Department of Biology, Ecology and Evolution, University of Fribourg (Switzerland)
Habitat occupation strategies and breeding behaviour in reed
buntings (Emberiza schoeniclus)
Martin Keiser
Organisms often have various possibilities to enhance their reproductive success. In my thesis,
I focus on four interacting factors that affect breeding performance, namely the breeding
habitat, the mating partner, the ratio of male and female offspring produced, and the
occurrence of extra-pair matings. Additionally, I show an alternative sexing protocol for birds
that applies a nested PCR design with two different primer sets.
All studies were carried out in the “Grande Cariçaie” reed belt at the southeastern coast of
Lake Neuchâtel, Switzerland. There, we had the unique opportunity to apply a large-scale
habitat alteration experiment within the scope of a conservation scheme where we created four
different habitat types or plots according to their vegetation age. The study species was the
reed bunting (Emberiza schoeniclus), a small migratory passerine bird with two broods per
season. Reed buntings are sexually dimorphic and show high levels of extra-pair paternity.
The results of the habitat alteration experiment revealed that reed buntings preferentially
occupied older habitat types with more vegetation and avoided plots without standing
vegetation. Males that were the first time on the breeding site choose their territory in plots
according to their vegetation density while returning males showed site fidelity. Due to the
structural heterogeneity within the four habitat types female reed buntings were able to select
nest sites with more vegetation cover than was average for the focal plot. Predation accounting
for most nest losses was about 30 % lower in the oldest plots than in younger ones. Therefore,
the number of fledglings per nest was significantly higher in the oldest habitat types.
Returning reed buntings significantly increased their fitness in terms of number of fledged
offspring by mating with experienced partners compared to couples where both were the first
time on the breeding site. A reason for this could be that returning couples placed their nests in
older habitat patches with more protecting vegetation. Additionally, even within the same
habitat age, returning couples had a lower nest predation rate, probably because they started
their first brood about one week earlier then inexperienced couples, when predator density
might still have been low, and / or predators might have not yet had developed their search
image for reed bunting nests.
The experimental habitat alteration had no influence on the offspring sex ratio, even though it
is known that habitat quality can influence sex ratio decisions in other bird species.
Finally, males that engaged in extra-pair mating sired significantly more offspring than males
without extra-pair paternity, even within their own nest. There was however no significant
influence of the manipulated habitat types on the proportion of extra-pair paternity. The main
reason for that was probably that females mostly choose neighbouring males as extra-pair
partners, regardless in which plot age they had their territory.
The Jury
Prof. Dr. Dietrich Meyer, Ecology and Evolution, University of Fribourg, Switzerland
Prof. Dr. Philipp Heeb, Laboratoire CNRS, University Paul Sabatier, Toulouse, France
Prof. Dr. Louis-Félix Bersier, Ecology and Evolution, University of Fribourg, Switzerland
Prof. Dr. Felix Mauch, Plant Biology, University of Fribourg, Switzerland