Nest Visibility Research Articles

Behaviour and landscape contexts determine the effects of artificial light on two crepuscular bird species

ContextArtificial light at night (ALAN) is increasing worldwide, with many ecological effects. Aerial insectivores may benefit from foraging on insects congregating at light sources. However, ALAN could negatively impact them by increasing nest visibility and predation risk, especially for ground-nesting species like nightjars (Caprimulgidae).ObjectivesWe tested predictions based on these two alternative hypotheses, potential foraging benefits vs potential predation costs of ALAN, for two nightjar species in British Columbia: Common Nighthawks (Chordeiles minor) and Common Poorwills (Phalaenoptilus nuttallii).MethodsWe modeled the relationship between ALAN and relative abundance using count data from the Canadian Nightjar Survey. We distinguished territorial from extra-territorial Common Nighthawks based on their wingboom behaviour.ResultsWe found limited support for the foraging benefit hypothesis: there was an increase in relative abundance of extra-territorial Common Nighthawks in areas with higher ALAN but only in areas with little to no urban land cover. Common Nighthawks’ association with ALAN became negative in areas with 18% or more urban land cover. We found support for the nest predation hypothesis: the were strong negative associations with ALAN for both Common Poorwills and territorial Common Nighthawks.ConclusionsThe positive effects of ALAN on foraging nightjars may be limited to species that can forage outside their nesting territory and to non-urban areas, while the negative effects of ALAN on nesting nightjars may persist across species and landscape contexts. Reducing light pollution in breeding habitat may be important for nightjars and other bird species that nest on the ground.

Habitat geometry rather than visual acuity limits the visibility of a ground-nesting bird's clutch to terrestrial predators.

The nests of ground-nesting birds rely heavily on camouflage for their survival, and predation risk, often linked to ecological changes from human activity, is a major source of mortality. Numerous ground-nesting bird populations are in decline, so understanding the effects of camouflage on their nesting behavior is relevant to their conservation concerns. Habitat three-dimensional (3D) geometry, together with predator visual abilities, viewing distance, and viewing angle, determine whether a nest is either visible, occluded, or too far away to detect. While this link is intuitive, few studies have investigated how fine-scale geometry is likely to help defend nests from different predator guilds. We quantified nest visibility based on 3D occlusion, camouflage, and predator visual modeling in northern lapwings, Vanellus vanellus, on different land management regimes. Lapwings selected local backgrounds that had a higher 3D complexity at a spatial scale greater than their entire clutches compared to local control sites. Importantly, our findings show that habitat geometry-rather than predator visual acuity-restricts nest visibility for terrestrial predators and that their field habitats, perceived by humans as open, are functionally closed with respect to a terrestrial predator searching for nests on the ground. Taken together with lapwings' careful nest site selection, our findings highlight the importance of considering habitat geometry for understanding the evolutionary ecology and management of conservation sites for ground-nesting birds.

Eastern Wood-Pewee (Contopus virens) reproductive success in red pine plantations and deciduous forests in Ontario, Canada

Pine plantations comprise about 7% of total world forest cover and are increasing across the globe. We compared settlement times, breeding densities, and the effects of time, habitat, and nest-site characteristics on the nest success of Eastern Wood-Pewees (Contopus virens) in red pine (Pinus resinosa) plantations and deciduous forest stands in south-central Ontario, Canada, in 2007 and 2008. Our goal was to evaluate the quality of these 2 habitats for this declining aerial insectivore. Pine plantations and deciduous forest stands were settled nearly simultaneously and at similar breeding densities, suggesting no preference for either habitat. Nest success in pine plantations (22%) was lower than in deciduous forests (35%), corresponding to higher counts of red squirrels (Tamiasciurus hudsonicus) and Blue Jays (Cyanocitta cristata) in plantations. Daily nest survival was lowest when nestlings were about 5 d old, but improved substantially as nestlings aged, and over the nesting season. In both habitats, increased nest visibility was correlated with decreased nest survival. In pine plantations, nest survival was higher where trees were more dispersed, while in deciduous forests, nests situated farther from tree trunks had higher survival rates. In both habitats, Eastern Wood-Pewees may use outward branches, when available, to detect movement and then evade potential nest predators. Although pine plantations provide breeding habitat for Eastern Wood-Pewees, management that increases hardwood understories and overstories may help to reduce visibility of Eastern Wood-Pewee nests and to reduce the populations of generalist songbird predators.

Behavioural and heart rate responses to stressors in two populations of Little Penguins that differ in levels of human disturbance and predation risk

Species that are constantly exposed to disturbances, such as human disturbance or non‐lethal contacts with predators or conspecifics, can experience chronic stress. Within a species range, variation in the frequency and predictability of such disturbances can lead to population differences in stress responses. Here, we investigated the stress response of Little Penguins Eudyptula minor to an introduced predator and a conspecific at two South Australian colonies that differed in habitat, conspecific density, levels of human disturbance and predation risk (high, low). We used playback experiments of Cat Felis catus or Little Penguin calls and recorded the behaviour and physiological (heart rate) response of adults in relation to playback type (Cat, Penguin) as well as habitat characteristics (habitat type, nest type, nest visibility) and number of conspecifics present. Our results showed that individuals from the high‐disturbance colony (also living in a mixed habitat with fewer neighbours) exhibited higher vigilance and heart rate responses than individuals from the low‐disturbance colony (living in a closed habitat with a high number of neighbours). Our results highlight that guidelines for managing penguin species cannot be generalized across populations and need to be colony‐specific.

Impact of brood parasitism and predation on nest survival of the fan‐tailed gerygone in New Caledonia

Predation and brood parasitism are common reasons for nesting failure in passerine species and the additive impact by invasive species is a major conservation concern, particularly on tropical islands. Recognising the relative contribution of the different components of nesting failure rates is important to understand co‐evolutionary interactions within brood parasite–host systems. In the remote archipelago of New Caledonia, the fan‐tailed gerygoneGerygone flavolateralisis the exclusive host of the brood‐parasitic shining bronze‐cuckooChalcites lucidus. Additionally, invasive rodents also possibly have an impact on breeding success. To estimate the impact of potential nest predators, we 1) video monitored nests to identify predators, 2) estimated the probability of predation based on nest visibility and predator abundance and 3) tested the possibility that the location of experimental nests and lack of odour cues decrease the predation by rodents. In addition, we estimated nest survival rates using data collected in different habitats over the course of eight breeding seasons. Nesting success of fan‐tailed gerygones was relatively low and predation was the main cause of nesting failure. We recorded mainly predation by native birds, including the shining bronze‐cuckoo, whereas predation by rats was rare. In open habitats predation by cuckoos was much lower than predation by other avian predators. Neither predator activity around nests nor nest visibility influenced the probability of predation. Experimental nests in more accessible locations and containing an odorous bait were more exposed to rodent predation. Apparently, the fan‐tailed gerygone has either never been specifically vulnerable to predation by rats or has developed anti‐predator adaptations.

Land-sharing vs. land-sparing urban development modulate predator-prey interactions in Europe.

Urban areas are expanding globally as a consequence of human population increases, with overall negative effects on biodiversity. To prevent the further loss of biodiversity, it is urgent to understand the mechanisms behind this loss to develop evidence-based sustainable solutions to preserve biodiversity in urban landscapes. The two extreme urban development types along a continuum, land-sparing (large, continuous green areas and high-density housing) and land-sharing (small, fragmented green areas and low-density housing) have been the recent focus of debates regarding the pattern of urban development. However, in this context, there is no information on the mechanisms behind the observed biodiversity changes. One of the main mechanisms proposed to explain urban biodiversity loss is the alteration of predator-prey interactions. Using ground-nesting birds as a model system and data from nine European cities, we experimentally tested the effects of these two extreme urban development types on artificial ground nest survival and whether nest survival correlates with the local abundance of ground-nesting birds and their nest predators. Nest survival (n=554) was lower in land-sharing than in land-sparing urban areas. Nest survival decreased with increasing numbers of local predators (cats and corvids) and with nest visibility. Correspondingly, relative abundance of ground-nesting birds was greater in land-sparing than in land-sharing urban areas, though overall bird species richness was unaffected by the pattern of urban development. We provide the first evidence that predator-prey interactions differ between the two extreme urban development types. Changing interactions may explain the higher proportion of ground-nesting birds in land-sparing areas, and suggest a limitation of the land-sharing model. Nest predator control and the provision of more green-covered urban habitats may also improve conservation of sensitive birds in cities. Our findings provide information on how to further expand our cities without severe loss of urban-sensitive species and give support for land-sparing over land-sharing urban development.

Are predation rates comparable between natural and artificial open-cup tree nests in boreal forest landscapes?

Nest predation studies often use artificial nests to secure sample sizes and nest distribution patterns that allow empirically testing differences in predation rates between ecological units of interest. These studies rely on the assumption that natural and artificial nests experience similar or consistent relative predation rates across ecological gradients. As this assumption may depend on several factors (for example differences in predator community, nest construction, parental care patterns), it is important to test whether artificial nests provide adequate and comparable estimates of predation rates to natural nests. In this study, we compare predation rates of above-ground natural open-cup nests, artificial nests and natural nests with artificial eggs along a forest gradient from edge to interior (interior, transition zone and edge) and within two nest visibility classes (visible and concealed). Our aim was to determine whether nest structure affects comparability between nest types along these ecological gradients in boreal forests. Our results indicated important contributions of nest type, nest visibility and location along the forest edge-interior gradient, but no variable had strong significant effects on predation rates, except exposure time that showed lower predation rates at longer exposure times. Predation rates in visible and concealed nests remained similar for all nest types, but not along the forest edge-interior gradient. Here, artificial nests showed much lower predation rates than natural nests, whereas natural nests with artificial eggs tended to have higher predation rates than natural nests. We conclude that artificial nests in boreal forests represent an adequate measure of relative nest predation risk in open-cup natural nests along some ecological gradients, but results on predation rates along forest edge-interior gradients obtained from artificial nests should be interpreted with care.

The new faces of nest predation in agricultural landscapes\u2014a wildlife camera survey with artificial nests

European populations of many ground-nesting farmland birds have declined in recent decades. Increases in predator populations and nest predation may play an important role in this decline, along with habitat loss. However, the role of various predators has often remained unclear. We conducted a study with artificial nests and wildlife cameras (n = 104) in agricultural landscapes during 2015–2016 in South Finland. Our trials formed a 400-m wide gradient from forest to field. The aim of our study was to monitor nest survival and nest predators in a spatial and temporal scale. We tested the effect of distance to the forest and nest visibility to nest predation. During an 8-day period, 39.4% of the artificial nests were predated. Fifty percent of the predators were birds, 40% mammals, and 10% remained unknown. The three dominant predators of our artificial nests were the raccoon dog (Nyctereutes procyonoides) with 11 nests and the hooded crow (Corvus corone cornix) and the magpie (Pica pica) with 10 depredated nests each. Our analysis indicates that avian predators preyed upon nests in open fields further away from the forest edge, whereas mammalian predation concentrated closer to the forest edge. Predation occurred more likely at the beginning of the survey and nest survival increased as days passed. Our study highlights the efficiency of using wildlife camera traps in nest predation studies. We also suggest that the ongoing expansion of alien predators across Europe may have a greater impact on ground-nesting bird populations than previously anticipated.

Patterns of predator behaviour and Wood Warbler Phylloscopus sibilatrix nest survival in a primaeval forest

Understanding the foraging behaviour of predators is key to interpreting the role of anti‐predator adaptations of birds in reducing nest losses. Conducting research in primaeval habitats, with a low level of direct human interference, is particularly valuable in the understanding of predator–prey interactions. Using nest cameras, we investigated the identity and behaviour of potential and actual predators appearing at Wood Warbler Phylloscopus sibilatrix nests, and the importance of different predator groups for nest survival, in the primaeval part of Białowieża Forest (Poland). Mammals formed the main predator group (30 of 32 nest depredations), particularly medium‐sized carnivores (24 of 32), which attacked nests more frequently than merely passing by. This contrasted with other species, especially small rodents, which were commonly recorded near nests but rarely attacked them. Most nest attacks (22 of 32) took place at night and nest survival did not depend on nest visibility, indicating a reduced utility of nest concealment in defence against predators using mainly sound or olfaction when hunting. Daily nest survival declined strongly with nest progression (from egg‐laying to fledging of chicks), probably due to increased predator detection of nests containing older and louder chicks, rather than to increasing parental activity at nests during the day. The set of actual nest predators differed from some previous studies in human‐transformed habitats, showing that Wood Warblers may face different threats in modified vs. near‐pristine environments.

Great Reed Warbler singing behavior and conspicuous song structures are not nest-location cues for the Common Cuckoo

In some systems, brood parasites may be attracted by vocal or visual signals connected with host breeding. We studied a Great Reed Warbler (Acrocephalus arundinaceus) population where annually 30–50% of nests are parasitized by the Common Cuckoo (Cuculus canorus). We observed host males and quantified their song-related behaviors, including time spent singing, distance of movements and time spent singing in particular positions on a reed stem. We predicted that nests of more exposed males (i.e., those spending more time singing, moving a larger total distance, and spending more time on the top of stems) would be more likely to be parasitized than the nests of less exposed males. Additionally, we measured male song characteristics that we assumed to be most audible, and thus potentially the most conspicuous to the Common Cuckoo. We counted the number of “kara” syllables per song and measured their peak frequencies. Since these song structures are of low frequency and thus might be audible at longer distances, we predicted that males producing more kara syllables or uttering kara syllables of lower peak frequencies would also be more parasitized. However, we found that neither male singing behavior nor conspicuous song characteristics were significant predictors of parasitism. Only the visibility of host nests to the parasite, which we treated as a covariate, proved to be significant. Visible nests were more often parasitized than hidden nests. Our findings indicate that the Cuckoo females use nest visibility, or host behavior other than male singing, as the cue to locate host nests.

Can hedgerow management mitigate the impacts of predation on songbird nest survival?

Nest predators can have significant impacts on songbird reproductive success. These impacts may be amplified by habitat simplification and here we test whether sympathetic management of farmland hedgerows can reduce nest depredation, especially by corvids. We test whether songbirds select nest sites according to structural features of hedgerows (including nest visibility and accessibility), and whether these features influence nest predation risk. Songbirds selected nesting sites affording higher vegetation cover above the nest, increased visibility on the nest-side of the hedgerow and reduced visibility on the far side of the hedge. Nest survival was unrelated to corvid abundance and only weakly related (at the egg stage) to corvid nest proximity. Nest survival at the chick stage was higher where vegetation structure restricted access to corvid-sized predators (averaging 0.78 vs. 0.53), and at nests close to potential vantage points. Overall nest survival was sensitive to hedgerow structure (accessibility) particularly at low exposure to corvid predation, while the overall impact of corvid exposure was dependent on the relationship involving proximity to vantage points. Nest survival over the chick stage was much higher (0.67) in stock-proof, trimmed and mechanically cut hedgerows, (which tended to provide lower side visibility and accessibility) than in recently laid, remnant or leggy hedgerows (0.18). Long-term reductions in the management of British hedgerows may therefore be exposing nesting songbirds to increased predation risk. We recommend regular rotational cutting of hedgerows to maintain a dense woody structure and thereby reduce songbird nest predation.

Decoration Increases the Conspicuousness of Raptor Nests.

Avian nests are frequently concealed or camouflaged, but a number of species builds noticeable nests or use conspicuous materials for nest decoration. In most cases, nest decoration has a role in mate choice or provides thermoregulatory or antiparasitic benefits. In territorial species however, decorations may serve additional or complementary functions, such as extended phenotypic signaling of nest-site occupancy and social status to potential intruders. The latter may benefit both signaler and receiver by minimizing the risk of aggressive interactions, especially in organisms with dangerous weaponry. Support for this hypothesis was recently found in a population of black kites (Milvus migrans), a territorial raptor that decorates its nest with white artificial materials. However, the crucial assumption that nest decorations increased nest-site visibility to conspecifics was not assessed, a key aspect given that black kite nests may be well concealed within the canopy. Here, we used an unmanned aircraft system to take pictures of black kite nests, with and without an experimentally placed decoration, from different altitudes and distances simulating the perspective of a flying and approaching, prospecting intruder. The pictures were shown to human volunteers through a standardized routine to determine whether detection rates varied according the nest decoration status and distance. Decorated nests consistently showed a higher detection frequency and a lower detection-latency, compared to undecorated versions of the same nests. Our results confirm that nest decoration in this species may act as a signaling medium that enhances nest visibility for aerial receivers, even at large distances. This finding complements previous work on this communication system, which showed that nest decoration was a threat informing trespassing conspecifics on the social dominance, territory quality and fighting capabilities of the signaler.

震旦鸦雀在镶嵌型芦苇收割生境中的巢址选择

PDF HTML阅读 XML下载 导出引用 引用提醒 震旦鸦雀在镶嵌型芦苇收割生境中的巢址选择 DOI: 10.5846/stxb201312132949 作者: 作者单位: 辽宁大学,辽宁大学生命科学院,辽宁大学生命科学院,北京师范大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家青年科学基金项目(31301888); 国家重点基础研究发展计划(2006CB403305); 辽宁大学青年基金项目(2012LDQN11) Nest-site selection of reed parrotbills in the mosaic reed harvesting habitats Author: Affiliation: Liaoning University,,,Beijing Normal University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:大规模的芦苇收割会对在该生境中繁殖的鸟类产生严重影响。为降低芦苇收割对鸟类繁殖的负面影响,许多地区的湿地管理者逐渐采用了镶嵌型的芦苇收割方式。但是,这种新的芦苇管理方式对鸟类繁殖期生境选择的作用机理尚不清楚。震旦鸦雀是一种主要分布在我国东部、完全依赖芦苇生境而生存的珍稀鸟类,已被IUCN定为全球性近危物种。大规模的芦苇收割导致其适宜生境丧失,被认为是该物种面临的一个主要威胁。选择山东黄河三角洲国家级自然保护区为研究地区,采用AIC 信息准则法,从巢址微生境、巢域斑块和全模型3个水平上对可能影响震旦鸦雀巢址选择的生境因子进行了逻辑斯蒂回归分析,并重点探讨芦苇镶嵌收割对其巢址选择的影响以及不同水平的相互效应。结果发现,震旦鸦雀的巢址选择受巢址微生境和巢域斑块尺度双重水平的影响,但巢址微生境因子的影响要大于巢域斑块因子。在巢址微生境水平上,影响震旦鸦雀巢址选择的因素有:1.5-2.5 m旧芦苇的密度、2.5 m以上新芦苇的密度、香蒲密度和巢的可见度;在巢域斑块水平上,影响因素包括芦苇生境类型、旧芦苇斑块面积的比例和植被盖度;在综合模型中,影响因素有1.5-2.5 m旧芦苇的密度、2.5 m以上新芦苇的密度、香蒲密度、巢的可见度和植被盖度。综上,震旦鸦雀倾向于在植被盖度较高、具有一定比例(18.3%)旧芦苇面积、1.5-2.5 m旧芦苇密度较高、可见度较低的生境斑块中筑巢。研究中,78.7%(n=141)的震旦鸦雀将巢筑在新旧芦苇混合的微生境中,其中36.9%的巢址附近旧芦苇的比例在一半以上;53.2%(n=111)的巢筑于新、旧两种芦苇茎秆之上,22.3%的巢的支撑芦苇中旧芦苇所占比例在一半以上。研究结果表明,旧芦苇在震旦鸦雀巢址选择和筑巢过程中发挥了重要作用。由于大范围的芦苇收割在微生境水平上可降低1.5-2.5 m旧芦苇的密度,在巢域斑块尺度上可降低旧芦苇斑块面积的比例,因此建议,在震旦鸦雀的繁殖地,未来的芦苇收割应采用镶嵌收割的形式,并至少应保留面积在20%以上的结构较好的旧芦苇斑块,以供震旦鸦雀选择巢址和繁衍后代。 Abstract:The impact of an ongoing loss and fragmentation of reedbeds on reed-inhabiting passerine birds has received much attention in recent years. In addition, global commercial reed harvesting is another important anthropogenic factor threatening the existence of passerine birds. According to previous studies, large-scale winter reed cutting has greatly reduced the number of reed-inhabiting passerine birds across the world. Thus, a new reed harvesting method called 'mosaic reed cutting' has been introduced in many natural reserves to reduce the impact that reed harvesting has on the reed-inhabiting birds. However, the precise impact of the mosaic reed cutting on the habitat use by passerine birds, especially the nest-site selection, has not been well studied. Reed parrotbill (Paradoxornis heudei) is an endemic reedbed-inhabiting bird that is native to East China, and it is currently listed as "near threatened" mainly because of the loss of the wintering and breeding habitats due to the ongoing over-harvesting. In this study, we chose the Yellow River Delta Nature Reserve as a study site to assess the effect of mosaic reed cutting on the nest-site selection and habitat use by reed parrotbills. As habitats can be destroyed by reed harvesting on different spatial scales, we measured 17 variables to determine the nest-site selection of reed parrotbills in the microhabitat (eight variables), territorial patch (nine variables), and full model scales. In total, 141 nests were found and the nest-site characteristics of all the nests were measured during 2008 and 2011-2012. One unused control plot was randomly chosen for each nest and the corresponding habitat variables were also measured. We investigated the nest-site selection of reed parrotbills using binomial logistic regression that was based on two different levels, microhabitat nest-site and nesting patch. The relevant factors for each level were selected based on the Akaike's Information Criterion. The results showed that the nest-site selection of reed parrotbills depended largely on the scales of both microhabitat and nesting patch. However, microhabitat appeared to exert a stronger impact than the nesting patch. In the microhabitat, the nest-site selection positively correlated to the density of dry reed with stems 1.5-2.5 m high, but it was negatively affected by the density of green reed with stems over 2.5 m high, the density of cattail (Typha orientalis), and the visibility of the nest. In nesting patch, the nest-site selection was positively associated with the percentage of dry reed-patch area and vegetation cover, as well as the reed habitat type. However, by combining the two levels, the ultimate factors included all of the above, except for the percentage of dry reed-patch area and reed habitat type. Therefore, reed parrotbills preferred to nest on higher-density dry reed with stems 1.5-2.5 m high, in the microhabitat with lower nest visibility, higher percentage of dry reed-patch area, and habitats with higher vegetation coverage of nesting patch. Thus, 78.7% (n = 141) of birds built their nests in mixed habitats that included both dry and green reed stems and the percentage of dry reeds exceeded 50% in 36.9% of the nests; 53.2% (n = 111) of birds built their nests on substrates formed by both dry and green reeds, and the percentage of dry reeds in these substrates exceeded 50% in 22.3% of the nests. Thus, we concluded that the dry reed left during the mosaic reed harvesting is critical to the nest-site selection and nesting of reed parrotbills, in which both the density of dry reed stems in the microhabitat and the percentage of dry reed-patch area in nesting patch can be significantly reduced by extensive reed harvesting. We further recommended that future reed management should ensure that the reedbed retains at least 20% of dry reed to provide a sustainable nesting habitat for reed parrotbills. 参考文献 相似文献 引证文献

Selection for protection from insolation results in the visual isolation of Yellow-eyed Penguin Megadyptes antipodes nests

SummaryThe concealed and widely dispersed nests of the rare and endangered Yellow-eyed Penguin Megadyptes antipodes, or “hoiho”, have been considered to reflect an essential requirement for the visual isolation of nest sites from conspecifics. However, this may be a consequence of selection for habitat features that provide protection from insolation, thereby minimising the risk of heat stress. To help improve the understanding of hoiho nesting requirements and the effectiveness of habitat restoration, we aimed to determine whether visual isolation from conspecifics or protection from insolation is the primary driver of hoiho nest site selection. We compared the mean maximum distance of visibility and the mean percentage insolation cover of active nests with randomly sampled unused sites in flax Phormium tenax and Hebe elliptica coastal scrub at Boulder Beach, and in coastal forest at Hinahina Cove, New Zealand, 2006–2007. Results of univariate tests and the evaluation of logistic regression models suggested that the amount of insolation cover was more important than visibility for hoiho nest site selection, particularly in flax and scrub. In addition, Spearman's correlations indicated that decreasing insolation cover significantly increased the visibility of nests in the forest habitat, and had a similar effect on inter-nest distance in flax. We infer that hoiho nest site selection and distribution are influenced primarily by the location and density of micro-habitat features (particularly within 1 m of the ground) that provide optimal protection from insolation, possibly along with other important features such as a firm backing structure. Strong selection for these features results in the typical but non-essential visual isolation of nest sites from conspecifics. Restoration of nesting habitats with a relatively high density and diversity of vegetation and solid structures within 1 m of the ground may eventually provide an optimal availability and quality of suitable nest sites.

Common Cuckoos Cuculus canorus change their nest‐searching strategy according to the number of available host nests

In recent decades, numerous studies have examined factors affecting risk of host nest parasitism in well‐known avian host–parasite systems; however, little attention has been paid to the role of host nest availability. In accordance with other studies, we found that nest visibility, reed density and timing of breeding predicted brood parasitism of Great Reed Warblers Acrocephalus arundinaceus by the Common Cuckoo Cuculus canorus. More interestingly, hosts had a greater chance of escaping brood parasitism if nesting was synchronized. Cuckoo nest searching was governed primarily by nest visibility at high host‐nest density. However, even well‐concealed nests were likely to be parasitized during periods when just a few hosts were laying eggs, suggesting that Cuckoos adjust their nest‐searching strategy in relation to the availability of host nests. Our results demonstrate that host vulnerability to brood parasitism varies temporally and that Cuckoo females are able to optimize their nest‐searching strategy. Moreover, our study indicated that Cuckoos always manage to find at least some nests to parasitize. Thus, in this case, the co‐evolutionary arms race should take place mainly in the form of parasitic egg rejection rather than via frontline pre‐parasitism defence.

Nest-Site Characteristics Affecting the Risk of Nest Predation in the Madagascar Paradise FlycatcherTerpsiphone mutata: Identification of Predators and Time of Nest Predation

Abstract I investigated nest-site characteristics affecting the risk of nest predation in the Madagascar Paradise Flycatcher Terpsiphone mutata. Several nest predators have been identified in the study area, and the time of nest predation has also been determined. Two variables, the distance from the nest to the nearest tree and nest visibility, were revealed to have effects on nesting success/failure in this species: nests further from other trees and better concealed by vegetation had higher probabilities of fledging success. Distance from the nearest tree may be a factor affecting predation by a nocturnal, arboreal snake species. On the other hand, nest visibility may affect the probability of being found by diurnal, visually oriented predators. Nest-site characteristics are expected to differ between the nests preyed upon by diurnal and nocturnal predators. Contrary to expectation, no significant difference was observed between the characteristics of nest sites preyed upon in two time categories. The ...

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.

Can Habitat Alteration and Spring Angling Explain Largemouth Bass Nest Success?

AbstractLargemouth bass Micropterus salmoides nest in shallow littoral areas, making them vulnerable to negative effects of habitat alteration due to development of lake shorelines and fishing during the spring nesting period. For instance, alteration of shorelines may reduce the quality and abundance of nesting habitat, and the high visibility of nests and the aggressive guarding behavior of nesting males increase their vulnerability to fishing. In 2004, we monitored nest distribution and success and quantified local nest habitat features, lakewide angler effort, and lakeshore development patterns in five Michigan lakes to determine the extent to which habitat alteration and fishing limit the number of nests that produce swim‐up fry. Lakes spanned a range of lakeshore dwelling densities (8–22 dwellings/km), allowing us to determine the extent to which nest success varies within and among lakes due to local (e.g., substrate and cover) and lakewide (e.g., dwellings/km and fishing effort) factors. Surprisingly, local habitat characteristics were not important determinants of the probability that a nest would produce swim‐up fry (P > 0.05). At the whole‐lake scale, however, nest success was negatively related to dwelling density; the probability of producing swim‐up fry declined from 0.77 in the lake with the lowest dwelling density to 0.45 in the lake with the highest dwelling density (P = 0.018). Lakewide estimates of angling effort could not explain the difference among lakes, indicating the likely importance of quantifying angling at finer spatial scales. Knowledge of the magnitude of anthropogenic effects and the spatial scale at which they operate is integral for the management of black bass Micropterus spp.

Factors Determining Pochard Nest Predation Along a Wetland Gradient

Waterfowl management on breeding grounds focuses on improving nest success, but few studies have compared waterfowl nest success and factors affecting nest survival along a wetland gradient and simultaneously identified nest predators. We monitored nests (n = 195) of common pochards (Aythya ferina) in Trebon Basin Biosphere Reserve, Czech Republic, during 1999–2002. Daily nest survival rates (DSRs, logistic-exposure) declined from island (0.985, 95% confidence interval, 0.978–0.991) to overwater (0.962, 0.950–0.971) and terrestrial (0.844, 0.759–0.904) nests. The most parsimonious model for DSRs included habitat class (DSRs: island > overwater > terrestrial) and nest visibility. Nest survival was improved by reduced nest visibility, increased water depth, and increased distance from the nest to habitat edge in littoral habitats. On islands, nest success increased with advancing date and increased distance to open water. A model of constant nest survival best explained the data for terrestrial nests. There were no observer effects on DSRs in any habitat. In 2003, artificial nests (n = 180; 120 contained a wax-filled egg) were deployed on study plots. The model that best explained variation in DSRs for artificial nests included only 1 variable: habitat class (DSRs: island ≥ overwater > terrestrial). Mammalian predation of artificial nests (by foxes [Vulpes vulpes] and martens [Martes spp.]) was more likely in terrestrial habitats than in littoral habitats or on islands. By contrast, corvids and marsh harriers (Circus aeruginosus) prevailed among predators of overwater and island nests. Our data indicate that artificial islands and wide strips of littoral vegetation may represent secure breeding habitats for waterfowl because those habitats allow nests to be placed in areas that are not accessible to, or that are avoided by, mammalian predators. Management actions should be aimed at preserving these habitats. This, along with creation of new artificial islands, could help to enhance breeding productivity of pochards and possibly other waterfowl species inhabiting man-made ponds.

Biodiversity and Ecotourism: Impacts of habitat disturbance on an endangered bird species in Madagascar

At the inaugural ceremony of the Ranomafana National Park, Madagascar, ecotourism was hailed as a tool to achieve sustainable development and to conserve endangered species. This study shows however, that ecotourism has a negative impact on some species that it was intended to protect. In particular, the breeding success of the Pitta-like Ground Roller, Atelornis pittoides, (Family: Brachypteraciidae, Order: Coraciiformes) has been jeopardized by heavy tourism in some areas. From the years 2000 to 2002, I investigated nesting behavior, success, and distribution of A. pittoides at three study localities (Parcelle 1, Vohiparara-Sahamalaotra, and Talatakely) within the Park. Ranomafana is one of the biodiversity hotspots in Madagascar, making it particularly appealing to tourists. However, in an effort to promote tourism, vegetation around Ground Roller nests is often cleared to increase nest visibility. Because Pitta-like Ground Rollers are easily captured from their ground nests, tour guides often target them to demonstrate some of Madagascar's unique fauna. I surveyed A. pittoides, using line transects, point counts, and mist netting, to examine Ground Roller distribution and density. I also investigated levels of habitat disturbance. Tourist disturbance was found to affect the breeding behavior, biology, and success of A. pittoides through the modification of the nesting habitats. Increased noise levels, frequent nest visits, and increased predation were among the main factors contributing to nest failure. The nests of A. pittoides in non-tourist areas were more successful than in areas subjected to heavy tourist traffic and nests built farther from tourist trails had a greater probability of success than those closer to the trails.