Hi Akos and welcome to WAB
The "fish bait trick" you refer to was described by wildlife photographer David Boag in his book 'The Kingfisher' published in 1982, a similar technique having been previously described in Rosemary and Ron Eastman's book of the same title published some 13 years earlier, though in both cases they actually used containers rather larger than "a bucket".
However and with all due respect to David Boag, the Eastmans and to you, it is a technique which in this enlightened age many consider simply too dangerous to employ.
The dangers of encouraging a Kingfisher to dive into any container (and particularly one as small as a bucket) must be obvious - should the bird clip and damage or even break a wing on entry or exit this could seriously impair its ability to fly and hunt or, worse still, could result in drowning
As we are now in the midst of the breeding season this could prove disastrous for an entire brood and, in my opinion, the practice simply cannot be condoned.
As you imply in the final paragraph of your 2nd post, in wildlife photography the wellbeing of the subject must always come first and no photo is worth endangering the subject.
As for your perch in a bucket tip, personally I wouldn't want to have to cart around too many 5 litre buckets full of concrete and, if I may say so, it sounds a little over-engineered (or are you a bucket salesman perhaps?)
What's wrong with simply sharpening the end of your perches and sticking them in the ground? Or, if the ground is too hard, I use a very short length of metal tubing (typically copper plumbing pipe) with one end flattened, which I drive into the ground at a suitable angle and into which I then insert the easily removable perch. It works for me
Finally, I would certainly reiterate what TBR and Steve S have said about the legalities of trying to get photographs of Kingfishers here in the UK and this is why I now intend, on advice, to include the Reminder you'll find at the end of this post in every post I make about Kingfishers in future.
Jeff
(Schedule 1 Licence holder for Kingfishers and Barn Owls)
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REMINDER
As a fairly rare and easily disturbed bird, the Kingfisher is afforded the highest degree of legal protection under Schedule 1 of the Wildlife and Countryside Act 1981. If you “intentionally or recklessly” disturb a Kingfisher whilst trying to photograph it “in, on, at or near” the nest or whilst it has dependent young, and without the necessary Licence from Natural England, you may be committing a criminal offence punishable by a fine of up to £5,000 and/or a prison sentence of up to 6 months.
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