Parasites and Scottish ptarmigan numbers.

Area of Science:

• Avian ecology
• Parasitology
• Wildlife health

Background:

• Red grouse (Lagopus lagopus scoticus) commonly host high levels of parasitic threadworm (Trichostrongylus tenuis) and tapeworms.
• Scottish ptarmigan (Lagopus mutus) populations exhibit distinct ecological patterns that warrant investigation into their parasite burdens.

Purpose of the Study:

• To compare the prevalence and intensity of parasitic infections in Scottish ptarmigan with those in red grouse.
• To investigate the relationship between ptarmigan population density, habitat geology, and parasite infection rates.
• To assess the role of parasites in observed ptarmigan population dynamics.

Main Methods:

• Field surveys of Scottish ptarmigan populations across different geological substrates (granite vs. schist/limestone).
• Post-mortem examination of ptarmigan to quantify the presence and abundance of internal parasites, specifically threadworms and tapeworms.
• Analysis of ptarmigan population densities in relation to geological type and parasite infection data.

Main Results:

• A high proportion (70%) of Scottish ptarmigan lacked threadworms, and only 4% had tapeworms, contrasting sharply with red grouse.
• Threadworm prevalence was significantly lower (12%) in ptarmigan on granite hills with low densities compared to those on schists and limestones (43%) with high densities.
• Other parasites and pathogenic bacteria were found infrequently across the surveyed ptarmigan population.

Conclusions:

• Parasitic infections, particularly threadworms, are less prevalent and intense in Scottish ptarmigan than in red grouse.
• Ptarmigan population density and underlying geology appear to influence threadworm prevalence, suggesting density-dependent or habitat-specific factors.
• The hypothesis that parasites drive cyclic ptarmigan declines on the Cairngorms granite massif is unlikely, given irregular fluctuations over richer rock types.