Abstract
Nestbox programmes are frequently implemented for the conservation of cavity‐nesting birds, but their effectiveness is rarely evaluated in comparison with birds not using nestboxes. In the European Palaearctic, Red‐footed FalconFalco vespertinuspopulations are both of high conservation concern and are strongly associated with nestbox programmes in heavily managed landscapes. We used a 21‐year monitoring dataset collected on 753 nesting attempts by Red‐footed Falcons in unmanaged natural or semi‐natural habitats to provide basic information on this poorly known species; to evaluate long‐term demographic trends within this population; and to evaluate response of demographic parameters of Red‐footed Falcons to environmental factors including use of nestboxes. We observed significant differences among years in laying date, offspring loss and numbers of fledglings produced, but not in egg production. Of these four parameters, offspring loss and, to a lesser extent, number of fledglings exhibited directional trends over time. Variation in laying date and in numbers of eggs were not well explained by any one model of environmental factors, but instead by combinations of models, each with informative terms for nest type. Nevertheless, laying in nestboxes occurred 2.10 ± 0.70 days earlier than in natural nests. In contrast, variation in both offspring loss and numbers of fledglings produced were fairly well explained by a single model including terms for nest type, nest location and an interaction between the two parameters (65 and 81% model weights, respectively), with highest offspring loss in nestboxes on forest edges. Because, for other species, earlier laying dates are associated with more fit individuals, this interaction highlighted a possible ecological trap, whereby birds using nestboxes on forest edges lay eggs earlier but suffer greater offspring loss and produce lower numbers of fledglings than do those in other nesting settings. If nestboxes increase offspring loss for Red‐footed Falcons in heavily managed landscapes where populations are at greater risk, or for the many other species of rare or endangered birds supported by nestbox programmes, these processes could have important demographic and conservation consequences.