Common breeding forest birds
Summary
The populations of common breeding forest birds in Finland have, on avergae, improved since the beginning of the monitoring that started in 1979. During the 2000s, the idicator has remained stable, with no clear observable improving or diminishing trend. However, the trends of individual species differ from each other. Resident birds that favor old-growth coniferous forests have mostly declined (see winter birds in forests), but the populations of most migratory birds have increased. Southern species have benefited from climate warming.
Status
The status of the indicator is most likely good, but there is uncertainty in the assessment of both the reference value and the current state due to strong fluctuations. With 90 percent certainty, the populations of common breeding forest birds have increased by at least 3 percent compared to the turn of the 1970s and 1980s, but it is also possible that the improvement has been more significant.
Of the 29 species in the indicator, the populations of two species – the Eurasian wren and the mistle thrush – have more than tripled compared to the early 1980s. The populations of seven other species are now more than 20 percent higher than at the start of the monitoring period. The populations of the capercaillie, coal tit, Eurasian treecreeper, Eurasian bullfinch, and the greenish warbler have remained stable. The most significant declines have been seen in the hazel grouse, wood warbler, willow tit, crested tit, and brambling, whose populations are 30–70 percent lower than at the start of the monitoring period.
Trend
The trend of the indicator is stable. Since the year 2000, forest breeding bird populations have, with 90 percent probability, declined by at most 0.8 percent per year, but the decline has likely been significantly less than this. The current stable period was preceded by a period of improvement during the first two decades of the monitoring period (1979–1999). The indicator has shown fluctuations over several years, which are particularly explained by the large population variations of species that feed on seeds.
Although the overall trend of the indicator appears stable, the population trends of individual included species vary greatly. If the analysis is limited to the ten species that most strongly avoid clear-cut areas and young forests during the breeding season (greenish warbler, wood warbler, goldcrest, red-breasted flycatcher, Siberian tit, coal tit, crested tit, Eurasian treecreeper, brambling, and common redpoll), the trend has been clearly declining (Lehikoinen et al. 2024).
Significance
The indicator is one of the measures of the state of biodiversity in forest ecosystems. The population trends of common forest birds reflect the vitality of these species. Locally, this is evident in the diversity and abundance of forest birds.
The habitat requirements of the common breeding birds included in the indicator vary significantly, but they all share a preference for forested environments over open or shrubland areas. The indicator includes species such as the capercaillie, willow tit, and crossbills, which are typically associated with coniferous and mixed coniferous forests. The wood warbler, on the other hand, clearly prefers deciduous forests. However, many species have flexible habitat requirements. The species most dependent on mature and old, contiguous forests include the capercaillie, greenish warbler, willow tit, Siberian tit, crested tit, Eurasian treecreeper, red-breasted flycatcher and Siberian jay.
Of the 29 species in the indicator, ten are resident birds that remain on their territories mostly year-round. There are 14 clear migratory species, of which six are long-distance migrants traveling outside Europe. Migratory birds are also affected by conditions along their migration routes and in their wintering areas—generally more so the farther they migrate. Most of these species have a distribution centered to the south of Finland, which is why climate change is improving their breeding conditions as they can expand their range northward. The temporary growth in the indicator in the 1990s was likely due to the recovery of forest bird populations from the decline in resident and short-distance migratory species caused by the very cold winters of the 1980s (Lehikoinen and Väisänen, 2023). Northern species such as Siberian tit, Siberian jay and brambling, however, are suffering from climate warming, and their range has contracted in the south.
The capercaillie and hazel grouse included in the indicator can be hunted.
Bird monitoring forms one of the most central and reliable datasets for tracking biodiversity in Finnish nature (see below “Background Data”).
References
Data used
The indicator is based on monitoring censuses coordinated by the Finnish Museum of Natural History and conducted partly by volunteer birdwatchers with professional-level bird knowledge and partly by paid researchers.
The most important monitoring method for terrestrial birds are line transect censuses, with data available in the open databases of the Finnish Biodiversity Information Facility, maintained by the Finnish Museum of Natural History (see below “More Information about the Data”). Since 2006, line transect censuses have been conducted throughout Finland on a standardized network that covers every 25 kilometers. There are a total of 566 six-kilometer routes, of which approximately half are counted annually. Before 2006, the routes were chosen by the counters themselves. The establishment of standardized routes improved the data coverage and the reliability of the results. In addition to line transect counts, monitoring data is also collected through point and mapping counts.
The time series for forest breeding birds begins in 1979, when sufficient monitoring data started to accumulate for 19 of the 29 species included in the indicator. The Eurasian wren, capercaillie, mistle thrush, and common redpoll were added to the indicator in the early 1980s, and the Eurasian sparrowhawk, three-toed woodpecker, Siberian tit, Siberian jay, red-breasted flycatcher, and pine grosbeak were added in the mid-2000s.
Species included in the indicator:
Eurasian sparrowhawk – Accipiter nisus
Hazel grouse – Tetrastes bonasia
Capercaillie – Tetrao urogallus
Eurasian woodcock – Scolopax rusticola
Three-toed woodpecker – Picoides tridactylus
Eurasian wren – Troglodytes troglodytes
European robin – Erithacus rubecula
Common redstart – Phoenicurus phoenicurus
Mistle thrush – Turdus viscivorus
Song thrush – Turdus philomelos
Greenish warbler – Phylloscopus trochiloides
Wood warbler – Phylloscopus sibilatrix
Chiffchaff – Phylloscopus collybita
Goldcrest – Regulus regulus
Willow tit – Poecile montanus
Siberian tit – Poecile cinctus
Crested tit – Lophophanes cristatus
Coal tit – Periparus ater
Eurasian treecreeper – Certhia familiaris
Spotted flycatcher – Muscicapa striata
Red-breasted flycatcher – Ficedula parva
Siberian jay – Perisoreus infaustus
Chaffinch – Fringilla coelebs
Brambling – Fringilla montifringilla
Eurasian siskin – Carduelis spinus
Common redpoll – Carduelis flammea
Crossbill species – Loxia sp.
Pine grosbeak – Pinicola enucleator
Eurasian bullfinch– Pyrrhula pyrrhula
More information about the data:
Indicator calculation
The indicator for common breeding forest birds is produced by the Finnish Biodiversity Information Facility of the Finnish Museum of Natural History. It combines estimates of population trends for individual species into a single index number. This multi-species indicator updates automatically and its index value represents the relationship to a reference year, which for the forest breeding bird indicator is the year 2000.
The calculation of the multi-species indicator begins with assessing the population trends of individual species. These trends are evaluated based on the number of bird pairs observed during counts, using generalized linear statistical models that account for differences between counting locations and dependencies between consecutive years.
Species-specific estimates, based on sampling-dependent statistical models, always contain uncertainty. This uncertainty is considered and incorporated into the multi-species indicator using Monte Carlo simulations.
For estimating indicator status reported at this site, comparisons have been calculated between the start and end periods of the time series produced by the Finnish Biodiversity Information Facility, as well as annual population trend estimates for different time periods.
Indicator as a CSV-file:
More information on the indicator calculation methodology:
Updates and changes to the indicator
August 23, 2024: The indicator was significantly updated in August 2024. During this update, the indicator’s name was changed from “Forest Breeding Birds” to “Common breeding forest birds.” Additionally, the species list for the indicator was revised to include the Eurasian woodcock, three-toed woodpecker, mistle thrush, common redpoll, pine grosbeak, and Eurasian bullfinch, while the common buzzard and blackcap were removed. In the updated version, the populations of all crossbill species breeding in Finland (common crossbill, parrot crossbill, and two-barred crossbill) are now combined, whereas the previous version only included the common crossbill. Due to these species changes and the addition of data from 2023, both the status and trend of the indicator have shifted in a more favorable direction.
Aleksi Lehikoinen
Senior Curator (Luomus), Head of the working Group on Birds
Päivi Sirkiä
Senior coordinator, group manager (Syke), Use of ecosystem information, systematic species surveys