Food availability and seasonal variation in nest predation pressure as factors influencing the timing of breeding of Namaqua sandgrouse in the Nama Karoo, South Africa

This study examines whether rainfall and its effects on food availability control the timing of migratory movements and breeding activity in the Namaqua Sandgrouse, Pterocles namaqua. Namaqua Sandgrouse exhibit a pattern of partial migration between two late-summer-rainfall regions, birds spending the summer months in the Nama Karoo and the winter months in the Kalahari. Across southern Africa, the breeding season for this species is unexpectedly variable, and not consistently correlated with periods of peak food availability. The main egg-laying periods in the late-summer-rainfall regions are: (a) in northwestern Namibia from January–May with a peak in May, (b) in southwestern Namibia in any month with a peak in July, (c) in the Kalahari from June to December, and (d) in the Nama Karoo from September to December. Breeding in the Nama Karoo often starts five months after food becomes abundant, and extends into the start of the rainy season, when food availability can reach the lowest levels in the annual cycle. This suggests that some factor(s) other than proximate food availability is/are involved in determining the timing of movements and breeding in this species, at least in some regions. The possible complicating influences of biannual breeding, moulting, adult nutritional reserves and seasonal variation in nest predation pressure are discussed. We conclude that further long-term monitoring throughout the range of the Namaqua Sandgrouse is required to unravel the potential contribution of three factors (food availability, pottern of migratory movement and risk of nest predation) to the timing of migratory movements and breeding seasons in this species.

Nest predation is an essential factor affecting bird population density, reproductive ecology and life cycle. However, there are still contradictory results about how nest predation pressure changes with urbanization. One of the reasons for the controversy is that previous studies often use artificial nests to investigate nest predation, but the result of artificial nests is often biased and contrary to that of natural nests. Therefore, it is important to perform nest predation experiments simultaneously with both natural and artificial nests. In this study, we examined the change of nest predation pressure on the Chinese Bulbul (Pycnonotus sinensis) along the urbanization gradient in Hangzhou, China. We detected 148 natural nests of Chinese Bulbuls and continuously monitored them in two continuous breeding seasons from 2012 to 2013. After the breeding season, we placed artificial eggs in natural nests of Chinese Bulbuls to investigate the changes in nest predation pressure and used infrared cameras to record the predators. We then calculated the urbanization synthetic index (USI) as the measure of the degree of urbanization and examined its relationship with nest predation pressure. We found that no matter whether natural nests or artificial eggs were used, the nest predation pressure always decreased significantly with the degree of urbanization. The average height of shrubs within 10 ​m of the nest differed significantly between the predated and unpredated nests, which also affected the risk of nest predation. Our study highlights the importance of using natural and artificial nests simultaneously to conduct nest predation experiments, which can reduce the bias or errors caused by only using artificial nests. We also recommend the use of infrared cameras in future nest predation studies, which has obvious advantages in monitoring and identifying potential predators.

Numerous hypotheses have been proposed to explain variation in reproductive performance and local recruitment of animals. While most studies have examined the influence of one or a few social and ecological factors on fitness traits, comprehensive analyses jointly testing the relative importance of each of many factors are rare. We investigated how a multitude of environmental and social conditions simultaneously affected reproductive performance and local recruitment of the red-backed shrike Lanius collurio (L.). Specifically, we tested hypotheses relating to timing of breeding, parental quality, nest predation, nest site selection, territory quality, intraspecific density and weather. Using model selection procedures, predictions of each hypothesis were first analysed separately, before a full model was constructed including variables selected in the single-hypothesis tests. From 1988 to 1992, 50% of 332 first clutches produced at least one fledgling, while 38.7% of 111 replacement clutches were successful. Timing of breeding, nest site selection, predation pressure, territory quality and intraspecific density influenced nest success in the single-hypothesis tests. The full model revealed that nest success was negatively associated with laying date, intraspecific density, and year, while nest success increased with nest concealment. Number of fledglings per successful nest was only influenced by nest concealment: better-camouflaged nests produced more fledglings. Probability of local recruitment was related to timing of breeding, parental quality and territory quality in the single-hypothesis tests. The full models confirmed the important role of territory quality for recruitment probability. Our results suggest that reproductive performance, and particularly nest success, of the red-backed shrike is primarily affected by timing of breeding, nest site selection, and intraspecific density. This study highlights the importance of considering many factors at the same time, when trying to evaluate their relative contributions to fitness and life history evolution.

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.

Urbanization changes the environment through physical constructions, disturbances, and altered resource availability. These modifications influence both prey and predator assemblages. Several studies have indicated that hole-nesting birds outnumber ground nesters in cities. Differential nest predation can be one reason behind this observation. We conducted a multi-year artificial nest predation experiment along an urban gradient by using artificial ground nests and nestboxes in Rovaniemi, Finland. Because visually searching avian predators dominate in cities, we predicted that nest predation of ground nests will increase with urbanization, whereas nests in holes will be better protected than ground nests. Ground nest predation increased with urbanization, being lowest in forest and rural areas, intermediate in suburban area and highest in urban area. However, there was no year-effects on artificial ground nest predation, suggesting that even a single-year results of artificial nest predation experiment can be reliable. In the city, ground nest predation was greater than nestbox predation. In forests, nestbox predation was greater than ground nest predation. Among ground nests, predation was greater in the city than in forests. Among nestboxes, predation was greater in forest than in urban or suburban habitats. Only the ground nest predation was greater in managed than in un-managed parks. Ground nest predation decreased with tree cover and increased with the patch area. No variables were entered in the models of the nestboxes. The results indicated that ground nesters might avoid urban areas as nesting sites. We assume that visually searching avian predators benefit from the lack of covering vegetation in city parks. However, because most avian nest predators, like corvids, are not effective nest predators of hole-nesting birds, urban areas are safe nesting areas for hole-nesters. The results suggest that nest predation is one important factor that could explain, why hole-nesting bird species outnumbered ground-nesting species in cities. The result give support for the hypothesis that nest predation pressure can modify urban bird assemblage structure.

Localized antipredator behaviors have been observed in a wide variety of taxa. Recent work has also shown that animals that provide parental care adjust their behavior when faced with variation in offspring predation pressure. This variation in offspring predation pressure may also influence the antipredator behavior of offspring if improved antipredator behaviors can increase their probability of survival. We tested if a natural gradient in nest predation pressure influenced antipredator behaviors of larval teleost fish (smallmouth bass, Micropterus dolomieu). We examined the predator avoidance of wild larvae from 6 populations that differed in nest predation pressure, and we also compared the recovery from a simulated predator attack of 2 populations at the opposite extremes of predation pressure. We found that larvae differed in their ability to avoid the nest predator, but larvae from lakes of low predation pressure responded similarly to larvae from lakes of high predation pressure. Generally, older offspring were not significantly better at avoiding predators relative to younger offspring, but we found a weak and significant positive correlation between the size of young offspring and their predator avoidance behavior. The recovery from a simulated predation event varied relative to predation pressure. Larvae from the site of high nest predation pressure exhibited reduced rates of maximal oxygen consumption and recovered faster than larvae from the low predation pressure site. Thus, variation in nest predation pressure had little influence on the antipredator behavior of offspring, which are provided with parental care but may have important metabolic consequences. Copyright 2011, Oxford University Press.

Wet grassland degradation is a global issue that involves both altered land cover patterns and ecological processes, which affect the distribution and abundance of species. The sharp decline in European wader bird (Charadrii) populations is a good example. The aim of this study is to test the hypothesis that the anthropogenic developmental stage of wet grassland habitats and landscapes drives avian nest predator abundance, and thus the predation pressure on nests, which is a major cause of wader bird declines. Using a macroecological approach we selected six wet grassland landscapes representing a gradient in both grassland habitat development and breeding wader population status in four European countries (Belarus, Iceland, Lithuania and Sweden). We (1) mapped wader and avian predator assemblages in multiple wet grassland patches in each landscape, (2) used artificial nests to estimate the relative rate of egg predation, and (3) analyzed relationships between nest predation pressure, corvid nest predators versus raptors, nest loss and the stage of wet grassland habitat and landscape development. We found (1) inverse relationships between the abundance of corvids and waders, as well as between wet grassland developmental stage and waders, and (2) a positive correlation between the probability of nest loss and the density of corvid birds. In conclusion, we found a clear macroecological pattern linking habitat quality, wader populations, nest predators and nest predation. These linkages stress the importance of including nest predation as a factor limiting wader bird populations, and that corvid control or management may be useful management tools.

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.

Cooperative breeding and anti-predator strategies of the azure-winged magpie (Cyanopica cyanus Pallas, 1776) in northern Mongolia

Many studies have compared songbird nesting success between forest edge and interior, but few have addressed potential factors underlying variation in nest predation pressure in relation to edge. We examined the relative abundance and species richness of songbird nest predators and the abundance of Brown-headed Cowbirds (Molothrus ater) in forest edge and interior within a fragmented, agricultural landscape in central Missouri, USA. Avian predators and cowbirds were more abundant in forest edges. There were no differences in small- or medium-sized mammalian predator abundance between edge and interior. Almost twice as many snakes were captured in edge as in interior. Predator species richness was significantly higher in forest edge. Forest vegetation structure was very similar between edge and interior, suggesting that differences in predator abundance and species richness were not driven by variation in habitat structure. Nest predator distribution in relation to habitat edge may therefore depend on factors at larger spatial scales, such as landscape context. We suggest that in areas fragmented by agriculture, nest predator assemblages in forest edges may differ from those in forest interior. Edges may attract a greater number of predator species, and some nest predators may be more abundant near the edges of forest patches, although the trend does not apply across all predator taxa. Generalizations about nest predators and edges should thus be made with caution, and conservation plans should consider the composition of local nest predator assemblages in order to predict potential impacts on nesting birds in edge habitat.

I tested three hypotheses that could explain variation in the timing of breeding in populations of House Wrens (Troglodytes aedon) at four sites in Costa Rica. The sites were located at 200-1,500 m elevation on both sides and on top of the central mountain range, and had climates differing in temperature, the severity of the dry season, and total rainfall. For the first hypothesis, that breeding is timed to coincide with peaks in food availability, I monitored the monthly abundance of arthropod prey and wren clutch initiations at the four sites. Cross-correlation analysis showed that at three sites, wrens initiated clutches several months prior to when prey levels were high. Indeed, breeding began when prey levels were at their annual low. At the fourth site, prey levels varied little throughout the year and House Wrens nested nearly year round. These results indicate that sufficient food to produce eggs or feed nestlings may have been available throughout the year. Breeding appeared to be timed so that juvenile dispersal and molt occurred when food was most plentiful. The second hypothesis, that breeding is timed to avoid seasons when nest predation is high, was not supported because the rate of nest predation did not vary temporally. The third hypothesis, that breeding is timed to avoid climatic events that can increase the physiological costs of reproduction, was not supported at the three lower elevation sites. Clutch initiation at the highest site, however, did not commence until the early dry season wind and mist subsided. The termination of breeding was not correlated with climatic changes at -any of the sites. Thus reproduction in tropical House Wrens seems generally to be timed to facilitate post-breeding activities, not activities associated with nesting itself.

Summary Wetland ecosystems throughout the world are threatened by drainage and intensification of agriculture. Consequently, many wetland species of conservation concern are now restricted to fewer and smaller sites, and maintaining these species often requires intensive habitat management. In Western Europe, breeding wader populations have declined severely as a result of wetland degradation, but very high levels of predation on eggs and chicks are now preventing population recovery. Wet grassland management for breeding waders has focussed on providing suitable nesting habitats, but the potential for management of landscape features to influence predation rates remains largely unknown. Using a 7‐year study of breeding lapwing Vanellus vanellus and redshank Tringa totanus we first identify features that influence nest predation, and then use this information to compare the magnitude of change in nest predation rates that could potentially result from future landscape management scenarios. As lapwing nest predation rates are higher (i) in fields further from patches of tall vegetation, (ii) close (<50 m) to field edges in wet fields, (iii) further from field edges in dry fields and (iv) in areas of low lapwing nesting density, we modelled a series of realistic scenarios in which the area of tall vegetation and the extent and distribution of surface water were varied across the reserve, to quantify the magnitude of change in nest predation rate that could potentially have been achieved through management. Modelled scenarios of changes in surface water and area of tall vegetation indicated that reduced surface flooding combined with removal of tall vegetation could result in significant increases in lapwing nest predation rates in areas with low nesting densities and nests in field centres. By contrast, a ~20% reduction in nest predation, corresponding to ~100 more chicks hatching per year, is predicted in scenarios with expansion of tall vegetation in areas with high lapwing nest density and nests close to field edges. Synthesis and applications. These management scenarios suggest that, for breeding waders in wet grassland landscapes, creating areas of tall vegetation and concentrating surface flooding (to encourage high nesting densities and influence nesting distribution) can potentially help to reduce the unsustainably high levels of nest predation that are preventing population recovery.

We examined whether regular researcher visits affected egg hatchability or nest predation for three ground-nesting bird species that incur high levels of nest predation, primarily by small mammals. Frequently visited finch-lark (Eremopterix verticalis and E. australis) nests suffered similar predation to nests visited infrequently, suggesting that regular visits had no additive effects on nest survival. A comparison of finch-lark nests visited for the second time either one or two days after the first visit found that predation during the first 24 h (7.4%) was lower than predation during the second 24-h period (9.9%), suggesting that the act of visiting a nest did not increase the risk of predation. Daily predation rates on Namaqua Sandgrouse (Pterocles namaqua) and finch-lark nests showed no observable trend with an increasing number of visits over time, indicating that frequent visits had no cumulative effect on predation probabilities. Nests of both Grey-backed Finch-lark (E. verticalis) and Black-eared Finch-lark (E. australis) discovered at the egg stage did not fledge significantly fewer young than nests discovered at the nestling stage, suggesting that investigator disturbance had no effect on egg hatchability. These results from the southern hemisphere subtropics support the findings of limited north-temperate studies that largely mammalian nest predation does not increase after researcher disturbance.

Nest predation is a major cause leading to reproductive failure of many avian species. Identifying nest predators is crucial for understanding the ecological context of nest predation and habitat management. The mountains of Southwest China harbors numerous species in the Phasianidae family, many of them endemic or threatened, however, little is known on the nest predation pressure on these ground breeders. We placed 32 artificial nests (each containing two chicken eggs) in broadleaf montane forests with different vegetation structure, and monitored predators with infrared-triggered cameras. The artificial nests were resembling nests of Golden Pheasant Chrysolophus pictus, a representative of the threatened species inhabiting montane broadleaf forest. We analyzed how environmental factors impact survival of artificial nests using Cox proportional hazards regression. With a failure rate of 62.5%, we recorded 40 predations where eggs were preyed or moved away, 19 predation attempts where animals spotted and contacted with, but failed to prey on or move away the eggs, and 109 pass-by events. Corvids, especially Large-billed Crow Corvus macrorhynchos was the primary culprit, committing all but one predations on artificial nests. Other potential predators included Pere David's Rock Squirrel Sciurotamias davidianus, Eurasian Jay Garrulus glandarius, Red-billed Blue Magpie Urocissa erythrorhyncha, Chinese Porcupine Hystrix hodgsoni and muridaes. We found that understory cover and vertical openness were the determining factors on survival of artificial nests. Presence of understory cover and low vertical openness significantly increased survival time of artificial nests. We didn't detect significant effects from horizontal openness and distance to nearest patrol trail. Further studies with real nests are however required to examine these conclusions, and to explore reproduction strategies of ground nesting pheasants coping with threats from avian predators.

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.