Predation Control Studies

Scientific Report

April 2014

PREDATION CONTROL STUDIES

Squirrels

At this time of year, for the past couple of years, we have spent a few weeks working towards a smart strategy for controlling grey squirrels by trapping, applying the same thinking that led to the GWCT mink raft. Squirrels are a bit more challenging than mink, so we had to develop some electronic gadgetry to help us do the research. This is a small pilot study, which may or may not lead to anything further. The usual plan would be to use the results of such a pilot as a sprat to catch bigger, external funding.

Fox control

After several years of learning computer modelling skills from fisheries biologists, Tom Porteus is approaching submission of his doctoral thesis. To summarise brutally an incredibly involved piece of work, Tom has used lamping data recorded for us by gamekeepers during 1995-2000 to derive estimates of the natural processes that – with culling – determine how many foxes are present on an estate: processes like cub production, immigration, and natural mortality. So we now have some idea, for instance, how quickly culled foxes are replaced, and how that varies around the country.

That was a real sweat, but it’s not the end. We can now turn the process around and answer ‘What if…?’ questions. We can take the circumstances of a real-world estate and model what would happen to fox density if we adopted a different culling strategy: more or less effort, a more seasonally focussed effort, with or without snares, with or without the means to control cubs at the earth. Watch this space over the next 12 months: it is going to be really fascinating.

Corvid traps

We have just started a new project on corvid trapping in Scotland for Scottish Natural Heritage. Ordinarily, killing birds is prohibited under UK wildlife law, but the lethal control of certain nuisance bird species – including common corvid birds – is specifically permitted by General Licences, regulated by the devolved countryside agencies: SNH, English Nature, etc.

SNH want to ensure that their licences are robust and defensible, enabling users to carry out control in the most effective ways without challenge or interference, where there is clear need. After consultation in 2013, SNH have contracted GWCT and SASA (Science & Advice for Scottish Agriculture) to get them better information on current corvid trapping practices. SNH wants to establish how many corvid traps are currently used, what kinds of trap they are, how effective different traps are in different circumstances, and to get some measure of the accompanying risks of poor welfare and non-target captures. This fact-finding exercise is fully supported by the shooting and land-owner organisations.

Dr Jonathan Reynolds

WOODCOCK WATCH – SATELLITE TAGGING IN 2013/14

The winter of 2013/14 has been an encouraging improvement on 2012/13 with a higher proportion of tags continuing data transmission through the winter. During our first winter many of our tags stopped transmitting regular data and it was assumed that reduced battery charge, due to the low levels of sunlight, were to blame. This year has been noticeably better; of the 16 birds we followed on their spring migration eight transmitted during the winter months.

Several of the birds that have returned to Britain did so later in the winter than would normally be expected. Whilst most surviving birds did eventually return to their capture sites, two of the birds performed shorter migrations. Olwen, caught in Wales in Spring 2013, only migrated as far as East Yorkshire, whilst Wensum, originally caught in Norfolk, spent the entire winter in Germany and the Netherlands. All of this seems to show some flexibility in their migration strategies and was likely a reaction to milder winter conditions.

The Woodcock Watch project continued into its third year with the deployment of 11 new tags in March 2014. These, along with the eight tags remaining from last year, give a total of 19 active tags across Europe. These include three birds that wintered in Cornwall, four from southern/central England, two from Ireland, three from Wales, four from Scotland, and one each from Norfolk, Lincolnshire and County Durham. The progress of these birds continues to be monitored via the www.woodcockwatch.com website. At the time of writing (10/4/14) most, but not all, birds have left the UK and are currently moving across the continent.

We have also deployed 40 new geolocator tags; 30 at a site in Cornwall and 10 in Wales. These smaller, lighter, cheaper tags complement our satellite tagging project by adding another source of data and by increasing the sample size at a comparatively low cost.

Other winter work

As well as the satellite-tracking study we have a number of other active winter projects. An ongoing radio-tracking study, carried out at a site in north Hampshire, has monitored the local movements of over twenty-five wintering woodcock. This project is looking at their day-to-day movements and has provided data on several aspects of wintering ecology, chiefly the use of different agricultural habitats as nocturnal feeding sites. This work has been complemented with a study of earthworm availability at different feeding sites across several common crop-types.

Breeding Survey 2013

In 2013, we conducted a repeat survey of breeding woodcock with the BTO to determine current population size and change in abundance and distribution since 2003. 820 randomly selected sites were surveyed for roding woodcock by over 700 volunteer surveyors.

The first estimate of abundance has now been calculated giving a provisional population estimate of 69,390 ‘pairs’ of breeding woodcock. This suggests a decline of around 19% since the 2003 survey when the population was estimated at 78,350 ‘pairs’.

Comparisons of site occupancy between the two surveys reflect this decline, with ten out of eleven regions having fewer occupied woodlands in the 2013 survey. Occupancy had declined most markedly in the South and West particularly in Wales where only 13% of suitable sites surveyed now have breeding woodcock. And whilst these declines where less marked in the North and East, South Scotland also showed a large decline – from 41% of sites occupied by woodcock in 2003, to 20% by 2013. Northern England was the only region where levels of site occupancy had increased.

The next step with the breeding survey data is to calculate changes in regional population sizes. Once trends in abundance and distribution have been fully investigated the data should provide the information necessary to determine the causes of the observed decline. Possible factors are likely to include declining woodland management, increased browsing by deer, drying out of woods, maturation of conifer plantations, increased recreational disturbance and increased predation. As far as possible, we hope to quantify the effects of these influences with our continued research in this area.

Dr Andrew Hoodless

UPDATE ON EAST STOKE & TROUT RESEARCH CENTRE

GWCT established its Salmon & Trout Research Centre at East Stoke in 2009, when government cut-backs meant that CEH (Centre for Ecology and Hydrology) had to withdraw from the site (which is owned by the Fishery Biological Association).

We moved our existing brown trout research team down there, and were able to expand our research programme to look at how to restore the UK’s declining population of Atlantic Salmon. The Centre is on the river Frome, historically one of the best salmon rivers on the south coast, and which, due to CEH’s historic involvement, is the best “instrumented” river in the country. This allows us to do research there that simply cannot be done on other rivers in the UK; it is a unique facility providing important new information on the biology and ecology of salmon that is, in large part, relevant across all salmon rivers.

As predicted, the low production of River Frome juvenile salmon in 2011, which subsequently resulted in the low smolt output for 2012, has, as predicted, resulted in a low return of 1sea winter (grilse) adults in 2013. However, total adult returns for 2013 also consist of 2 sea winter adult salmon which result from the strong output of smolts in 2010 and therefore the total adult returns remain around the average for the last decade. Since female adult salmon lay around 1200 eggs per kg of body weight they are sufficiently fecund that the salmon population should recover quickly from the temporary effects of the poor 2011 cohort. This neatly demonstrates two important strategies of fish such as Atlantic salmon. Firstly not to ‘put all your eggs in one basket’ but spread them between different age classes, so that if one age class is badly affected the other age classes can step in to fill the gap; and secondly make sure there are plenty of eggs in the basket by laying large numbers of them. The temporary blip of 2011 is further highlighted by the high numbers of juveniles produced in 2012, when the estimated population reached 106,000 and the estimated smolt output from these fish was one of the best the River Frome has produced in recent years. Our conclusion from all this is that the 2011 cohort was a minor setback in a river where the salmon population is continuing to recover.

A lot of staff resources in 2013 went into the design, manufacture and installation of the PIT tag readers at the Bindon Archimedes screw turbine hydro-electric site. In all we had to instrument the channel behind the turbine, 2 hatches on the main river channel and a smaller channel which acts as a fish pass. All the channels are different shapes necessitating bespoke designs for each of the PIT tag readers. However, we now have operating readers in all channels and a number of autumn migrating parr were detected migrating downstream through the site in October and November. During 2014 we will be able to detect Atlantic salmon smolts migrating through the turbine and compare their subsequent survival with those smolts that migrate through the site without entering the turbine. As far as we are aware this will be the first time anyone has managed to assess the impacts of a small head hydro scheme on a naturally migrating Atlantic salmon population right through to the adult stage, incorporating the important effects of turbine passage on mortality as the smolts enter salt water.

Dr Anton Ibbotson

POLICY - ENGLAND

BROWN HARES – PARLIAMENTARY BILL CALLS FOR A CLOSE SEASON

Brown Hares are a UK Biodiversity Action Plan species, the population of which is currently listed as “red” status because of severe declines in numbers in some parts of the country. Unlike other game species they do not have a close season. On the face of it this might seem odd, but delve a little deeper and the logic becomes apparent. Brown hares can cause severe damage to emerging crops, particularly spring sown sugar beet and vegetables. These crops are precision planted to create an optimum plant population density so where individual plants or parts of rows are grazed off then there is an impact on yield and profitability. Damage is particularly acute when crops are emerging during dry conditions as the hares will graze the growing points of the plants out to access the moisture retained there. The law currently permits farmers to shoot hares where damage is being caused, although the sale of shot hares is prohibited during the main breeding season.

In March Sir John Randall MP brought forward a Bill to introduce a close season and ban the killing of any hares between February and August. GWCT was not in favour of this; faced with no control options during this period farmers are likely to take pre-emptive action during the open season and shoot numbers down to very low levels as a precaution. We explained this to Sir John, as well as highlighting the problems posed by illegal coursing and presenting him with some of the extensive research we have carried out on hares over many years. Impressed by our evidence Sir John visited Loddington to see for himself and as a result instigated a series of changes to his proposed Bill, acknowledging in the process the contribution our science had made to reversing his opinions.

Lead Shot

The Lead Ammunition Group (LAG) was set up in 2009 to consider the potential adverse impacts arising from the use of lead ammunition in sport shooting. The LAG commissioned three Risk Assessments examining the effects on livestock grazing land which is shot over, the possible effects on the health of people eating lead-shot game and the impact on wildlife and the environment generally. These reports have now been completed and accepted by the LAG who are looking at the possible impacts and considering if any mitigation strategies are warrented. Once this has been established the Group will submit its findings to the Secretary of State who will then decide if any action is required. GWCT were closely involved in preparing the Risk Assessments and our Chairman, Ian Coghill sits on the main Group and has been working most recently on mitigation options.

Rodent Control- the need for improved practice.

Following residue testing of a range of non-target species, raptors in particular, the Health and Safety Executive (HSE) is proposing tighter restrictions on the use of rodenticides, particularly in the open countryside. Everybody who runs a shoot knows the problems that rats can cause around feeding hoppers and in game strips and the need for control. However, as the law currently stands anybody can purchase and put out poison provided they observe the instructions set out on the container. The HSE are unhappy about this but the government have signaled that they do not propose to bring forward restrictive legislation. The game industry has agreed to bring forward plans for operator training which will be launched later this year alongside a monitoring programme to track levels of impact of rodenticides on non-target species. A reduction in the numbers of non-target species with residues will surely help us to retain the ability to use rodenticides in the countryside.