Ringing the changes: What museum specimens reveal about climate change

Phenology -- the study of the timing of recurring natural phenomena -- tells us a great deal about changing climate and its effect on wildlife. Although phenology provides some of the oldest written biological records in Britain, the date when butterflies emerge each spring has only been recorded systematically for the past 30-40 years.

Records from the UK Butterfly Monitoring Scheme show that since 1976, spring has arrived 6-11 days earlier each decade due to rising temperatures. Now, ecologists from the Natural History Museum (NHM) and the University of Coventry have used some of the museum's 130,000 butterfly specimens collected over the past 200 years to look back at earlier springs.

They examined 2,600 specimens of four British butterfly species -- the Grizzled Skipper, the Duke of Burgundy, the Orange Tip and the Blue Adonis -- all held in the Museum's research collections. Collected between 1876 and 1999, each butterfly is mounted on a pin and labelled with when and where it was caught.

When they compared collection dates with temperature records, they found that in years with warm springs, collection dates were earlier than collection dates in cold, wet springs. The results also show March temperatures and rainfall were most critical in influencing how early these butterflies emerged.

According to Dr Steve Brooks, researcher at the Natural History Museum "Because they agree with observations over the last 30-40 years, our results show that natural history museum collections can provide vital historical information about how butterflies and other organisms respond to climate change."

Understanding the impact of these changes is important because different species depend on each other for food. "Long-term shifts in when British butterflies first emerge due to changing climate may mean the butterflies are no longer synchronised with the food plants on which their caterpillars depend. Many birds depend on caterpillars to feed their chicks but changes in the timing of butterfly life cycles may lead to insufficient caterpillars being present when they are needed by the young birds. By providing long term data from museum collections we can get a more accurate idea of the rates of these shifts in timing," he explains.

The team will now use the museum collections to study how all British butterfly species have responded to seasonal climate change over the past 150-200 years, as well as its impact on their food plants and egg laying dates in British birds to build a complete picture of how earlier springs are affecting food webs.