Di Maggio, R., Campobello, D., Tavecchia, G. and Sará M. 2016: Habitat- and density-dependent demography of a colonial raptor in Mediterranean agro-ecosystems Biological Conservation, vol 193 pag 116-123.
doi:10.1016/j.biocon.2015.11.016
Abstract: Agricultural intensification is considered the major cause of decline in
farmland bird populations, especially in the Mediterranean region. Food
shortage increased by the interaction between agricultural
intensification and density-dependent mechanisms could influence the
population dynamics of colonial birds. We used demographic data on
lesser kestrels (
Falco naumanni), a key species of
Mediterranean pseudo-steppes, to understand the importance of land-use
changes and density-dependent mechanisms in the light of its fluctuating
conservation status in the Western Palearctic. Our analysis indicated
an important influence of land uses (artichokes, arable and grassland
fields) and colony size on kestrel survival rates.
The strong habitat
effect revealed the unsuitability of intensive arable lands with respect
to extensive grasslands for lesser kestrels. Notably, artichokes, a
winter-intensive crop, proved to be a high-quality habitat as they were
associated with survival values equal to those of grassland. This is
likely due to prey availability and reveals that non-traditional crops
may provide suitable habitats for lesser kestrels. Information theory
gave strong support to the negative influence of colony size on
fecundity, albeit a small one, for its positive effect on survival
probability. The estimated population growth rate was negative for all
three habitats, indicating a decline over time and urging conservation
actions in all of the areas studied. This decline was much higher in
colonies surrounded by arable fields. In sensitivity analyses, λ
indicated that adult survival was the parameter with the greatest effect
on population growth, followed by survival of fledglings and fecundity.
Our study showed how the costs and benefits of group living interact
with agricultural intensification to drive species demography. In
addition, we integrated significant information on one of the largest
lesser kestrel populations to fine tune the most effective conservation
strategy to prevent the collapse of the species in a relevant part of
its range
