Climate and floral diversity shape Osmia bee abundance and nest predators in South Korea

Overcoming low breeding success is a major challenge for reversing population decline in threatened species. High nest predation rates are a common cause of low productivity in birds, but implementing evidence‐based management actions to reduce nest predation is challenging. Targeted breeding management requires a good understanding of where threatened species breed, the identity and distribution of nest predator species and the impact of these nest predators on breeding success. For rare and nomadic species, this information is hard to come by. The breeding success of regent honeyeater Anthochaera phrygia has declined over recent decades, and nest predation is the primary cause of breeding failure. We conducted point‐count surveys of nine avian and three mammalian nest predator species across 80% of the regent honeyeater’s contemporary breeding area in south eastern Australia. We used occupancy models to determine the presence of predator species at survey sites and spatial models to predict predator abundance and species richness across the breeding area. We incorporated predator predictions for regent honeyeater nest locations into nest fate and daily nest survival models. Predator abundance was correlated positively with tree hollow abundance and proximity to water and negatively with shrub cover. Regent honeyeater nest success showed no significant relationship with predator abundance or predator species richness. Given how abundant and widespread avian and mammalian nest predators were throughout the breeding area, improving regent honeyeater nest success is likely to require implementation of simultaneous nest protection measures to avoid potential compensatory nest predation. Further research is required to better understand the relationship between nest predator abundance and regent honeyeater nest success.

Nesting habitat characteristics and predation patterns in the European pond turtle Emys orbicularis (L., 1758): Implications for management and conservation measures

Seasonal declines in avian clutch size are well documented, but seasonal variation in other reproductive parameters has received less attention. For example, the probability of complete brood mortality typically explains much of the variation in reproductive success and often varies seasonally, but we know little about the underlying cause of that variation. This oversight is surprising given that nest predation influences many other life-history traits and varies throughout the breeding season in many songbirds. To determine the underlying causes of observed seasonal decreases in risk of nest predation, we modeled nest predation of Dusky Flycatchers (Empidonax oberholseri) in northern California as a function of foliage phenology, energetic demand, developmental stage, conspecific nest density, food availability for nest predators, and nest predator abundance. Seasonal variation in the risk of nest predation was not associated with seasonal changes in energetic demand, conspecific nest density, or predator abundance. Instead, seasonal variation in the risk of nest predation was associated with foliage density (early, but not late, in the breeding season) and seasonal changes in food available to nest predators. Supplemental food provided to nest predators resulted in a numerical response by nest predators, increasing the risk of nest predation at nests that were near supplemental feeders. Our results suggest that seasonal changes in foliage density and factors associated with changes in food availability for nest predators are important drivers of temporal patterns in risk of avian nest predation.

Die sulawesischen Regenwälder werden durch anthropogenen Einfluss in ihrer natürlichen Dynamik gestört. Waldstrukturen werden zerstört und durch Habitatfragmentierungen nachhaltig verändert. Es entstehen große Flächen von Waldrand-Lebensräumen. Im Rahmen dieser Arbeit wurde der Einfluss von Prädatoren, Vegetationsdeckung und anthropogenen Aktivitäten auf die Population von Vogelarten, die ihre Nester auf dem Boden oder in der Strauchschicht bauen, in ursprünglichen und veränderten Habitaten untersucht.Die Freilanduntersuchungen wurden auf Sulawesi in zwei unterschiedlichen Tälern (Palolo- und Napu-Tal) durchgeführt, wo die Zerstörungen und Habitatveränderungen ursprünglicher Waldgebiete sehr stark sind. Folgende Habitattypen wurden zum Vergleich ausgewählt: Naturwald und verschiedene Landnutzungstypen (Waldrand, Waldgarten, Kaffeeplantage und Sekundärwald).In Feldexperimenten mit künstlichen Nestern, die auf dem Boden und in der Strauchschicht installiert waren, sollte die Prädation auf das Gelege untersucht werden. Für die Identifizierung der Nesträuber wurden automatische Kameras in Nestnähe aufgebaut. Die Haupt-Prädatoren wurden mit Lebendfallen gefangen, die Arten bestimmt und ihre Dichte ermittelt. Des Weiteren wurden das natürliche Brutverhalten der oben genannten Vogelarten und die Störungen durch anthropogene Aktivitäten untersucht.Ergebnisse: In allen untersuchten Habitattypen gab es bei den Nestern auf dem Boden keinen signifikanten Unterschied in der Prädationsrate. Die Prädatoren waren auf allen Flächen gleichmäßig verteilt.Die Prädationsrate der Nester in der Strauchschicht unterschied sich aber signifikant mit den Habitattypen. Der höchste Prädationsdruck zeigte sich an Waldrändern und der geringste im Naturwald.Insgesamt wurden die Gelege auf dem Boden stärker beraubt als die Gelege in der Strauchschicht. Die Artenzahl und Abundanz von Prädatoren waren auf dem Boden höher als in der Strauchschicht. Im Vergleich der Habitattypen zeigte der Naturwald die geringste Artenzusammensetzung an Prädatoren. .Folgende Prädatoren wurden beobachtet: Bei den Nestern auf dem Boden: Nagetiere (z.B. Ratten) und Reptilien (z.B. Warane und Schlangen), Katzen und Hunde. Bei den Nestern in der Strauchschicht: Nagetiere (Muridae und Sciuridae), Zwergcuscus, Makkaken, Katzen, Vögel und Schlangen. Einige Prädatoren (z.B. Hausratte, Katzen und Hunde) wurden erst durch den Menschen in die Waldrandgebiete eingeführt. Die Familie der Muridia (Nagetiere) wie z.B.: Paruromys dominator und Rattus hoffmannistellte den Hauptanteil der Prädatoren.Es spielte auch die Anwesenheit von Top-Prädatoren, die wiederum Einfluss auf andere Räuber haben, eine Rolle. Top-Prädatoren (z.B. Viverra tangalunga - Malay palm civet) wurden nur im Naturwald entdeckt. Sie können in diesem Habitat die Anzahl kleiner Nagetiere (z.B. Ratten) reduzieren und das Risiko eines Nestraubes in der Strauchschicht vermindern. Das Fehlen eines Top-Prädators in den Waldrandgebieten mag dieses Risiko nicht mindern, da die Populationen kleiner Nagetiere nicht beeinflusst werden.Die Vegetationsdeckung scheint ein entscheidender Faktor für den Prädationsdruck in der Strauchschicht zu sein. Durch menschliche Aktivitäten werden die Strauchschichten im Waldrandbereich gelichtet und somit die Wahrscheinlichkeit, dass Prädatoren das Gelege entdecken, erhöht. Die Kombination zwischen Strauchdichte und starker Kronendeckung eines Naturwaldes kann die Nester in der Strauchschicht besser schützen. Die geringe Strauchdichte und schwache Kronendeckung in den Waldrandgebieten bieten diesen Schutz nicht.Die menschlichen Aktivitäten (z.B. Plantagenwirtschaft mit Kaffee und Kakao, Sammeln von Wildpflanzen, Nutz- und Brennholz und Fallenjagd) begünstigen die Strategien der Prädatoren beim Auffinden der Vogelnester und deren Gelege und stören das Brutverhalten der Vögel.Die expandierende Landwirtschaft und andere fortschreitende Landnutzungen sind zwei Hauptfaktoren, die die Wälder Sulawesis immer stärker bedrohen. Die Fragmentierung ursprünglicher Wälder, die daraus resultierenden Randeffekte, die Artenzusammensetzung der Prädatoren und ihre Abundanz, die Abwesenheit eines Top-Prädators, die reduzierte Vegetationsdeckung und die menschlichen Aktivitäten bewirken einen erhöhten Prädationsdruck auf die Nester in der Strauchschicht in Waldrandgebieten. Die Erkenntnisse dieser entscheidenden Faktoren können für das Management in einem Nationalpark nützlich sein und sollten berücksichtigt werden. Mit Hilfe eines Schutzkonzeptes können die optimalen Habitateigenschaften für die betroffenen Vogelarten erhalten bzw. neu geschaffen werden, damit auch unsere nachfolgenden Generationen die sulawesischen Waldgebiete und deren Vogelfauna in ihrer einzigartigen Vielfalt erleben.

Nest predation is the main cause of nest failure in passerine birds and thus is a key determinant of breeding traits. Accordingly, nest predator community composition and abundance modulate nest predation rates. When top predators are absent, mesopredator populations may become unchecked, which in turn increases the predation pressure on their prey species. We evaluated whether nest predator abundance and breeding traits of an endangered grassland bird, the Strange‐tailed Tyrant Alectrurus risora, differed between two protected areas: Iberá National Park (INP), where top predators have been extinct for 50 years, and Reserva El Bagual (REB), where Pumas Puma concolor still have a stable population. We measured abundances of potential nest predator species and during the 2015–2018 breeding seasons we monitored Strange‐tailed Tyrant nests and set camera traps to identify nest predators. Mesopredator abundance was higher in INP, and foxes were identified as the main nest predators. Nest predation rate was also higher in INP, where the daily nest predation rate and cumulative probability of nest predation were 0.05 ± 0.006 and 0.81, whereas in REB they were 0.04 ± 0.004 and 0.70, respectively. The 10‐fold higher frequency of fox records in INP could explain the higher nest predation rate observed, suggesting that the extinction of top predators may increase nest predation rates of endangered grassland birds in protected areas through release of native mesopredator species. The lower nest predation observed in REB was compensated for by a higher nest abandonment rate, which resulted in a similar fledgling production in the two study sites. Clutch size, hatching success and number of nestlings did not differ between study sites. The low breeding success recorded for this endangered species despite its populations being in protected areas of high conservation value is alarming given the global decline that grassland bird populations are facing.

In human-modified environments, ecological traps may result from a preference for low-quality habitat where survival or reproductive success is lower than in high-quality habitat. It has often been shown that low reproductive success for birds in preferred habitat types was due to higher nest predator abundance. However, between-habitat differences in nest predation may only weakly correlate with differences in nest predator abundance. An ecological trap is at work in a farmland bird (Lanius collurio) that recently expanded its breeding habitat into open areas in plantation forests. This passerine bird shows a strong preference for forest habitat, but it has a higher nest success in farmland. We tested whether higher abundance of nest predators in the preferred habitat or, alternatively, a decoupling of nest predator abundance and nest predation explained this observed pattern of maladaptive habitat selection. More than 90% of brood failures were attributed to nest predation. Nest predator abundance was more than 50% higher in farmland, but nest predation was 17% higher in forest. Differences between nest predation on actual shrike nests and on artificial nests suggested that parent shrikes may facilitate nest disclosure for predators in forest more than they do in farmland. The level of caution by parent shrikes when visiting their nest during a simulated nest predator intrusion was the same in the two habitats, but nest concealment was considerably lower in forest, which contributes to explaining the higher nest predation in this habitat. We conclude that a decoupling of nest predator abundance and nest predation may create ecological traps in human-modified environments.

Capsule Although stable in their preferred, wet habitats, Willow Tits have declined in woodland, probably because of habitat degradation rather than increases in avian nest predator and competitor numbers. Aims To elucidate the cause of the population decline by investigating variations with habitat and testing the hypothesis that an increase in nest predators or competitors (especially for nest-holes) could be responsible. Methods I analysed with respect to survey plot habitat over 30 years of Willow Tit abundance data from a national survey. I examined the relationships with the local abundance of key potential nest predators (woodpeckers and Jay Garrulus glandarius) and key potential competitors (other tit species and Nuthatch Sitta europaea). Results Willow Tits have declined in farmland and woodland in Britain, but not in their preferred, wet habitats. There was no evidence for any negative effect of competition and the only potentially important negative correlation with the abundance of a predator (Great Spotted Woodpecker Dendrocopus major) was limited to farmland, a relatively minor habitat. A negative relationship with Green Woodpecker Picus viridis probably reflects opposite habitat preferences. Conclusions Although correlative studies of competition and predation cannot be definitive, the evidence of this study suggests that the major cause of the Willow Tit's decline in Britain is habitat degradation, especially in woodland. Possible mechanisms for this degradation are discussed.

Urban areas have been considered “safe zones” for nesting birds because of low abundance of predators, and consequently low predation pressure. We studied risk of artificial ground nest predation across an urban gradient at regional (100×100 km) and local scales (5×5 km, within town) in Finland, Italy, and Spain. Risk of nest predation differed between countries, being greatest in Spain (66%), intermediate in Finland (51%), and lowest in Italy (29%). At the regional scale, risk of nest predation in Finland was lower in small villages and in forest area than in more urbanized sites. In Spain, the risk of nest predation was lower in villages than in the other habitat types. No differences in nest predation risk among habitat types were observed in Italy. At the local level, the risk of nest predation in Finland was higher within the town than in the surrounding forest. In Spain, the risk of nest predation in the surrounding forest area was as high as in the most urbanized areas. No difference in nest predation risk was observed between study plots in Italy at the local level analysis. Our results indicate that nest predation in town centers and their residential areas is similar to or higher than in villages and forest areas refuting the safe nesting zone hypothesis. Risk of nest predation also differed between residential area types within towns. Moreover, the abundance of potential nest predators differed between countries. Magpies and crows were more abundant in Finland than in Italy and Spain, whereas cats, dogs and pedestrians were less abundant in Finland than in the other countries. In Finland, risk of nest predation increased with the abundance of magpies. In Italy and Spain, risk of nest predation increased with the number of pedestrians and in Italy also with the number of cats. In all countries, the risk of nest predation increased with the visibility of the nest. According to our results, urban areas cannot be seen as “safe nesting zones”. Actually, changes in nest predation pressure may cause changes in habitat selection patterns and affect bird community structure in urban environments.

Habitat management and patterns of predation of Northern Lapwings on wet grasslands: The influence of linear habitat structures at different spatial scales

Effects of roadside edge on nest predators and nest survival of Asian tropical forest birds

Nest predation is such an important determinant of the reproductive success of many birds, particularly passerines, that its dynamics are of great interest to ecologists and wildlife managers. The large body of literature devoted to assessing these dynamics, however, has not succeeded in producing much consensus as to what makes a nest more or less likely to be depredated. The idea that nest predation increases at habitat edges, for instance, was very popular for a time, but in fact most studies do not find such an ‘edge effect’, and in a few sites nest predation actually decreases towards the edge (Lahti, 2001). Perhaps the nearest we have come to a definitive statement about nest predation is that it is exacerbated by habitat fragmentation at the landscape scale (Donovan et al., 1995). This hypothesis has strong intuitive appeal: the nesting success of forest birds, for instance, seemingly must decline if their habitat is broken up into small pieces surrounded by a matrix known to harbor an abundance of generalist predators. Apparently, we cannot maintain even this moderate and unsurprising generalization. Spanhove et al. (2009) found, among several Afromontane forest fragments, that the lower the edge-to-area ratio (in other words, the larger a patch and less convoluted its shape), the more likely a forestdwelling passerine nest will be ravaged by predators. Thus, their focal bird, the white-starred robin Pogonocichla stellata, might actually benefit from a fragmented forest habitat, with more edge and lower habitat patch sizes. To some extent, at least in the largest patch in the study site, predation rates were highest in the less disturbed interior of the patch, where nesting tended to occur later in the season and under denser canopy and sparse herbaceous cover. Can landscape fragmentation really benefit some bird species? I believe that the answer is yes, but that conservationists and managers ought to regard this point as trivial, and that more productive questions in avian reproductive success lie elsewhere. The reality of our ecological situation, in Kenya’s Taita Hills as elsewhere, is that distinctive habitats for wildlife have been and often continue to be greatly shrunk and subdivided. Species like the whitestarred robin, which are common, have a broad range and inhabit a variety of forest types as well as shrublands, are not the species of concern in this situation. Many species might benefit from fragmentation, in which case we are in the serendipitous situation of having inadvertently managed a landscape in their favor. Managers should, of course, consider the nesting and other habitat requirements of a threatened species before drafting a plan; this goes without saying. The point here is that very few of these plans will ever need to be drawn up for birds that benefit from fragmentation. Nevertheless, studies that buck the general trends in ecological correlates of nest predation are valuable red flags for those who wish to understand the factors underlying the reproductive success of birds. From Spanhove et al. (2009), one can gather four candidate explanations for their surprising result and its apparent inconsistency with other studies: the use of artificial nests in many studies, different life histories or habitat requirements of the prey species, the scarcity of Afrotropical studies, and different nest predator assemblages. Dozens of studies of nest predation, including assessments of edge and other fragmentation effects, have used natural as well as artificial nests, with no clear distinction overall in their findings (Lahti, 2001), and so this factor is unlikely to be key. Nest site and other behavioral and lifehistory traits will certainly be important determinants of reproductive success, but studies during the last 40 years in the temperate zone have already assessed nest predation for a broad array of species with a range of nesting habits and life histories. This brings us to the scarcity of studies of tropical birds, and birds of the Afrotropics in particular. In recent years, nest predation studies on African birds have become more common (e.g. Schaefer et al., 2005; Hanson, Newmark & Stanley, 2007; Kotze & Lawes, 2007; Lloyd, 2007; Boukhriss, Selmi & Nouira 2009), but a tentative conclusion that one might draw from them as a whole is that general ecological correlates of nest predation are not

Wind farm implementation is a rapidly growing source of landscape transformation that may alter ecological processes such as predator–prey interactions. We tested the hypothesis that wind farms increase the activity of nest predators and, ultimately, increment ground-nest predation rates. We placed 18 plots in Iberian shrub-steppes (11 at control and seven at wind farm sites), each one comprised nine artificial ground-nests (three quail eggs/nest). Artificial nests were placed during two events: at the beginning (April) and at the end (June) of the breeding season in 2016 (n = 324 artificial nests). We estimated the relative abundance of avian and large mammalian predators in the surroundings of each plot and recorded nest fate after 12 days exposure. We also measured variables at landscape and microhabitat scale that potentially affect predator abundance and nest predation. Wind farm sites contained higher cover of gravel roads and more large mammalian predators. Moreover, the abundance of large mammalian predators increased with surrounding cover of both trees and gravel-roads. Avian predator abundance and nest predation rates did not differ between control and wind farm sites, though nest predation did increase with the surrounding cover of crops and gravel roads. Lastly, nest predation was higher at the end of the breeding season and decreased with moss and lichen cover. Our results support previous evidence on the increase of mammalian predator abundance as the surface area of gravel-roads increases, pointing towards a potential mechanism for wind farms leading to rise ground-nest predation. Future wind energy projects should minimize the development of gravel-roads for wind turbine access or maintenance.

Area sensitivity in songbirds is commonly attributed to increased nest predation in forest fragments. In 1995 and 1996, we tested whether the nest predators and nesting success of an area-sensitive forest bird, the Eastern Yellow Robin (Eopsaltria australis), varied with fragment size, and we also conducted an artificial nest experiment. The study occurred in two small (55 ha) and two large (>400 ha) forest fragments in a matrix of agricultural land in New South Wales, Australia. Predation accounted for 95% of all failures of 282 robin nests, and the survival of robin nests was negatively correlated with how frequently we observed avian nest predators near nests (i.e. nest-predator activity). Of 461 artificial nests, 84% were depredated, nearly all (99%) by birds. Thus, birds were important predators of nests. The abundance, species richness, and activity of avian nest predators were not related to fragment size. Survival of robin nests averaged 19%; nests in small fragments had a 22% chance of producing at least one fledgling compared with 15% in large fragments, but the difference was not significant. Survival of artificial nests averaged 12% in both small and large fragments. Nest-predator activity accounted for the most variation (68%) in the fate of robin nests, followed by the cumulative density of open-cup nesters (16%). The placement of robin nests had no influence on nest fate. We conclude that nest predation was not area dependent and propose food supply as an alternative hypothesis to explain area sensitivity. We suggest that, rather than being related to fragment size, nest predation increases with decreasing forest cover in a landscape. Increased nest predation in fragmented compared with contiguous landscapes may lower the population viability of songbirds in a region, and hence regional numbers. Therefore, the spatial scale at which fragmentation influences nest predation and songbird populations must be considered carefully.

Area sensitivity in songbirds is commonly attributed to increased nest predation in forest fragments. In 1995 and 1996, we tested whether the nest predators and nesting success of an area-sensitive forest bird, the Eastern Yellow Robin (Eopsaltria australis), varied with fragment size, and we also conducted an artificial nest experiment. The study occurred in two small (55 ha) and two large (>400 ha) forest fragments in a matrix of agricultural land in New South Wales, Australia. Predation accounted for 95% of all failures of 282 robin nests, and the survival of robin nests was negatively correlated with how frequently we observed avian nest predators near nests (i.e. nest-predator activity). Of 461 artificial nests, 84% were depredated, nearly all (99%) by birds. Thus, birds were important predators of nests. The abundance, species richness, and activity of avian nest predators were not related to fragment size. Survival of robin nests averaged 19%; nests in small fragments had a 22% chance of producing at least one fledgling compared with 15% in large fragments, but the difference was not significant. Survival of artificial nests averaged 12% in both small and large fragments. Nest-predator activity accounted for the most variation (68%) in the fate of robin nests, followed by the cumulative density of open-cup nesters (16%). The placement of robin nests had no influence on nest fate. We conclude that nest predation was not area dependent and propose food supply as an alternative hypothesis to explain area sensitivity. We suggest that, rather than being related to fragment size, nest predation increases with decreasing forest cover in a landscape. Increased nest predation in fragmented compared with contiguous landscapes may lower the population viability of songbirds in a region, and hence regional numbers. Therefore, the spatial scale at which fragmentation influences nest predation and songbird populations must be considered carefully.

Contrasting effects of eucalyptus, pine and oak plantations on nest predation risk in Mediterranean grasslands