Predation of simulated willow ptarmigan nests: the influence of density and cover on spatial and temporal patterns of predation

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Abstract
Predation of eggs is a major loss in production for many populations of grouse, yet often the identity of the predators, their pattern of search, and their impact on spacing of nests is unknown. We set out clutches of quail eggs to simulate willow ptarmigan (Lagopus lagopus) nests at three densities (100/km2, 50/km2, and 27/km2) to (i) investigate the effects of nest density and concealment on predation rates, (ii) investigate the temporal and spatial patterns of predation, (iii) identify nest predators, and (iv) compare predation rates on artificial nests and nests of willow ptarmigan. Predation on artificial nests was not dependent on density. Predation was lowest in the 1st week, when nests were covered to simulate conditions during laying, and increased in week 2. Thereafter it increased on two plots and declined on four others. Artificial nests had a higher probability of being taken by a predator if they were adjacent to a nest that had been taken previously, suggesting that predators concentrate their search in areas where they have been successful. Neither amount of cover at the nest nor distance to marker stakes influenced predation rate. Predation on artificial nests was lower than on ptarmigan nests. Red foxes (Vulpes vulpes) took most clutches at artificial nests positioned beside boards coated with petroleum jelly, followed by Arctic ground squirrels (Spermophilus parryi), and least weasels (Mustela nivalis). Artificial nests were useful for identifying potential nest predators and investigating their search patterns, but did not give a good index of the extent or temporal pattern of predation on natural nests.