There is nothing more soul-destroying than an heron visiting your koi pond. Your fish will start disappearing rapidly as these skilful and determined thieves work out how to bypass your protection measures to access one meal after another. You will soon understand that the term bird brain is a misnomer. Herons are clever - very clever!
Herons are non-swimming carnivorous birds which feed on live aquatic prey and are thereforegenerally found around wetlands and watercourses. They will eat fish, reptiles, amphibians, crustaceans, molluscs, and aquatic insects. They commonly employ the technique of sitting motionless beside shallow water and waiting for prey to swim into range. They may also walk slowly around the area where they intend to feed and snatch prey when they happen to see it. Herons have been known to use their feet to stir and flush out their prey. Some species are clever enough to lure prey by adding bait to the water to attract the fish. Although rivers and wetlands are the heron's natural habitat, these birds are found throughout the UK and do stray into gardens with ponds. And therein lies a big problem for koi keepers!
No pond is deep enough
As herons don't swim in the wild, it is tempting to think that creating a deep pond will help to protect your fish. But herons are determined birds who will not be deterred by deep water. They will hop in and swim a little, somewhat like ducks, if they need to. Unfortunately, greedy koi will sense movement on the surface of the water, think that there may be food available and move to the surface. In other words, the heron landing on the water drives koi straight towards it.
Herons are incredibly patient birds. They will sit motionless for hours next to your pond waiting for an opportunity to strike. Your fish will have to move eventually, even if they are congregating at the bottom of the pond in the winter months. Herons will keep watch or make repeat visits until they get what they want.
Will a net protect your pond?
Sadly, netting over your pond may not provide sufficient protection for your stock. Herons will work out ways to destroy it, get underneath it or push it down into the water. Only a metal grid will prevent herons from fishing in your pond. They will quickly work out how to avoid other protective measures including electrified fencing. In case you are considering it, standing a plastic heron next to the pond won't deter herons for very long and might actually attract them to your garden if the are searching for a mate.
To make matter's worse, herons have amazing timing. They tend to arrive at dusk or dawn when human activity is limited. If you aren't up and about at the crack of dawn or watching your pond as the light fails, you will likely miss the arrival and departure of a heron who is targeting your koi.
Herons are a protected species and so you absolutely cannot do anything to hurt them and you can't kill them. If a heron has found your pond, you will have to get creative. Place obstacles around the edge of the pond, increase human activity at dusk and dawn and spray water at any herons which come close. But do be aware that herons will soon work out that the water is harmless! Place flashing lights, reflective surfaces and sounds to deter the birds. Windchimes are good investments as they emit sounds, move and reflect light. You could also consider keeping a radio on, tuned to a talk channel. Finally, provide hiding places for your fish in the pond to enable them to protect themselves.