How many observation days are needed to reliably describe bird migration? Hur många observationsdagar behövs för att tillförlitligt beskriva fågelflyttning?

The total number of migrating birds is needed, for example, to estimate collisions risk as part of the assessment process for wind-power parks. This estimation is often based on a small sample of observation days, making estimates uncertain. To determine the number of days needed to obtain reliable figures we used observations of migrating birds obtained from the Signilskär bird observatory, Åland, Finland during the autumn seasons from 2009 to 2013. We sampled 1–14 days during each 14 day time window and used linear extrapolation and Poisson regression with weather covariates to estimate the total number of migrating birds and distribution of estimates. We calculated the head-wind and side-wind components according to the species’ most common flight directions. We found that observations should cover at least 90% of the migration period to obtain precise results and 70–90% to obtain results sufficiently reliable to use in practice. Linear extrapolation is the best model for small samples. The larger the proportion of days observed, the better is Poisson regression with weather covariates

The Barnacle Goose (Branta leucopsis) in the archipelago of southern Finland - population growth and nesting dispersal

We studied the population growth and expansion of Barnacle Goose (Branta leucopsis) in Helsinki archipelago, southern Finland. Barnacle Goose breeding was first recorded in Helsinki in 1989. During our study 1996-2013 the number of nesting geese increased from 24 to 740 pairs. We analyzed the role of protected islands in the population growth, and the factors behind differences in growth rates. Our study data consisted of 104 islands. Of these, 29 are protected from private recreational activity (nature reserve ormilitary areas) and were established prior to the start of our study. We predicted that protected areas would have a positive impact on Barnacle Goose population growth. In part of the study period (2002-2013) the population growth in our study area was much steeper in protected islands compared to islands with open access. However, breeding densities in those unprotected islands were higher than in protected islands in the early years of the study. We found that the most important factors affecting pair numbers in islands are island size and the time it has been inhabited, in addition to island distance from the islands southeast of Helsinki, where breeding expansion started. Island protection had no effect on the breeding geese numbers or current densities on the islands. Results indicate that early breeders like Barnacle Geese do not benefit from island protection probably because the recreational use of the islands is scant early in the spring.Peer reviewe

Can common forest bird species tolerate disturbances in neighbouring areas? A case study of the Vuosaari Harbour construction in southern Finland

Urbanization and other human activities can lead to decreasing animal populations in nearby areas. The impact of human activitiesmay vary depending on the characteristics of the areas and region or on the strength of the disturbance. We investigated forest bird population changes in an EU Natura 2000 area during the construction of the new Helsinki Vuosaari Harbour in southern Finland in 2002-2011 as part of an environmental impact assessment. We evaluated whether the changes observed were linked with the harbour construction work by comparing the populations at sites near the development with those corresponding values obtained from national common bird monitoring in southern Finland. Themean population changes of 23 boreal forest bird species that inhabited the Natura 2000 area and southern Finland were significantly and positively correlated, but the population inside the Natura 2000 study area also showed lower mean numbers (a mean decline of 9% occurred over the study period). Our case study emphasizes the importance of intensive monitoring before, during and after work at the construction site and in the surrounding areas to detect actual changes in the populations.Peer reviewe