Les oiseaux communs de métropole

Operational since 1989, the temporal monitoring index of common birds (STOC index) reveals very different trends between bird species. Trends differ according to species type (generalist or specialist) as well as specific habitat (agricultural, forest, urban) or geographic location.

Over the period 1989-2021, the decline of specialist bird species is steep (-24%) while generalist species are increasing in abundance (+19%). Specialist bird populations declined during the 1990s. Over the past decade, they appear to stabilize for forest habitat species, but continue to decline in built-up and agricultural areas.

Habitat degradation or loss, intensive agricultural practices, and climate change remain among the primary threats facing bird populations.

The STOC index studies year-to-year variations in two bird groups. Specialist birds whose survival depends on specific environmental conditions and which are found only in specific habitats (agricultural, built-up, forest areas) and generalist birds that tolerate a wide range of environmental conditions, thriving in diverse habitats and using a wide variety of resources. Over the period 1989-2021, specialist bird abundance is in decline with a population decrease of 24%.

After generally increasing in the early 2000s, the abundance of generalist species (14 species covered by the STOC index) has dropped significantly since 2012 (-9 points over 2012-2021). However, it remains increasing over the 1989-2021 period (+19%).

These trends promote homogenization of bird communities and impoverishment of species at the metropolitan scale. Indeed, habitat specialist species have stricter ecological requirements than generalist species and a narrower range of environmental conditions. In the event of disturbances, these species are more affected than generalist species, which are theoretically more tolerant of change. A decline in specialist population abundance thus reflects habitat disturbance, qualitative or quantitative, such as reduced food resources, increased disturbance, or reduced nesting site availability.

Over the 1989-2021 period, specialist bird species declined by an average of 24%. Monitored bird populations fell sharply during the 1990s. Over the past decade, they appear to stabilize for forest habitat species, but continue to decline in built-up and agricultural areas.

With stability in specialist species of forest habitats (22 species covered by the STOC index), bird populations in wooded areas show the smallest declines. Species dependent on agricultural habitats (24 species covered by the STOC index) and built-up areas (13 species covered by the STOC index) are most severely affected, with populations declining by 36% and 33% respectively over this period.

Other variants of the STOC-EPS index enrich the general protocol for particular habitats. This indicator is adapted to state forests with the STOC-ONF index and to mountain areas above 1,800 m altitude with the STOM index (temporal monitoring of mountain birds). This latter monitoring, coupled with the European Bird Census Council, a vast network of common bird counting programs across Europe (12 countries), revealed a 7% decline in mountain bird populations over the past decade. Conversely, it also demonstrated the close link between certain mountain species dynamics and the absence of intensive agriculture (such as the Eurasian Skylark, whose populations decline in the countryside while increasing in mountains).

More specific monitoring programs are also conducted: on particular sites (STOC-Site index) or in nature reserves (STOC-RNF index). The STOC index monitoring in French nature reserves (RNF) shows the positive impact of protection and management of natural habitats on common bird population trends. A 2019 study of 94 metropolitan reserves demonstrates the biodiversity sanctuary role of such protection: while common bird populations declined by an average of 6.6% across metropolitan France between 2004 and 2018, they increased by 12.5% during the same period in nature reserves.

Species life cycles are also tracked with a STOC index dedicated to wintering species (SHOC: temporal monitoring of wintering common birds). Trends in the 87 species of this latter monitoring largely confirm those observed by the STOC index. Among these analyzed species, 13 show significant increasing trends, 12 show decline, and 62 have uncertain trends. Wren, Eurasian Skylark, and Rook populations are declining while Great Spotted Woodpecker and Wood Pigeon, which increase during breeding, also increase in winter (confirmed by both STOC and SHOC indices).

• Methodology • The STOC index (also called STOC-EPS index), a standardized monitoring program from citizen science • Alauda arvensis • Dendrocopos major • Passer domesticus • Turdus merula • EPOC & EPOC-Oiseaux de France (EPOC-ODF): two national surveys complementing the STOC program