There is an excellent treatise here supplemented with NBN Data showing the decline of this once popular species
Wall Brown Decline
I have noted this species on the peripheral Field Margin adjacent to a dry stone wall well trodden and
near cattle. The annual sightings petered of circa 2011/12 and was also mirrored by a specimen at Ogden LNR on the Easterly side of the reservoir near to the stone walling before going onward up the clough
It begs the question as to where if any there might be strongholds in Calderdale per chance hanging onto to areas of small suitable micro climate Some of the reasons for its decline are given below
Evidence suggests butterfly is dying out because warmer weather is causing generations to hatch out too late in the year to survive There is more here
Wall Brown and Climate Impact
micro-climate at the inland sites was on average 1.2C warmer than at coastal sites, suggesting that cooler conditions by the sea enabled the butterfly to maintain its traditional life-cycle.
It begs the question where is it seen in Calderdale and Why and whether numbers could be augmented at this sites by adding bred numbers
