Abstract :
[en] The first response of organisms to human-induced environmental changes is most
often behavioural. Therefore, a greater ability of behavioural flexibility, such as in
terms of habitat selection, constitutes an asset to persist in human-altered
environment. Moreover, because human activities frequently cause unprecedented
environmental changes leading to ecological novelties, organisms face the difficulty
to respond adaptively to these conditions that are novel in regard to their species’
evolutionary past. In such context, it is not uncommon for an individual’s choices to
no longer maximize its fitness rewards, a phenomenon known as ecological trapping.
This thesis focuses on early-successional bird species in a mixed farmland-forest
landscape in Southern Belgium, where agriculture and forestry activities have
generated structurally different open-habitat types available to these species. How
these habitat types, varying in their novelty, affect these birds was investigated
through the thesis according to three Essential Biodiversity Variables: community
composition, species population and species trait.
Studying how the conversion of intensive grassland into Christmas tree plantations
(CTPs) – a novel habitat type with significant extent in the study landscape – alters
bird community composition showed that growing CTPs locally enhances bird
diversity and abundance in impoverished farmland. The European Stonechat
(Saxicola rubicola) is one of the species using CTPs as a breeding habitat, along with
grassland and clear-cut patches in plantation forests also available in the landscape.
As a winner species and, thus, an exception among the farmland avifauna, focussing
on the Stonechat is interesting to investigate how a species can flourish in humanaltered
landscapes.
A dataset about habitat preference, reproductive performance and survival, recorded
on a three- to five-year period, was used to determine whether habitat selection by
stonechats is adaptive. Results indicate that stonechats preferentially settle in clearcut
patches than in grassland and CTPs, but they do not reach better fitness in the
preferred habitat type. On the opposite, they face difficulties to provide their offspring
with food in clear-cut patches as breeding season progresses. Albeit lower nestlings’
body conditions do not seem to carry over into their survival, the habitat selection by
stonechats appears non ideal in the study landscape, but without significant fitness
consequences. Nest search revealed that the use of a novel habitat (CTPs) in this
species is accompanied with higher individual flexibility in nest placement. Although
unusual for the species, off-ground nests built in CTPs do not however induce any
fitness loss for breeders in comparison to traditional on-ground nests.
As an applied contribution, this thesis provides new insights about the use and the
quality of some open-habitats in a farmland-forest landscape for breeding earlysuccessional
bird species. In particular, it is among the first researches to address the
impact of CTPs on biodiversity. More conceptually, all together the results show that
a species can benefit from novel habitats emerging in the landscape as a result of
human activities, despite habitat selection may not be ideal. They highlight the importance of individual behavioural flexibility to thrive in novel environmental
conditions.
