TL;DR: It is proposed that seasonal plumage colours have evolved to resolve a trade-off between the effects of natural and sexual selection on colouration, especially in seasonal environments.
Abstract: Some birds undergo seasonal colour change by moulting twice each year, typically alternating between a cryptic, non‐breeding plumage and a conspicuous, breeding plumage (‘seasonal plumage colours’). We test for potential drivers of the evolution of seasonal plumage colours in all passerines (N = 5901 species, c. 60% of all birds). Seasonal plumage colours are uncommon, having appeared on multiple occasions but more frequently lost during evolution. The trait is more common in small, ground‐foraging species with polygynous mating systems, no paternal care and strong sexual dichromatism, suggesting it evolved under strong sexual selection and high predation risk. Seasonal plumage colours are also more common in species predicted to have seasonal breeding schedules, such as migratory birds and those living in seasonal climates. We propose that seasonal plumage colours have evolved to resolve a trade‐off between the effects of natural and sexual selection on colouration, especially in seasonal environments.
01 Jan 2019
TL;DR: In this article, the authors explored whether the difference in dawn traffic amplitude on weekends versus weekdays had a differential effect on detection of songbird vocalizations, and found that American Robins and Northern Cardinals have masked vocalizations and were detected more as traffic noise increased.
Abstract: Traffic noise may vary due to variation in human behavior and changes the acoustic environment of roadside habitat. Songbirds living in roadside habitat may be affected by traffic noise due to their dependence on vocal communication for important behaviors such as mating song. We explored whether the difference in dawn traffic amplitude on weekends versus weekdays had a differential effect on detection of songbird vocalizations. There was no difference in the number of species detected on weekends (median = 5) versus weekdays (median = 5) at 06:00 when the difference in traffic amplitude was greatest (5 dB) and at 09:00 when the difference in traffic amplitude was the least. Different species can have different responses to traffic noise based on whether their vocalizations are masked by traffic noise and their persistence in urban areas, affecting observable trends in community-level analyses. To address species-specific response, we explored how increasing traffic noise affected masked and unmasked species detection and specifically explored the behavior of three songbird species. American Robins and Northern Cardinals have masked vocalizations and were detected more as traffic noise increased, while the Red-winged Blackbirds have unmasked vocalizations and were detected less as traffic noise increased. These results opposed expectations and suggest other behavioral acclimations may impact detection of these species. Conducting more experiments on individual species detection and behavioral response will help ecologists understand mechanisms behind community-level trends in detection. Increased knowledge of bird behavior in roadside habitat will better inform management of traffic noise in areas with sensitive species.