An estimate of the diversity and threat levels of avian chewing lice (Phthiraptera: Ischnocera, Amblycera), with a call for “pre-emptive red listing”

Many parasites are intimately tied to a single host species, and thus likely to go extinct if their host vanished, making the parasites and hosts co-endangered. As endangered host species taken into breeding or relocation programs are often routinely treated against parasites, conservation-induced extinction of parasite species is likely to be a problem for parasite conservation. Moreover, the representation of parasites in the IUCN Red List is poor. For parasitic lice (Phthiraptera), only a single species has been evaluated, despite over 150 louse species being known from highly threatened bird hosts. Here, we calculate the Index of Specificity (IS) for all louse genera occurring on avian hosts. We use this to estimate that the true diversity of avian chewing lice is 41,627–42,410 species, of which only 4535 (~ 11.0%) are presently known. We then use these IS values to predict the unknown diversity of lice on highly threatened host species, estimating that the number of host-specific louse species exclusively parasitizing highly threatened bird hosts may be an order of magnitude higher than presently known (1162 vs. 108 species). In order to forestall the conservation-induced extinction of further louse species, we here propose a “pre-emptive red listing” of louse species that are not currently known or described formally but are likely to occur on highly threatened hosts. Ideally, any future breeding or relocation program involving these hosts should take care to also survey louse species on the hosts and, as far as possible, conserve these concurrently with their hosts.