Since I've always been very fond of hedgehogs, for some reason, I looked into this a while back. At the end of the Second World War, there were an estimated 30 million hedgehogs in the UK — that's thirty million. There are now thought to be under a million. That's a staggering decline.
Although badgers are partly responsible, the main culprit is, as usual, the most dangerous mammal on the planet — man. The building-up of areas, and above all the decline in hedges (which provide a safe space for both hedgehogs and birds, but also a porous boundary) in both fields and gardens account for much of the damage.
I remember sitting out on hot summer evenings on the terrace in front of our modest garden in south Lyon. We'd be sipping a drink, and quite late in the evening, hedgehogs would come tootling out, the way they do, and fossick around in that sedate way they have. My former wife never put any chemicals on anything in the garden, although of course neighbours did, and we shouldn't kid ourselves that rain doesn't wash that stuff into your garden. We had no dog (that helps) but we did have a cat — somehow they found a way of co-existing. The other thing that was a great delight was glow-worms — they are apparently particularly sensitive to chemicals in the garden. I didn't see a glow-worm in my life, other than on Bodmin Moor on a school training exercise in 1970, until we had that garden in France in the nineties. Haven't seen one since. We have a big hedge around our garden now, and the birds love it. Most of the neighbours don't, of course. Our garden's a bit jungle-like. Animals tend to prefer that to a garden drawn up with set squares and T squares…
If you can get hold of it, get hold of a wonderful piece called “Consider The Hedgehog” by someone called Katherine Rundell. She writes brilliant short pieces on animals of all kinds. Common ones and not so common, i.e. the albatross. They were collected and published in a book called The Golden Mole. Can't recommend these pieces highly enough.
Edit: one of the single most astonishing and encouraging things about the first Covid lockdown, particularly, was how fast nature came back and re-established its rights. Apparently, big fish were seen swimming in the canals in Venice in a way that hadn't been seen in decades. They're very polluted, normally. I have a photo of a hopoo perched on the roof of the house opposite, which I've posted on this forum in the past. It's a superb photo, just because I was lucky. I used a telephoto lens, so got close up.He heard the (extremely discreet) click of the camera, and he was gone. Apparently, hopoos are shy birds and very rarely come into towns. I like to think he'd flown across the Med from Africa to spend summer in Europe.