What Do Swans Eat and Drink?
Swans are primarily herbivores – which essentially means that the main source of food is plant matter. It is true to say that they will eat some small invertebrates (small water beetles, pond skaters, etc....) every now and again, but this is quite rare. It’s only the cygnets in their first couple of weeks of life which consume animal matter in anything but an insignificant amount. The more developed the swans get, the less animal matter they consume.
However, having said that, adult swans, as well as their cygnets, will unintentionally eat some animal matter in their day to day lives. This is mainly as a result of tiny fish, tadpoles, worms, molluscs, fish and frogs eggs, etc... being entangled, or stuck, to the weed that the swan eats.
You may have heard of the freshwater mussel, or, the swan mussel, as it’s more commonly known as. The name swan muscle is actually a misnomer. Swans don’t actively seek out and eat swan mussels. If they are consumed, it will be purely incidental - they are quite large, 10 to 15cm when fully grown, not the sort of food item a swan normally chooses to eat.
When it comes to drinking, that’s simple – water! Just water, and lots of it. Swans mainly drink freshwater because that’s what their bodies are designed for and most of the places you find Mute Swans have freshwater, rather than saltwater.
But swans can drink seawater. Many species of ducks and swans have a gland which is located near the eyes and below the skin, which extracts the salt from the bloodstream. This salt is then concentrated into a liquid and is removed from the body by passing out through the nares, the holes in the bill.
If the swans reside in an area where there is a freshwater inlet, the birds will often gather round that region and drink the water from that location, rather than ‘pure’ seawater.
Whenever possible, the Mute Swan prefers to eat and drink afloat on the water. There are two main reasons for this.
Firstly, it takes less energy to paddle or swim, than it does to walk about on land. And conserving energy is an important issue. As you know, all birds are warm blooded and it takes a considerable number of calories to burn to keep them at their optimum temperature, about 40 to 41 degrees Celsius. Any energy they waste needlessly walking around on land (when they don’t need to), amounts to extra food they’ve got to consume in order to keep their body working in an optimum condition.
Not only do swans prefer to dine whilst on the water, they also actually prefer the food items that are floating, too. Normally, surface weed, etc... is relatively easy to pick up and eat because food found below the surface is often anchored to the river or lakebed, and that means using more energy to uproot it, compared to free, easily to pick up, floating pond weed, etc...
Secondly, there are fewer predators residing in, or on the water, that could harm the swans. In fact, for an adult swan, there are no natural aquatic predators, although, some people say that otters and mink could kill a swan. It’s only the young cygnets that have any real threat from water living predators. These would be fish like pike and zander. On the land, however, the swans are not quite as safe. Dogs and foxes pose significant sources of danger. In places like Abbotsbury Swannery, dogs are not allowed entry into the attraction for this reason.
The Problem With Eating Vegetation
Going back to the food of swans, I will now go through the main diet of a swan.
As mentioned above, Mute Swans are mainly on the lookout for plant material to eat. The range of vegetable matter they will eat is quite broad, however, some are more commonly on the menu than others.
The Mute Swan needs food for energy, essential bodily functions, fat for a layer of insulation to keep warm (as well as to cushion internal organs and a store of energy), growth and repair. Just like us humans, there are a range of food stuffs the swans can eat to meet all of its nutritional needs.
Swans are physiologically designed to eat plants, in particular, they like green plants. The problem is that, for swans, raw vegetation is notoriously difficult to digest. That’s because it contains a lot of cellulose.
Cellulose is basically the main constituent of the cell walls in plants. The human body is unable to digest cellulose and passes through our body as insoluble fibre. Animals, such as cows and horses, can digest cellulose, since their gut contains a certain bacteria that are able to break it down but have to possess large, heavy stomachs to accommodate the food, long enough, to permit the good digestion of the cellulose.
Swans and other birds that eat a lot of vegetation, are unable to obtain a lot of nutrients from cellulose rich foods because they would have to have much larger stomachs to get as much out of the foods as cows, etc... do, and this would pose a problem; they’d be unable to fly because they’d be too heavy with that huge stomach.
As previously mentioned in the section on the Biology of a Swan, Mute Swans have no teeth (by the way, no bird has teeth), instead they have a gizzard. The gizzard’s job is to grind the food down into a pulp. This increases the surface area of the food which means it will be more likely to be digested, since more of the food will be exposed to the various bacteria and chemicals present in the swan’s gut.
But even after the gizzard has ground the food down into a mush, little in the way of goodness is extracted from the plant material because the swan is unable to hold onto it long enough to allow the bacteria and chemicals to do their job completely.
As a result of the swan extracting relatively modest amounts of nutrients from the vegetation, the Mute Swans have to devote a large proportion of their day to foraging. The idea being that they meet their nutritional requirements by extracting a little in the way of sustenance from a large mass of food.
It has been suggested that for a Mute Swan feeding off wet vegetation, it could eat in excess of 3.5kg per day – which equates to about 30 to 35% of its body mass.
What’s On The Menu
Specifically, the plants commonly eaten by Mute Swans include:
Canadian Pond Weed/Elodea (Ranunculus rionnii)
Watercrow Foot/Streamer Weed (Elodea canadenesis)
Potamogeton (Potamogeton perfoliatus)
Floating Sweet Grass (Glyceria fluitans)
Hornwort (Ceratophyllum demersum)
Marsh Yellow-Cress (Rorippa palustre)
Creeping Bent (Agrostis stolonifera)
Plantago (Plantago major)
Yellow Cress (Rorippa pulustris)
Marsh Foxtail (Alopecurus geniculatus)
Green Algae – (Vaucheria and Cladophora)
Foxtail Stonewort (Lamprothamnium papulosum)
Eel Grass (Zostera marina)
Sea Plantain (Plantago maritima)
Saltmarsh Grass (Puccinellia maritima)
Sea arrow Grass (Triglochin maritima)
Beaked Tasselweed (Ruppia maritima)
All of the above are natural sources of food, but for many swans, they have an additional source of nutrition – food fed to them from the public, or their keepers.
Swans are a charismatic birds so people see them as a positive aspect to their lives. Birds in urban areas or those in private collections/sanctuaries, are fed a variety of food item they wouldn’t normally see in the wild. Bread and grain are frequently used as food for wildfowl. It is quite common for many ducks, geese and swans to be fed so regularly that we can consider many populations to be semi domesticated.
As an aside, swans are able to swallow when feeding underwater. So, when they bring their head above water again, it is to breathe and look around for predators and territory intruders.