Tuning towards tomorrow? Common nightingales Luscinia megarhynchos change and increase their song repertoires from the first to the second breeding season

Auteurs: Sarah Kiefer, Christina Sommer, Constance Scharff, Silke Kipper and Roger Mundry
Bron: JOURNAL OF AVIAN BIOLOGY, Volume 40 Issue 2, Pages 231-236
Abstract: In many oscines, song repertoire size correlates with male quality and female mate choice, and can vary with age. In a cross-sectional field study in common nightingales Luscinia megarhynchos, one y old birds had substantially smaller repertoires than did older ones. In laboratory experiments males can acquire new song types during this period. This longitudinal field study therefore investigates whether individual nightingales increase their repertoires from the first to the second breeding season.
We report a striking repertoire turnover, with an average overall increase of 24% of the first season's repertoire, resulting from added and dropped song types (54% and 30%, respectively). The number of added song types correlated positively with the size of the first season's repertoire. These results are consistent with the notion that repertoire size in nightingales correlates with male quality, although the overlap between repertoire sizes of first and second season birds makes it impossible to discriminate age based solely on repertoire size. Comparing the number of song types an individual sang in both seasons ('permanent song types') revealed a lower overlap than reported for subsequent seasons. The frequencies with which these were sung in the first season were less predictive of how often they were sung in the second season than was the case between later years.
This drastic repertoire turnover from the first to the second season may be a selective process in response to the local song types, constrained by genetic makeup and shaped by early experience.

Why Female Birds Seek Extra Mates: Study Of Blue Tits Fuels Debate

When female birds mate with males other than their social partners and have broods of mixed paternity, the offspring sired by these "extra-pair" fathers may often get a head start in life, according to a new report. The discovery adds fuel to the debate about why some female birds seek those extra mates in the first place.

The report is published online on April 30th in Current Biology, a Cell Press publication.

"A diverse range of explanations have been proposed to account for female participation in extra-pair copulations," said Michael Magrath of University of Groningen, The Netherlands. "The explanations that have received most attention suggest that females stand to gain genetically superior offspring by having their eggs fertilized by males that are of higher genetic quality or that are genetically more compatible."


Lees meer: ScienceDaily

Differential responses of red knots, Calidris canutus, to perching and flying sparrowhawk, Accipiter nisus, models

Auteurs: Kimberley J. Mathot, Piet J. van den Hout, Theunis Piersma
Bron: ANIMAL BEHAVIOUR, Volume 77, Issue 5, May 2009, Pages 1179-1185
Abstract: According to the threat-sensitive predator avoidance hypothesis, prey should match the intensity of their antipredation response to the degree of threat posed by predators. We used controlled indoor experiments to investigate the ability of red knots to discern between high- and low-threat encounters with a representative predator, the sparrowhawk.
The behaviour of knots was compared across three conditions: no predators present (very low predation threat), presentation of a perching sparrowhawk model (low predation threat) and presentation of a gliding sparrowhawk model (high predation threat). In all behavioural parameters measured, red knots showed evidence of discriminating between the different levels of predation risk. Knots responded immediately to the presence of sparrowhawks with escape flights, and the duration of escape flights was longer following the gliding sparrowhawk events than following perching events. Similarly, the proportion of time spent vigilant increased with increasing level of predation threat, while the proportion of time spent feeding decreased.
These results show that knots recognize variations in the level of predation threat, and adjust their antipredator responses accordingly. Furthermore, model sparrowhawks were introduced into the experimental arena at similar distances to the knots, which suggests that knots are able to use cues other than distance to predator to gauge the immediate level of threat that a predator poses.

Owls change colour

Climate change is having a direct effect on the plumage of some birds, according to new research from Italy. The red form of Scops Owl has become commoner than the grey form.

The Scops Owl can be found in two main colour morphs, one dull grey and the other rusty red. Grey birds survive better in years when the climate is cool and dry, while red birds thrive in warm, wet conditions.


Lees meer: Birdwatch