The rock ptarmigan (Lagopus muta) is the main game-bird in Iceland and it has a population that varies cyclically, peaking every ≈10 years. The goal of the ptarmigan health project is to study how different health parameters relate to population changes during one population cycle. The present study aims to increase the understanding of the functions of the preen gland, specifically the effect of body size, sex, and age on the size of the preen gland in ptarmigans. Also, the relationship between the preen gland and the abundance of ectoparasites is explored. Preen glands were sampled and analyzed in the laboratory from ptarmigans collected in North-East Iceland from 2007-2012. Results indicate that the preen gland mass is largely influenced by collection year, to a much greater extent than by body size. In addition, mean preen gland mass was higher in males than in females, as well as in adult birds than in juvenile birds. Furthermore, it was observed that larger preen glands produce more preen oil than smaller glands, which indicates that preen gland activity is reflected on gland size. The size of the preen gland showed a negative relationship with parasite richness and parasite burden. This study supports the conclusion that the gland is part of the outer defenses against ectoparasites and that the function of the preen gland may be important in fighting ectoparasites in ptarmigans in Iceland and warrants further research.

Keywords: preen gland, Lagopus muta, population changes, preen oil, ectoparasites.