Nocturnal singing by diurnal birds in Afrotropical highlands

Most bird species are active by day. However, even typically diurnal species have been observed to sing by night, although the functions and mechanisms of this behaviour are not well understood. In our study, we focused on nocturnal singing by diurnal birds in Afrotropical highlands (Bamenda Highlands, Cameroon). We recorded 48-h soundscapes in 18 random recording sites using autonomous sound recorders to examine the occurrence and intensity of nocturnal singing among diurnal birds. We applied three definitions of night—the time period between: (1) astronomical, (2) nautical and (3) civil dusk and dawn, which may include or exclude beginning of dawn chorus from the night-time period. We recorded 53 bird species, representing seven orders and 27 families. Of 50 typically diurnal species, only three sang by astronomical night, producing in total 10 songs. Applying the nautical night definition did not change the meaning of the results—the same three species produced 12 vocalisations. By civil night, 21 species were recorded singing. From the analysed 2128 vocalisations produced by civil night, 2109 were produced during 25 min period between nautical and civil dawn (22–47 min before sunrise), what suggests that civil night covers the beginning of dawn chorus and should not be considered as a nighttime. Our study reveals that in Afrotropical highlands, unlike in temperate regions, diurnal birds stay silent at night. Using astronomical and nautical definition of night gives similar results. The intensive singing recorded between nautical and civil dawn (included into nautical night), we interpreted as the beginning of dawn chorus rather than true night singing. We suggest that precise definition of nighttime is required to compare the results of different studies and to better understand the phenomenon of night singing by diurnal birds.

Dawn singing in Brown Creeper (Certhia americana)

The dawn chorus of birds is an impressive display in which many individuals of a variety of species sing concurrently before sunrise. Brown Creeper (Certhia americana) is a small passerine bird that has not been well studied and is thought not to sing during the dawn chorus. Here, we used automated recordings to analyze Brown Creeper singing during the 2015–2017 breeding seasons from April through August in order to identify patterns in the timing and quantity of singing. We found that Brown Creepers did sing before sunrise, most often between April and early June and then more sporadically through mid July. We did not find any seasonal changes in song rates before sunrise, but we did find non-linear seasonal trends in both the timing and total duration of dawn singing bouts. Dawn choruses began earlier and lasted longer from April through mid June after which they began later and became shorter. Our results highlight the benefit of using automated recording techniques to study natural history of difficult to study species and add to our understanding of Brown Creeper natural history.

Artificial light at nigh drives early dawn chorus onset times of the Saffron Finch (Sicalis flaveola) in an Andean city

Urban birds around the world have to cope with dominant city stressors as anthropogenic noise and artificial light at night by adjusting the temporal and spectral traits of their acoustic signals. It is widely known that higher anthropogenic noise and artificial light levels can disrupt the morning singing routines, but its influence in tropical urban birds remains poorly explored. Here, I assessed the association between light and noise pollution with the dawn chorus onset of the Saffron Finch (Sicalis flaveola) in an Andean city of Colombia. I studied 32 urban sites distributed in the north of the city, which comprise different conditions of urban development based on the built cover. I annotated the time when the first individual of the Saffron Finch was heard at each site and then I obtained anthropogenic noise and artificial light at night measurements using a smartphone. Findings of this study show that Saffron Finches living in highly developed sites sang earlier at dawn than those occupying less urbanized sites. Unexpectedly this timing difference was related to artificial lighting instead of anthropogenic noise, suggesting that artificial light could drive earlier dawn chorus in a tropical urban bird. Saffron Finches could take advantage of earlier singing for signaling territorial ownership among neighbors, as expected by the social dynamic hypothesis. However, findings of this study should be interpreted carefully because the dawn chorus is a complex phenomenon influenced by many multiple factors. Future studies need to assess the influence of ALAN on the dawn chorus timing of Neotropical urban birds by taking into account the influence of confounding factors related to urbanization as well as meteorological, ecological, and social drivers.