|British Butterflies: Education: What is a Common Butterfly?
|Thats a common butterfly isn't it?
What makes a particular species of butterfly common compared to being rare? Its a question which many people have asked me.
Many people will tell you that butterflies in general were a far commoner sight in our towns and countryside 50 years ago than they are today... yet why is it that we still describe some species as being 'common'?
"... many butterflies that were once common when I was boy, over 40 years ago are rarely if ever seen in my area (today). For instance I simply cannot recall the last time I saw an Orange-tip. Red Admiral is another example which I see only very occasionally."
Mr I. Blease, September 2010
Above: The Small Tortoiseshell is a 'common' butterfly but how many have you seen this year?
|That's a common species...
The term 'common' is somewhat difficult to define. When we describe species as being common or rare our conclusion is based on the relative abundance of each species.
A good example is the Silver-studded Blue which could be described as 'common' on the Butterfly Conservation Reserve at Prees Heath compared to say the Small Tortoiseshell which is 'relatively' uncommon there... however, if you look at the distribution and numbers of Silver-studded Blue compared to Small Tortoiseshell across the whole of the UK, you come up with a complete opposite conclusion.
So, we can safely say that in the UK as a whole, the Small Tortoiseshell is more common than the Silver-studded Blue... but...
At the risk of being common...
The problem with defining species this way is that it only takes into account relative abundance at a particular moment in time. Evidence based on written records shows that butterfly numbers and species have been declining for more than 100 years due to human activity. Humans have had a huge impact on the environment since the moment we first settled the land and started farming back in the neolithic period which started over 6,000 years ago.
Its fairly safe to say that abundance wise, there would have been a far greater number of butterflies in the UK 6,000 years ago than there are today and there would have been many more species present which are now extinct in Britain. Butterflies would have been a very noticeable part of everyday life in neolithic Britain during the spring and summer months.
Being common today is rare compared to the past
So we may conclude that although species today may be described as being common relative to other species, if we compare the present abundance to that of the past, we would be hard pushed to honestly say that any species of butterfly is common... in fact, almost all butterfly species across the world are 'rare' compared to the past.
Why does this matter
Due to habitat loss which is increasing due to 'development' and changes in agricultural farming practices across the globe, many of our relatively common species are becoming more and more uncommon. To understand this is to get a clearer picture of what we as human beings are doing to the ecosystems and biodiversity which we rely on for our own survival. Butterflies are the perfect indicator of these changes as their complex life cycles mean that small changes in their habitat has a huge impact on butterfly numbers.
Above: Visit Prees Heath at the right time of year and you could be forgiven for thinking that the Silver-studded Blue is a 'common' butterfly.UK species status definitions
The following species status definitions are use throughout this web site.
Resident: A species which is continually resident in Britain with stable breeding populations.
Uncommon Resident: A species which is continually resident in Britain but whose overall population is at risk due to a loss of habitat.
Rare Resident: A species which is continually resident in Britain but whose general distribution is small and fragmented with an overall low population level.
Migrant: A species which occurs as a migrant in Britain. It may be able to breed here during the summer months but unable to survive our cold, damp winters. Migrants are normally reported in the UK every year.
Rare Migrant: A species which occurs as a rare migrant in Britain. It may be able to breed here during the summer months but unable to survive our cold, damp winters. Rare Migrants may not be seen in Britain for many years.
Extinct: A species which is extinct in the UK, usually as a result of habitat loss.
Introduction: A species which occurs in the UK as an accidental introduction.