Multiple Long-Term, Landscape-Scale Data Sets Reveal Intraspecific Spatial Variation in Temporal Trends for Bird Species.

Quantifying temporal changes in species occurrence has been a key part of ecology since its inception. We quantified multidecadal site occupancy trajectories for 18 bird species in four independent long-term, large-scale studies (571 sites, ~1000 km latitude) in Australia. We found evidence of a year × long-term study interaction in the best-fitting models for 14 of the 18 species analysed, with differences in the temporal trajectories of the same species in multiple studies consistent with non-stationarity. Non-stationarity patterns in occupancy were not related to the distance from a species niche centroid; species in locations further from their niche centroid did not demonstrate differing temporal trajectories to those closer to their niche centroid. Furthermore, temporal trajectories of species were not associated with climatic values for each study relative to their niche. Our findings demonstrate the need for multiple long-term studies across a species range, especially when tailoring conservation decisions for populations.