Macrocyclic lactone treatments for livestock can have detrimental effects on the arthropod populations in livestock faeces. For the last twenty years, avoidance of these products has been a standard recommendation on livestock farms that are managed for wildlife by the Royal Society for Protection of Birds (RSPB). However, the continued decline in the populations of birds (in particular the red-billed chough Pyrrhocorax pyrrhocorax) that are dependent on dung invertebrates on islands in the Inner Hebrides of Scotland prompted us to investigate the effects of livestock treatments that are commonly used on these islands. We conducted a replicated field plot study over two years to quantify the effects of livestock treatments containing copper, deltamethrin and triclabendazole on invertebrate density in pooled, artificial faecal pats on the island of Islay. We found that the density of arthropod larvae was significantly reduced by the triclabendazole and deltamethrin treatments in both years and by as much as 86% when the treatments were combined. Copper-containing boluses did not consistently affect abundance of arthropod larvae. These results suggest that veterinary treatment of livestock might contribute to a reduction in the food supply of chough.

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In Great Britain, red billed chough (Pyrrhocorax pyrrhocorax) breed in discrete populations along the west coast: on Islay and Colonsay, in the Inner Hebrides of Scotland; on the Isle of Man; in Wales; and in Cornwall. Chough are dependent on pastures grazed by cattle and sheep, and their survival is therefore dependent on sympathetic management of grassland. The Scottish population is in decline and all other populations are growing or stable. Sixty-three farmers in these locations whose farms were known to support feeding chough were asked questions about their farm management using a structured, questionnaire-based personal interview. Islay farms were significantly larger and had more grazing area, with the lowest stocking densities. Welsh farms had the least cropping area and the smallest number of cattle. Cornwall had the smallest number of sheep per farm. Welsh farms were more likely not to house cattle during winter. Liver fluke in sheep and ticks and tick-borne disease were a higher concern on Islay than other locations and abortion in sheep was of highest concern on the Isle of Man. Islay farmers used between four and 13 times as many treatments per year as farmers at other locations and the application 2 rate of triclabendazole (TCBZ) was higher on Islay. The rate of application of other products, including macrocyclic lactones ML, did not differ among locations. The study described here shows clear differences in the farm grazing management, in the priority given to animal health problems and in the frequency of application of veterinary parasiticides among four locations that provide feeding habitat for chough in the UK. These differences suggest that the viability of chough populations might be favoured by higher intensity grazing, and by low rates of application of veterinary parasiticides of either the TCBZ or synthetic pyrethroid SP, or both classes of parasiticides.

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