Revisiting an old question: Which predators eat eggs of ground-nesting birds in farmland landscapes?

Hedgerows interact with forests to shape the abundance of mesopredators and their predation rate on eggs in farmland landscapes

Nest predation is the main cause of reproductive failure, particularly in ground-nesting birds on farmlands. Understanding the links between nest predation and habitat change can help design effective management schemes to constrain the negative impact of predation pressure on birds. However, the mechanisms underlying the relationships between landscape attributes, predator distribution, and nest predation are still unclear. Here, we use an experimental approach to examine the effects of distance to the hedgerow as well as hedgerow and forest densities on the abundance of major mesopredators of ground nests of our study area (i.e., corvids) and on the predation rate of artificial ground nests (n = 2576). We found evidence that landscape configuration influenced predation patterns differently depending on the predator species. Nest predation by corvids was more likely in homogeneous and open agricultural landscapes with a low density of forest and hedgerows, whereas predation by other predators was more likely close to hedgerows. Nest predation by corvids and the abundance of corvids also tended to be lower in landscapes dominated by grasslands. Other variables such as road density and distance to human settlements had contrasted effects on the likelihood of a nest being depredated by corvids, i.e., no effect with proximity to human settlements and decreasing trend with road density. Altogether, our results suggest that landscape features interact with mesopredator distribution and their predation rates of ground nests. Therefore, from a conservation and management perspective, a heterogeneous agricultural landscape that includes a mixture of crops associated with patches of forests, hedgerows, and grasslands offering alternative food to generalist predators should contribute to reducing ground-nesting bird predation.

Report of a magpie preying on a post-fledgling Daurian redstart

A magpie (Pica pica) preying on a fledgling of Daurian redstart (Phoenicurus auroreus) was incidentally recorded with a video shot by mobile phone on 26 May 2021, providing direct evidence for magpie predation. It also shows that predation is an important factor that affects the survival of fledglings, indicating that survival of fledglings should be considered in evaluating breeding success of birds. The fledgling was about 13-day-old posthatching, and it was on its first day of leaving the nest when the incident occurred. It was preyed upon by a magpie 10 m away from the nest by two attempts under strong defensive behaviour from the female.

Detectability and predator strategy affect egg depredation rates: Implications for mitigating nest depredation in farmlands

Predation is a major evolutionary force in animal ecology. Mechanisms by which prey coloration provides camouflage has been widely studied. However, predator response to prey camouflage and concealment has received less attention. Understanding vegetation structure effect on depredation success could help managers design strategies to mitigate the depredation of managed species (e.g., threatened or hunted). We aimed to investigate the relationship between depredation rate, nest camouflage and concealment in ground-nesting birds of farmlands, and their predators. We set up an experiment of 2576 artificial ground nests to assess the role of egg coloration (white, light green, and dark green), egg size (small, medium, and large), and vegetation structure (vegetation height and land use) in nest survival rates. We also explored the role of predator searching strategies by analysing clumped depredation and multiple depredation events. Of the nests, 34.0% were depredated, with corvids as the predators 78.5% of the time. Corvid depredation decreased by 40-60% in grasslands and spring crops above a vegetation height of 30 cm. In contrast, vegetation height and land use may be of far less importance in avoiding depredation by other predators. The probability of depredation was spatially clumped, suggesting that predators increase search effort in areas where a nest was previously encountered. Neighboring depredation and depredation repetition were more frequent in corvids than in other predators. Our study indicates that nests in vegetation higher than 30 cm had a drastic reduction in depredation rates by corvids. Management of vegetation structure is a key tool to mitigate depredation risk, and improving the availability of alternative food resources may be a complementary tool.

Camera trap data suggest uneven predation risk across vegetation types in a mixed farmland landscape

Ground-nesting farmland birds such as the grey partridge (Perdix perdix) have been rapidly declining due to a combination of habitat loss, food shortage, and predation. Predator activity is the least understood factor, especially its modulation by landscape composition and complexity. An important question is whether agri-environment schemes such as flower strips are potentially useful for reducing predation risk, for example, from red fox (Vulpes vulpes). We employed 120 camera traps for two summers in an agricultural landscape in Central Germany to record predator activity (i.e., the number of predator captures) as a proxy for predation risk and used generalized linear mixed models (GLMMs) to investigate how the surrounding landscape affects predator activity in different vegetation types (flower strips, hedges, field margins, winter cereal, and rapeseed fields). Additionally, we used 48 cameras to study the distribution of predator captures within flower strips. Vegetation type was the most important factor determining the number of predator captures and capture rates in flower strips were lower than in hedges or field margins. Red fox capture rates were the highest of all predators in every vegetation type, confirming their importance as a predator for ground-nesting birds. The number of fox captures increased with woodland area and decreased with structural richness and distance to settlements. In flower strips, capture rates in the center were approximately 9 times lower than at the edge. We conclude that the optimal landscape for ground-nesting farmland birds seems to be open farmland with broad extensive vegetation elements and a high structural richness. Broad flower blocks provide valuable, comparatively safe nesting habitats, and the predation risk can further be minimized by placing them away from woods and settlements. Our results suggest that adequate landscape management may reduce predation pressure.

Quail eggs in artificial nests change their coloration when exposed to ambient conditions: implication for studies on nest predation

Quail eggs have been widely used in field experiments, mainly to study factors associated with the risk of nest predation. Some shortcomings of using quail eggs in this type of study have been previously addressed (e.g., these eggs might be too big for some predators of eggs of small birds). Here, we show experimental evidence of another shortcoming of the use of these eggs in field experiments. Quail eggs exposed to sunlight rapidly faded in colour after three days, both in the visible and UV spectra, and this change was related to the amount of solar radiation received. This caused changes in the camouflage of the eggs, which may be perceived by predators with different visual systems (dichromatic, trichromatic, and tetrachromatic (for both violet- and UV-sensitive species)). Therefore, the results of field studies of nest predation using quail eggs might be questioned in those cases in which the camouflage has been altered due to the rapid changes in coloration, as this can affect the resulting predation rates. We recommend that researchers planning to use quail eggs should perform a prospective assessment of changes in coloration of eggs exposed to environmental conditions in the nest sites used by the target species.

Does Experimental Non-Reclaimed Sites Differ from Technically Reclaimed Areas in the Risk of Artificial Bird Nest Predation?

Areas left to natural development have been found to be sites with higher diversity and conservation value of local communities, including bird communities, compared to artificial reclamation of post-industrial areas. Most of the studies conducted so far have focused primarily on bird communities of post-mining areas, in terms of the diversity and richness of species. Our study dealt with bird nest predation on specific case of two experimental sites (20 and 32 ha) with more than a 20-year history of primary spontaneous succession established within the technical reclamation of the Radovesická spoil heap (approx. 1,200 ha, North Bohemia, Czech Republic). In the spring of 2018, we conducted a predation experiment using artificial nests (ground and elevated), installed within both succession areas and beyond, in the adjacent artificially reclaimed areas. We monitored the way of restoration and the distance of the nest placement from the succession-reclamation sites edge. The rate of predation was very high: 92.5 % in reclaimed area and 89.4 % in spontaneous successions. None of the observed factors analysed in the generalised linear model (GLM) have conclusively explained the risk of predation. The two experimental succession sites did not differ from the surrounding reclaimed sites in terms of the risk of predation, nor did they significantly influence predation risk on reclaimed sites. We believe that both relatively small and mutually isolated areas do not provide enough of an inner environment without or with at least a limited effect of predation pressure coming from adjacent reclaimed areas.