Bit of a long post here, but Ill try to keep it simple. 25 years ago, the GCT did a lot of research on fox movement by radio tracking. Their research was based mainly on predation of wild birds, partridges in particular & did not necessarily apply to reared birds. In short, their research showed that killing foxes at this time of year was basically a waste of time, for 2 reasons. There were so many foxes about that it didn't matter there would be another one soon enough, & also wild birds particularly partridges are well capable of looking after themselves. However.. there research showed that the crucial time for fox control was January to March, when vixens are pregnant, accompanied by dogs & are establishing territories. Foxes in the surrounding areas are doing the same, if you take them out then, than the gap is less likely to be filled, as other foxes in the area have territories too. There will always be a case later on when a vixen will move her cubs in to a vacant area, I have had them move them from over a mile away, but its not usual, unless she senses extreme danger.
So, on my farm 100 hectares, I have a good chance of a pair of breeding foxes. Plus the surrounding 4 sq hectares, I then have a further 4 pairs. Thats 10 foxes plus say a couple more 12-15 foxes. I have 3 months to get rid of them before cubbing & the crops getting too tall.
Heres what happened on my farm. In the first lockdown I invested in NV & a Thermal, the first 2 years I shot 165 foxes, the third year I shot 30, last year I shot 2, this spring time from feb till start September I only saw 3 foxes, I shot 2 of them, old Longarse I left alone, & he leaves me alone, who knows he might even be keeping other dogs away. I shot 9 since harvest, mainly cubs & 2 vixens. Haven't seen one since. It can be done, my nearest town is 3 miles away, & I have a river on one side. Maybe other farmers now are doing there bit, but Ive not heard anything. Also I dont keep stock anymore, lambing & calving time is a fox magnet, they come from far & wide. Hare numbers are now approaching ridiculous, partridge pheasant plovers skylarks are up too. Probably none of this applies if you got poults that need protection in the summer & autumn. the bottom line is .. if you got foxes breeding on or near your patch, you left it too late, stop them & it makes a hell of a difference. I been doing this for half a century but I feel I turned a corner now. It would be good to hear others experiences too. Good luck