Predators use various tactics to find and depredate bird nests. This study examines a possible tactic of visually orientated predators termed “delayed nest-visit”. This consists in remembering the positions of incubating parents and subsequent easy depredation of eggs when the parents are away from their nests. Conditions for use of this tactic were experimentally simulated by installing artificial nests with quail eggs and plastic dummies of northern lapwings (Vanellus vanellus) at 11 actual breeding grounds with various
habitat conditions in southern and eastern Bohemia, Czech Republic. Habitat, presence of the dummy, and their interaction significantly affected nest survival. While 17.2 % of the nests baited with the dummy were depredated, this occurred in only 6.9 % of the nests without the dummy. This depredation rate was affected by the visibility of the dummies in particular habitats. The results suggest that predators may remember the nest position to delay their first visit to a previously located bird nest from a remote place and may use
this tactic to easily capture the clutches. The use of this tactic showed that at least some predator species are able to apply much more sophisticated approaches in search of birds’ nests than previously assumed.
During the winter period 2006/2007, research was carried out on the distribution and number of black grouse in coniferous lowland forest, Bory Dolnośląskie and the Karkonosze Mountains in southwest Poland. During 27 workshops, more than 800 members of various hunting clubs and representatives of the local State Forest Service presented information about place i.e., forest compartments and date when black grouse was seen. Next, this information was put on forest maps. Birds that could be seen twice of more were arbitrarily excluded by time-space analysis. In Bory Dolnośląskie, a declining black grouse population was present in 12 hunting districts covering 50.5 thousands ha of forest. The estimate of this species was 60 birds, i.e., 1.18 birds per 1 000 ha. In the Karkonosze Mountains, increasing black grouse population occurred in 8 hunting districts within a forest area of 30.1 thousands ha. The black grouse number was estimated to 169 birds, i.e., 5.61 birds per 1 000 ha. In the heather-land of Bory Dolnośląskie, 200 artificial nests were distributed on transect lines between the habitat (A) where black grouse is still present and the one (B) where it disappeared, and 14 movable digital cameras with movement detector triggered by infrared sensor were temporarily located at randomly selected nests that were destroyed by predators. The picture analysis showed that raven (Corvus corax) destroyed 93.9% and red fox (Vulpes vulpes) 6.1% of the nests. All the nests were damaged within 7 days. The rate of nest damage was faster in habitat B. Population dynamics of lowland and mountain black grouse population is analysed and discussed.
A study was made of the influence of trampling by grazing animals on the nesting success of real nests (meadow pipit, Anthus pratensis; water pipit, Anthus spinoletta; and skylark, Alauda arvensis) and simulated nests (caps from jam-jars filled by green plasticine) on pasture in the Orlické Mountains and on unmanaged alpine meadows in the Jeseníky Mountains (Czech Republic, Central Europe). While the pasture was continuously grazed by livestock at high densities, unmanaged alpine meadow was grazed only by wild large herbivores at far lower densities. Trampling was the primary cause of nest failure in the Orlické Mountains, but was infrequent in the Jeseníky Mountains. The number of real nests lost by trampling corresponded to simulated nests within the localities. Spatial distribution of simulated nests had no effect on their survival on intensively grazed fields. The results indicate that grazing animals negatively influenced the nesting success of real and simulated nests of grassland passerines on continuously grazed mountain pasture. The use of simulated nests was an adequate method of predicting trampling losses by natural nests.
The study aimed to recognize whether the activity of a semi-aquatic invasive carnivore – the American mink Neovison vison – is related to the distribution of waterbird colonies. For this reason, we monitored mink occurrence in lake reedbeds and the fate of artificial nests imitating those of the great crested grebe Podiceps cristatus. The location of artificial nests in the grebe colony increased the probability of their survival compared to those placed outside the grebe colony. During the study, mink activity increased over time. In general, it was lower in colonies than outside of them, suggesting that the presence of natural nests does not increase the probability of mink occurrence in lake reedbeds. However, mink activity was negatively correlated with the distance from the lake shoreline and differed spatially according to the presence or absence of natural grebe nests. In grebe colonies, the probability of mink occurrence at greater distances from the lake shoreline was higher than outside, which can be explained by optimizing swimming effort while searching for prey. In conclusion, mink activity in colonies was lower than in areas with no waterbird nests, and nest location in a colony decreased predation risk by mink.
Higher nest predation at habitat edges is a major problem for conservation biology. We studied nest predation using artificial nests resembling great reed warblers’ nests at edges and interiors of reedbeds in four large wetlands in Europe: Lake Hornborga (Sweden), Lake Neusiedl (Austria), Lake Velence (Central-Hungary) and Kis-Balaton marshland (West-Hungary). Nest losses showed great local and temporal variation, and in general there was larger nest predation at the edges than in the interior reedbeds. Predation rates of artificial nests along different reedbed edges showed great variation. In contrast, predation rates of interiors were more similar across all experiments, with less variation. This may indicate the existence of a habitat-specific predation rate with less variation in interiors of large habitats, while edges are more exposed to the influences of other factors, which resulted in higher variation of predation rates among study sites. Therefore, reedbed conservation should prefer large stands if considering only passerine nest predation, because (1) nest survival seems to be higher in interior than at edges, and (2) because interiors are less variable, i.e. more stable than edges. The designation of reedbeds cannot rely on reedbed edges, where predation can change due to factors not related to the reed habitat at all.