Biology Reference
In-Depth Information
Thomas and Cuthill (
2002
) have adopted a stochastic dynamic programming
(SDP) model that in the European robin (
Erithachus rubecula
) the daily singing and
foraging routines largely depend on an individual's fat reserves, advancing two
further hypotheses that overnight loss of fat reserves is higher on colder nights and
that birds sing more at dawn when their fat reserves are high.
In silveryes (
Zosterops lateralis
), a small passerine of 11-14 g distributed
throughout Australia, New Zealand, and many South Pacific islands, Barnett and
Briskie (
2007
) have observed that the dawn chorus largely depends on the amount
of fat accumulated in a singer's body. They proved that artificially fed males were
singing longer and with a higher-quality repertoire.
Dawn and dusk choruses are largely considered phenomena of diurnal animals
(birds, frogs), but this process has been observed also in nocturnal animals such
as owls.
In the little owl (
Athene noctua
), the dusk chorus has been interpreted by
Hardouin et al. (
2008
) as a distinct phenomenon independent of air temperature
and more intense than at dawn. An increased variability in vocal activity has been
observed at dusk compared to dawn. From playback experiments conducted in
February and March, these authors have hypothesized that food rather than air
temperature is a dusk constraint. Nocturnal owls are inactive in diurnal time and at
dusk they have the minimum energetic budget, but these authors are also inclined to
consider the dusk chorus in the context of social functions.
7.5.2 The Behavioral Hypothesis
According to this hypothesis the choruses are the result of interindividual acoustic
relationships, a semetic network that is established between close individuals.
The behavioral hypothesis has been proven in black-capped chickadee (
Poecile
atricapillus
) dawn choruses. These choruses represent an interactive communica-
tion network, as shown by the study carried out by Foote et al. (
2010
), who when
working on 19 focal males have observed that the levels of frequency matching was
higher than expected. All the males were observed to match two or three males
simultaneously and sequentially.
In playback experiments conducted by Amrhein and Erne (
2006
) on the winter
wren (
Troglodytes troglodytes
), in which the presence of an intruder was simulated
inside the territory of a singing male before sunrise (dawn chorus time), it was
found that the day after the supplementary song the resident male was singing at
dawn more vigorously but not after sunrise. A preventive territorial proclamation
seems the mechanism triggered by the administration of a simulated intruder and
demonstrates, at least in this species, that the dawn period is used extensively for
territory defense. Other playback experiments conducted on this focal species in
spring and autumn by Erne and Amrhein (
2008
) have confirmed that intruder
simulation before sunrise and after sunset produces a significant increase of song
output the next day, although in autumn the effect is less important (Fig.
7.4
). This
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