Nest predators of woodland open-nesting songbirds in central Europe

I used time-lapse videotaping to identify predators of open songbird nests in fragmented deciduous woodland (nine plots, 2–10 ha each) in the Czech Republic from 2002 to 2006. I documented 22 species of predators at 171 nests of 13 species (mainly Blackcap Sylvia atricapilla , Song Thrush Turdus philomelos , Common Blackbird Turdus merula , Yellowhammer Emberiza citrinella and Chaffinch Fringilla coelebs ). The main predators were Pine Marten Martes martes (37% of 178 predation events), Jay Garrulus glandarius (29%), Buzzard Buteo buteo (7%) and Great Spotted Woodpecker Dendrocopos major (7%); mammals accounted for 48% of total predation. At least 3% of nests were depredated by multiple predators. In spite of their local abundance, Hooded Crows Corvus cornix did not present a serious threat for shrub nesting songbirds (< 1% of total predation). No predation by mice was recorded, suggesting that their importance has been overestimated in artificial nest studies. The proportional species composition of predators depended on which species occupied the monitored nest and location (study plot), but not on the year or the time of season. Corvids and raptors accounted for a relatively larger percentage of total predation of small ('warblers') and large ('thrushes') prey species, respectively, whereas carnivores were important predators of all prey species. Active nests of thrushes were only rarely robbed by Jays (< 4% of 52 events), presumably due to parental nest defence. Predation by woodpeckers was spatially clumped, probably due to individual foraging specialization. Predation by the other major predators was documented on most/all study plots.     

Tropical forest fragmentation and nest predation – an experimental study in an Eastern Arc montane forest, Tanzania

When a habitat becomes fragmented and surrounded by another habitat this generally causes an increase in predation pressure at habitat transitions, often referred to as an edge effect. Edge effect in the form of enhanced nest predation intensities is one of the most cited explanations for bird population declines in fragmented landscapes. Here, we report results from a nest predation experiment conducted in a tropical montane forest landscape in the Uzungwa Mts., Tanzania. Using artificial nests with chicken eggs, we determined predation rates across a fragmentation gradient. The proportion of indigenous forest in four landscapes used in the study were 0.29, 0.58, 0.75 to 1.0. Nest predation intensities on artificial nests were about 19% higher inside intact forest than at edges in fragmented forest landscapes. Furthermore, predation intensities were relatively constant across a forest fragmentation gradient. Our results thus challenge the applicability and generality of the edge effect, derived from studies almost exclusively conducted in temperate regions rather than tropical forest ecosystems. Nest predation levels differences between tropical montane forest and that reported in other forest ecosystems are discussed.     

Predators at bird nests in a northern hardwood forest in New Hampshire

ABSTRACT.   Nest predation is the primary cause of nest failure in most passerine birds, and increases in nest predation associated with anthropogenic habitat disturbance are invoked as explanations for population declines of some bird species. In most cases, however, the identity of the nest predators is not known with certainty. We monitored active bird nests with infrared time-lapse video cameras to determine which nest predators were responsible for depredating bird nests in northern New Hampshire. We monitored 64 nests of 11 bird species during three breeding seasons, and identified seven species of predators during 14 predation events. In addition, we recorded two instances of birds defending nests from predators and, in both cases, these nests were ultimately lost to predation. These results contrast with other studies in terms of the relatively high proportion of nests depredated by raptors and mice, as well as the absence of any predation by snakes. The diverse suite of predators in this and other studies is likely to confound our understanding of patterns of nest predation relative to fragmentation and habitat structure.     

Predation of experimental nests is linked to local population dynamics in a fragmented bird population

Artificial nest experiments (ANEs) are widely used to obtain proxies of natural nest predation for testing a variety of hypotheses, from those dealing with variation in life-history strategies to those assessing the effects of habitat fragmentation on the persistence of bird populations. However, their applicability to real-world scenarios has been criticized owing to the many potential biases in comparing predation rates of artificial and natural nests. Here, we aimed to test the validity of estimates of ANEs using a novel approach. We related predation rates on artificial nests to population viability analyses in a songbird metapopulation as a way of predicting the real impact of predation events on the local populations studied. Predation intensity on artificial nests was negatively related to the species' annual population growth rate in small local populations, whereas the viability of large local populations did not seem to be influenced, even by high nest predation rates. The potential of extrapolation from ANEs to real-world scenarios is discussed, as these results suggest that artificial nest predation estimates may predict demographic processes in small structured populations.     

Predation as a landscape effect: the trading off by prey species between predation risks and protection benefits

1. Predators impose costs on their prey but may also provide benefits such as protection against other (e.g. nest) predators. The optimal breeding location in relation to the distance from a nesting raptor varies so as to minimize the sum of costs of adult and nest predation. We provide a conceptual model to account for variation in the relative predation risks and derive qualitative predictions for how different prey species should respond to the distance from goshawk Accipiter gentilis nests. 2. We test the model predictions using a comprehensive collection of data from northern Finland and central Norway. First, we carried out a series of experiments with artificial bird nests to test if goshawks may provide protection against nest predation. Second, we conducted standard bird censuses and nest-box experiments to detect how the density or territory occupancy of several prey species varies with distance from the nearest goshawk nest. 3. Nest predation rate increased with distance from goshawk nest indicating that goshawks may provide protection for birds' nests against nest predation. Abundance (or probability of presence) of the main prey species of goshawks peaked at intermediate distances from goshawk nests, reflecting the trade-off. The abundance of small songbird species decreased with distance from goshawk nests. The goshawk poses little risk to small songbirds and they may benefit from goshawk proximity in protection against nest predation. Finally, no pattern with distance in pied flycatcher territory (nest box) occupation rate or the onset of egg-laying was detected. This is expected, as flycatchers neither suffer from marked nest predation risk nor are favoured goshawk prey. 4. Our results suggest that territory location in relation to the nest of a predator is a trade-off situation where adult birds weigh the risk of themselves being predated against the benefits accrued from increased nest survival. Prey species appear able to detect and measure alternative predation risks, and respond adaptively. From the prey perspective, the landscape is a mosaic of habitat patches the quality of which varies according to structural and floristic features, but also to the spatial distribution of predators.     

Compounding effects of habitat fragmentation and predation on bird nests

Habitat fragmentation and invasive species are two of the greatest threats to species diversity worldwide. This is particularly relevant for oceanic islands with vulnerable endemics. Here, we examine how habitat fragmentation influences nest predation by Rattus spp. on cup‐nesting birds in Samoan forests. We determined models for predicting predation rates by Rattus on artificial nests at two scales: (i) the position of the bird's nest within the landscape (e.g. proximity to mixed crop plantations, distance to forest edge); and (ii) the microhabitat in the immediate vicinity of the nest (e.g. nest height, ground cover, slope). Nest cameras showed only one mammal predator, the black rat (Rattus rattus), predating artificial nests. The optimal model predicting nest predation rates by black rats included a landscape variable, proximity to plantations and a local nest site variable, the percentage of low (<15 cm) ground cover surrounding the nest tree. Predation rates were 22 ± 13% higher for nests in forest edges near mixed crop plantations than in edges without plantations. In contrast, predation rates did not vary significantly between edge habitat where the matrix did not contain plantations, and interior forest sites (>1 km from the edge). As ground cover reduced, nest predation rates increased. Waxtags containing either coconut or peanut butter were used as a second method for assessing nest predation. The rates at which these were chewed followed patterns similar to the predation of the artificial nests. Rural development in Samoa will increase the proportion of forest edge near plantations. Our results suggest that this will increase the proportion of forest birds that experience nest predation from black rats. Further research is required to determine if rat control is needed to maintain even interior forest sites populations of predator‐sensitive bird species on South Pacific islands.     

Exclosure fences around nests of imperiled Florida Grasshopper Sparrows reduce rates of predation by mammals

Increasing nest survival by excluding predators is a goal of many bird conservation programs. However, new exclosure projects should be carefully evaluated to assess the potential risks of disturbance. We tested the effectiveness of predator exclosure fences (hereafter, fences) for nests of critically endangered Florida Grasshopper Sparrows (Ammodramus savannarum floridanus) at a dry prairie site (Three Lakes; 2015–2018) and a pasture site (the Ranch; 2015–2016) in Osceola County, Florida, USA. We installed fences at nests an average of 8 days after the start of incubation, and nest abandonment after fence installation was rare (2 of 149 installations). Predation was the leading cause of failure for unfenced nests at both sites (48–73%). At Three Lakes, nest cameras revealed that mammals and snakes were responsible for 61.5% and 38.5% of predation events, respectively, at unfenced nests. Fences reduced the daily probability of predation (0.016 for fenced nests vs. 0.074 for unfenced nests). The probability that a fenced nest would survive from discovery to fledging was more than double that of unfenced nests (60.4% vs. 27.7%). However, we found no difference in daily nest survival at the Ranch between the year before nests were fenced (2015; 0.874) and the year when all but one nest were fenced (2016; 0.867) because red imported fire ants (Solenopsis invicta) were responsible for 86% of predation events at fenced nests at the Ranch. The use of cameras at fenced nests revealed that site‐specific differences in nest predators explained variation in fence efficiency between sites. Our fence design may be useful for other species of grassland birds, but site‐specific predator communities and species‐specific response of target bird species to fences should be assessed before installing fences at other sites.     

Quantifying the relative predation pressure on bumblebee nests by the European badger (Meles meles) using artificial nests

Bumblebee populations are declining. Factors that impact the size and success of colonies act by either limiting resource availability (bottom‐up regulation) or causing mortality, for example, pesticides, disease, and possibly predation (top‐down regulation). The impact of predation has not been quantified, and so, the current study used novel artificial nests as a proxy for wild bumblebee nests to quantify the relative predation pressure from badgers in two habitats: woodland and grassland, and at two nesting depths: surface and underground. Badgers occur across most parts of the UK and are known to predate on bumblebee nests. We found that significantly more artificial nests (pots containing bumblebee nest material) were dug up compared with control pots (pots without bumblebee nest material). This shows that artificial nests have the potential to be used as a method to study the predation of bumblebee nests by badgers. In a location of high badger density, predation pressure was greater in woodland than grassland, whereas no difference was observed in relation to nest depth. Woodland and grassland are shared habitats between bumblebees and badgers, and we suggest that higher predation may relate to activity and foraging behavior of badgers in woodland compared with grassland. We discuss how badger predation in different habitats could impact different bumblebee species according to their nesting behaviors. Understanding the relative impact of badger predation on bumblebee colonies provides key information on how such top‐down regulation affects bumblebee populations.     

Forest fragmentation and avian nest predation in forested landscapes

Summary The size of forest fragments, the use of land bordering fragments, and the distance of nests from an edge all affect the frequency of predation upon bird nests in Maine (USA), an area where the forest has been fragmented by roads, but not significantly reduced in area. We placed artificial nests containing quail eggs in forests of different sizes and at various distances from the edge to test which of these factors was most important in describing predation. Predation was greatest in small tracts surrounded completely by land. Large areas and those bordered on at least one side by a large water body had lower predation rates. This suggests that influx of predators from nearby habitats may be responsible for much of the nest predation in forest fragments.     

Nesting Success of Costa Rican Lowland Rain Forest Birds in Response to Edge and Isolation Effects

Although open-cup nesting birds generally face increased risk of nest depredation from forest edge predators and brood parasites in fragmented temperate landscapes, little information exists to assess such risks in tropical birds. We compared nesting success of real birds' nests in large and small forest fragments to a control site in Caribbean lowland wet forest of Costa Rica. Pooling across species, nesting success was significantly greater in unfragmented forest than in either small, isolated fragments or the La Selva Biological Reserve, which is at the tip of a forest 'peninsula' embedded in a largely deforested landscape. Nesting success in isolated fragments did not vary according to distance from edge, suggesting that predators in fragments act throughout these forest patches. The case for increased nest predation as a plausible mechanism to explain the documented decline of forest interior bird populations in this fragmented tropical landscape is enhanced by a simple demographic model that suggests nesting success is likely too low to maintain populations at La Selva and in the fragments. The fact that the large (> 1000 ha) La Selva forest reserve is experiencing nest predation rates similar to those in much smaller fragments is cause for concern. Our results make a strong case for additional studies to document the identities of nest predators in both fragmented and unfragmented forests in such tropical forest landscapes.     

Identifying predators clarifies predictors of nest success in a temperate passerine

1.  Nest predation negatively affects most avian populations. Studies of nest predation usually group all nest failures when attempting to determine temporal and parental activities, habitat or landscape predictors of success. Often these studies find few significant predictors and interpret patterns as essentially random.
2.  Relatively little is known about the importance of individual predator species or groups on observed patterns of nest success, and how the ecology of these predators may influence patterns of success and failure.
3.  In 2006 and 2007, time-lapse, infrared video systems were deployed at nests of Swainson's warblers ( Limnothlypis swainsonii Audubon) in east-central Arkansas to identify dominant nest predators and determine whether factors predicting predation differed among these predators.
4.  Analysis of pooled data yielded few predictors of predation risk, whereas separate analyses for the three major predator groups revealed clear, but often conflicting, patterns.
5.  Predation by ratsnakes ( Elaphe obsoleta ) and raptors was more common during the nestling period, whereas predation by brown-headed cowbirds ( Molothrus ater ) occurred more during incubation. Additionally, the risk of predation by raptors and cowbirds decreased throughout the breeding season, whereas ratsnake predation risk increased.
6.  Contrary to expectations, predation by ratsnakes and cowbirds was more common far from edges, whereas raptor predation was more common close to agricultural edges.
7.  Collectively, our results suggest that associating specific predators with the nests they prey on is necessary to understand underlying mechanisms.     

基于红外相机技术和人工巢试验分析白冠长尾雉巢潜在捕食者

为了了解保护区内外的白冠长尾雉繁殖生态,2014年3—7月在河南董寨国家级自然保护区和保护区外湖北平靖关村利用人工巢试验(以鸡蛋为诱饵)、红外相机技术和栖息地样方调查搜集巢捕食信息,对其巢捕食率、巢潜在捕食者和影响巢捕食的栖息地因子进行研究.两轮试验分别为繁殖期前期3—4月和繁殖期中期5—6月.试验共放置巢149个,其中红外相机监测62个,累计相机日1315个,拍摄照片7776张,视频6950个.结果表明: 保护区外(平靖关)巢捕食率高于保护区内(董寨),繁殖期前期和繁殖期中期保护区内外差异均极显著.平靖关捕食者种类数(11和6种)在繁殖期前期和中期均高于董寨(7和5种),平靖关捕食者比例较高的是啮齿类和鸦科鸟类,董寨捕食比例较高的是貉.平靖关坡度和乔木盖度对巢捕食影响显著,而董寨的落叶盖度对其影响显著.在红外监测的人工巢中共发现野生白冠长尾雉访问人工巢13巢18次.     

Forest fragmentation and rhinocryptid nest predation in central Chile

Fragmentation of forest landscapes can raise the intensity of nest predation by increasing the abundance and richness of generalist or introduced predators. Understory foraging birds, such as rhinocryptids, can be highly vulnerable to nest predation in fragmented landscapes because they often place their nests on the ground. Temperate deciduous forests in Chile have been intensively fragmented in the last centuries, causing changes in nest predator densities. We tested if predation of artificial nests, mimicking those of rhinocryptids, placed on and above ground was higher in the remnant fragments of central Chile due to an increase in predator abundance. The rate of nest predation in forest remnants was larger than in native continuous forest. Small mammals were the main nest predators. Despite high predation rates, the abundance of rhinocryptids is higher in forest remnants, suggesting that fragments might constitute ecological traps.     

An artificial bird nest experiment in urban environments: Lessons from a school‐based citizen science programme

Maintaining suitable vegetation within urban environments is crucial for wildlife conservation in the face of anthropogenic habitat change. Here, we report on a citizen science project, involving students from seven schools across south‐eastern Australia, that investigated the effectiveness of urban vegetation as habitat for bird nests. The ‘nest concealment hypothesis’ posits that vegetation should obscure the nest from predator detection, thus reducing the likelihood of predation. To test this, participating school‐aged citizen scientists constructed artificial nests, which were placed in garden trees within school grounds and monitored for signs of predation. We found no evidence to support the nest concealment hypothesis, with no relationship between the density of vegetation immediately surrounding a nest and its likelihood of predation (binomial model:  = 1.714, P = 0.190). It was observed that 80% of the nests experienced predation. This aligns with mounting evidence suggesting that other factors, such as olfaction and adult defence, may be more important factors in the protection of bird nests. It is important to note that artificial nests are unreliable, and therefore, the veracity of the overall conclusions is limited. However, in conducting this experiment, we demonstrate the suitability of this method as a school‐based citizen science activity. This study exemplifies that field‐based experiments can used to engage future generations with conservation science.     

Power lines,roads, and avian nest survival: effects on predator identity and predation intensity

相似文献   

Predator–prey interactions between the South Polar skua Catharacta maccormicki and Antarctic tern Sterna vittata

Antarctic terns have to co‐exist in a limited space with their major nest predator, the skuas. We conducted artificial nest experiments to evaluate the roles of parental activity, nest location and nest and egg crypsis in this simple predator–prey system. Predation on artificial (inactive) nests was higher in traditional nesting sites than in sites previously not occupied by terns, which suggests that skuas memorized past tern breeding sites. Predation on artificial nests in inactive colonies was higher than in active (defended) colonies. Parental defense reduced predation in colonies to the level observed in artificial nests placed away from colonies. This suggests that communal defense can balance the costs of attracting predators to active colonies. Within colonies, predation was marginally higher on experimental eggs put in real nests than on bare ground. Although it seems that the presence of a nest is costly in terms of increased predation, reductions in nest size might be constrained by the need for protective nest structures and/or balanced by opposing selection on nest size. Predation did not differ markedly between artificial (quail) and real tern eggs. A simultaneous prey choice experiment showed that the observed predation rates reflected egg/nest detectability, rather than discrimination of egg types. In summary, nesting terns probably cannot avoid being detected, and they cannot defend their nest by attending them. Yet, by temporarily leaving the nest, they can defend it through communal predator mobbing, and at the same time, they can benefit from crypsis of unattended nest and eggs.     

Nest predation in Reed Buntings Emberiza schoeniclus: an experimental study

Predation is a major cause of nest failure in many bird species. High levels of nest loss may be a consequence of habitat fragmentation, leading to increased amounts of edge habitat. Yet the evidence for generally high nest predation rates along edges in fragmented landscapes is ambiguous. Using real nests of Reed Buntings Emberiza schoeniclus in which artificial Reed Bunting and real Japanese Quail Coturnix japonica eggs were placed, we experimentally tested for edge effects on nest predation in highly fragmented reed Phragmites sp. habitats in the Swiss lowlands. We also examined seasonal patterns of predation and the impacts of nest visits by observers. We found evidence for an edge effect at the water-sided reed edge, with nests located closer to the water being more likely to be predated than those further away. Predation probability increased from early to late season, suggesting that nest predation may be density dependent. Probability of nest predation was only weakly influenced by whether or not a nest was visited. Our results suggest that the intensive reed management currently applied in Swiss nature reserves may result in unnaturally high levels of nest losses in the Reed Bunting, because reed bands are not wide enough to allow nest placement at a safe distance from reed edges.     

Nest predation in Australian urban environments and the role of the pied currawong,Strepera graculina

Abstract An experiment, involving 2000 members of the public, determined the identity of nest predators in urban environments. Experimental nests of halved tennis balls covered with coconut fibre and wool were manufactured to resemble the nests of willie wagtails, Rhipidura leucophrys. The identity of predators was determined by analysis of imprints left in artificial eggs made of coloured modelling clay. Sixty-four per cent of nests were preyed upon, with most predation being the result of large birds. Direct observations of predation (n = 134) indicated that pied currawongs were the most common large bird, accounting for 52% of all predation. Predation incidence was higher in gardens with more trees and in which kookaburras, Dacelo novaeguineae, were fed frequently. Among nests placed in trees, nest predation was correlated with nest height. Eggs camouflaged by speckling experienced a similar incidence of predation to plain eggs. This study provides evidence to support the contention that pied currawongs are a major threat to the persistence of small birds in Australian urban environments.     

Nest predation in forest birds: influence of predator type and predator's habitat quality

We used the introduction of a generalist nest predator, the red squirrel Tamiasciurus hudsonicus, and of a large herbivore, the Sitka black-tailed deer Odocoileus hemionus sitkensis, to the islands of Haida Gwaii (Queen Charlotte Islands, British Columbia, Canada) to study how predator assemblage and habitat quality and structure influenced nest predation in forest birds. We compared losses of natural nests to predators on islands with and without squirrels. We selected nine islands with or without squirrel or deer and used 506 artificial nests put on the ground or in shrubs to further analyse variation of nest predation with predator assemblage and habitat quality for the predators. For both natural and artificial nests predation risk was higher in presence of squirrels. But predation risk varied within island categories. In presence of squirrels it was highest in stands with mature conifers where it fluctuated from year to year, in response to fluctuations in squirrel abundance. Vegetation cover around the nest had little effect on nest predation by squirrels. Where squirrels were absent, nest predation concentrated near predictable food sources for corvids, the main native predators, and increased with decreasing vegetation cover, suggesting that removal of the vegetation by deer increased the risk of predation by native avian nest predators that use visual cues. Predation risk in these forests therefore varies in space and time with predator composition and with quality of the habitat from the predators' perspective. This temporal and spatial variation in predation risk should promote trade-offs in the response of birds to nest predation, rather than fine-tuned adaptations to a given predation pattern.     

Predation on artificial avian nests is higher in forests bordering small anthropogenic openings

Habitat edges alter the diversity of avian communities and are often associated with higher rates of nest predation. However, most previous studies on habitat edges have been conducted along long linear corridors or at the transition between large field and forest patches in agricultural systems. Less is known about predation rates when the habitat edge is the result of a small interior forest opening. We assessed predation rates on artificial nests mimicking ground and shrub nesters in Northern Michigan forests perforated by small clearings used previously for oil and gas extraction. Nests were placed at varying distances from the edges of these clearings, and in similar spatial arrangements within unfragmented interior forest plots. Predation rates increased in forests near edges, but significant impacts were limited to shrub nests. Markings on predated clay eggs indicated that the type of predation also differed. Scratch marks were the most prevalent egg indentation, but eggs with poked holes were twice as common near the forest edge. The increase in the number of poked eggs suggests that a higher density of avian predators occurred in forests near an edge. Predation rates at forest edges did not vary by distance from the forest edge. Surveys of the avian community revealed differences between edge and interior forests: American Crows Corvus brachyrhynchos and Blue Jays Cyanocitta cristata, two species known to predate bird nests, were more common near edges. Our results suggest that small forest openings alter the avian community and may adversely impact reproductive output in some species. If the alteration of these processes results in population‐level impacts, small forest perforations should be avoided when possible and reforestation of abandoned well‐pads should be encouraged.