4.4. Small-scale landscape characteristics and weather: lack of
impact on population growth
Surprisingly, small-scale landscape structures did not significantly
influence population growth rate in this study. One explanation to this
could be the way we formed these variables. By measuring the density of
linear structures such as roads, main drainage ditches and riversides,
we aimed at quantifying the potentially beneficial effect of edge
habitats; for example, woody perennial vegetation, such as Salixsp. or Betula sp., providing an important source of larvae and
insects to feed the nestlings. However, our variables lacked the
information whether the roadside or drainage ditch had any such
vegetation. Most likely they had at least some taller vegetation most of
the time, but every few years the farmers tend to cut down the bushes
along their driveways. It is possible that crop type diversity (SHANG)
served as an indirect indicator of smaller average field plot size thus
suggesting a greater availability of important edge habitat (ditches,
field margins) for nesting.
Concerning the weather variables, likewise, Vepsäläinen (2005) did not
find a link between weather conditions of previous year’s breeding
season and Ortolan Bunting densities. These results suggest that other
variables are primarily driving the Ortolan Bunting declines.