Spacing behaviour and habitat use of rock ptarmigan (Lagopus mutus) at low density in the Italian Alps

Studies of rock ptarmigan Lagopus mutus in northern latitudes have shown that, in the breeding season, the majority of cocks pair monogamously and defend small territories, whilst in most populations, a small proportion of cocks are polygynous or remain unmated. Little is known, however, on spacing behaviour and habitat use of alpine rock ptarmigan populations occurring at low densities at the southern edge of the species’ range. From 1995 to 1997, we trapped, radio-tracked and observed birds in the Central Italian Alps (elevation 2,000–3,000 m) in order to investigate spacing behaviour and habitat use in alpine landscapes where habitats offering rich food and cover are patchy. Both sexes were selective in their habitat use, and cocks did not establish territories on bare ground, artificial or nutrient rich grasslands or bogs. In the breeding season, cocks had larger home ranges than hens (cocks 99 ± 57 ha, hens 50 ± 25 ha) that overlapped with the ranges of neighbouring cocks and hens. Cocks were monogamous and defended relatively large territories (core areas of home ranges: cocks 37 ± 26 ha, hens 24 ± 12 ha), which corresponded with low spring densities (0.47–2.29 cocks km⁻² and 0.35–1.60 pairs km⁻²). Territory size of individual cocks was negatively correlated with the amount of high quality habitat in the core-area. Our results suggest increased home ranges and large breeding territories in low density alpine rock ptarmigan populations, compared to populations occurring at higher densities in the central and northern alps, and on subarctic and arctic grounds at northern latitudes, confirming the predictions of models on food-based territoriality.