Hen Harrier and Short-eared Owl status and trends Finland

Common birds of prey survey started in Finland in 1982. Monitoring relies on volunteers and is coordinated by the Finnish Museum of Natural History Luomus. Birds of prey are surveyed with several methods. In a Raptor Grid study (1982–), territories and nests of birds of prey are reported from 10 × 10 km study plots. Some 130 study plots of 100 km2 participate each year. Long-term trends of the HH and SEO were modelled based on the annual numbers of occupied territories in the Raptor Grid study plots using the program TRIM. Since data are scarce especially on the SEO, observations from line-transect censuses (covering the whole country every 25 km) were also included to complement trend calculations. A Raptor Questionnaire study (1986–) gathers information on numbers of checked nest types (over 37 000 annually), territories, nests with eggs or chicks, fledged broods and other occupied territories within areas of local ornithological societies of BirdLife Finland. Everyone ringing raptors from nest sites are expected to report their data with Raptor Questionnaires. Approximately 280 ringers or working groups return questionnaires annually. The breeding parameters and geographic distribution of the species are based on the Raptor Questionnaire data. In addition, population size estimates of raptors are based on enquiries sent to local raptor experts in 1998. Trajectories of population size estimations since 1998 within local ornithological societies were modelled based on trend indices, resulting in overall national population estimates of the species in 2018. Both HH and SEO are migratory in Finland and their breeding population levels fluctuate considerably due to vole cycles. HH population declines in Finland with an annual rate of −2.5% according to the long-term data (1982–2018). With this rate of moderate decline (p<0.01), the HH population has decreased by −59% since the beginning of monitoring in 1982. In a short-term (2007–2018), the annual rate of decline is even steeper (−6.0%). The estimated population size of HH is 1132 pairs (min–max 824–1464 pairs) in 2018. Based on means of the yearly averages in the long-term data, the breeding parameters of the HH are: clutch size 4.7 eggs/clutch (standard deviation sd = 0.6, N=183 nests), 4.1 young/successful nest (sd=0.5, N=295) and 3.3 young/active nest (sd=1.1, N=351). On average, 20.7% of breeding attempts fail. SEO population declines with an annual rate of −3.2% based on the long-term data (1982–2018). As a result of this moderate decline (p<0.01), the SEO population has decreased by −69% since 1982. In the short term (2007–2018), the annual rate of decline is −7.0%. The estimated population size of SEO is 762 pairs (min–max 39–1485 pairs) in 2018. Breeding parameters of the SEO are: clutch size 6.0 eggs/clutch (sd=1.0, N=673 nests), 4.4 young/successful nest (sd=0.8, N=746) and 3.5 young/active nest (sd=1.0, N=945). On average, 20.7% of breeding attempts are unsuccessful. Both HH and SEO are most numerous in Northern and Western Finland. No specific conservation plans for the species are implemented.