I was looking for those plastic heron statues to buy on the internet and found this article. A lot of these ideas I have heard already on this forum but others may not have who are new. I will not be using the plastic heron after reading this:
Herons, cranes, egrets, storks and other wading birds flying overhead soon discover the ponds in our gardens. Although they might look beautiful wading in your pond, you don't want these birds feeding on your prize koi or other valuable or beloved fish. Their persistent fishing excursions could quickly decimate your pond's population. There are various ways to protect its inhabitants from these attractive but hungry predators.
It's best to incorporate a protective design when first constructing your pond. These birds normally land next to a pond, and slowly wade in to deeper and deeper water on their long legs to catch a fish. If they can't ease into deeper water this way, they won't enter the pond. You can construct your pond by having the sides go straight down instead of sloping in as on a beach. If you expect young children to visit, it's best to protect them from falling into deep water by having a shallow area filled with bog plants completely encircling the pond. Beyond the boggy border, a pond built to include a sudden plunge into deep water will deter the birds from entering.
Our ponds here in Nyon were designed with that strategy in mind. Our upper pond has sides that plunge straight down one meter deep, which no bird dares to enter. Our lower pond is completely bordered by bog plants, and just beyond them the pond sides go straight down for half a meter. Our ponds are also filled with many tall plants rising out of the water, set close to one another. This prevents any bird that does manage to enter from spreading its wings to take flight again, so it doesn't risk entering at all.
We've seen the pond of one member of our club which incorporates a similar principle, but without using tall plants. She stretches fine clear nylon fishing line in a zig-zag pattern across her pond, about 30 centimeters above the water surface. This almost invisible grid even keeps birds from wading through the pond, let alone spreading their wings to fly off with her koi. Other ponds keep the birds out by having the fishing line stretched just outside their perimeters, also about 30 centimeters above the ground. Birds landing nearby try to walk into the pond, but are confused and stopped by this simple barrier, so they fly off to find a more accessible pond.
Some authors of pond books advise solutions that we don't recommend. One is to erect a statue of a heron in or by your pond, on the theory that these territorial birds will avoid a pond that's already occupied by one of their own species. It's much more likely to attract another heron--a live and hungry one that concludes there must be good eatin' in your pond. A heron decoy is also certain to attract real herons during the breeding season. We've seen photos of a real heron standing right next to a plastic heron, so a statue is no deterrent.
Some authors also advise covering your pond with netting, the kind that farmers use to keep birds from eating fruit off their trees. This would work only if you create a tall cage of netting over your entire pond. If it's not tall enough, many of your aquatic plants will reach the roof of the cage, then bend and distort because they can grow no taller. To avoid the unattractive appearance of a cage, some authors advise you to stretch netting across your pond just above or just below the water surface. In either case, no aquatic plants can emerge much above the surface, precluding the beauty that plants add to a decorative pond. If it's placed just below the surface, the netting is also likely to trap some fish that come to the surface, depending on the size of the fish and the mesh of the netting. Using a coarser mesh to permit plants and fish to pass through eliminates the protective factor, because a bird's beak can easily get through the larger openings in the netting.
Other deterrents recommended by some authors seem more amusing than effective: One idea is to glue a plastic fish onto a rock in shallow water. The theory is that a visiting bird will get frustrated in not being able to fly away with it, and won't return to your pond. Another idea is to float a plastic alligator in your pond to scare off hungry birds. That could be effective in tropical climes where birds might recognize this natural predator, but not in Switzerland. These devices are actually sold in pond-supply stores and catalogs, and we can't help wondering who buys them.
