The conservationist's dilemma: an update on the science, policy and practice of the impact of predators on wild birds (3)

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I’ve been the RSPB’s Conservation Director since May 2011. As I settle into the job, I’ll be blogging on all the big conservation topics and providing an inside view of our conservation projects. I hope you enjoy reading it and feel inspired to join in t

The conservationist's dilemma: an update on the science, policy and practice of the impact of predators on wild birds (3)

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I spent half-term with the family in the sun in the Cairngorms National Park.  As we have two of our most iconic reserves there, Abernethy and Insh Marshes, I was keen to pay a visit.  It was great to hear that the number of lekking male capercaillie at Abernethy has increased this year but alas, we failed to see any on our (very) early morning drive.  We wait with trepidation to see how the June weather turns out as our research shows a strong correlation between poor productivity and wet Junes.  At least Scotland seems to have had the better of the weather this month.

The visit to Insh Marshes was my first.  Lying on the floodplain of the River Spey, the site is special for its breeding waders (snipe, curlew, lapwing, redshank), rare plants (eg string sedge) and invertebrates.  It's a magical place. The floodplain still has many characteristics of a naturally-functioning system and, as I saw on site, in the wet winter of 2015 one of the tributaries has cut a new path, creating dynamic wet features alive with wildlife. 

 It’s an interesting year for Insh as we are undertaking a study of lapwing productivity.  In recent years we have noted a decline in their productivity but previous research has not been able to identify the main cause.  This year we have a dedicated researcher monitoring the nests and the chicks to find out what happens.  The initial results show that many early nests were lost during the night with significant fox activity identified on the trail cameras and badgers also present.  We are now actively considering whether we need to start fox control there next year as the flood regime means it isn’t practical to install an anti-predator fence.

As always, our approach to the issue of predation is based on evidence and guided by our Council agreed policy.  

Our 2007 review of the evidence of the impacts of predation on wild birds concluded that generalist predators, such as foxes and corvids, can sometimes reduce the population levels of ground-nesting birds (such as waders, seabirds and gamebirds), and a more recent (soon to be published) review confirms these findings.  By contrast, the evidence that breeding songbird numbers are limited by predation is weak. Rather, there is compelling evidence – some of it experimental – that changes in farming practices have led to the declines of many farmland songbirds, and emerging evidence that numbers of some woodland songbirds have declined due to long-term changes in woodland structure.

Deciding to use lethal predator control is something we never take lightly.

Our approach means that we seek evidence of a problem, check whether there is a non-lethal solution, make sure that the killing of predators would be legal, effective and not harm their own conservation status.  If we can satisfy ourselves of all these things then we can make a decision.  As in previous years (see here and here), I have included tables below which show the lethal vertebrate control undertaken on reserves (which now number 210 sites covering more than 150,000 hectares across the UK).  Some of the numbers are higher than in previous years as the dataset covers a longer period (17 months) due to a change in the annual reporting schedule. 

Finally, it is worth remembering that non-lethal approaches, although not realistic in some circumstances, can be very effective.  To illustrate this point, I have included a graph to show how well anti-predator fences are performing.  We now have fences at 28 reserves protecting breeding waders over 874 ha. At sites with anti-predator fences, lapwing productivity has been consistently above that necessary for population maintenance (0.6 chicks fledged per pair), even though at most sites only a proportion of the suitable habitat is protected by the fence (Fig. 1).

This is a fantastic result and a great return for the effort invested by our ecologists and reserve teams.

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Vertebrates controlled on RSPB reserves in 2014-15

Below are tables summarising the vertebrate control undertaken by RSPB and our contractors on reserves during the period 1 April 2014 to 31 August 2015.  The recording period is longer than in previous years as we altered our annual reporting timetable.  The extended period means that larger numbers of vertebrates were killed than in the previous 12 month reported period.  Only reserves where control was undertaken during the year have been included.  Vertebrate control commissioned by third parties as part of existing rights is not included here.

a) For conservation reasons

NB Feral means released birds outside their normal range.

b) For other reasons

 

Fig. 1. Mean lapwing productivity at RSPB reserves with anti-predator fencing, at which productivity has been regularly monitored. Bars show + one standard error. The figures above the bars show the number of reserves with anti-predator fencing, at which productivity has been regularly monitored.

And to close, here's another gratuitous picture of the stunning Insh Marshes (credit Andy Hay, rspb-images.com)

 

Comments
  • Martin,

    I too spent the half-term period in and around the Cairngorms National Park and just missed you at Abernethy – one day too early according to the warden.  Good to see that lapwing breeding success on our Charity’s reserves is now at a population sustaining level.  Well done for following Elmley NNR’s management prescriptions – http://tinyurl.com/orytzn2 - it is a winning formula.

    During my travels, it was also very noticeable, all around the keepered moors in Speyside, Deeside and the Monadhliaths, that threatened waders were thriving – curlew, golden plover, lapwing, snipe, oystercatcher, redshank, dunlin, common sandpiper all in profusion in comparison to many traditional lowland haunts.  So, where farmers and other land managers cannot afford to fence off suitable lapwing or other wader habitat, or where it is impractical to do so (like Insh Marshes), lethal predator control will continue to be necessary if we are to stem wader decline and emulate the success of many moorland management regimes.  Perhaps NE, NRW and NIEA would do well to follow SNH’s example and introduce a Countryside Stewardship/Glastir AES Predator Control Option to incentivise, further, farmers and land managers to carry out such control? see here - http://tinyurl.com/qxqc37r   The badger will continue to cause problems where fencing is not in place too – here’s hoping they don’t spread to Abernethy to add to the capercaillie and other ground nesters’ predation challenges (from foxes, corvids and pine martens).

    Interesting set of figures and commentary as well.  Somewhat surprised that you state that ‘….the evidence that breeding songbird numbers are limited by predation is weak.’  You will be aware of the paper by Dr Christopher Paul Bell and researchers from the BTO and University of Cambridge that argued predation by sparrowhawks may be a sufficient explanation for the decline in red-listed house sparrows in Britain, see here - http://tinyurl.com/zjq8n32   Their findings were replicated in last year’s paper from researchers at the BTO and University of St Andrews who suggested that ‘….an increase in sparrowhawks may have led to an overall decrease in the number of house sparrows visiting garden feeding stations in the UK’ and went on to say that ‘This may reflect a change in behaviour of house sparrows to avoid feeding stations frequented by sparrowhawks, or a reduction in house sparrow population size as a result of sparrowhawk increase’, see here – http://tinyurl.com/jns33nw   I have yet to meet anyone who believes that if were it not for sparrowhawks, house sparrow numbers on garden bird feeding stations would have remained stable while they declined everywhere else!

    Couple this with the findings from the GWCT’s Upland Predation Experiment at Otterburn where the amber-listed meadow pipit enjoyed a threefold increase in breeding success in response to generalist predator control, see here -  http://tinyurl.com/nv2xacn and to the more recent joint RSPB/GWCT study at Hope Farm and Loddington which found that in areas of high predator density, songbird numbers increased when predator control was carried out, and decreased when it ceased, see here -  http://tinyurl.com/jk5syrv - then the evidence seems much less thin.

    Then of course there is the evidence that badger and fox predation was adversely affecting red-listed breeding skylarks during the SAFFIE Project, (to save time, go to pages 591 - 597 here) – http://tinyurl.com/zyanwtz and the University of East Anglia’s findings from its red-listed woodlark study that set out to see if climate change was adversely affecting woodlark populations, only to discover that the effects of weather on productivity were minor compared to an increased rate of nest predation through the period of study, which saw productivity reduced by ~50% by 2004 compared to 1971, see here - http://tinyurl.com/z8wplz9.

    And I expect the evidence will ‘thicken’ even further when the International Whinchat Study Group reports on its current Salisbury Plain study.  It was rather depressing to hear from a researcher at last year’s BTO AGM & Conference that, although much suitable red-listed whinchat habitat is available (Salisbury Plain is not only the largest area of unimproved grassland in Western Europe but also a military training area where disturbance is low and where there has been no agricultural intensification), nest success and subsequent fledging rates are around 24% lower than in comparable Russian and Swiss study areas.  Of the 199 nests monitored, an astonishing 89% were predated, mainly at night by mammalian predators such as badgers and foxes.  This whinchat population there is felt to be unsustainable in the long run.  

    Not to be outdone, and at the same conference, a researcher studying red-listed wood warblers in the New Forest has charted a 50% population decline during the period 2011-14.  (BBS indicates that the wood warbler has suffered the 4th greatest decline in numbers since the inception of the scheme in 2000).  Moreover, the fledging rate there is 50% lower than the national average, mostly due to predation, with jays and badgers largely responsible in 2013.  New Forest rides and glades will be sadder places in spring and summer if we lose the shivering, sibilant trill of wood warblers in full and glorious song.

    And then there is the paper in this month’s Scottish Birds that I was reading only yesterday.  Researchers in Culbin Forest in Moray (including one from the RSPB Centre for Conservation Science) have found that pine marten predation is probably the main cause for the decline in breeding success of nestbox-nesting, crested tits there, see here - http://tinyurl.com/q2zf8ru.  Overall breeding success there has declined since the late 1990s, coincident with increased predation – from 77% prior to 1997 to 19% thereafter.  Soon to be an amber-listed species again perhaps?

    Meanwhile anecdotal evidence of predation limiting breeding success has been cited in the case  of red-listed ring ouzel on the NY Moors, see here - http://tinyurl.com/gsnkuqk and a researcher found that predation of juvenile ring ouzels was the main apparent cause of mortality in a declining population in the eastern Grampians, see here - http://tinyurl.com/zn6cyv8  

    Therefore, given all of the foregoing, I would challenge the assertion that ‘evidence that breeding songbird numbers are limited by predation is thin’.  I contend that it is anything but, and getting thicker, year on year.  

    Now this may be because hitherto, much predation research has been thin.  Researchers from the University of Reading found that the chances of detecting an impact of predation on bird populations depended upon the methods used to assess the predators.  It went to recommend that the findings from studies which use opportunistic data, for a limited number of predator species, should be treated with caution and that future studies employ bespoke census techniques to monitor predator abundance for an appropriate suite of predators, see here - http://tinyurl.com/j2o2c35

    Their findings suggest that if a study is based on good quality abundance data for a range of predator species, then it is more likely to detect an effect than if it relies on opportunistic data for a smaller number of predators.  

    What is needed then is more predation research and it is good to see that the BTO - in the light of AES failure to stem the decline of farmland nesting birds - has decided to research predation further, see here - http://tinyurl.com/zae5suq  

    Of course none of the foregoing takes into account the enormous, cumulative, additive depredations of domestic and feral cats and non-native grey squirrels, see here - http://tinyurl.com/oo6ujgh , here - http://tinyurl.com/c6c87jv, here - http://tinyurl.com/o83ua3j, here - http://tinyurl.com/h8buz4b, and here - http://tinyurl.com/jgn9pgn.  

    Anyway, all that said, looking forward, keenly, to reading the new report.

  • Great stuff - and, as you say, based on sound science, as is the RSPB way. We don't have the top predators - like wolves, bears and lynx - that could achieve a natural balance in many cases, anymore so it will always be necessary to intervene in some situations. It would have been fascinating to see what effect White-tailed Eagles might have had in East Anglia had the proposed reintroduction gone ahead - perhaps they'll get here one day!

  • No one likes lethal predator control but it is partly an indirect result of intensive farming. This means that the habitat for ground nesting birds, especially waders that need soft muddy ground has been lost on most farms due to drainage and that now days the only way to supply this type of habitat is largely through nature reserves. These attract the waders as they have nowhere else to nest. In turn this attracts the predators rather like the only service station on a long motorway attracts people. So to give the ground nesting birds a chance some predator control  becomes inevitable such is the loss of our wet lands.

    So well done RSPB on handling a very difficult subject.

  • Great work Martin. Would it be true to say that predation is really a compounding problem where the population of a given species has been driven to very low levels by other factors, such as habitat change (e.g. lapwing), or where breeding populations are naturally clustered (e.g. little terns)? So lethal predator control may be an option in the early days of species recovery, but will be less relevant as (or if) those populations begin to increase in density and range? Many of our breeding waders are now confined to so few places, in such low numbers, that any level of predation can prevent recovery. You don't really say above that predator control might be a short-term necessity before populations become resilient to such losses.

  • Martin - nice to see those figures. I'm sure you'll be told that they are too high and too low by different groups of people.

    150,000ha is a vast area.  

    Good to see that fences are working so well - I saw Lapwing chicks wisely sticking to their side of the fence at Rainham earlier in the spring.  Another RSPB success story.