Swans Breeding


Swans are doing well in Britain - censuses carried out every decade, or so, (they’re not done over a strictly regular time period) have indicated a positive, rising trend – in the last one, in 2002, the number of Mute Swans in Great Britain was estimated to be in the order of 31,700 swans. That’s Mute Swans, it does not including the numbers of Whooper Swans and Bewick Swans, that migrate to the U.K. every winter, from Iceland and the Arctic, respectively.

The reasons behind the increase in population size have been previously discussed in another section (see Where To Find Swans), what we need to look at in this section is when swans breed -  with respect to their age and time of year, as well as why they breed.

Why Swans Breed

Swans have an inbuilt tendency to want to reproduce. All living things are inclined to reproduce. Life wants to live. But not just to sustain the numbers, but to increase the numbers of a particular organism. It’s the way the world’s giant ecosystem works. Each component supports another in some size, shape or form. 

As previously mentioned in the section, Role of Swans, Mute Swans fit into the world’s ecosystem by fulfilling the role of ensuring the energy and nutrients continue to be recycled in the habitats in which they live.

A swan is successful in life if it lives long enough to breed and ‘duplicate’ itself, so its genes are passed onto the next generation. 

But if a pair of swans needs to replace itself, it needs to reproduce more than just two birds. That’s because for a pair of swans to successfully ensure its genes are passed on forever, it must ensure its offspring are also able to pass on their genes – the offspring mustn’t die before successfully raising more Mute Swans to maturity.

Of course, there’s no way a pair of swans can definitely ensure that’s going to occur, but what nature does do is to hard-wire living things to reproduce as many living things as possible, or at least, as many offspring the environment can sustain. So, that’s why swans tend to breed every year (provided they’re physically able to do so); the object being to produce as many cygnets as possible to increase the likelihood of their genes continuing to contribute to the gene pool of Cygnus olor.

Age of Breeding Swans

Mute Swans in their first year are probably not physically able to breed, but many certainly engage in courtship behaviour, though. Some swans have been known to successfully breed in their second year, but this is rare.

Most Mute Swans will not breed until at least their third or fourth year of life –some will never breed simply because they are loners, they’re unable to find a mate or a pair will not find a suitable territory. It’s not the norm for Mute Swans to be loners though, but it does happen.

It has been discovered that the female swans are likely to breed at a younger age than the males, about 1 year younger.

Once a pair have established a territory and bred, they will probably continue to breed every year for the rest of their lives, unless there is a loss of partner due to death or ‘divorce’ (this is not common) or maybe, they are ousted from their territory by another pair of swans.

Time of Year Swans Use to Breed

Swans generally breed in the spring, normally anytime from March till June. Now, it’s important to be specific about what we mean by breeding. In my mind, breeding means doing something that is essential for the production of offspring. To me courtship is not mating or breeding – it’s just courtship.  Mating, nest building and care of offspring are all parts of breeding.

The earliest I’ve personally witnessed mating (as part of the breeding process) has been in February. That’s quite early, but not exceptionally so. The day in question was very cold; the air temperature was around freezing point, with a bitterly cold wind, along with some light snow showers falling either side of the two swans mating. The swan pair had been very actively courting each other in the preceding days, so, I wasn’t overly surprised to see them mating - in spite of the weather.

The earliest I have personally known for the eggs to be laid is March, but I have read accounts of cygnets hatching in March, too. That would mean the eggs would have been laid in February – that’s very early.

The normal time for eggs to be laid is generally March/April/May with the subsequent hatching of the cygnets just over a calendar month later – see the sections on Where Do Swans Nest? and Swan’s Incubating Eggs for more details.

Why do many animals (not just  swans, of course!) choose to breed in the spring?

The answer to this question is essentially food, shelter and warmth.

Firstly, food. Raising young is a demanding job, the whole process requires food, and lots of it. That’s because it exerts an extra strain on the parents – they’ve got to be more active and vigilant than normal to protect the cygnets from predators, etc...

Also, the pen swan (the female swan that forms part of a breeding pair) loses a significant proportion of her weight during her time on the nest incubating the eggs (see section on Where Do Swans Nest?). So, she’s got to eat more than normal to make up for this weight loss. 

The cob swan (the male swan that forms part of a breeding pair) will be especially active guarding the territory and chasing off intruders to his patch, so he’ll be particularly hungry, too.

Lastly, the young cygnet when hatched and swimming around in the water, will be hungry as well.

Those three things will mean that Mother Nature must provide a veritable banquet for our feathered friends to feast on, if they are to flourish. And that’s exactly what she does. The spring plants start to grow strongly again and insects are bursting into life. All of these are more than welcome to the hungry bills of the Mute Swans! And this bounty will last right the way through to autumn.

Shelter - swan families need shelter. After the baby swans have hatched and left the nest, they will not go back to their birth place as a matter of course. What swans do though is to build little ‘nests’ made from plants and old twigs, etc... that are often used as preening and resting spots for the next few months. Not all Mute Swan pairs do this, but a lot do.

Lastly, the weather needs to be fairly warm, too. Young swans have a relatively large surface area and that makes them more susceptible to the cold. It takes many weeks for the cygnets to grow proper feathers (they hatch with fluffy down) and to grow large enough for their surface area to volume ratio to go down enough to make them less vulnerable in the low temperatures.

With them being born in the spring, nature has given them the opportunity to have the greatest length of time possible for the weather to be good enough to allow the pair to raise cygnets to being mature enough to fly off and start their own individual lives.

So, you can now see why birds born in the latter part of spring and early summer may have a reduced chance of surviving a whole year because they’re got a shorter period of time to get large enough and strong enough to successfully weather the winter.

Early or Late Breeding – What is Best?

It’s a balancing act between being too early and too late.

The advantages of breeding early include the fact that the young swans have got a lot of time from hatching, to the onset of winter, to get sufficiently hardy enough to withstand the cold weather.  Also, when the pen swan lays her clutch early, there is more time to lay another set of eggs, should anything happen to the first one. Events such as floods and outside interference can destroy nests and their eggs.

The disadvantages of being the first to breed include the fact that flooding could be more likely earlier in the season. In addition, any heavy rain could have a chilling effect on the cygnets, increasing mortality rates. There will also be less natural food available for young Baby Swans in April and early May.

For late breeding Mute Swan pairs, there will be a relative abundance of natural food compared to a month or so earlier - so cygnets not getting enough food is unlikely. With the weather being warmer and it being likely to be drier, flooding is less likely and the chances of the baby swans dying as a result of very low temperature are reduced, as well.

The main problem for them is the fact that there in less time for the offspring to get sufficiently strong and developed enough (lower surface area and more insulating covering from their feathers) to survive the cold weather ahead in the late autumn and winter.

Who Are The Winners?

Research has shown that it’s the early breeders that successfully raise a greater proportion of their offspring to flying off and leaving their parents.  The extra time invested in raising their young over the spring and summer, wins over the risk of the weather being bad enough in the early season, placing a greater element of risk to the breeding pair.

An early bout of unseasonably cold weather in the autumn will prove more likely to be fatal to a young swan from a late breeding family.

That’s one reason why late breeders usually lay fewer eggs that those Mute Swans that lay early in the spring. If fewer eggs are laid in the nest, the breeding cycle is speeded up because there is less time between the first egg being laid and the first egg hatching. Hence the young can be out and about getting fattened up as soon as possible. See the section on Swans Care of Eggs.

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