Nesting success in Redshank Tringa totanus breeding on coastal meadows and the importance of habitat features used as perches by avian predators

Capsule Nest survival rates could not be explained by distance to habitat edges or other features used by predators.

Aims To investigate if predation on Redshank nests was affected by habitat characteristics at a local scale.

Methods We examined survival rates of Redshank nests on coastal meadows on the Baltic island of Gotland, Sweden, over two breeding seasons. We analysed nest survival rates in relation to several habitat characteristics that may benefit predators searching for nests. We examined existing studies concerning predation rates on wader nests in relation to edges and habitat features potentially used by avian predators.

Results We found no significant effects of distance to habitat edge or to nearest potential lookout for avian predators or to shoreline. Abundance of Lapwings Vanellus vanellus, an aggressive species with active nest-defence, did not have any significant effect on nest survival rate, nor did vegetation concealment of nests. Nest survival rates were significantly different between years and lower later in the season.

Conclusions There is only weak support for general effects on wader nest predation rates of proximity to edges and features used by avian predators. Simple mechanical management actions such as removal of trees and bushes on coastal meadows may not directly, and by itself, result in higher reproductive success of waders. Further understanding is needed of the behaviour of predators and the composition of the predator community in different landscapes in order to increase the efficiency of management actions to remove threats to vulnerable species on coastal meadows.     

An ecological paradox: More woodland predators and less artificial nest predation in landscapes colonized by noisy miners

Many passerine bird populations, particularly those that have open‐cup nests, are in decline in agricultural landscapes. Current theory suggests that an increase in habitat generalist predators in response to landscape change is partially responsible for these declines. However, empirical tests have failed to reach a consensus on how and through what mechanisms landscape change affects nest predation. We tested one hypothesis, the Additive Predation Model, with an artificial nest experiment in fragmented landscapes in southern Queensland, Australia. We employed structural equation modelling of the influence of the relative density of woodland and habitat generalist predators and landscape features at the nest, site, patch and landscape scales on the probability of nest predation. We found little support for the Additive Predation Model, with no significant influence of the density of woodland predators on the probability of nest predation, although landscape features at different spatial scales were important. Within woodlands fragmented by agriculture in eastern Australia, the presence of noisy miner colonies appears to influence ecological processes important for nest predation such that the Additive Predation Model does not hold. In the absence of colonies of the aggressive native bird, the noisy miner, the influence of woodland predators on the risk of artificial nest predation was low compared with that of habitat generalist predators. Outside noisy miner colonies, we found significant edge effects with greater predation rates for artificial nests within woodland patches located closer to the agricultural matrix. Furthermore, the density of habitat generalist predators increased with the extent of irrigated land‐use, suggesting that in the absence of noisy miner colonies, nest predation increases with land‐use intensity at the landscape scale.     

Does cowbird parasitism increase predation risk to American redstart nests?

Brood parasitism and nest predation are major causes of reproductive failure for many bird species nesting in fragmented landscapes. While brood parasites and predators may act independently, they could also interact if brood parasites increase the likelihood that predators detect nests. In this study, we examined the interaction between cowbird parasitism and nest predation in a 10 year study on 466 American redstart Setophaga ruticilla nests in central Alberta, Canada. We used advanced nest survival models to examine the support for three mechanisms that might lead to a positive correlation between brood parasitism and nest predation: 1) the presence of a cowbird nestling might increase the detection of the nest by predators, 2) nests with lower cover are more likely to be detected by both cowbirds and predators, and 3) cowbirds and predators may co-occur in landscapes of similar structure. Twelve percent of nests were parasitized and those nests had a 16–19% higher rate of failure due to predators compared to unparasitized nests. Daily nest predation rates increased during the nestling stage for both groups, but more strongly for parasitized nests. Loud begging by the cowbird nestling and/or higher parental feeding rates for the cowbird may have increased nest detectability to predators. Brood parasitism and nest predation were also positively related to forest cover, indicating landscape level effects were influential. Most nest predators were forest species and we suspect cowbirds responded positively to forest cover because of the increased abundance of songbird hosts. Nest-site features had less of an impact on nest predation or brood parasitism, although nests with higher overhead cover were less susceptible to predators. Our study shows how multiple mechanisms, particularly the behavioral effects of the brood parasite nestling and landscape structure, can lead to a positive relationship between nest predation and brood parasitism.     

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.     

Nest Predation Risk on Ground and Shrub Nests in Forest Margin Areas of Sulawesi, Indonesia

Forest loss and fragmentation in Indonesia may seriously affect the survivorship of forest birds and lead to local extinction of bird populations. We used 786 artificial nests baited with quail eggs to examine the effect of habitat alteration on nest predation in Lore Lindu National Park, Sulawesi. Natural forest and four habitats of forest margin areas: forest edge, forest gardens, coffee plantations, and secondary forest, were studied. Two types of artificial nests, ground and shrub nests were placed in these habitats at two different locations for a period of 8 days. In addition, we used automatic cameras and cage-traps to identify the predators. Nests in shrubs experienced significantly higher predation rates in forest margin areas than in natural forest. Predation on ground nests did not differ significantly between these habitat types, but was significantly higher than that on shrub nests in each habitat except forest edge. Rodents were the most common predators of both nests, but shrub nests were also susceptible to Dwarf cuscus (Strigocuscus celebensis), squirrels, and tree snakes. The nest predation rates we found were among the highest found in tropical rainforests, probably a consequence of the unique predator assemblages of Sulawesi. These results suggest that egg survival is negatively affected by human intervention and that human-induced habitats might have only limited importance for the conservation of Sulawesi's largely endemic understorey avifauna. These considerations might be important since forest margins comprise significant proportions of protected areas on Sulawesi and play an important role in future Park zoning concepts as well as in conservation-oriented land use management.     

Predation on artificial nests in relation to forest type: contrasting the use of quail and plasticine eggs

Previous studies of avian nest predation have focused on how human-induced changes in the landscape influence the frequency of predation However, natural variation in the abundance of predators due to their choice of habitat can also influence predation rate To determine if predation on artificial nests was influenced by forest stand type, we placed ground and shrub nests containing quail and plasticine eggs in contiguous coniferous, mixedwood and deciduous stands in the southern boreal mixedwood forest of central Canada Nest predators were identified using remotely triggered cameras and marks left in plasticine eggs, while the relative abundance of nest predators such as squirrels and corvids were estimated using acoustic-visual surveys Using the fate of quail eggs to calculate predation rate, we found that predation was significantly higher in coniferous (67%) than in deciduous (17%) or mixedwood (25%) forest, with similar predation on ground (37%) and shrub (29%) nests Using plasticine eggs to calculate predation rate, nests in coniferous forest still suffered higher rates of predation, although predation rates were 15–20% higher, and ground nests suffered significantly higher rates of predation than shrub nests Quail eggs seemed to suffer lower rates of predation because small mammals were unable to penetrate the shell, but could leave marks on plasticine eggs The higher predation rate in coniferous forest was likely caused by higher abundance of red squirrels Tamiasciurus hudsonicus , the presence of fishers Martes pennanti and a simplified understory which may have made it easier for predators to find nests relative to the deciduous and mixedwood forest Plasucine eggs provide new insights into nest predation by identifying predation events by smaller predators such as mice that are missed when using quail eggs     

Predation on artificial ground nests in relation to forest fragmentation, agricultural land and habitat structure

The impacts of forest fragmentation agricultural land and habitat structure on depredation of artificial ground nests were studied in the cultivated area in central Finland and in the forest dominated area in Finnish Lapland The overall predation rate did not differ between the regions The overall predation rate was also independent of landscape characteristics forest patch size and the distance to patch edge However, nest predation was clearly affected by the agricultural land since the robbing rate in forest edges was higher near farmlands than further away This effect was caused by avian predators which proportional importance in predation was higher in the agricultural landscape than in the forest landscape In both regions, depredation correlated positively with high numbers of pine and spruce This can be mainly explained by the preference of predators over coniferous forest habitat as a living or hunting area     

Predation risk effects on fitness related measures in a resident bird

Predation risk is thought to be highly variable in space and time. However, breeding avian predators may create locally fixed and spatially fairly predictable predation risk determined by the distance to their nest. From the prey perspective, this creates predation risk gradients that potentially have an effect on fitness and behavioural decisions of prey. We studied how breeding avian predators affect habitat selection (nest location) and the resulting fitness consequences in a northern population of resident willow tit ( Parus montanus ). Data included 429 willow tit nests over a four year period in a landscape containing a total of 33 avian predator nests. Willow tit nests were located randomly in the landscape and no predator avoidance in habitat selection or emptying of territories in proximity to predators was observed. Nestling size, however, was positively associated with distance from predator nests (n=252). Nestling mass and wing length were about 4.5% smaller close to predator nests compared to nestlings raised far from predator nests. Tarsus length also exhibited a positive relationship with increasing distance from predator nest but this was limited to habitats of young forests and pine bogs or dense mixed forests (4% increase). It is likely that habitat structural complexity influenced the perception of predation risk in different habitats. Our results indicate that willow tits do not provide reliable cues of predator free habitats for settling migrants. Nonetheless, breeding avian predators may create predictable predation risk in the landscape which is an important factor affecting reproductive success and potentially the demography of prey populations.     

千岛湖栖息地片段化效应对鸟类巢捕食风险的影响

为了解栖息地片段化对鸟类巢捕食风险的影响,我们于2010年4-8月,在千岛湖地区选取16个岛屿,分别在岛屿边缘和内部区域用放置鸡蛋(大型卵)和鹌鹑(Coturnix japonica)蛋(小型卵)的方法进行人工模拟地面巢试验,研究不同体积大小鸟卵的巢捕食率及其差异,分析巢捕食率与岛屿面积、隔离度、形状指数和植物物种丰富...     

Effects of nest-site characteristics and parental activity on cowbird parasitism and nest predation in Brown-and-yellow Marshbirds

ABSTRACT Nest‐site selection and nest defense are strategies for reducing the costs of brood parasitism and nest predation, two selective forces that can influence avian nesting success and fitness. During 2001–2002, we analyzed the effect of nest‐site characteristics, nesting pattern, and parental activity on nest predation and brood parasitism by cowbirds (Molothrus spp.) in a population of Brown‐and‐yellow Marshbirds (Pseudoleistes virescens) in the Buenos Aires province, Argentina. We examined the possible effects of nest detectability, nest accessibility, and nest defense on rates of parasitism and nest predation. We also compared rates of parasitism and nest predation and nest survival time of marshbird nests during the egg stage (active nests) with those of the same nests artificially baited with passerine eggs after young fledged or nests failed (experimental nests). Most nests (45 of 48, or 94%) found during the building or laying stages were parasitized, and 79% suffered at least one egg‐predation event. Cowbirds were responsible for most egg predation, with 82 of 107 (77%) egg‐predation events corresponding to eggs punctured by cowbirds. Nests built in thistles had higher rates of parasitism and egg predation than nests in other plant, probably because cowbirds were most active in the area where thistles were almost the only available nesting substrate. Parasitism rates also tended to increase as the distance to conspecific nests increased, possibly due to cooperative mobbing and parental defense by marshbirds. The proportion of nests discovered by cowbirds was higher for active (95%) than for experimental (29%) nests, suggesting that cowbirds used host parental activity to locate nests. Despite active nest defense, parental activity did not affect either predation rates or nest‐survival time. Thus, although nest defense by Brown‐and‐yellow Marshbirds appears to be based on cooperative group defense, such behavior did not reduce the impact of brood parasites and 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.     

Birds nesting survival in disturbed and protected Neotropical savannas

Fragmentation and other habitat disturbances are long known to negatively affect birds, in large part by decreasing nest success due to high nest predation rates. The factors, however, that cause this decrease in nest success are still poorly understood and may vary among regions or species. Here, we show that nest survival is also lower in a disturbed landscape versus a protected cerrado (savanna-like) Neotropical landscape. Also, we tested the importance of garbage in the nest, brood parasitism, microhabitat and bird family in nest survival, controlling for temporal effects. We monitored 144 birds’ nests in a disturbed landscape and 150 nests in a natural reserve of cerrado vegetation in central Brazil, between September and December 2006. We used Program MARK to estimate nest survival probabilities and evaluate the effect of covariates in nest success in the disturbed area. Nest daily survival rate (DSR) was higher in the reserve (survival probability = 29.4%) than in the disturbed landscape (survival probability = 16.6%). Nest daily survival rate (DSR) was smaller in nests with garbage (survival probability = 9.3%) than in nests without garbage (survival probability = 19.5%) in the disturbed landscape. Effects of habitat disturbance on nest survival differed among bird families, with finches and tanagers being more affected mostly due to high nest predation rates. Conservation and management of birds in disturbed landscapes should include actions to decrease nest predation. In poor rural or suburban areas in developing countries, such as Brazil, actions like better garbage treatment may help conserve birds in disturbed landscapes.     

Nocturnal nest predation: a potential obstacle to recovery of a Florida Scrub-Jay population

ABSTRACT.   Population declines among birds are often linked to habitat change and associated increases in nest predation rates. In species of conservation concern identifying nest predators is an important first step in developing management strategies to mitigate low nesting success caused by depredation. Because predator composition varies geographically and with landscape factors habitat restoration may need to be tailored to reduce locally important predators. We used miniature video cameras to identify nest predators in a population of Florida Scrub-Jays ( Aphelocoma coerulescens ) significant to conservation. At 22 nests we observed 25 predation events; 22 (88%) of these events were nocturnal. Yellow rat snakes ( Elaphe obsoleta ) had the highest daily predation rate and accounted for 76% of egg and nestling losses. Florida Scrub-Jays are vulnerable to nocturnal nest predation because their vigilance behavior is ineffective against nocturnal predators, breeders cannot defend against nocturnal predators, and brooding females are at risk of being killed by nocturnal predators. If current habitat restoration efforts do not reduce numbers of yellow rat snakes and improve scrub-jay nesting success, management actions to reduce populations of nocturnal snakes may need to be considered.     

The influence of fragment size and edge on nest predation in urban bushland

To test the effects of habitat fragmentation and edge on the rate of nest predation in an urban ecosystem, 20 artificial nests each containing 2 plasticine eggs were distributed in each of 24 bushland sites in Sydney, Australia. the eastern yellow robin Eopsaltria australis was adopted as a target species, and variables of nests, eggs and nesting behaviour were manipulated in experiments. Sites ranged in size from 3.8 ha to 14717 ha and were divided into three size classes: 1) 0–10 ha. 2) 11–100 ha and 3) ≥101 ha. Nests were positioned either around the edge of the fragment (within 50 m from the fragment boundary) or within the centre of the fragment (< 50 m from the fragment boundary). The predation rate was calculated as the percentage of nests that had one or both eggs damaged or removed after 15 d of exposure. Nest predation rates were high (average 70.6%) but were not affected by patch size or distance from fragment edges. Predators were identified by marks of the beak or teeth left in the plasticine eggs. Nest predators identified were birds, black rats, brown antechinus and ringtail possum, with the majority of predation being by birds (61.7%), Our findings differ from those of most previous studies of nest predation, and perhaps reflect the ubiquity of generalist predators and the degree of habitat modification throughout remnants of bushland in the urban environment.     

Nest predation and habitat change interact to influence Siberian jay numbers

We studied Siberian jays, breeding in northern Sweden, to examine the potential for interactions between nest predation and reduced vegetation heterogeneity around nest sites to cause a decrease in jay numbers. Parent behaviour and nests are highly cryptic in the species. Our 12-year data showed, however, that nests had a probability of only 0.46 to be successful and produce at least one nestling. Nest predation was intense and a main cause of nest failure. All predators that could be identified were visually oriented hunters, mostly other corvids able to colonize taiga forest only close to human settlements. Consistent with the idea that predators used visual cues, nest predation increased with parental activity, which suggests that predators used parental provisioning trips to locate nests. Furthermore, a reduction in daily nest survival rates with decreasing amount of nesting cover was more pronounced in areas with high corvid activity as predicted when cover mediates the hunting efficiency of visual oriented predators. Declining temperatures interacted with the effects of habitat characteristics to further reduce daily nest survival rates suggesting that parents were not able to increase nest visitation rates to satisfy the higher energy demands of their nestlings without endangering the nest. Our results identify a mechanism through which predation and human-induced reduction in nesting cover on a larger scale may interact to cause a reduction in Siberian jay numbers larger than expected from habitat loss alone.     

Predation of Lapwing Vanellus vanellus nests on lowland wet grassland in England and Wales: effects of nest density, habitat and predator abundance

There is concern that predation of Lapwing Vanellus vanellus nests may create additional pressure on declining populations of this species in Europe. At seven sites in England and Wales, daily nest predation rates on 1,390 nests were related to variables using Generalised Linear Mixed Models. The strongest predictor was Lapwing nest density (number of nests within 100 m): predation rates declined as nest density increased. Since nocturnal species, probably mammals, have been identified as the major predators of Lapwing nests at these sites, these results suggest that Lapwings are able to deter mammalian predators or may settle to nest at high densities in areas with low predation pressure. At the site level, there was no relationship between Lapwing nesting density and fox density, and a positive relationship with Carrion Crow Corvus corone nesting density. There was a weaker effect of distance to field boundary: nests closer to boundaries were more likely to be predated. Weak interactive effects between crow density and both nest visibility and distance to vantage point were identified in models using a reduced subset of nests. These were counter-intuitive, did not persist in the larger data set, and do not have obvious explanations. If Lapwings nesting at high density are able to deter predators, there are implications for land management. Smaller areas could be managed within potential breeding habitat to encourage Lapwings to nest in dense colonies. Selection of larger fields for such management, where nests could be located far from the field boundary should improve the value of such measures.     

Anti-predator adaptations in nesting Marsh Tits Parus palustris: the role of nest-site security

A proposal that nest predation is the most important selective pressure shaping nest-site use of Marsh Tits Parus palustris was checked in a long-term study (almost 500 nests) carried out in the Białowieża National Park (eastern Poland) in primeval conditions, where the birds breed in natural holes and their nests are at risk from a variety of predators. It was predicted that predation rates would depend on hole attributes, so that Marsh Tits should use the most secure holes. Predation was responsible for 70% of total nest losses. Predation risk depended on hole attributes. Nests in dead wood were predated significantly more often than those in live wood. Nests in old woodpecker holes were predated more frequently than nests in holes of other origin, and nests situated closer to the entrance were more at risk than ones further from it. The entrance size did not influence overall predation risk, but small entrance size was important in preventing access by larger predators. These differences can account for the very rare use of holes in dead wood or of woodpecker holes, the fact that they nest in holes with small entrances and relatively far from the entrance. It is concluded that the patterns of nest-site use found in this species are best explained as anti-predator adaptations, which have evolved and are maintained by the pressure of nest predators. This study also indicates the possible limits of, and constraints on, these adaptations.     

Forest fragmentation relaxes natural nest predation in an Afromontane forest

Nest predation is widely regarded as a major driver underlying the population dynamics of small forest birds. Following forest fragmentation and the subsequent invasion by species from non-forested landscape matrices, shifts in predator communities may increase nest predation near forest edges. However, effects of human-driven habitat change on nest predation have mainly been inferred from studies with artificial nests, despite being regarded as poor surrogates for natural ones. We studied variation in predation rates, and relationships with timing of breeding and characteristics of microhabitats and fragments, on natural white-starred robin Pogonocichla stellata nests during three consecutive breeding seasons (2004–2007) in a Kenyan fragmented cloud forest. More than 70% of all initiated nests were predated during each breeding season. Predation rates nearly quadrupled between the earliest and the latest nests within a single breeding season, increased with distance to the forest edge, and decreased with the edge-to-area ratio of forest fragments. These spatial relationships oppose the traditional perception of edge and fragmentation effects on nest predation, but are in line with results from artificial nest experiments in other East African forests. In case of inverse edge and fragmentation effects on nest predation, such as shown in this study, species that tolerate edges for breeding may be affected positively, rather than negatively, by forest fragmentation, while the opposite can be expected for species restricted to the forest interior. The possibility of inverse edge effects, and its conservation implications, should therefore be taken into account when drafting habitat restoration plans.     

The nest predator community of grassland birds responds to agroecosystem habitat at multiple scales

Nest predation is the leading cause of reproductive failure for grassland birds of conservation concern. Understanding variation in nest predation rates is complicated by the diverse assemblage of species known to prey on nests. As part of a long‐term study of grassland bird ecology, we monitored populations of predators known to prey on grassland bird nests. We used information theoretic approach to examine the predator community's association with habitat at multiple scales, including local vegetation structure of grassland patches, spatial attributes of grassland patches (size and shape), and landscape composition surrounding grassland patches (land cover within 400 and 1600 m). Our results confirmed that nest predators respond to habitat at multiple scales and different predator species respond to habitat in different ways. The most informative habitat models we selected included variability in local vegetation (CV in the density of forbs), local patch (area and edge‐to‐interior ratio), and landscape within a 1600 m buffer around grasslands (percent of land covered by human structures and development). As a separate question, we asked if models that incorporated information from multiple scales simultaneously might improve the ability to explain variation in the predator community. Multi‐ scale models were not consistently superior to models derived from variables focused at a single spatial scale. Our results suggest that minimizing human development on and surrounding conservation land and the management of the vegetation structure on grassland fragments both may benefit grassland birds by decreasing the risk of nest predation.     

A predator's perspective of nest predation: predation by red squirrels is learned,not incidental

Nest predation has been used to explain aspects of avian ecology ranging from nest site selection to population declines. Many arguments rely on specific assumptions regarding how predators find nests, yet these predatory mechanisms remain largely untested. Here we combine artificial nest experiments with behavioural observations of individual red squirrels Tamiasciurus hudsonicus to differentiate between two common hypotheses: predation is incidental versus learned. Specifically, we tested: 1) whether nest survival could be explained solely by a squirrel's activity patterns or habitat use, as predicted if predation was incidental; or 2) if predation increased as a squirrel gained experience preying on a nest, as predicted if predation was learned. We also monitored squirrel activity after predation to test for evidence of two search mechanisms: area‐restricted searching and use of microhabitat search images. Contrary to incidental predation and in support of learning, squirrels did not find nests faster in areas with high use (e.g. forest edges). Instead, survival of artificial nests was strongly related to a squirrel's prior experience preying on artificial nests. Experience reduced nest survival times by over half and increased predation rates by 150–200%. Squirrels returned to and doubled their activity at the site of a previously preyed on nest. However, neither area‐restricted searching nor microhabitat search images can explain how squirrels located artificial nests more readily with experience. Instead, squirrels likely used cues associated with the nests or eggs themselves. Learning implies that squirrels could be increasingly effective predators as the density or profitability of nests increases. Our results add support to the view that nest predation is complex and broadly influenced (e.g. by predator experience, motivation), and is unlikely to be predicted consistently by simple relationships with predator activity, abundance or habitat.