Abstract
The monitoring used in management of the northern European rock ptarmigan population today is manly based on hunting statistics and index counts at spring. Line transect distance sampling using pointing dogs have been suggested to use, all tough there have been skepticism regarding validation of the assumptions. The method estimates the local population, including yearly production. In this study the key assumptions of line transect distance sampling using pointing dogs have been tested on rock ptarmigan: (1) Birds on the transect line are found by certainty with a decreasing discovery rate with increasing distance to line, (2) birds are found at their initial location, and (3) measurements are exact. Additional, other factors influencing the discovery rate were tested. Experiments were done during late summer and early autumn in 2022 and 2023.
The result of this study shows that all rock ptarmigans within 0-30m from the transect line were found, with an 100% discovery rate directly on the line. The activity of the birds when approached depended on their prior activity, and it was more likely for the birds to become passive after being active, than becoming active after being passive. This indicates that the normal response is to freeze when approached. There was no significant difference in distance measurements made for an observation, although measurements made too short were greater than those who were made too long. The best models to explain discovery rate included the bird’s distance to the line and distance moved. The distance to the line had a strong negative effect, while the distance moved had a weak positive effect. Whether or not the birds moved closer or further away from the line were not part of the best models. This indicates birds are more likely to be found the longer they move, and their absence is not a result of moving closer or further away when approached. Weather conditions and wind direction did not contribute to the best model, which can be explained by fairly “normal” conditions and should therefore not be excluded in further research on the topic.
The result of this study indicates line transect distance sampling using pointing dogs does not violate with the key assumptions when used on rock ptarmigan. Further research needs to be made to determine the usefulness of covariates. To better know the functionality of this monitoring approach on rock ptarmigan, a full study design in different topographical landscapes and scale should be tested.
Keywords: Rock ptarmigan, Lagopus muta, distance sampling, wildlife management, monitoring