Even in a best case scenario, where dividing the predators into mammals and birds was possible, a great deal of uncertainty would still exist in the interpretation of which predator was first at the nest. () noted that nests were fairly often visited by several predators, and they thus had to classify these nests as having been predated by unknown predators.Several authors conducting experiments with cameras have concluded that nest cues are unreliable for identifying predators (Larivière ) elucidates how the use of cameras in nest predation studies has increased in recent years.While bird populations have declined, predator populations have developed in the opposite direction: evidence shows that the European populations of many predator species preying upon ground-nesting bird nests have grown considerably during recent decades (Panek and Bresinski ) underlined that the importance of nest predation has increased over recent years: they found a 25% increase in the overall predation rate over their 12-year study period in Poland.In addition to the native species, several invasive alien predators are also present, e.g., the raccoon (). For example, Finnish hunting bag statistics show an enormous increase in raccoon dog numbers: during the last 20 years, the raccoon dog hunting bag has increased over threefold (1996: 61,000, 2016: 212,000; LUKE ).We are also able to (4) record the exact predation date.Artificial nests provide little insight in to predation rates of natural nests.On the other hand, the areas also needed forest patches at least 300 m in width, allowing us to place cameras within the forest, 150 m from the forest/field edge (hereafter, forest edge).
We first test the effect of two different habitat-related factors on the level of nest predation: (1) distance from the forest and nearest tree (stalking perch for predatory birds) and (2) the effect of visibility of the nest from the air on predation.Fifty percent of the predators were birds, 40% mammals, and 10% remained unknown.The three dominant predators of our artificial nests were the raccoon dog () with 10 depredated nests each.Because of the Finnish climate and high yearly precipitation, all fields are drained and larger fields are usually separated by open ditches, creating narrow edge areas along field boundaries.Spring wheat, spring barley, spring oats, and rye are the most common crop types, along with oil-seed crops, beans, and peas.
Search for predating test:
Predators show varying relationships to, e.g., cover types and scale (Cox et al. Predator identification has often been based on the use of artificial nests and dummy eggs, and possible predators have been identified by marks left either on the dummy eggs or in the nest surroundings (Andrén ).