Predation survival of ground nesting birds in grass and wheat fields: Experiment with plasticine eggs and artificial nests

There are no agricultural activities in Hungarian energy grass plantations (Elymus elongatus (Host) Runemark before harvesting in August, so the breeding success of the ground-nesting Common pheasant (Phasianus colchicus L.) and Common quail (Coturnix coturnix (L.)) is probably higher than in the neighbouring intensively managed grain fields. The dominant nest predators of these bird species (e.g. Red fox Vulpes vulpes L.) prey mostly on small mammals, thus the abundance of small mammals can influence the survival rates of ground-nesting birds. These assumptions were tested using artificial ground-nests and small mammal live traps in late May 2005. Of the nests, 25 were placed in the energy grass field which covered 60 ha and another 25 in the wheat field which area was 20 ha. Each of the nests contained one chicken egg, one quail egg and one plasticine dummy-egg. Real eggs were placed for the evaluation of nest predation rates and artificial plasticine eggs for predator identification from tooth and bill imprints. Following the placement of artificial nests, they were checked repeatedly between 16.00 and 18.00 every day. In both plots, 25 traps were set up, baited for 4 nights with quail egg and for another 4 nights with plasticine egg. Artificial nests lasted for 3 days in the wheat field and for 4 days in the energy grass field. The major predators in wheat were birds (16%) and mammals (84%), whereas in energy grass all predation (100%) was caused by mammals. There was no significant difference between types of predators in the two habitats. On-spot observations, traces and marks left on plasticine eggs, several droppings and the patterns of nest predation all suggested that the majority of nests were destroyed by Red fox. A significantly higher proportion of plasticine eggs were damaged in wheat (80%) than in energy grass (48%). Based on marks left on plasticine eggs, small mammal abundance was higher in wheat (80%) than in energy grass (33%), the latter habitat not yielding any small mammal captures at all. Traps in the wheat field caught significantly more small mammals with plasticine eggs (14) than with quail eggs (5). Plasticine eggs had greater attraction effect on small mammals, thus could negatively influence experiments with artificial ground nests.