Thinking like a fox: how might gamebird releasing impact fox populations?

Fox With A Rabbit www.davidmasonimages.com

4 minute read

By Jenny Coomes and Dr. Jen Brewin

This spring, GWCT researchers will be starting a new research project looking into one of the most contentious issues around the release of gamebirds in the UK: the idea that gamebird releasing may support foxes and other generalist predators into an area.

Despite being a topical subject, which generates much interest and speculation, currently there is no firm evidence to show whether gamebird releases either do or do not lead to local increases in fox population size. If they do, these predators might have a greater negative impact on local wildlife populations, so it is very important to address the question with robust science.

To examine the issue, researchers from GWCT are setting out to collect data over the next 18 months looking at the number of foxes present at several sites in central southern England that release gamebirds (pheasants and/or red-legged partridges), and a similar number of sites that do not. Comparing these sites will allow us to address the question “Do released sites support more foxes than non-release sites?”

Foxes are very difficult to monitor and the best method to assess numbers for this kind of research is to walk a fixed distance route (called a transect) at our chosen sites and be on the look out to collect fox droppings, called scats. The transects will be around 3km long and we will be walking at 16 sites, twice a month for a whole year. This means we will be walking 1152km or 715 miles – the equivalent of 27 and a half marathons!

Whilst walking the transects, we will also count the number of released gamebirds we see, so we can be sure that non-releasing sites really do have relatively few gamebirds, and the releasing sites really do have more. This is an important aspect of the scientific design – ensuring that we collect data which is robust, reliable and accurate.

After we have collected the fox scats, there are a number of things we will do with them. First we will use the number of scats per site to estimate the number of foxes and will compare this with our gamebird data. Second, the scats will be sent to a lab to be ‘genotyped’. This technique analyses DNA in the scat and because, like all living things, the genetic code of every fox is unique, it allows us to identify the individual fox that produced each scat.

We can then make a better estimate of the total number of foxes at each site which is important for answering our question. Third, we are also interested in finding out how much of the fox diet is made up of gamebirds so we will be examining our collected scats closely for evidence, and can do this in two ways. The slightly more messy method is to break the scats apart, wash them to remove soil and non-food items, before looking under a microscope to detect parts of pheasant and red-legged partridge feathers.

Looking through fox poo may not be the most glamorous job (!) but it is a vital part of our understanding of how released gamebirds impact fox populations.

The second way to examine fox diet uses DNA to identify all the prey items (not just gamebirds) in the scat. Small sequences of DNA called ‘primers’ are added to the scat sample which then attach to the prey DNA. The primers act as markers so that when the DNA sample is scanned, the prey sequences show up and we can identify the prey eaten by the fox.

It’s a bit like scanning the barcode in a supermarket, each item has its own unique barcode which is identified by the scanner and tells you what the item is. DNA analysis is a relatively new technique and has many different uses such as finding out what animal species are present in our rivers, identifying predators of crop pests and discovering which insects are likely to pass on diseases.

There are a number of other methods in our toolkit to help us find out how many foxes are at our sites, including trail cameras set up along our transect routes and handheld thermal imaging cameras for scanning across a landscape and counting foxes at night.

Trail cameras are a common method to record elusive animals, you can even set one up in your garden to capture any usually unseen visitors, but thermal imaging technology hasn’t yet been used in research to estimate numbers of nocturnal animals. We are still developing exactly how we might use these techniques to support the project, but they have potential in studying a species which is otherwise very difficult to observe in the wild.

Assessing whether the location or number of foxes in the landscape changes with the number of gamebirds released in an area, or whether their diet changes, will help us understand whether these predators might be having an increased impact on other species such as ground nesting birds, particularly those that are of conservation concern.

Carrying out robust scientific research to address fundamental issues such as this, as well as communicating and applying those findings to help develop effective and positive countryside management, is one of the core objectives here at the GWCT. The results of this study are expected towards the end of 2023, and we hope they will be worth the wait.

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Fox study

at 11:24 on 23/01/2022 by Roger Bray

This project will be interesting, time consuming and complicated, both the field work and lab work, but it’s one that needs doing. The advent of DNA analysis is a game changer in such studies. Lots of things to think about, including the email contributions above, and ideas to discuss before finalising the study methods.

fox control

at 18:17 on 19/01/2022 by AlanHine

I am a member of a small shoot syndicate in cambs . we decided to put down more birds for the 21/22 season and because of our increased investment have increased our predator control .As a result we have culled many more foxes than in any previouse season . As the cost of chicks and feed goes up so will the effort to control predators

Rabbit population

at 17:59 on 19/01/2022 by Geoffrey bazeley

Hi I have been dismayed by the collapse of the rabbit population in our area and indeed the whole of the country if not the world , no one has looked at this situation and the impact it must behaving on the fox population and indeed all animals and birds that feed on rabbits no one has reported on it ,where it came from is it man made what is the future I have tried to contact country file about this issue but no go with them they only like to report about good things it is obvious no rabbits fewer foxes. In this age of dogwoods they are always moaning about fox hunting but no worries about what they feed on or all the land that is being use for house building or road building all these things affect fox populations

Vulpine influence upon game bird release ……..

at 8:00 on 19/01/2022 by Alec Swan

I will admit that I'm wondering about the point to the research, if we consider two aspects to the question; Firstly ~ If we provide an opened door larder, then predators will take advantage of that …….. and Secondly ~ the question of predation by any alpha predator falls in to two sectors …. reared and released game aren't really affected that much - Q: a heavy fox population? A: rear another 500 pheasants …. the problem with the major predators are really only a concerning influence over non-reared though protected wildlife ~ it would seem to be lunacy to most that we offer blanket protection to our vulnerable waders and hedgehogs whilst also offering total protection to those predators who would work against our best efforts! …….. Authorised and possibly licensed predator reduction in areas of the greatest threat has to be the way forward. I've wandered away from our friend Reynard, my apologies! Should the day ever arrive when foxes are given total protection ~ then our best efforts at environmental enhancement will all be for nothing.

Pheasants and releasing

at 23:02 on 18/01/2022 by DCS

"Some are better than none" Stands to reason that an area dense in released birds or other possible food sources will sustain an increased volume of foxes or other predators. We've observed constant pressure on a resident fox to defend/mark their territory. When this resident population are removed, new individuals are quick to move in on what they see as a bountiful territory to possess. For this reason if a resident fox population is managed and monitored, allowing them to defend this territory, all whilst having a much lower density of foxes within said territory , Thus preventing a larger influx of outsiders pressuring hard on both released and wild prey species, until they too define a territory to push others out. Areas which have no released game or poor populations of wild prey, would seem to show more overlapping or a softening in defence of said territory, this leading to an increase of individuals patrolling said area, which in turn can increase predation on wild species. Just my own observations..

Fox populations

at 14:38 on 18/01/2022 by Piers Austin

In areas where game birds are released and your attempts to estimate fox populations, you need to take into account the numbers of foxes shot by diligent game keepers who carry out the necessary predator control. In any experiment you also need a control i.e. an area where game birds are released and no predator control carried out. Also, you need a baseline of how many foxes there were before any game birds were released! Not easy by any means.

Fox killing

at 14:34 on 18/01/2022 by Martin Bailey

Presumably there will be no killing of foxes, by any means, on the survey sites during the period of the survey? It would also be interesting to do a follow-up study to determine whether areas where foxes are killed have more or less predation on game birds. This would be an interesting follow-up to the study that showed areas with more fox control had more problems with lamb killing by foxes than areas where foxes weren't killed. On the subject of otters, re Nick vZ's post above, what kind of ducks were they? How healthy are the rivers in the area? It's never as simple as 'otters kill ducks so they should be controlled'. Where rivers are healthy and there are plenty of fish, frogs and other animals available, it's unlikely that otters would focus so heavily on one duck pond.

Fox control

at 14:20 on 18/01/2022 by Steven Heys

If fox control is undertaken at gamebird release sites and not the the control sites then surely there will be a higher number of foxes in terms of new DNA found at release sites,. The moment you create a vacuum it will be filled by new foxes looking for territory and/or availability of food. Will this possible variable be taken into account?

Fox study

at 12:50 on 18/01/2022 by Simon Kibble

With the timings of such a study falling in a period when the rabbit populations are suffering through the chronic haemoragiing disease as well as myxomatosis I like to bet the fox is running out of rabbits as a food option. For years the rabbit has provided for us all the fox included. We are seeing hardly any foxes in the recent years across the farmhouse acreages and the story is true elsewhere. No rabbits less foxes presumably down to insufficient food to sustain Cubs. A question that I have put forward already to the gwct but it would be good for the researches to have an angle on it for sure

Other genalist predators

at 14:56 on 13/01/2022 by Nick vZ

This sounds like a really good follow up to the wader recovery experiments in the Acvon Valley. Would it be possible to collect scats from other generalist predators as well. I'm thinking here of mainly of badgers and the other mustelids. Recently an otter at lest 1200 mm long was seen on a local pond. It has wiped out at least 40 ducks so far. We are needing some sensible rules to allow us to control generalist predators if we want to maintain a reasonable "Balance through wise use". THe same is true of all top end predators. The so called conservationaist simply don't do the Maths and the number of meals that each individual requires each year.

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