I am no lover of magpies and give carrion crows no quarter. But the overwhelming reason for the decline in wild bird numbers is farming. The massive changes even in my lifetime (45 years) have had a dire effect on farm land birds, some species have been pretty much decimated. Vermin is easy to blame but fundamentally the reason lies in the farmers chemical store ( and silage clamp I would argue too).
It may depend on ur area and type of farming but blaming farmers is the easy excuse (bit like blaming global warming for everything) yes modern farming techniques generally don't help but there are vast areas of countryside where modern farming involes using a quad bike instead of walking and thats the only real change for decades yet birds are still declining. Why
And as brewsher? said wot about all the urban areas that should provide decent habitat for song birds farming shouldnae influence those populations
In my area i'd say that farming really hasnae changed that much in past 30yrs, most of the 'good' chemicals pesticides are now banned, burns are actually running fairly clean now, when i was a boy i can think of plenty of burns running full of slurry/effluent.
The fields i ferretted as a boy have not changed, no hedges taken out or ponds drained, only real change is far more vermin. In fact if anything more hedges have been planted and ponds dug.
Go to a similar area/farming type 30 miles away the difference in ground nesting birds is amazing, the only difference is a decent keepers near to grouse moors
The GWCT has done mant studies so has Songbird survival and more often than not where predators are not managed prey birds often struggle to fledge enoug chicks to keep the population stable never mind rising.
I would imagine there is possibly an argument for not shooting Magpies/corvids all year round, generally the main damage is caused by nest predation rather than killing adults, so if u have any time issues target ur control to early spring/summer, so hammer them early spring thrpou summer. But benefits of shooting them later on wil be minimal locally as new ones will only come in to fill void, alhou it is always 1 less corvid which is always a good thing but where numbers are high probably wasting ur time.
Someone mentioned birds with no head, i'd say more likely to be sparrow hawk kills (althou classic tawny owl in pheasant poults below roost too) than magpie/corvid
Ps Does anyone know who operates the camera's? Is it rsppb or a private owner?
Really be surprised rsb released footage and amazed not far more of it the ammount of nests they monitored over the years.
Can always remember a few years ago osprey chicks where taken by a buzzard 2 yrs on trot and that was the 1st 2 yr of monitoring.