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.     

The influence of landscape features on nest predation rates of grassland‐breeding waders

In Europe, lowland wet grasslands have become increasingly fragmented, and populations of waders in these fragments are subject to unsustainably high levels of nest predation. Patches of taller vegetation in these landscapes can support small mammals, which are the main source of prey for many predators. Providing such patches of habitat could potentially reduce levels of nest predation if predators preferentially target small mammals. However, predator attraction to patches of taller vegetation for foraging, shelter, perching and/or nesting could also result in local increases in predation rates, as a consequence of increased predator densities or spill‐over foraging into the surrounding area. Here we assess the influence of taller vegetation on wader nest predation rates, and the feasibility of managing vegetation structure to alter predator impacts. Between 2005 and 2011, the nest distribution and hatching success of Northern Lapwings Vanellus vanellus, which nest in the open, and Common Redshanks Tringa totanus, which conceal their nests in vegetation, were measured on a 487‐ha area of wet grassland in eastern England that is primarily managed for breeding waders. Predation rates of Lapwing nests increased significantly with distance from patches of taller vegetation, and decreased with increasing area of taller vegetation within 1 km of the nest, whereas neither variable influenced Redshank nest predation probability. These findings suggest that the distribution and activity of nest predators in lowland wet grassland landscapes may be influenced by the presence and distribution of areas of taller vegetation. For Lapwings at least, there may therefore be scope for landscape‐scale management of vegetation structure to influence levels of predation in these habitats.     

Using Nest Temperature to Estimate Nest Attendance of Piping Plovers

Abstract: Recent technological innovations allow remote monitoring of avian nest temperature that minimizes disturbance and expense without altering clutch sizes. However, the efficacy of such techniques has not been determined for ground-nesting birds. We compared the efficacy of 2 techniques, iButton® data loggers (Maxim/Dallas Semiconductor Corp., Sunnyvale, CA) and custom-built thermocouples, to measure nest temperature of piping plovers (Charadrius melodus) relative to nest attendance at Cape Cod National Seashore, Massachusetts, USA. Neither technique affected hatching success (U = 389.5, P = 0.874) or rates of predation of nests containing devices (P = 0.894). We estimated nest attendance successfully with thermocouples in nests as long as air and surface temperatures were <29° Cand 43° C, respectively. Although iButtons could not be used to determine duration of on-bouts and off-bouts of incubating piping plovers, they were effective at determining when nests were abandoned or predated. We recommend the use of thermocouples for studying nest attendance of ground-nesting birds, in general, and of threatened and endangered species, in particular, where disturbance should be minimized and altering clutch sizes is not feasible.     

Predation on wader nests in Europe

The population declines of waders in Europe are widely considered to have resulted from habitat loss and degradation due to agricultural changes. However, recent empirical evidence suggests that levels of predation on wader nests are unsustainably high in many cases, even in some situations where breeding habitat is otherwise favourable. We review the published and 'grey' literature on nest predation on waders in Europe and quantify the relative importance of the major predators. Nest cameras offer the least biased method of identifying and quantifying nest predators. A small number of camera studies, in combination with others utilizing nest temperature loggers, indicate that nocturnal/mammalian predators make the largest contribution to wader nest predation. More than half of site-years or studies reviewed reported clutch failure rates of over 50% attributable to predation alone, a rate that is likely to be associated with declining populations, although parameters such as chick and adult survival will also affect population trends. Correlates of wader nest predation are documented, with time of season, field type and management, distance to habitat/field edge, wader nest density, and abundance of mammalian predators being most consistently identified. Future directions of research into wader productivity are discussed, and we suggest that studies quantify additional life-history parameters such as chick survival, as well as examining the predator community, wherever possible.     

Increasing temperatures increase the risk of reproductive failure in a near threatened alpine ground-nesting bird,the Cape Rockjumper Chaetops frenatus

A major cause of reproductive failure in birds is nest predation. Predation risk depends on predator type, as predators vary in their ecology and sensory modalities (e.g. visual vs. olfactory). Snakes (generally olfactory predators) are a major nest predator for small birds, with predation strongly associated with higher temperatures. We investigated nest survival in a ground-nesting alpine species, the Cape Rockjumper Chaetops frenatus, endemic to alpine fynbos in southwestern South Africa. We collected 3 years of nest data, testing whether nest survival was related to (1) habitat stage (early post-fire vs. late post-fire habitat, ≤ 3 and > 3 years since fire respectively), (2) nest concealment and (3) temperature. We found that nests had better survival at lower temperatures, with snake predation (our main source of predation) increasing in higher temperatures.     

Nest placement and nesting success in two finch species colonizing a recently established plantation in an arid region

This study examines variations in nest placement and its effects on nesting success in the Desert Finch (Rhodospiza obsoleta) and the Linnet (Carduelis cannabina) which coexist in a recently established plantation (novel habitat) in a desert region in Jordan. A comparison with other habitats (old plantation in the desert and native, Mediterranean-type, habitat of the Linnet) showed that each species displayed similarity in nest placement patterns across habitats. Nest concealment predicted nesting outcome in the Linnet, whereas nest height predicted nesting outcome in the Desert Finch. Daily survival rates were significantly higher in Desert Finch nests compared to the Linnet's, perhaps because Desert Finches placed nests higher in the novel habitat, which lacked aerial nest predators. In accordance with predation theories of life history evolution, we provide evidence that variation in nest placement among the two species in a novel habitat resulted from previous exposure to different predation risks.     

Microhabitat nest‐site selection by ducks in the boreal forest

The boreal forest is one of the North America’s most important breeding areas for ducks, but information about the nesting ecology of ducks in the region is limited. We collected microhabitat data related to vegetation structure and composition at 157 duck nests and paired random locations in Alberta’s boreal forest region from 2016 to 2018. We identified fine‐scale vegetation features selected by ducks for all nests, between nesting guilds, and among five species using conditional logistic regression. Ducks in the boreal forest selected nest sites with greater overhead and graminoid cover, but less forb cover than random sites. Characteristics of the nest sites of upland‐ and overwater‐nesting guilds differed, with species nesting in upland habitat selecting nests that provided greater shrub cover and less lateral concealment and species nesting over water selecting nests with less shrub cover. We examined the characteristics of nest sites of American Wigeon (Mareca americana), Blue‐winged Teal (Spatula discors), Green‐winged Teal (Anas crecca), Mallards (Anas platyrhynchos), and Ring‐necked Ducks (Aythya collaris), and found differences among species that may facilitate species coexistence at a regional scale. Our results suggest that females of species nesting in upland habitat selected nest sites that optimized concealment from aerial predators while also allowing detection of and escape from terrestrial predators. Consequently, alteration in the composition and heterogeneity of vegetation and predator communities caused by climate change and industrial development in the boreal forest of Canada may affect the nest‐site selection strategies of boreal ducks.     

Testing the importance of nest concealment: does timing matter?

ABSTRACT.   Nest concealment by vegetation is considered an important factor affecting predation rates for many passerines and, therefore, is frequently measured in studies examining nest predation. However, the time when concealment measurements are made may affect the results of such studies, particularly in highly seasonal ecosystems where characteristics of the vegetation later in the breeding period may differ considerably from those at the time of nest-site selection. We used artificial nests baited with quail ( Coturnix sp.) eggs in a highly seasonal tropical dry forest in Jalisco, western Mexico, to test the effects of seasonal change in concealment on nest predation. We placed 40 open-cup, artificial nests in shrubs at the end of the dry season and again at the beginning of the rainy season in 2007, and monitored the fate of the nests and the degree of concealment by vegetation during both periods. Nest concealment was significantly greater during the wet season than during the dry season. The percentage of nests predated was marginally higher during the dry (100%) than the wet (72.5%) season, and daily nest survival was lower during the dry than the wet season. Our results suggest that, in highly seasonal environments such as tropical dry forests, delayed measurement of nest concealment after nest completion rather than during nesting may constitute a significant source of error.     

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

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Interactive effects of time and vegetation on reproduction of redshanks (Tringa totanus) breeding in Wadden Sea salt marshes

As shown for various species, nesting waders are non-randomly distributed on wetlands and preferentially select riparian nest-sites adjacent to limnic or marine waterbodies. Studying the redshank Tringa totanus, we tested the hypotheses that, in a coastal wader species which conceals its clutch in vegetation, predation and hatching success are affected by vegetation zonation, and that breeding in lower salt marsh areas has negative consequences for reproduction. We further predicted effects of timing of breeding and breeding experience/age of adults potentially reflected by egg biometrics both on nest-site selection and reproduction. Effects of vegetation, space, time and individual quality on hatching success of redshanks were studied in the German part of the Wadden Sea. Dominant plant species, vertical vegetation structure and nest concealment varied significantly between nests. Variation in nest concealment was relatively low: about 90% of clutches were classified as being well concealed. This variation was explainable by vegetation structure but not by vegetation composition at the nest-site, distance to shoreline, and time of clutch initiation. Vertical vegetation structure varied by dominant plant species but not by distance to shoreline and time of clutch initiation. Hatching success of clutches was low (10.6%) due to high predation (daily predation rate: 7.4%). Hatching success and duration of clutch survival were negatively and predation positively related to the date of clutch initiation. Furthermore, negative relationships were found between egg size and predation and duration of survival, respectively. We assume that concealed nests, early breeding and breeding experience diminish predation in salt marsh breeding redshanks. Thus, redshank reproduction appears to be affected by interactive effects of timing of breeding and vegetation facilitating early breeding. In contrast to open-nesting species, breeding in riparian habitats next to waterbodies may be disadvantageous for species breeding concealed in vegetation if these are covered by less structured vegetation.     

Do seasonal patterns of rat snake (Pantherophis obsoletus) and black racer (Coluber constrictor) activity predict avian nest predation?

Avian nest success often varies seasonally and because predation is the primary cause of nest failure, seasonal variation in predator activity has been hypothesized to explain seasonal variation in nest success. Despite the fact that nest predator communities are often diverse, recent evidence from studies of snakes that are nest predators has lent some support to the link between snake activity and nest predation. However, the strength of the relationship has varied among studies. Explaining this variation is difficult, because none of these studies directly identified nest predators, the link between predator activity and nest survival was inferred. To address this knowledge gap, we examined seasonal variation in daily survival rates of 463 bird nests (of 17 bird species) and used cameras to document predator identity at 137 nests. We simultaneously quantified seasonal activity patterns of two local snake species (N = 30 individuals) using manual (2136 snake locations) and automated (89,165 movements detected) radiotelemetry. Rat snakes (Pantherophis obsoletus), the dominant snake predator at the site (~28% of observed nest predations), were most active in late May and early June, a pattern reported elsewhere for this species. When analyzing all monitored nests, we found no link between nest predation and seasonal activity of rat snakes. When analyzing only nests with known predator identities (filmed nests), however, we found that rat snakes were more likely to prey on nests during periods when they were moving the greatest distances. Similarly, analyses of all monitored nests indicated that nest survival was not linked to racer activity patterns, but racer‐specific predation (N = 17 nests) of filmed nests was higher when racers were moving the greatest distances. Our results suggest that the activity of predators may be associated with higher predation rates by those predators, but that those effects can be difficult to detect when nest predator communities are diverse and predator identities are not known. Additionally, our results suggest that hand‐tracking of snakes provides a reliable indicator of predator activity that may be more indicative of foraging behavior than movement frequency provided by automated telemetry systems.     

Nesting Success in Crimson Finches: Chance or Choice?

In avian systems, nest predation is one of the most significant influences on reproductive success. Selection for mechanisms and behaviours to minimise predation rates should be favoured. To avoid predation, breeding birds can often deter predators through active nest defence or by modifying behaviours around the nest (e.g. reducing feeding rates and vocalisations). Birds might also benefit from concealing nests or placing them in inaccessible locations. The relative importance of these strategies (behaviour vs. site selection) can be difficult to disentangle and may differ according to life history. Tropical birds are thought to experience higher rates of predation than temperate birds and invest less energy in nest defence. We monitored a population of crimson finches (Neochmia phaeton), in the Australian tropics, over two breeding seasons. We found no relationship between adult nest defence behaviour (towards a model reptile predator) and the likelihood of nest success. However, nest success was strongly related to the visibility of the nest and the structure of the vegetation. We found no evidence that adult nest building decisions were influenced by predation risk; individuals that re‐nested after a predation event did not build their nest in a more concealed location. Therefore, predator avoidance, and hence nest success, appears to be largely due to chance rather than due to the behaviour of the birds or their choice of nesting sites. To escape high predation pressures, multiple nesting attempts both within and between seasons may be necessary to increase reproductive success. Alternatively, birds may be limited in their nest‐site options; that is, high‐quality individuals dominate quality nest sites.     

Black-capped vireo nest predator assemblage and predictors for nest predation

Nest predation is a major limiting factor for songbird productivity, including the federally endangered black-capped vireo (Vireo atricapilla). However, nest predator information is limited across the range of the black-capped vireo in central and southwest Texas. We monitored nests in 3 counties within the breeding range of black-capped vireos in Texas in 2008 and 2009 and used continuous recording digital video cameras to record predation events. We video-monitored 115 nests and documented 39 predation events by at least 9 predator species. Overall, we observed avian species (51%, n = 39), specifically brown-headed cowbirds (Molothrus ater; n = 12), and snakes (26%, n = 39) as the most frequent nest predators. The estimated daily nest survival rate during the laying and incubation stage was 0.985 (95% CI = 0.967–0.993) and 0.944 (95% CI = 0.921–0.961) during the nestling stage. In addition, we analyzed models of predator-specific nest predation using multinomial logistic regression. Effect of nest height on predation rate was significant for snakes; nest stage was significant for nests depredated by avian predators. By identifying and increasing our knowledge of nest predators and vegetation characteristics associated with greater risk of predation in multiple locations within the black-capped vireo's range, we can effectively manage habitat to benefit recovery efforts of the species. © 2012 The Wildlife Society.     

Nest predators of Lance-tailed Manakins on Isla Boca Brava, Panamá

ABSTRACT.   Nest predation is often the primary cause of nest failure for passerines. Despite this, little is known about predation rates and the nest predators of birds in the tropics. I used video cameras to monitor seven Lance-tailed Manakin ( Chiroxiphia lanceolata ) nests on Isla Boca Brava, Panamá. One nest fledged young and six nests failed due to predation. I recorded five predation events involving four avian predators and one mammalian predator. Crested Oropendolas ( Psarocolius decumanus ) predated two nests and a Roadside Hawk ( Buteo magnirostris ) and a Black-chested Jay ( Cyanocorax affinis ) each predated one. The mammalian predator was a common opossum ( Didelphis marsupialis ). All avian predation was diurnal; the mammalian predation was nocturnal. My results suggest that tropical birds are subject to a diverse suite of nest predators, and that avian predators may be an important cause of nest failure at my study site.     

Predation risk of eggs and nestlings relative to nest‐site characteristics of the Bull‐headed Shrike Lanius bucephalus

Appropriate nest‐site selection is one of the most important ways to minimize loss of reproductive investment due to predation. We determined the environmental characteristics associated with nest predation during the incubation and nestling periods of arboreal nesting Bull‐headed Shrikes on the oceanic Minami‐Daito Island where the predator community has low species diversity and includes only three introduced mammals: Ship Rat Rattus rattus, Japanese Weasel Mustela itatsi and Feral Cat Felis catus. Egg predation declined with increasing grassland cover around nests, whereas nestling predation declined with increasing nest concealment and nest height. Our results suggest that effective nest‐site characteristics for avoiding nest predation differ during the incubation and nestling periods and are dependent on the predator species and their search strategies, at least in habitats with low predator species diversity.     

Phenology largely explains taller grass at successful nests in greater sage‐grouse

Much interest lies in the identification of manageable habitat variables that affect key vital rates for species of concern. For ground‐nesting birds, vegetation surrounding the nest may play an important role in mediating nest success by providing concealment from predators. Height of grasses surrounding the nest is thought to be a driver of nest survival in greater sage‐grouse (Centrocercus urophasianus; sage‐grouse), a species that has experienced widespread population declines throughout their range. However, a growing body of the literature has found that widely used field methods can produce misleading inference on the relationship between grass height and nest success. Specifically, it has been demonstrated that measuring concealment following nest fate (failure or hatch) introduces a temporal bias whereby successful nests are measured later in the season, on average, than failed nests. This sampling bias can produce inference suggesting a positive effect of grass height on nest survival, though the relationship arises due to the confounding effect of plant phenology, not an effect on predation risk. To test the generality of this finding for sage‐grouse, we reanalyzed existing datasets comprising >800 sage‐grouse nests from three independent studies across the range where there was a positive relationship found between grass height and nest survival, including two using methods now known to be biased. Correcting for phenology produced equivocal relationships between grass height and sage‐grouse nest survival. Viewed in total, evidence for a ubiquitous biological effect of grass height on sage‐grouse nest success across time and space is lacking. In light of these findings, a reevaluation of land management guidelines emphasizing specific grass height targets to promote nest success may be merited.     

Nest Predation Management: Effects on Reproductive Success in Endangered Shorebirds

Abstract Many species have suffered population declines through loss of suitable habitat. In addition, current agricultural land use and human settlements favor generalist predators, which pose an increasing threat to ground-nesting bird species such as shorebirds (waders). During the last 2 decades, nest exclosures have been used to control nest-predation rates and often improved hatching success. We evaluated the effectiveness of protective nest-cages to boost reproductive success in the endangered southern dunlin (Calidris alpina schinzii) and ultimately to halt the population decline. We found that exclosures successfully increased the survival probability of nests and, thereby, the number of hatchlings, without markedly elevating the predation rate on incubating adults. Nest exclosures did not, however, translate into an increased number of fledglings and recruits produced/breeding adult in the population, showing that factors other than nest survival are also important for population development. Our results highlight that conservation efforts aimed only at removing high nest-predation pressure may be insufficient to preserve declining species such as the southern dunlin.     

Experimental evidence for edge-related predation in a fragmented agricultural landscape

Abstract This study tested the hypothesis that increased predation of experimental nests occurs close to a forest edge in a fragmented agricultural landscape. Artificial nests and eggs of willie wagtails Rhipidura leucophrys and superb fairy-wrens Malurus cyaneus were used in experiments to assess the extent and nature of predation occurring throughout the known breeding seasons of these species. Predators were identified by the imprints they left in plasticine eggs, and by remote photography. Surveys of avian predators were undertaken to investigate the relationship between predation intensity and predator distribution and abundance. Avian predators accounted for almost all predation for which a predator could be identified (96%). Five of seven predator species photographed attacking wagtail nests were corvids or artamids. Fairy-wren nests suffered relatively low rates of predation (29%) compared to wagtail nests (87%). Increased predation at the habitat edge was recorded for wagtail nests only; predation was correlated with the distribution and abundance of predatory avian species. The different extent and pattern of predation on fairy-wren nests could be explained by problems in detecting predation by mammals, and by possible failure of avian predators to locate the cryptic nests.     

Nest predation of Common Pheasants Phasianus colchicus

The Common Pheasant Phasianus colchicus is currently the most abundant, widespread and economically important gamebird in Europe. The Game and Wildlife Conservation Trust has undertaken several recent studies of Pheasant breeding ecology to improve the management of this species. Although predation is often the most important cause of nest failure in declining ground-nesting birds in agricultural landscapes, the causes of predation and the identity of predators are often unknown. In this paper, we analyse data from approximately 450 nests of radiotagged hen Pheasants collected from six sites between 1990 and 2003 and present results on the fate and survival rates of Pheasant nests in relation to habitat, predation control and other covariates. Survival rates during the laying stage and incubation stage were 28 and 37%, respectively, and overall nest survival was 10%. Nest predation rates were significantly lower on two sites where intensive predation control was undertaken than on four sites with only low levels of predation control. Red Foxes Vulpes vulpes and corvids were the most important nest predators, accounting for at least half of all predation events. We assess these results in the context of other ground-nesting farmland birds.     

Experiments with artificial nests on predation in reed habitats

We performed nest predation experiments with artificial nests in reedbeds investigating whether nest predation pressure is different at the water-reed edge and the grassland-reed edge compared with the reed interior. Furthermore, we tested the effects of vegetation structure (reed density, height and thickness) and the effect of other nest site characteristics (distance from edge, water depth) on the success of artificial nests. The experiments were completed 3 times during the breeding season in 2001 at Lake Neusiedl, Austria. Each artificial nest resembled Great Reed Warbler (Acrocephalus arundinaceus) nests and contained one plasticine and one Quail (Coturnix coturnix) egg and the predators were identified by marks left on the eggs. The potential predators were birds, probably the Marsh Harrier (Circus aeruginosus), gulls (Larus spp.) and reed warblers (Acrocephalus spp.). Nest survival data were analysed using the Mayfield method, and we performed a discriminant analysis for the data of vegetation and nest site characteristics. The nest predation was higher at the edges than in the reed interior, and was most pronounced in April, before the new reed sprouted. The reason for this finding was probably that after May the new reed contributed to greater concealment of the nests through the higher reed density and height.