Abstract
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.
Highlights
Islay, Oronsay and Colonsay are the southernmost islands of the archipelago known as the Inner Hebrides of Scotland
Farm and landscape scale studies conducted by the Royal Society for Protection of Birds (RSPB) over 2 years found inconsistent evidence of reductions in dung insect populations that could be associated with routine use of MLs12,13, these products have since the late 1990s been recommended not to be used on farms where chough feed[14]
The initial attractiveness of the faeces, as indicated by the number of arthropods counted on its surface within 15 minutes after presentation did not differ according to the treatments given to cattle within either year (Table 1, in which the relevant results are for the whole surface sample at week 0)
Summary
A significant adverse effect in vitro of low concentrations of TCBZ (0.001 to 0.1%) on the survival and development of the greater wax moth Galleria mellonella has recently been demonstrated[26] It is not clear how these concentrations relate to those that are present in the faeces of treated animals and whether any detectable effect should be expected after routine treatment of livestock. These previously published studies on deltamethrin and triclabendazole were bioassays, conducted in laboratories and did not examine all the species that are known to be important in the UK It is not known if the results can be extrapolated to the field conditions that are important to a feeding chough, which are adapted to breaking apart older more friable dung containing developing larvae. The study was designed to provide the rigour of a controlled and replicated design but under conditions that matched the natural environment for the invertebrates and using the same, commercially available products exactly as they are used by farmers in that environment
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