Summary: 1. We studied lifetime arrival patterns in the barn swallow (Hirundo rustica L.) in relation to variation in ecological conditions, as reflected by the normalized difference vegetation index (NDVI) in the Sub‐Saharan winter quarters and at stopover sites in North Africa. 2. Migratory birds have recently advanced their arrival dates, but the relative role of microevolution and phenotypic plasticity as mechanisms of response to changing environmental conditions remains unknown. To distinguish between these two possibilities, we investigated the change in the arrival date using cross‐sectional and longitudinal analyses. 3. We predicted that the effect (i.e. slopes) of environmental conditions in stopover or winter areas on arrival date should be similar using cross‐sectional and longitudinal analyses in case phenotypic plasticity is the underlying mechanism, or they should differ in case microevolution is the mechanism. 4. As expected according to a previous cross‐sectional study, we found an advance in the arrival date when ecological conditions improve in stopover areas and a delay in the arrival date when ecological conditions improve in the winter quarters. 5. Change in the arrival time at the breeding grounds due to ecological conditions found en route and, in the winter areas, was mainly due to phenotypic plasticity as shown by similarities in the slopes found in these relationships using cross‐sectional and longitudinal analyses. 6. We also investigated sex and age of barns swallows as sources of variation in the arrival time with respect to conditions experienced in winter and stopover areas. We found that earlier arrival at the breeding grounds due to prevailing ecological conditions found en route in North Africa was similar for males and females of all age‐classes. In contrast, individuals tended to delay departure when ecological conditions improved in the winter quarters, but this delay differed among age classes, with old individuals delaying departure more than middle‐aged and yearling birds. 7. The migratory response of individuals to changing climatic conditions experienced during different parts of their life provides evidence for individuals responding differently to prevailing conditions in the winter quarters depending on their age, but not to conditions experienced en route during spring migration.

Population viability analysis (PVA) has become a basic tool of current conservation practice. However, if not accounted for properly, the uncertainties inherent to PVA predictions can decrease the reliability of this type of analysis. In the present study, we performed a PVA of the whole western European population (France, Portugal, and Spain) of the endangered Bonelli's Eagle ( Aquila fasciata ), in which we thoroughly explored the consequences of uncertainty in population processes and parameters on PVA predictions. First, we estimated key vital rates (survival, fertility, recruitment, and dispersal rates) using monitoring, ringing, and bibliographic data from the period 1990–2009 from 12 populations found throughout the studied geographic range. Second, we evaluated the uncertainty about model structure (i.e., the assumed processes that govern individual fates and population dynamics) by comparing the observed growth rates of the studied populations with model predictions for the same period. Third, using the model structures suggested in the previous step, we assessed the viability of both the local populations and the overall population. Finally, we analyzed the effects of model and parameter uncertainty on PVA predictions. Our results strongly support the idea that all local populations in western Europe belong to a single, spatially structured population operating as a source–sink system, whereby the populations in the south of the Iberian Peninsula act as sources and, thanks to dispersal, sustain all other local populations, which would otherwise decline. Predictions regarding population dynamics varied considerably, and models assuming more constrained dispersal predicted more pessimistic population trends than models assuming greater dispersal. Model predictions accounting for parameter uncertainty revealed a marked increase in the risk of population declines over the next 50 years. Sensitivity analyses indicated that adult and pre‐adult survival are the chief vital rates regulating these populations, and thus, the conservation efforts aimed at improving these survival rates should be strengthened in order to guarantee the long‐term viability of the European populations of this endangered species. Overall, the study provides a framework for the implementation of multi‐site PVAs and highlights the importance of dispersal processes in shaping the population dynamics of long‐lived birds distributed across heterogeneous landscapes.

In a rapidly changing world, it is of fundamental importance to understand processes constraining or facilitating adaptation through microevolution. As different traits of an organism covary, genetic correlations are expected to affect evolutionary trajectories. However, only limited empirical data are available. We investigate the extent to which multivariate constraints affect the rate of adaptation, focusing on four morphological traits often shown to harbour large amounts of genetic variance and considered to be subject to limited evolutionary constraints. Our data set includes unique long-term data for seven bird species and a total of 10 populations. We estimate population-specific matrices of genetic correlations and multivariate selection coefficients to predict evolutionary responses to selection. Using Bayesian methods that facilitate the propagation of errors in estimates, we compare (1) the rate of adaptation based on predicted response to selection when including genetic correlations with predictions from models where these genetic correlations were set to zero and (2) the multivariate evolvability in the direction of current selection to the average evolvability in random directions of the phenotypic space. We show that genetic correlations on average decrease the predicted rate of adaptation by 28%. Multivariate evolvability in the direction of current selection was systematically lower than average evolvability in random directions of space. These significant reductions in the rate of adaptation and reduced evolvability were due to a general nonalignment of selection and genetic variance, notably orthogonality of directional selection with the size axis along which most (60%) of the genetic variance is found. These results suggest that genetic correlations can impose significant constraints on the evolution of avian morphology in wild populations. This could have important impacts on evolutionary dynamics and hence population persistence in the face of rapid environmental change.