Nest-predation at the edge: an experimental study contrasting two types of edges in the dry Chaco, Paraguay

Forest fragmentation leads to the creation of isolated forest patches with subsequent impact on forest-interior flora and fauna. Forested corridors have been suggested to alleviate some of the impact by increasing the connectivity between remnant forest patches. However, both fragmentation and corridors increase the ratio of edge to core habitat. We studied nest predation of artificial nests at edges between I) contiguous forests and pastures and 2) forested corridors and pastures, in a forest-dominated landscape in the dry Chaco, Paraguay, The aim was lo determine if nest predation was higher near habitat edges compared to within forests and pastures, with special emphasis on edges at forested corridors. We found that predation rates were similar at edges and in interior habitats. Nest predation was higher for both ground and shrub nests in forested areas than in pastures, Predation rates were also higher for both ground and shrub nests at edges along forested corridors compared to edges neighbouring contiguous forests. Forested corridors connecting contiguous forests may thus act as an ecological sink for some species breeding here. Analysis of predator categories revealed that ground nests in pastures were relatively more depredated by mammals and less by birds, compared to both shrub nests in pastures and ground nests in forests.     

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.     

Different nest predator faunas and nest predation risk on ground and shrub nests at forest ecotones: an experiment and a review

This study examined predator faunas of artificial ground and shrub nests and whether nest predation risk was influenced by nest site, proximity to forest edge, and habitat structure in 38 grassland plots in south-central Sweden. There was a clear separation of predator faunas between shrub and ground nests as identified from marks in plasticine eggs. Corvids accounted for almost all predation on shrub nests whereas mammals mainly depredated ground nests. Nest predation risk was significantly greater for shrub than for ground nests at all distances (i.e. 0, 15 and 30 m) from the forest edge. However, nest predation risk was not significantly related to distance to forest edge, but significantly increased with decreasing distance to the nearest tree. Different corvid species robbed nests at different distances from the forest edge, with jays robbing nests closest to edges. We conclude that the relationship between the predation risk of grassland bird nests and distance to the forest edge mainly depends on the relative importance of different nest predator species and on the structure of the forest edge zone. A review of published articles on artificial shrub and ground nest predation in the temperate zone corroborated the results of our own study, namely that shrub nests experienced higher rates of depredation in open habitats close to the forest edge and that avian predators predominantly robbed shrub nests. Furthermore, the review results showed that predation rates on nests in general are highest <50 m inside the forest and lower in open as well as forest interior habitats (≥50 m from the edge). Received: 16 March 1998 / Accepted: 30 July 1998     

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.     

Predation on artificial nests in a forest dominated landscape – the effects of nest type, patch size and edge structure

We studied the effects of forest patch size and forest edge structure on nest predation in a boreal coniferous forest landscape. The following predictions were tested. Nest predation should be higher in small than in large stands, in edges than in interior areas of forest stands, and in barren forest/clear–cut edges created by forestry than in natural forest/open marsh edges. Four types of artificial above ground nests (total of 261) were used; open cup nests with reindeer Rangifer t. tarandus hair, open cup nests with domestic hen Gallus domesticus feathers, and unlined open cup and nest–box nests. Nests were baited with one Japanese quail Coturnix coturnix japonica egg. Nest–boxes were depredated significantly less than open cup nests of all types. No edge- or stand size–related nest predation was found. The predation rate, regardless of the nest type, did not differ relative to the edge type and vegetation characteristics. However, better horizontal visibility of open cup nests due to more open vegetation structure increased predation risk in man–made edges compared to inherent edges. The results suggest that edge–related nest predation is absent or weak in forest dominated landscapes. This may be due to predator types present in the landscape and/or predators habitat use in forest dominated areas. Therefore, it might be that findings documented in other areas, such as in agricultural dominated landscapes, cannot be directly applied to managed forest landscapes.     

Effects of Edge Habitat and Nest Characteristics on Depredation of Artificial Nests in Fragmented Australian Tropical Rainforest

Variation in nest predation levels associated with rainforest fragmentation (edge effects) was assessed in Australia's Wet Tropics bioregion. Artificial nests were placed in the forest understorey at seven edge sites where continuous forest adjoined pasture, seven interiors (about 1 km from the edge), and six linear riparian forest remnants (50–100 m wide) that were connected to continuous forest. Four nest types were also compared, representing different combinations of two factors; height (ground, shrub) and shape (open, domed). At each site, four nests of each type, containing one quail egg and two model plasticine eggs, were interspersed about 15 m apart within a 160 m transect during September–October 2001. Predators were identified from marks on the plasticine eggs. The overall depredation rate was 66.5% of 320 nests' contents damaged over a three-day period. Large rodents, especially the rat Uromys caudimaculatus, and birds, especially the spotted catbird Ailuroedus melanotis, were the main predators. Mammals comprised 56.5% and birds 31.0% of predators, with 12.5% of unknown identity. The depredation rate did not vary among site-types, or between open and domed nests, and there were no statistically significant interactions. Nest height strongly affected depredation rates by particular types of predator; depredation rates by mammals were highest at ground nests, whereas attacks by birds were most frequent at shrub nests. These effects counterbalanced so that overall there was little net effect of nest height. Mammals accounted for 78.4% of depredated ground nests and birds for at least 47.4% of shrub nests (and possibly up to 70.1%). The main predators were species characteristic of rainforest, rather than habitat generalists, open-country or edge specialists. For birds that nest in the tropical rainforest understorey of the study region, it is unlikely that edges and linear remnants presently function as ecological population sinks due to mortality associated with increased nest predation.     

Species traits and the response of open‐habitat species to forest edge in landscape mosaics

Human driven changes in land‐use have increased the need to understand how landscape structure affects species distribution. We studied how forest edges affected the distribution of birds in grasslands recently encroached by forest patches. We investigated how species’ biological traits influenced their response to vegetation change near forest edges. We censured birds along 300‐m line transects run into the open habitat perpendicularly to forest edges. We recorded habitat variables and landscape context along each transect and characterized edges and forest patches. We recorded 33 bird species in 153 transects for a total of 654 individuals. We analyzed species response to edges with generalized linear mixed models. Habitat preference was prevalent to explain species response to forest edges. The abundance of open‐habitat birds such as skylark Alauda arvensis decreased significantly in the vicinity of edges. This negative response extended within 150 m from the edge. The effect was disproportionately higher in open‐habitat species with high conservation concern. The abundance of species feeding or/and breeding in both forest and open habitat, such as woodlarks Lullula arborea, sharply increased near edges (positive edge response). Abundance of shrub and non‐shrub dependent species increased with distance to edge. The two species groups did no differ in abundance/distance to edge relationship. Intensity of species response to forest edges varied among transects in relation to transect vegetation characteristics. Edge length or aspect, diet and nest height had no direct effect. We discuss the possible role of variation in resources and nest predation risk to explain observed patterns.     

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

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

Contrast in edge vegetation structure modifies the predation risk of natural ground nests in an agricultural landscape

Nest predation risk generally increases nearer forest-field edges in agricultural landscapes. However, few studies test whether differences in edge contrast (i.e. hard versus soft edges based on vegetation structure and height) affect edge-related predation patterns and if such patterns are related to changes in nest conspicuousness between incubation and nestling feeding. Using data on 923 nesting attempts we analyse factors influencing nest predation risk at different edge types in an agricultural landscape of a ground-cavity breeding bird species, the Northern Wheatear (Oenanthe oenanthe). As for many other bird species, nest predation is a major determinant of reproductive success in this migratory passerine. Nest predation risk was higher closer to woodland and crop field edges, but only when these were hard edges in terms of ground vegetation structure (clear contrast between tall vs short ground vegetation). No such edge effect was observed at soft edges where adjacent habitats had tall ground vegetation (crop, ungrazed grassland). This edge effect on nest predation risk was evident during the incubation stage but not the nestling feeding stage. Since wheatear nests are depredated by ground-living animals our results demonstrate: (i) that edge effects depend on edge contrast, (ii) that edge-related nest predation patterns vary across the breeding period probably resulting from changes in parental activity at the nest between the incubation and nestling feeding stage. Edge effects should be put in the context of the nest predator community as illustrated by the elevated nest predation risk at hard but not soft habitat edges when an edge is defined in terms of ground vegetation. These results thus can potentially explain previously observed variations in edge-related nest predation risk.     

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.     

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.     

Effects of vegetation, corridor width and regional land use on early successional birds on powerline corridors

Powerline rights-of-way (ROWs) often provide habitat for early successional bird species that have suffered long-term population declines in eastern North America. To determine how the abundance of shrubland birds varies with habitat within ROW corridors and with land use patterns surrounding corridors, we ran Poisson regression models on data from 93 plots on ROWs and compared regression coefficients. We also determined nest success rates on a 1-km stretch of ROW. Seven species of shrubland birds were common in powerline corridors. However, the nest success rates for prairie warbler (Dendroica discolor) and field sparrow (Spizella pusilla) were <21%, which is too low to compensate for estimated annual mortality. Some shrubland bird species were more abundant on narrower ROWs or at sites with lower vegetation or particular types of vegetation, indicating that vegetation management could be refined to favor species of high conservation priority. Also, several species were more abundant in ROWs traversing unfragmented forest than those near residential areas or farmland, indicating that corridors in heavily forested regions may provide better habitat for these species. In the area where we monitored nests, brood parasitism by brown-headed cowbirds (Molothrus ater) occurred more frequently close to a residential area. Although ROWs support dense populations of shrubland birds, those in more heavily developed landscapes may constitute sink habitat. ROWs in extensive forests may contribute more to sustaining populations of early successional birds, and thus may be the best targets for habitat management.     

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

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

Edge effects reduce the nesting success of Acadian Flycatchers in a moderately fragmented forest

ABSTRACT.   Forest fragmentation can create negative edge effects that reduce the reproductive success of birds nesting near the forest/nonforest interface, and threaten bird populations deeper in remnant forest habitats. Negative edge effects may be more pronounced in landscapes that are moderately fragmented, particularly where agriculture is the primary land-use fragmenting forests. Information about the extent and strength of edge effects at a site can help guide conservation actions, and determine their effectiveness. We examined edge effects for birds breeding in a nearly contiguous forest fragmented by relatively narrow agricultural corridors in Illinois (USA). We measured rates of nest predation and brood parasitism for Acadian Flycatchers ( Empidonax virescens ) over a continuum of distances from the edge of an agricultural inholding. Nest predation and brood parasitism were highest near the edge and decreased with increasing distance from the edge. Given the cumulative effects of nest predation and brood parasitism on reproductive success, we determined that forest within 600 m of the inholding was sink habitat. We found, however, that deeper forest interior areas currently serve as source habitat, and that conversion of the entire 205 ha agricultural corridor to forest would add 1350 ha of source habitat for Acadian Flycatchers. Such results provide support for a local conservation strategy of forest consolidation and establish baseline measures necessary to determine the relative effectiveness of any subsequent reforestation efforts.     

Predation rate on artificial nests increases with human housing density in suburban habitats

Predation causes most nest failure in birds. Predator communities are likely to vary across a gradient of increasing urbanization, so nest predation also is likely to vary across this gradient. Although predation is thought to decline with increasing urbanization, relatively little is known about variation in predation pressure within strata along an urban gradient and how factors known to affect nest success, such as nest location, interact with urban variables, such as human housing density. Native habitats are frequently fragmented and isolated by suburban residential development, thus we quantified predation rates on artificial nests located in natural oak scrub patches within a suburban matrix in south-central Florida. We examined patterns of predation based on nest location relative to habitat edges, artificial nest weathering treatment, nest shrub height, and human housing density. Over two 18-d trials, we placed a total of 240 nests, each containing a single quail egg and a clay sham, along three roadside transects. Nest predation was not influenced by proximity to edge, nest weathering, or trial date, but was highest at high housing density and lowest at low housing density. The proportion of quail eggs removed from nests increased with human housing density. Birds were the most frequent predators of artificial nests, but the relative frequency of predation by birds or mammals did not differ relative to any of our treatments. Higher rates of nest predation with increasing human housing density within suburban habitats may reflect changes in habitat structure and composition that increase the vulnerability of nests to predation or changes in the composition of the predator community. Our results modify the conclusions of previous studies by suggesting that at scales smaller than the entire urban gradient, nest predation may increase with human housing density, one common measure of urbanization.     

Edge effect on bird nest predation in the fragmented caldén (<Emphasis Type="Italic">Prosopis caldenia</Emphasis>) forest of central Argentina: an experimental analysis

Clearing of caldén (Prosopis caldenia) forests for agriculture and cattle raising in east-central La Pampa Province, central Argentina, has created a highly fragmented landscape, a condition that has resulted in adverse effects on birds in other forests, mainly through increased predation rates near forest edges. We evaluated bird nest predation rates using artificial nests, assessing the effects of forest fragment size, distance to the edge and nest height. We measured survival rate of 570 artificial nests located in trees, in bushes and on the ground, at different distances from the edge, in six forest fragments ranging in size from 2.1 to 117.6 ha, during two consecutive breeding seasons. Nest predation rates were significantly related with the number of days of exposition of the nest, nest height and distance to the edge, whereas fragment size and year of the experiment were not associated with predation rates. Ground nests were less likely to be predated than those located in bushes and trees. Predation rates decreased with the distance to the edge, showing a pattern consistent with the existence of an edge effect.     

Land Use and Small Mammal Predation Effects on Shortgrass Prairie Birds

ABSTRACT Grassland birds endemic to the central shortgrass prairie ecoregion of the United States have experienced steep and widespread declines over the last 3 decades, and factors influencing reproductive success have been implicated. Nest predation is the major cause of nest failure in passerines, and nesting success for some shortgrass prairie birds is exceptionally low. The 3 primary land uses in the central shortgrass prairie ecoregion are native shortgrass prairie rangeland (62%), irrigated and nonirrigated cropland (29%), and Conservation Reserve Program (CRP, 8%). Because shortgrass–cropland edges and CRP may alter the community of small mammal predators of grassland bird nests, I sampled multiple sites on and near the Pawnee National Grasslands in northeast Colorado, USA, to evaluate 1) whether small mammal species richness and densities were greater in CRP fields and shortgrass prairie–cropland edges compared to shortgrass prairie habitats, and 2) whether daily survival probabilities of ground-nesting grassland bird nests were negatively correlated with densities of small mammals. Small mammal species richness and densities, estimated using trapping webs, were generally greater along edges and on CRP sites compared to shortgrass sites. Vegetation did not differ among edges and shortgrass sites but did differ among CRP and shortgrass sites. Daily survival probabilities of artificial nests at edge and CRP sites and natural nests at edge sites did not differ from shortgrass sites, and for natural nests small mammal densities did not affect nest survival. However, estimated daily survival probability of artificial nests was inversely proportional to thirteen-lined ground squirrel (Spermophilus tridecemlineatus) densities. In conclusion, these data suggest that although land-use patterns on the shortgrass prairie area in my study have substantial effects on the small mammal community, insufficient data existed to determine whether land-use patterns or small mammal density were affecting grassland bird nest survival. These findings will be useful to managers for predicting the effects of land-use changes in the shortgrass prairie on small mammal communities and avian nest success.     

Habitat and Landscape Effects on Brood Parasitism,Nest Survival,and Fledgling Production in Swainson's Warblers

ABSTRACT Numerous factors, including nest predation and brood parasitism, may limit populations of neotropical migratory birds. However, nest predation and brood parasitism are not constant, and temporal, biological, habitat, and landscape factors can affect the likelihood of these events. Understanding these patterns is important for species of conservation concern for which managers seek to provide quality habitat. One such species, the Swainson's warbler (Limnothlypis swainsonii), is a neotropical migrant that breeds primarily in bottomland hardwood forests of the southeastern United States. Little is known of factors influencing reproductive success of this rare, yet locally abundant, species. From 2004 through 2007, we examined factors influencing reproductive success of Swainson's warblers at 2 sites in eastern Arkansas, USA, St. Francis National Forest and White River National Wildlife Refuge. We used 2-stage modeling to assess the relationship between 1) temporal and biological, and 2) habitat and landscape factors and brood parasitism, nest survival, and fledgling production. Brood parasitism was greater in this population (36%) than reported elsewhere (≤ 10%), but decreased throughout the breeding season. Nest survival was comparable to or lower than in other populations of this species and increased throughout the breeding season. The probability of brood parasitism was greater near forest edges. Although nests of Swainson's warblers were often associated with giant cane (Arundinaria gigantea), nest survival had a weak negative association with cane density. For nests that were successful, the best predictor of number of Swainson's warblers fledged was brood-parasitism status: nonparasitized nests fledged 2.75 young, whereas parasitized nests fledged 0.60 Swainson's warblers. Our findings suggest that managing and restoring relatively high-elevation bottomland forests that are located far from agricultural edges should increase Swainson's warbler productivity.     

Breeding occupancy and success of two hole-nesting passerines: the impact of fragmentation caused by forestry

We studied the distribution and the reproductive success of the pied flycatcher Ficedula hypoleuca and the redstart Phoenieurus phoenicurus in relation to forest patch size, edge type (clearcut vs natural), distance from the forest edge, and vegetation characteristics in a forest-dominated landscape. Breeding performances were recorded in up to 72 forest patches during 1992–1994 for birds breeding in nest-boxes. In the spring, breeding individuals of both species arrived earlier in large forest patches (> 1 ha) than in smaller ones. Pied flycatchers arrived earlier on clearcut edges than natural edges but in the redstart there was no preference for a particular edge type. The territory distance from the forest to open land edge did not affect the arrival dates of either species. In the case of the pied flycatcher, the proportion of unpaired males was highest in patches < 1 ha in size and in the case of the redstart this applied to patches < 5 ha in size. Pairing success was not related to the forest edge type or the nest's distance from the edge. Nest predation was not patch-size nor edge-related for either of the species, but in the combined data for both species nest predation was higher at clearcut edges than at natural edges. Clutch size, brood size and the survival of nestlings to the fiedgling stage (fledgling/egg. %) were independent of the patch size, edge type and nest's "distance from the forest edge.     

Habitat edges affect patterns of artificial nest predation along a wetland-meadow boundary

Wetland habitats are among the most endangered ecosystems in the world. However, little is known about factors affecting the nesting success of birds in pristine grass-dominated wetlands. During three breeding periods we conducted an experiment with artificial ground nests to test two basic mechanisms (the matrix and ecotonal effects) that may result in edge effects on nest predation in grass-dominated wetland habitats. Whereas the matrix effect model supposes that predator penetrate from habitat of higher predator density to habitat of lower predator density, thus causing an edge effect in the latter, according to the ecotonal effect model predators preferentially use edge habitats over habitat interiors. In addition, we tested the edge effect in a wetland habitat using artificial shrub nests that simulated the real nests of small open-cup nesting passerines. In our study area, the lowest predation rates on ground nests were found in wetland interiors and were substantially higher along the edges of both wetland and meadow habitat. However, predation was not significantly different between meadow and wetland interiors, indicating that both mechanisms can be responsible for the edge effect in wetland edges. An increased predation rate along wetland edges was also observed for shrub nests, and resembled the predation pattern of real shrub nests in the same study area. Though we are not able to distinguish between the two mechanisms of the edge effect found, our results demonstrate that species nesting in wetland edges bordering arable land may be exposed to higher predation. Therefore, an increase in the size of wetland patches that would lead to a reduced proportion of edge areas might be a suitable management practice to protect wetland bird species in cultural European landscapes.