There can be little doubt that foxes have the potential to impact the game harvest and bird conservation efforts, not least because they will take “sitting birds” (i.e. females on eggs), which results in the death of the female and her offspring. Generally speaking, as with livestock, linking fox predation with declines in a gamebird species is difficult – it’s hard to be sure that it was the fox that caused the decline and it wasn’t just part of a bigger picture. Similarly, it can be difficult to find any correlation between fox numbers and losses to the game population.
Perhaps the most detailed assessment of the role predators have on the game harvest comes from work done by the Game & Wildlife Conservation Trust (GWCT) as part of a six-year study on Salisbury Plain in southern England. The GWCT biologists intensively culled predators in some parts of the study site but left them alone on others.
The results of the study were striking, showing that the autumn partridge density was three-and-a-half times greater on the ‘culled’ site than on the non-culled site after only three years. Unfortunately, what this study wasn’t able to show was which predator(s) was responsible – all predators were culled, not just foxes. With this in mind, the biologists started radio-tracking the partridges and, in doing so, found that foxes were responsible for most of the deaths resulting from predation. Interestingly, GWCT biologist Jonathan Reynolds, in his Fox Control in the Countryside special report, noted:
“Even if foxes had eaten all the partridges present, partridges could never be more than a few percent of fox diet. Thus partridges were probably not very important to foxes, but foxes were very important for partridges.”
So, while reports of large ‘hauls’ of game being taken from the stomach of a single fox (such as a report from County Durham in north-east England of a gamekeeper opening up a fox he shot to find 13 recently-eaten grouse chicks in its stomach) are rare, even relatively low occurrence in the diet can seemingly have significant consequences for the gamebird population. Moreover, given that foxes are only one of a collection of predators, their impact can be additive.
In 2007, for example, David Baines and colleagues at the GWCT published data on the mortality of the black grouse (Tetrao tetrix)—a gamebird in serious decline in the UK—in three areas of Britain: north Wales; northern England and the Scottish Highlands. Baines and his co-workers found that foxes were a significant predator of the grouse, taking 33% of adult birds on the Welsh site and 48% in the Scottish Highlands – these may not look like massive percentages, but the biologists also found that raptors (i.e. birds of prey) were important predators too and, together, foxes and raptors exerted a significant impact on the grouse population.
There is also some evidence suggesting there are certain seasons when predation is more likely. One study found that about a quarter of the “large birds” taken by foxes in an area of southern Sweden were pheasants; the bulk of these were taken during the cubbing season (i.e. when foxes had cubs to feed). Similarly, on their study site in Dorset, Jonathan Reynolds and Stephen Tapper found that 70% of their foxes' diets were medium-sized birds and mammals (300g-3.5kg) and most of these were taken between April and June (cubbing season).
Across northwest Europe, many ground-nesting wader populations have seen substantial declines and viable breeding colonies are being increasingly confined to isolated protected areas. A great deal of time, effort and money has gone into trying to understand the influence of predators on wader breeding success and overall numbers, as well as to reducing predator populations in and around these reserves. Fencing and predator removal/control schemes have resulted in increased hatching and/or fledging success for several species including plovers, dunlin, redshank and lapwings.
Recent work by Rebecca Laidlaw at the University of East Anglia and colleagues, published in the journal Ibis during 2015, suggests that habitat management can play a role in reducing nest predation by foxes. Their research, conducted on redshank and lapwing nests at the Berney Marshes RSPB reserve in Norfolk between 2005 and 2011, found that nests situated in fields close to verges with tall grass were less likely to be predated than those elsewhere on the reserve. The suggestion is that small mammals tend to be restricted to taller patches of vegetation and this increased availability of their primary prey means that foxes don’t need to search the open fields nearby for nests. It’s a bit like putting out food in the garden to distract the visiting foxes from eyeing up the chickens.
Ultimately, there can be little doubt that controlling predators (including foxes) can increase the percentage of game and waders surviving, although it should not be assumed that predators are the only sources of loss. Back in 1935, Adrian Middleton published his study of the factors controlling partridge numbers in Britain, as part of which he looked at clutch losses between 1911 and 1924. Middleton found that foxes were the most significant predator of the birds and their nests, but he also observed that almost as many nests were destroyed by careless farm hands (344) as were raided by foxes (347). This was obviously several decades ago and practices have improved significantly since then, but it illustrates that even factors we may consider trivial, such as accidental destruction, may have sizeable impacts on these populations.