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.