Titmice are a better indicator of bird density in Northern European than in Western European forests

Mira Kajanus (1) , Jukka Forsman , Maximilian Vollstädt (1) , Vincent Devictor (2) , Merja Elo (3) , Aleksi Lehikoinen (4) , Mikko Mönkkönen (3) , James Thorson (5) , Sami Kivelä (1)

1 University of Oulu
2 UMR ISEM - Institut des Sciences de l'Evolution de Montpellier
3 JYU - University of Jyväskylä
4 LUOMUS - Finnish Museum of Natural History
5 NMFS - NOAA National Marine Fisheries Service

Population sizes of many birds are declining alarmingly and methods for estimating fluctuations in species’ abundances at a large spatial scale are needed. The possibility to derive indicators from the tendency of specific species to co-occur with others has been overlooked. Here, we tested whether the abundance of resident titmice can act as a general ecological indicator of forest bird density in European forests. Titmice species are easily identifiable and have a wide distribution, which makes them potentially useful ecological indicators. Migratory birds often use information on the density of resident birds, such as titmice, as a cue for habitat selection. Thus, the density of residents may potentially affect community dynamics. We examined spatio-temporal variation in titmouse abundance and total bird abundance, each measured as biomass, by using long-term citizen science data on breeding forest birds in Finland and France. We analyzed the variation in observed forest bird density (excluding titmice) in relation to titmouse abundance. In Finland, forest bird density linearly increased with titmouse abundance. In France, forest bird density nonlinearly increased with titmouse abundance, the association weakening toward high titmouse abundance. We then analyzed whether the abundance (measured as biomass) of random species sets could predict forest bird density better than titmouse abundance. Random species sets outperformed titmice as an indicator of forest bird density only in 4.4% and 24.2% of the random draws, in Finland and France, respectively. Overall, the results suggest that titmice could act as an indicator of bird density in Northern European forest bird communities, encouraging the use of titmice observations by even less-experienced observers in citizen science monitoring of general forest bird density

Domaines: Biodiversité et Ecologie

Mira Kajanus, Jukka Forsman, Maximilian Vollstädt, Vincent Devictor, Merja Elo, et al.. Titmice are a better indicator of bird density in Northern European than in Western European forests. Ecology and Evolution, 2022, 12 (2), pp.1284-1296. ⟨10.1002/ece3.8479⟩. ⟨hal-03755748⟩