Loïc A. Hardouin, Dominique Robert and Vincent Bretagnolle (2008): A dusk
chorus effect in a nocturnal bird: support for mate and rival assessment
functions. Behav. Ecol. Sociobiol. 62(12), 1909-1918.
Abstract: The dawn chorus is a striking feature of spring mornings and a
characteristic behaviour of many bird species, particularly the passerines.
Dawn singing has been considered a reliable signal of male quality for mate
and rival assessment. Singing is presumed to be relatively costly at dawn
both because air temperatures are relatively low and because birds have not
fed overnight. Models of optimal daily routine predict the existence of a
?dusk chorus? in nocturnal birds, although this prediction has received
little empirical attention. Nocturnal birds at dusk may be energy-limited
because of a lack of daytime feeding, and singing at dusk may thus ensure
signal reliability. Here, we used an observational and experimental approach
to study vocal behaviour at dusk and dawn in a nocturnal raptor, the little
owl Athene noctua. We assess whether male little owls adjust their vocal
behaviour according to feeding stage (i.e. period of the night), ambient air
temperature and territorial context (i.e. spontaneous calling behaviour vs
elicited calling by intrusion). Across different temperatures, we find that
both spontaneous vocal activity and inter-individual variability in call
duration increased at dusk, clearly indicating a dusk chorus phenomenon.
Results from playback presentations suggest that food, rather than air
temperature, is likely to be more constraining at dusk. We discuss how
comparing dusk and dawn choruses in nocturnal and diurnal species can
provide insights into both mechanistic and functional aspects of signalling
For reprints please contact Loïc A. Hardouin (Email:
Ioana Chiver, Bridget J. M. Stutchbury and Eugene S. Morton (2008): Do male
plumage and song characteristics influence female off-territory forays and
paternity in the hooded warbler? Behav. Ecol. Sociobiol. 62(12), 1981-1990.
Abstract: Extra-pair fertilizations are common in many socially monogamous
species, and paternity studies have indicated that females may use male
vocal performance and plumage ornaments as cues to assess male quality.
Female off-territory forays may represent a key component of female choice
and male extra-pair mating success, and female foray behaviour is expected
to be strongly influenced by indictors of male quality. In this study, we
examined how male song and ornamentation affect how often females left their
territories, which males they visited and extra-pair paternity in a socially
monogamous passerine, the hooded warbler (Wilsonia citrina). We radiotracked
17 females during the fertile period and quantified male vocal performance
(song output and rate) and plumage characteristics (size of the black
melanin hood and colour of the black hood, yellow cheeks and breast areas).
We obtained blood samples and determined paternity at 35 nests including
those of 14 females that we radiotracked. Eleven (65%) of the 17 females
forayed off-territory, whilst fertile and female foray rate was positively
correlated with the number of extra-pair young in the nest. Females that
left their territories more frequently were paired with males that sang at a
low rate. In addition, extra-pair mates had higher song rates than the
social mates they cuckolded (5.3 songs/min vs. 4.4 songs/min). Female
off-territory forays or extra-pair paternity were not significantly related
to male plumage characteristics. Our results indicate that a high song rate
influences both the foray behaviour of a male?s social mate and the
likelihood that he will sire extra-pair offspring with neighbouring females.
For reprints please contact Ioana Chiver (Email:
Dr. Sonja Amoser