Given their sensitivity to environmental change, butterflies are recognised as an important barometer for the health of Jersey's ecosystems. Whilst the monitoring of butterfly populations has been carried out in the UK since 1976, Jersey's Butterfly Monitoring Scheme was initiated in 2004. Data is collected by a team of volunteers across 39 sites which cover wildlife, agricultural and urban areas. The counts of butterflies are converted into an annual index of abundance for each species using the national methodology. By giving the count of butterflies in 2004 a value of 100, the subsequent long-term trend in abundance can be monitored over time. Improvements in the modelling technique means that the data is recalibrated regularly.

It is important to note that, by the time Jersey's monitoring programme started, butterflies had been in substantial decline nationally for nearly 30 years. Jersey faces a similar challenge, as shown by the fact that large areas of the Island are now lacking in butterflies, especially in Jersey's interior.

Large annual fluctuations in butterfly populations are to be expected, principally in response to weather conditions, so it is important to consider long-term trends not comparisons between years. Jersey is beginning to see a moderate long-term increase in butterfly abundance from the low 2004 base but this is not a consistent picture. There has been an observed increase in semi-natural habitat sites which are managed for their conservation interest, demonstrating that conservation intervention is working. Elsewhere, butterfly populations in urban areas are decreasing and those in agricultural areas are fluctuating but level overall.