Optimising monitoring for trend detection after 16 years of woodland-bird surveys

1. Long-term biodiversity monitoring programs provide important information about species’ trajectories and broader environmental change. Often constrained by funding and organisational capability and commitment, monitoring programs need to be optimised to maximise ecological and economic efficiencies, as part of sound adaptive management.

2. The monitoring design requirements for detecting biodiversity trends, across assemblages of species with different traits, can be informed by historical datasets. Using data from a landscape-scale (c. 2,500 km2) bird monitoring program encompassing 151 sites visited 3 times annually over 16 years, we used resampling to simulate different monitoring designs. We quantified the capacity of modified monitoring regimes to detect population trends for 65 bird species with different densities, detectabilities and specialisations.

3. The majority (58%) of species exhibited a significant decline in relative abundance, with the ability to detect trends...