How Small Heath butterflies respond to changing temperatures
Adapting to change – is it possible?
Climate change affects the distribution, abundance and phenology (timings of life cycle stages) of organisms, and butterflies are no exception. Changing temperatures can affect butterfly life cycle speeds, how quickly or slowly they reproduce and, consequently, their population numbers too. Warmer or colder weather also impacts their flight activity, territorial behaviours and breeding success.
When environmental temperatures change, organisms need to respond; they need to regulate their bodies at an optimum temperature, in order to survive. We put on warmer clothes in winter and add ice to our drinks in the hotter months. Other species don’t have the luxury of these tools. They generally respond to changing temperatures in three ways: through internal bodily mechanisms (‘physiological thermoregulation’), by changing their behaviour and therefore increasing warming or cooling (‘behavioural thermoregulation’), or by moving to more favourable climatic conditions (‘microclimate selection’).
In an ever-changing climate, those butterflies who rely primarily on behavioural thermoregulation, and so are less dependent on their environment, are predicted to be less negatively affected by climate change than those butterflies who rely mostly on microclimate selection.
Therefore, it is vital to understand how small heath butterflies respond to temperature, in order to predict how their populations will change and make sure we manage our nature reserves and heathland to help them have a safer future.
Intern Alex carrying out a wildlife survey in Harmony Woods, Hampshire. Photo taken by Alex Marshall
Taking temperatures and measuring behaviour
ATU and PTES intern, Alex Marshall, is taking on the challenge. She’s setting out to investigate how changes in temperature affect the behaviour of small heath butterflies. Alex’s study site is Harmony Woods near Andover, Hampshire. Working with ecologists and other volunteers from environmental charity Andover Trees United, Alex is determining which response mechanism is used most often by small heaths, and how this differs with changes in temperature.
If environmental temperatures do have significant effects on either the microhabitat (small, specific habitat) they choose to live in or their behavioural thermoregulation, this will provide important insights into their ecology in relation to climate change. It will help us understand how their survival may be impacted by global warming and habitat loss, and then do something about it. There are really practical ways that we can help small insects and other invertebrates like butterflies. Creating ditches or mounds changes a microhabitat and makes it much more diverse. Imagine being as small as a butterfly. The cool or shade created by a ditch will be significant compared with the temperature on adjacent flat ground exposed to the sun. Alex’s study is helping us build our knowledge about how butterflies modify their temperature and allowing us to work out the best ways to help them.
Words are written in collaboration with PTES: https://ptes.org/grants/internship-projects/how-small-heath-butterflies-respond-to-changing-temperatures/