Identifying and diagnosing population declines: a Bayesian assessment of lapwings in the UK

We combine data from separate ring recovery and survey studies to provide indices of estimated abundance for the UK lapwing Vanellus vanellus population. Using a descriptive state space model, we demonstrate the observed decline in population size in relation to directly interpretable parameters describing the demographic characteristics of the population. The Bayesian approach readily provides information that is directly relevant to the conservation of this important bird species. The method proposed extends previous work in this area in several ways. Restrictive normality assumptions that have traditionally been imposed are removed, in addition to the assumption of constant measurement error by using information relating to the index variability across time to account fully for this source of uncertainty within the model. We also provide model-averaged inference to help to inform management policy and uses.