Paternity in male animals can be influenced by their phenotypic signals of quality. Accordingly, the behavior underlying patterns of paternity should be flexible as signals of quality change. To evaluate the dynamics of paternity allocation, we analyzed paternity before and after manipulating plumage coloration, a known signal of quality, in male barn swallows Hirundo rustica. We found that, in successive breeding bouts, only males whose plumage color was experimentally enhanced received greater paternity from their social mates, demonstrating evidence for flexible and dynamic paternity allocation and the importance for males of maintaining signals of quality well after pair bond formation.

No abstract

In the socially monogamous barn swallow, previous studies of individuals in the European subspecies Hirundo r. rustica have shown that a male's tail streamer length is under strong sexual selection and is positively associated with several measures of reproductive success, including a low probability of being cuckolded by other males. The prominence of these results has led to subsequent experimental and correlational investigations of individuals in the phenotypically divergent subspecies H. r. erythrogaster in North America, where it has been shown that male tail streamer length is not as strongly associated with reproductive success as in European populations. We examined relationships between male tail streamer length and patterns of: (1) social mate selection and reproductive success, and (2) extra‐pair paternity in 265 progeny of 53 social fathers within a New York barn swallow population. Although tail streamers in this population were sexually dimorphic, male tail streamer length did not predict patterns of mate selection, seasonal reproductive success, or extra‐pair paternity. Moreover, in contrast to the strong positive relationships between paternity and male streamer length in European populations, summarized in this paper, we found no positive relationship between a male's paternity of young in the nest he is attending and his tail streamer length in our study population in New York. Our results further corroborate recent suggestions that the function of sexual signals varies geographically in this species, although we await additional experimental analyses on streamer lengths to understand the maintenance of sexual dimorphism in this trait.

On 25 March 2006, a complex frontal system moved across the Sierra-Cascade Mountains and intensified rapidly over the Intermountain West where it produced one of the strongest cold-frontal passages observed in Salt Lake City, Utah, during the past 25 yr. Observational analyses and numerical simulations by the Weather Research and Forecast (WRF) Model illustrate that the frontal system propagated discretely across the Sierra-Cascade Mountains and western Nevada. This discrete propagation occurs in a synoptic environment that features a mobile upper-level cyclonic potential vorticity (PV) anomaly that is coupled initially with a landfalling Pacific cyclone and attendant occluded front. The eastward migration of the upper-level cyclonic PV anomaly ultimately encourages the development of a new surface-based cold front ahead of the landfalling occlusion as troughing, confluence, and convergence downstream of the Sierra Nevada intensify preexisting baroclinity over Nevada. Trajectories show that the new cold front represents a boundary between potentially warm air originating over the desert Southwest, some of which has been deflected around the south end of the high sierra, and potentially cool air that has traversed the sierra near and north of Lake Tahoe, some of which has been deflected around the north end of the high sierra. Although diabatic processes contribute to the frontal sharpening, they are not needed for the discrete propagation or rapid cold-frontal development. Forecasters should be vigilant for discrete frontal propagation in similar synoptic situations and recognize that moist convection or differential surface heating can contribute to but are not necessary for rapid Intermountain West frontogenesis.