe and the sterling efforts of men with guns, we would all be drowning under a duvet of grey feathers a mile thick!! Most songbirds ( hate that phrase) only have a couple or three broods at most.

  11. I think the whole issue of culling needs to be questioned. Most people with common sense reasoning mistakenly think that if the population of a bird or any other animal is X and you kill Y number of that animal, then the overall population is X - Y. It just isn't as simple as this. Overall population numbers tends to be more related to ecological carrying capacity and food availability limitations, especially at times of the year when food is restricted, rather than the amount of that species predated (culling can be seen as a type of predation).

    The reason for this is that most species produce far more offspring than can survive, and the overall amount of birds that survive is often down to food availability, particularly in the winter. Likewise reproductive success revolves around things like available territories, and the food availability in that territory during the breeding season. It is for this reason that birds or indeed any other animal can withstand quite a lot of predation, or culling, before it has any significant effect on the overall population. This is simply because the limits of ecological carrying capacity mean that many individuals won't survive, and if a certain proportion are predated, this just allows more of the rest of the population to survive.

    Undoubtedly these ecological mechanisms are the reason why corvids don't tend to effect overall songbird numbers, because the amount of songbird youngsters which survive has more to do with food availability and the other constraints of ecological carrying capacity, rather than the amount predated.

    Those in favour of culling corvids often wrongly assume that if they didn't kill the amount of corvids they do, that the population would be that much bigger, by the factor of how many they would normally have culled This is simply not the case for the reasons I've explained. Intense maintained culling can effect numbers at a local level, but probably not at a national level. In other words, if keepers are killing large amounts of corvids on a shoot, it may depress numbers of corvids locally, but this won't significantly reduce the overally corvid population, or their overall predation of other nesting birds.

    The large populations of corvids often has far more to do with food availability from human sources, including ironically food put out for Pheasants, than it has to do with a lack of culling or predators. I've greatly simplified it all, but I've found that lots of advocates of culling, or those who claim songbirds are adversely effected by corvids lack a basic grasp of ecological population dynamics, and tend to naively think that population levels of an animal are purely determined by predation or culling of that species. I realise that many reading Mark's blog are ecologically literate enough to understand much of this, but I thought it was worth making these points to clarify the issues.

    1. ...and hence the reason why so many of us voice habitat improvement; providing increased carrying capacity -of food resource, territories where birds can find a livelihood as of prime importance and predators generally being a background factor, ensuring survival of the fittest as it has for centuries. Hence concern at the uniform monoculture of our lowland cereal ’praries’ of modern farming, the Heather of the upland grouse Moorland, and the futility of culling crows as a mainstay of wader Conservation. What impact those millions of released pheasant on our native bird populations?

      What is so scary is the gross misunderstanding of these dynamics by some with conservation at heart, a host of those who live and work on the land who have looked no further than the folklore handed down to them on vermin and pests, and then the rest of mankind who haven’t a clue and will believe what they are told.

      Surely education is essential. We’ve had Attenborough on Climate Change, what we need is population ecology as it relates to conservation issues from rewilding to Raptor Persecution, farming for sky lark, curlew and grey partridge, to beavers. The science is there, we just need to help folk understand it.

    2. Yours is a grand understanding of the overall ecological dynamic but as you allude to corvid 'problems' are mostly very, very localised. You can have forty or fifty corvid stomachs hanging around one lambing field at a cold time of year when there is precious little else for those stomachs to be filled by. They then become a very real and quickly expensive problem. Turn your back to complete another task when they are concentrating their group attentions on one target and you have a dead lamb or an eyeless ewe in need of dispatching. Culling licences take ages to apply for, eyes take seconds to remove. Culling licences administered on a farm to farm basis instead of as general licences require many more hours of work in the processing - this means in these times of lower departmental budgets trying to afford more workers in the licensing department (against the real world trend) - more time that farmers have to mess about with pretendy paperwork to nobody's profit and the detriment of everyone's dignity (farmers don't appreciate/do paperwork). That is why general licences broadly work. If they were abused there would be a dearth of crows, wood pigeons, ravens etc. Where is that dearth?

  12. I must admit, I would not cry any tears if magpies went away forever. That is a personal thing though. I went through a very stressful time, kept seeing magpies all over the place, and that old tale about magpies being bad luck somehow got turned into a genuine mental health trigger. I ended up having to move house to a different area with a much lower magpie population, it got so bad. That is just me though.

  13. Following from Ste B comments above About carrying capacity and food availability.

    On this basis the there must have been a big reduction of corvids recently here on the Suffolk sandlings caused by the introduction of pig feed bins on free-range pig farms. This must have had far more effect than any in shots by keepers.

    This feeding would sustained they birds through the winter when they should have been starving out and help them top up their teenagers as soon as they could get there.
    The fields were black with hundreds of corvids.
    I don't know whether the BTO or can ever identify.any resulting population change?

    There was a lot of weight on the field too, Guls So I don't know how they're going to fair now. II came across a research paper by a Dutch research group who had tracked guls movements.. the stopping points were pig farms on the satellite map.

    Have pig bins come to a free-range pig farm near you yet?

  14. If Natural England doesn't require that people individually apply for licences or report numbers culled, how can we ever get an accurate picture of the scale of the problems?

      1. If there is no scarcity of the species in question why would you advocate the spending of public money (which actually is scarce these days) monitoring numbers culled? If it ain't broke why fix it? Furthermore will licence returns actually tell you accurate figures? Probably not. It all comes down to trust and that is the scarcest thing of all these days.

        1. Peter - you'd have said that the system of GLs up until Tuesday wasn't broke - but it was unlawful and you can see in this blog that significant change is ion the way.


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