Mark-recapture population estimation of the highly endangered noctuid moth Arytrura musculus

Abstract

The study was inspired by a high-profile legal case on the removal of grey willow (Salix cinerea) shrubs from 5 hectares of wetland in the Kék-Kálló valley, North-Eastern Hungary. This action allegedly caused a serious damage to the local population of Arytrura musculus, a night-flying noctuid moth strictly protected under Natura 2000 and Habitats Directive Annex II and IV, by destroying the overwintering larvae. Our aim was to estimate the population density of the species in the affected area using a Capture-Mark-Recapture (CMR) method during its peak flight period. To attract the moths, we used various types of lamps, including a standard 125W MV bulb, in front of white sheets, and live capture light traps with 8W fluorescent tubes. These were operated simultaneously at multiple locations. Each specimen was marked with a unique serial number on the hindwing, using fineliner marker pens. A total of 94 captures occurred (78 first captures and 16 recaptures), of which 80 were used for our statistical analysis. The longest recorded movement of any one individual was 2.5 km. Daily population size ranged from 11 to 117, and the estimated total population for the entire survey period was 226 individuals. Based on the recorded movements, the location of collecting lights, and the vegetation coverage patterns identified from aerial photos, the effective survey area was calculated as 38 hectares. It gives a minimal density of 6 adults (imagos) per hectare, which, although a cautious underestimate, is much less than the previously claimed value of 1200 individuals (larvae) per hectare, deduced from a single light trapping occasion.