It is well established that artificial night lighting can influence animal orientation, but there is less information about its effects on other behaviors. Previous work suggested that light pollution can affect both seasonal and daily patterns of behavior. The aim of our study was to investigate the effects of artificial night lighting and daytime traffic noise on the timing of dawn and dusk singing in 6 common songbirds. We recorded singing behavior in 11 nonurban plots: 2 plots with light, but no noise, 3 with light and noise pollution, 3 with noise, but no light, and 3 undisturbed forests. Our results show that artificial night lighting, but not noise, leads to an earlier start of dawn singing in 5 out of 6 species, ranging on average from 10 min for the song thrush to 20 min for the robin and the great tit. This effect was strongest at higher light intensities. W e further show that dusk song is also affected: 3 species continued dusk singing for longer in lighted areas, but the effect was smaller than that observed for dawn song (from about 8 min for the blackbird to 14 min for the great tit). For all species, onset and cessation of singing changed relative to sunrise and sunset with the progress of the s eason. Rain delayed the onset of singing at dawn and advanced the cessation at dusk. We discuss the implications of our findings in the context of sexual selection.

Artificial night lighting rather than traffic noise affects the daily timing of dawn and dusk singing in common European songbirds

The avian dawn chorus is a daily period of high song output performed predominantly during the breeding season. Dawn chorus performance varies at both the individual and species level. The many extrinsic factors that may relate to dawn chorus start times for different North American bird species have received little attention. In this study, we consider relationships between dawn chorus start times and ambient temperature, precipitation, cloud cover, lunar phase, and Julian date for six common bird species living in a northern temperate rural area. Overall, birds began singing earlier with full or third quarter moon (when moonlight is present at dawn) and with increasing temperature at nautical twilight, and birds began singing later with the presence of cloud cover and precipitation. Our results indicate that a different suite of environmental factors influenced the chorus start times of different species and to different degrees. Alder flycatchers begin singing earliest in this group of birds, followed by Song Sparrows, White-throated Sparrows, American Robins, Eastern Phoebes, and Black-capped Chickadees. This investigation reveals that extrinsic abiotic factors have a significant effect on the dawn chorus start times of north temperate birds, and represents the first comprehensive study of dawn chorus start time variation in North American birds.

/pdf/dawn-chorus-start-time-variation-in-a-temperate-bird-1sljrdt4pd.pdf

Dawn chorus start time variation in a temperate bird community: relationships with seasonality, weather, and ambient light

In mammals, species with more frontally oriented orbits have broader binocular visual fields and relatively larger visual regions in the brain. Here, we test whether a similar pattern of correlated evolution is present in birds. Using both conventional statistics and modern comparative methods, we tested whether the relative size of the Wulst and optic tectum (TeO) were significantly correlated with orbit orientation, binocular visual field width and eye size in birds using a large, multi-species data set. In addition, we tested whether relative Wulst and TeO volumes were correlated with axial length of the eye. The relative size of the Wulst was significantly correlated with orbit orientation and the width of the binocular field such that species with more frontal orbits and broader binocular fields have relatively large Wulst volumes. Relative TeO volume, however, was not significant correlated with either variable. In addition, both relative Wulst and TeO volume were weakly correlated with relative axial length of the eye, but these were not corroborated by independent contrasts. Overall, our results indicate that relative Wulst volume reflects orbit orientation and possibly binocular visual field, but not eye size.

/pdf/relative-wulst-volume-is-correlated-with-orbit-orientation-2rbzovgzqf.pdf

Relative Wulst volume is correlated with orbit orientation and binocular visual field in birds

. In contrast to diurnal songs and calls, avian nocturnal vocalizations are understudied, and their occurrence and function are poorly understood. Here, using primarily the Birds of North America species accounts, I systematically examine the occurrence and potential factor(s) that contribute to nocturnal vocalizing across 749 species of breeding birds in North America and review proposed hypotheses on its function(s). Nocturnal vocalizations are reported from at least 30% of North American birds, across 18 of 22 orders, of which over 70% are considered diurnal. This indicates that nocturnal vocalizations are a taxonomically widespread behavior and are not restricted to nocturnal species as traditionally believed. Furthermore, it indicates that diurnal birds are extending activities into night-time hours, which may influence energy dynamics and reproductive success. Lack of significant phylogenetic signal suggests that nocturnal vocalizations are not merely a result of phylogeny, which leaves ecol...

/pdf/diurnal-and-nocturnal-birds-vocalize-at-night-a-review-24ohf4inv9.pdf

Diurnal and Nocturnal Birds Vocalize at Night: A Review

We have used behavioural tests to determine the intensity thresholds of colour vision in Bourke's parrots (Neopsephotus bourkii) and budgerigars (Melopsittacus undulatus). We have also examined the relationship between these thresholds and the optical sensitivities of single photoreceptors using morphological methods. Bourke's parrots lose colour vision in brighter light (0.4 cd m(-2)) than budgerigars (0.1 cd m(-2)) and both birds lose colour vision in brighter light (;end of civil twilight') than humans (0.02 cd m(-2), ;moonlight'). The optical sensitivities of single cones are similar in both birds (budgerigar 0.27 microm(2) sr, Bourke's parrot 0.25 microm(2) sr) but Bourke's parrots have more (cone to rod ratio, 1.2:1.0), thinner (2.8 microm) and longer rods (18.5 microm) than budgerigars (2.1:1.0, 3.4 microm, 13.3 microm). Bourke's parrots thus have an eye type that, with a flexible pooling mechanism, allows for high resolution or high absolute sensitivity depending on the light conditions. The results nicely agree with the activity patterns of the birds, Bourke's parrots being active during the day and in twilight while budgerigars are not normally active before sunrise and after sunset. However, Bourke's parrots have fewer cones than budgerigars, which implies that a smaller number of cones are pooled within each retinal integration area. That could explain why Bourke's parrots have a higher intensity threshold of colour vision than budgerigars. Furthermore, the study emphasises the need to expand the sensitivity measure so that photoreceptor integration units are used rather than single receptors.

The intensity threshold of colour vision in two species of parrot.

We postulated that the retinas of bird species that are the earlier singers are more sensitive to low light conditions than species that sing closer to sunrise. The selected species were the American

Comparison of the retinal structure and function in four bird species as a function of the time they start singing in the morning.

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Comparison of the retinal structure and function in four bird species as a function of the time they start singing in the morning.