LAUSR

Abstract Phenological mismatches—defined here as the difference in reproductive timing of an individual relative to the availability of its food resources—occur in many avian species. Mistiming breeding activities in environments with constrained breeding windows may have severe fitness costs due to reduced opportunities for repeated breeding attempts. Therefore, species occurring in alpine environments may be particularly vulnerable. We studied fitness consequences of timing of breeding in an alpine‐endemic species, the white‐tailed ptarmigan (Lagopus leucura), to investigate its influence on chick survival. We estimated phenological mismatch by measuring plant and arthropods used by ptarmigan in relation to their timing of breeding. We monitored 120 nests and 67 broods over a three‐year period (2013–2015) at three alpine study sites in the Rocky Mountains of Colorado. During this same period, we actively monitored food resource abundance in brood‐use areas to develop year and site‐specific resource phenology curves. We developed several mismatch indices from these curves that were then fit as covariates in mark‐recapture chick survival models. A correlation analysis between seasonal changes in arthropod and food plant abundance indicated that a normalized difference vegetation index (NDVI) was likely the best predictor for food available to hens and chicks. A survival model that included an interaction between NDVI mismatch and chick age received strong support and indicated young chicks were more susceptible to mismatch than older chicks. We provide evidence that individual females of a resident alpine species can be negatively affected by phenological mismatch. Our study focused on individual females and did not examine if phenological mismatch was present at the population level. Future work in animal populations occurring in mountain systems focusing on a combination of both individual‐ and population‐level metrics of mismatch will be beneficial.