28Human activities have caused a near-ubiquitous and evolutionarily-unprecedented increase in 29 environmental sound levels and artificial night lighting. These stimuli reorganize communities 30 by interfering with species-specific perception of time cues, habitat features, and auditory and 31 visual signals. Rapid evolutionary changes could occur in response to light and noise, given their 32 magnitude, geographical extent, and degree to which they represent unprecedented 33 environmental conditions. We present a framework for investigating anthropogenic light and 34 noise as agents of selection, and as drivers of other evolutionary processes, to influence a range 35 of behavioural and physiological traits, such as phenological characters and sensory and 36 signalling systems. In this context, opportunities abound for understanding contemporary and 37 rapid evolution in response to human-caused environmental change. The overcast night sky radiance in urban areas has been found to be as much as four orders of 55 magnitude larger than in natural settings (Figure 1) [5]. Similarly, increased noise levels affect a 56 sizable proportion of the human population. In Europe for instance, 65% of the population is 57 exposed to ambient sound levels exceeding 55 dB(A) [6], roughly equivalent to constant rainfall. 58Of the land in the contiguous U.S., 88% is estimated to experience elevated sound levels from 59 anthropogenic noise (Figure 1) [7]. These effects are not limited to terrestrial environments; 60 ocean noise levels are estimated to have increased by 12 decibels (an ~16-fold increase in sound 61 intensity) in the past few decades from commercial shipping alone [8], while an estimated 22% 62 of the global coastline is exposed to artificial light [3] and many offshore coral reefs are 63 chronically exposed to artificial lighting from cities, fishing boats, and hydrocarbon extraction 64 [9]. 65The changes in light at night and noise levels are occurring on a global scale similar to 66 well-recognized ecological and evolutionary forces such as land cover and climate change. In 67 4 parallel with research involving climate change [10], much of our understanding of organismal 68 response to noise and light is restricted to short-term behavioural reactions. Organismal 69 responses might be associated with tolerance to these stimuli in terms of habitat use [11,12] Status of research on anthropogenic light and sound in ecology 98Night lighting and noise are highly correlated in many landscapes (e.g., [21]). It is critical to 99 understand whether the selective pressures these stimuli exert are additive, synergistic (Figure 2), 100 or if they mitigate one another. Few studies have examined the influence of each simultaneously 101 (e.g., [21]). In one study, flashing lights combined with boat motor noise suppressed antipredator 102 behaviour in hermit crabs (Coenobita clypeatus) more so than noise alone [22]. Future research 103 should quantify both light and sound simultaneously in the same population. Existing r...

Noise may drive changes in the composition and abundance of animals that communicate vocally. Traffic produces low-frequency noise (<3 kHz) that can mask acoustic signals broadcast within the same frequency range. We evaluated whether birds that sing within the frequency range of traffic noise are affected by acoustic masking (i.e., increased background noise levels at the same frequency of vocalizations reduce detection of vocalization) and are less abundant in areas where traffic noise is loud (44-57 dB). We estimated occupancy, the expected probability that a given site is occupied by a species, and detection probabilities of eight forest-breeding birds in areas with and without traffic noise as a function of noise and three measures of habitat quality: percent forest cover, distance from plot center to the edge of forest, and the number of standing dead trees or snags. For the two species that vocalize at the lowest peak frequency (the frequency with the most energy) and the lowest overall frequency (Yellow-billed Cuckoo [Coccyzus americanus] and White-breasted Nuthatch [Sitta carolinensis]), the presence of traffic noise explained the greatest proportion of variance in occupancy, and these species were 10 times less likely to be found in noisy than in quiet plots. For species that had only portions of their vocalizations overlapped by traffic noise, either forest cover or distance to forest edge explained more variation in occupancy than noise or no single variable explained occupancy. Our results suggest that the effects of traffic noise may be especially pronounced for species that vocalize at low frequencies.

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Our understanding of the evolution and function of animal displays has been advanced through studies of vocal performance. A widely used metric of vocal performance, vocal deviation, is limited by being applicable only to vocal trills, and also overlooks certain fine-scale aspects of song structure that might reflect vocal performance. In light of these limitations we here introduce a new index of vocal performance, "frequency excursion". Frequency excursion calculates, for any given song or song segment, the sum of frequency modulations both within and between notes on a per-time basis. We calculated and compared the two performance metrics in three species: chipping, swamp, and song sparrows. The two metrics correlated as expected, yet frequency excursion accounted for subtle variations in performance overlooked by vocal deviation. In swamp sparrows, frequency excursion values varied significantly by song type but not by individual. Moreover, song type performance in swamp sparrows, according to both metrics, varied negatively with the extent to which song types were shared among neighbors. In song sparrows, frequency excursion values of trilled song segments exceeded those of non-trilled song segments, although not to a statistically significant degree. We suggest that application of frequency excursion in birds and other taxa will provide new insights into diverse open questions concerning vocal performance, function, and evolution.

Cooperation and conflict are regarded as diametric extremes of animal social behaviour, yet the two may intersect under rare circumstances. We here report that territorial competitors in a common North American songbird species, the chipping sparrow (Spizella passerina), sometimes form temporary coalitions in the presence of simulated territorial intruders. Moreover, analysis of birds' vocal mating signals (songs) reveals that coalitions occur nearly exclusively under specific triadic relationships, in which vocal performances of allies and simulated intruders exceed those of residents. Our results provide the first evidence that animals like chipping sparrows rely on precise assessments of mating signal features, as well as relative comparisons of signal properties among multiple animals in communication networks, when deciding when and with whom to form temporary alliances against a backdrop of competition and rivalry.