Bread and similar food such as biscuits and cakes are a good source of carbohydrate but they offer little else in the way of nutritional value for any birds, including waterfowl like ducks, swans and geese. Bread is the equivalent of junk food for birds and, just as with humans, too much of it can lead to weight gain and malnutrition.
Moderate feeding of bread when mixed with other bird food is not as harmful which is why it's fine to give it to your garden birds in small amounts. But when you're feeding ducks in a public area you won't know who else and how often other people have been feeding them. If the duck pond is in a busy area then the ducks could subsist almost solely on bread fed to them which can lead to some serious dietary problems.
Too many carbohydrates will eventually lead to obesity in birds and they will become sluggish and may find it difficult to fly. This makes it harder for them to evade predators such as foxes and dogs and losing the ability to fly can also disrupt their natural migration patterns.
Overfeeding ducks bread means their ducklings may become malnourished which can stunt their growth and development. A disorder known as "angel wing" in which the wings grow abnormally outwards is thought to be caused by a carbohydrate-rich diet. Ducklings, cygnets and goslings will also not learn to forage for natural foods as the source of bread is so easy to come by.
When ducks are fed too much bread not all of it will be eaten and the leftovers will eventually go soggy and rotten leading to greater algae growth that can clog waterways. This concentrates pollution, eventually eradicating fish and other pond life which not only destroys the ecosystem, but also removes more of the ducks' natural food sources.
Mouldy bread can also cause aspergillosis in waterfowl, a lung condition that is contracted from inhaling fungi spores. Common symptoms of aspergillosis include gasping, listlessness and dehydration and, if not caught early or left untreated, is fatal to ducks and waterfowl.
Click on the different types of food to find out what's good and what's not.
A carbohydrate rich diet means ducks will defecate more often which is pretty unpleasant underfoot, and bird faeces harbour bacteria responsible for a number of diseases including avian botulism which can wipe out entire flocks of birds. Leftover bread will also attract vermin such as rats and mice that carry all sorts of nasty bacteria and parasites, some of which are dangerous to humans.
As ducks become used to being fed they will start to lose their natural fear of people and may become aggressive in order to get more food. Some waterfowl such as geese and swans can be quite dangerous when riled and have been known to attack children. Their lack of fear also means they may start to take risks to reach sources of food which makes them vulnerable to predators.
Although wild ducks and waterfowl will live longer, healthier lives eating natural food such as aquatic plants, grasses and insects, if you want to feed the ducks there are many alternatives that are much more suitable and safer than bread. Some of these include:
Grapes that have been deseeded and cut in half.
Cracked corn, oats and other grains.
Frozen peas or sweetcorn that have been defrosted.
And try to vary what you feed them, so they don't become reliant on one single food type.
Alternatively you can buy duck and swan food that has been specially formulated for waterfowl. It even floats so the ducks can find it more easily!