Reduced compensatory growth capacity in mistimed 1 broods of a migratory passerine 2 3

Phenotypic plasticity has recently been proposed to increase population viability 15 when rapid anthropogenic environmental changes cannot be tracked by means of evolution. 16 This assumes that environmental changes do not constrain phenotypic plasticity itself, which 17 has rarely been examined in natural populations. In areas of climate warming, many long-18 distance migratory birds breed increasingly late relative to the period of peak food supply, and 19 the temporal mismatch may constrain plastic life-history traits such as nestling growth. We 20 combined 23 years of food availability and breeding data with a three-year experimental 21 manipulation of nestling growth trajectories in a Central-European population of collared 22 flycatchers to examine the potential impact of climate-related mistimed breeding on nestling 23 developmental plasticity. Timing of the food peak was predicted by winter climate, and the 24 median hatching date of broods was earlier in springs with earlier food peaks. However, the 25 adjustment of hatching date was incomplete and the population largely missed the food peak 26 in years with very early food peaks. After imposing a temporary, experimental food shortage 27 on nestlings, the extent of compensatory growth in body mass differed among years, and this 28 difference was apparently related to the distance of hatching dates from the yearly food peak. 29 Growth compensation declined with distance from the peak. These results suggest that 30 mistimed phenology may not only create permanently adverse conditions for migratory 31 species, but it may also constrain the plastic responses of individuals to temporary 32 disturbances. Therefore, climate change may not only favour but also restrict phenotypic 33 plasticity. 34 35 Keywords body mass gain · breeding date · global warming · insect phenology · long-distance 36 migrant 37 3 Introduction 38