The Role of Swans
Swans, are large, prolific, beautiful birds that are growing in number throughout this country that bring a lot of pleasure to a lot people. A more charismatic and well known bird, than the Mute Swan, in the United Kingdom, you’d be hard pressed to find. However, as graceful as they are, they serve a much more important purpose to the world than just being a nice sight for us to look at.
Scientifically speaking, Mute Swans, like all animals, play a crucial role in keeping our ecosystems healthy and diverse.
A healthy ecosystem is one in which the nutrients, and other components required for life (such as oxygen and carbon dioxide), are constantly being recycled by other living organisms. For example, a swan will breathe in the air, extract oxygen from it and release back into the atmosphere carbon dioxide when breathing out. The carbon dioxide is then taken back up by the plants, which is then eaten by the swans, the food then passes through their body and deposited back to the ground in their faeces. The faeces then provide food for other living things, etc...and the cycle continues.
Animals, such as birds, not only spread the nutrients throughout an ecosystem, they also spread the seeds of plants and the actual eggs of other animals. Swans are largely herbivores, in other words, they diet consists of primarily plant matter. It is inevitable that they will at sometime or other ingest seeds of plants and these can pass through their body, undigested. These ‘unopened’ seeds will be passed out of their bodies in the faeces and will have the effect of dispersing the seeds over a large area, facilitating plant growth well away from the parent plant.
It has also been shown that waterfowl (which includes ducks, geese and swans) increase the dispersal of invertebrates around the habitats. Live eggs have been found in the waste from swans, ducks and geese, hence spreading invertebrates from one habitat to another. The invertebrates can then help breakdown the faeces from the birds, which then increases the bioavailability of the nutrients to the plants. So the plants grow well, the birds have more to eat, etc....there are multiple beneficiaries.
Swans can also prevent overcrowding of plants. Case in point: One of the Mute Swan’s favourite foods is watercrow foot – a green plant that grows well in moderate to fast moving rivers and streams. It grows best in the summer, and they will spend many hours in the summer and autumn pulling it up from the river bed and eating it. In fact, they can eat quite large quantities. But it has been said that far from stripping the river or stream bare, they actually facilitate the growing of the weed and at the same time, help keep the rivers flowing freely.
The argument goes like this:
The swans eat the watercrow foot and the density of the watercrow foot decreases. The reduction of the density of the watercrow foot encourages more, enhanced, growth of the plant during the following growing season. (Swans do not actually eat the whole plant, so the roots remain in the riverbed, which means the plant will rejuvenate.)
Conversely, if the plant was allowed to grow unchecked, the river’s flow would be reduced because of the increased friction the plant would bring to bear on the moving water. This reduction on the speed of the river will increase the build up of silt and this would provide other plants the ability to grow, which would reduce the flow even more. Now, since the water’s flow is reduced there could be less throughput of nutrients in the system, it will support less life and the biodiversity of the habitat will suffer.
This is a very simple argument and there are many assumptions made, but the basic premise holds true.
Swans also prevent the overcrowding of other waterfowl. Geese, for example. The Canadian Goose has been marvellously successful over the past few years in breeding and spreading their numbers far and wide. So much so, that their numbers are becoming a problem in many areas. Culling may not be the most socially acceptable way to deal with these geese, so some landowners have taken to encouraging a pair of swans to take up residence on a section of water and the swan’s aggressive nature in defending its territory means that the geese are less likely to breed, or in some cases, driven off the water completely. This is often only really viable on relatively small bodies of water, such as ponds or a short section of river. In the U.S., you can actually hire a pair of Mute Swans to be placed onto a lake or pond to do this job for you!
In summary, the major role that swans play in the environment is in the facilitation of the flow of nutrients and oxygen through the ecosystem. They do this by providing the vehicle of the transportation and keeping open the channels of flow by preventing overcrowding which inhibits one part influencing another. So one part aids another part of the system and the system flourishes. As the old saying goes, water kept still long enough becomes stagnant and lifeless.