Nest Predation Rates Research Articles

Mixed effects of urbanization on density, nest survival, and nestling corticosterone of a generalist passerine

AbstractGeneralist species occupy a wide range of habitats and typically respond well to environmental disturbance. Highly disturbed urban areas may contain habitat that generalists can use and exploit; however, habitat use and quality of areas within urban landscapes are poorly understood. Here, we investigated habitat use of a generalist passerine, the red‐winged blackbird (Agelaius phoeniceus), in urban and rural grassland patches in greater metropolitan Chicago, USA. From 2012 to 2013, we conducted point counts on 30 grassland patches and searched for nests at a subset of these sites. We measured and weighed nestlings and collected fecal samples for corticosterone metabolite analysis. We found that population densities were greater in grassland patches in more rural areas, despite higher rates of nest predation and brood parasitism. We found that clutch size and number of young fledged did not differ between urban and rural areas. Average body mass and tarsus length of nestlings did not vary with urbanization, but nestlings in rural environments had significantly greater fecal corticosterone metabolites than urban nestlings. These results suggest that, even for widely successful generalist species, novel habitat can create a disconnection between habitat use and quality. The reason for this disconnection is unclear but may be related to perceived predation risk or other biotic or abiotic cues. Addressing the mechanisms behind undervaluation of habitat within urban landscapes will aid in wildlife conservation and management in novel environments.

Factors Affecting Nest Success and Predator Assemblage of Breeding Birds in Semiarid Grasslands

Woody encroachment has influenced wildlife distributions and, thus, predator-prey dynamics, for many taxa in North American grasslands. In 2015 and 2016, we examined how vegetative characteristics influenced avian nest predator assemblages and nest predation rates in semiarid grasslands of south Texas, where encroachment of woody plant species is common. We monitored 253 nests of 17 bird species and deployed infrared cameras at 107 nest sites within four vegetation types at our study sites. We also used data from a concurrent, multispecies monitoring project within our study area to assess predator activity within these same vegetation types. We divided bird species into four nest types based on nest shape and size (i.e., small, medium, and large cup-shaped nests and exposed nests with little structure). We then used logistic regression to examine relationships between shrub cover, concealment, and distance to edge and the probability of nest success and predation by snakes. We observed a significant decrease in nest success of our medium-sized, cup-shaped nest type when shrub cover increased at the nest site, indicating small increases in shrub cover (≈10%) could have substantial impacts on birds using this nest type. Snakes were our primary predator at camera-monitored nests (59%), and snake activity increased by 6.7% with every 10% increase in shrub cover at the nest site. Mesomammalian and large mammalian predators were most active in vegetation types predominated by herbaceous cover, small mammals were most active in vegetation types predominated by woody cover, and snake activity was highly variable. Predator activity did not reflect predator identity at camera-monitored nests, suggesting that potential nest predator activity may not accurately reflect the risk of nest predation. Results of our study will help inform management of bird species using semiarid grasslands affected by woody encroachment and offer recommendations for improved nest success.

English

Worldwide understorey nesting bird species such as bulbuls can also be highly vulnerable to nest predation in disturbed landscapes because they breed mainly on the lower stage of the forest. We test the following hypotheses: the transformation of forests into alternative land use systems and the vegetation’s variables at the nesting sites will affect the understorey nest predation rates. The nests of 12 understorey bird species were surveyed and vegetation variables were measured within five types of habitats along a gradient of increasing forest destruction in the north-eastern peripheral zone of the Korup National Park in Cameroon. Only the open-cup nest type suffers from predation, mostly egg predation. The general linear mixed model analysis suggests that the types of habitat do not affect nest daily predation rate which decreases with increasing trees and understorey plant density. The most deleterious impact of deforestation in this study area is the reduction of nesting sites whose characteristics remain unchanged across the landscape. These results underscore the need to give understorey nesting species, as well as other particularly sensitive groups, special consideration within conservation strategies such as the reduced-impact logging techniques.   Key words: Cameroon, deforestation, land-use system, nest predation, understorey birds.

Different nest predator guild associated with egg size in the Patagonian temperate forest

ABSTRACTCapsule: Studies of nest predation using artificial nests need to consider the effect of egg size on the types of predator that are detected.Aims: To estimate the nest predation rate in the Patagonian temperate forest and evaluate the influence of egg size on predator guild.Methods: On different plant species, we placed 108 nests each containing eggs of either Atlantic Canary Serinus canaria or Common Quail Coturnix coturnix, and a model clay egg of equal size to the real egg. Nest predators were identified from the marks left on the clay eggs or by videos recorded using camera traps.Results: 86% of the nests were predated. Birds, mainly Chimango Caracara Milvago chimango, were the main nest predators. A marsupial, the Monito del Monte Dromiciops gliroides, and rodents also contributed to nest predation. Nest predation rates were similar for both egg sizes but the nest predator guild was different. Birds and rodents preyed on both eggs but the Monito del Monte consumed mainly small eggs.Conclusion: Egg size did not influence the rate of nest predation but, instead, affected the nest predator guild. Consequently, in order to avoid underestimating the impacts of small predators, egg size should be considered in studies of nest predation.

Flash in the pan: how grassland renewal affects reproduction of Northern Lapwings Vanellus vanellus

ABSTRACTCapsule: Grassland renewal is associated with short-term beneficial effects on density and reproduction of Northern Lapwings Vanellus vanellus followed by long-lasting reduced breeding numbers after sward establishment.Aims: To assess short- and long-term effects of grassland renewal on the reproduction of Northern Lapwings.Methods: In the years 1999–2011 we counted breeding Northern Lapwings on 18 reseeded grassland plots in a chronosequence ranging from one year before until 3 years after reseeding. We also monitored nesting dispersion and hatching success in different habitats, particularly tillage, permanent grasslands and reseeded grasslands during sward establishment.Results: Grassland that underwent reseeding possessed several-fold more Northern Lapwings during the phase of sward establishment than before. In the subsequent years, breeding numbers significantly declined and remained low throughout the study period. In recently reseeded grassland, Northern Lapwings tended to breed in larger colonies. Although habitat-specific differences in hatching success were not significant, we found significantly higher nest predation rates in agriculturally improved grasslands than in tillage and reseeded grasslands during sward establishment.Conclusions: Due to its long-term adverse effects on density and reproduction of Northern Lapwings, grassland renewal should not be practised in areas with conservation responsibilities for grassland-breeding waders.

Variation in age-dependent nest predation between island and continental Rufous Fantail (Rhipidura rufifrons) subspecies

ABSTRACT Comparative studies of nest predation and identification of nest predators promote understanding of the selective environment that shapes avian life histories. Due to the low diversity of native mammalian and reptilian predators on oceanic islands, insular forest birds are assumed to incur lower nest predation rates than related continental species. We studied correlates of nest predation in insular and continental subspecies of Rufous Fantail (Rhipidura rufifrons) found on the island of Rota and in eastern Australia. Overall, daily survival rate (DSR) was similar between study sites, but egg stage DSR (laying and incubation) was higher in Australia than on Rota while nestling stage DSR was higher on Rota than in Australia. DSR was negatively related to nest age in Australia and the magnitude of this relationship varied by year. On Rota, DSR was higher in the nestling stage than during the egg stage and also higher on our study plot where Mariana Crows (Corvus kubaryi)—the principal nest predator...

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

Creation of roadside forest edges can have indirect effects on forest bird communities, as edges can promote species detrimental to forest-nesting birds such as nest predators. We assessed species-specific rates of nest survival of understory birds, relative abundances of specific nest predators and predator-specific rates of nest predation relative to the distance from roadside forest edge in a dry evergreen forest in northeastern Thailand. During the breeding seasons (February–August) of 2014–2016 we searched for nests along two, 1-km transects which ran perpendicular from the edge of a five-lane highway into the forest interior. To assess nest predator species, video cameras were placed on active nests of understory birds and multiple techniques were used to assess the relative abundances of the documented nest predators. We found 306 active nests of 26 species and recorded 179 predation events from 13 species of nest predators. Distance to edge influenced the daily nest survival rates for four of seven focal bird species, with three species having higher survival rates nearer to the edge. Four of six predators had higher relative abundances in the forest interior. Rats and the Common Green Magpie (Cissa chinensis) had higher abundances nearer the edge. Snake detections were too few to assess statistically. Nest predation rates for the top three predators, Northern Pig-tailed Macaque (Macaca leonina), Green Cat Snake (Boiga cyanea) and Crested Goshawk (Accipiter trivirgratus) were significantly greater in the forest interior. The fourth-most important, Common Green Magpie, was the only predator responsible for more nest predation events closer to habitat edge compared to interior. Our study suggests that the impacts of edges on nesting success are highly dependent on the nest predator community and the species-specific responses of predators to edges.

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.

Supplemental food alters nest defence and incubation behaviour of an open‐nesting wetland songbird

Climate‐driven increases in spring temperatures are expected to result in higher prey availability earlier in the breeding season for insectivorous birds breeding in wetland habitats. Predation during the incubation phase is a major cause of nesting failure in open‐nesting altricial birds such as the Eurasian reed warbler. The nest predation rate in this species has recently been shown to be substantially reduced under conditions of experimentally elevated invertebrate prey availability. Food availability near the nest may be an important determinant of adult incubation and nest defence behaviours during the incubation period. We used two experimental studies to compare incubation behaviour and nest defence in food‐supplemented and unsupplemented adult Eurasian reed warblers during the incubation phase. In the first study we measured nest defence behavioural responses to a taxidermic mount of a native predator (stoat Mustela erminea). In the second study we used temperature loggers installed in nests to measure breaks in incubation as a measure of nest vulnerability. Food‐supplemented birds responded aggressively to the presence of a predator more quickly than those in the unsupplemented group, suggesting they are closer to their nest and can more quickly detect a predator in the vicinity. Food‐supplemented birds also had shorter breaks in incubation (both in terms of maximum and mean off‐bout durations), presumably because they were foraging for shorter periods or over shorter distances from the nest. This study therefore identifies the behavioural mechanisms by which changes in food availability may lead to changes in nest survival and thus breeding productivity, in open‐nesting insectivorous birds.

Nest survival in year‐round breeding tropical red‐capped larks Calandrella cinerea increases with higher nest abundance but decreases with higher invertebrate availability and rainfall

Nest survival is critical to breeding in birds and plays an important role in life‐history evolution and population dynamics. Studies evaluating the proximate factors involved in explaining nest survival and the resulting temporal patterns are biased in favor of temperate regions. Yet, such studies are especially pertinent to the tropics, where nest predation rates are typically high and environmental conditions often allow for year‐round breeding. To tease apart the effects of calendar month and year, population‐level breeding activity and environmental conditions, we studied nest survival over a 64‐month period in equatorial, year‐round breeding red‐capped larks Calandrella cinerea in Kenya. We show that daily nest survival rates varied with time, but not in a predictable seasonal fashion among months or consistently among years. We found negative influences of flying invertebrate biomass and rain on nest survival and higher survival of nests when nests were more abundant, which suggests that nest predation resulted from incidental predation. Although an increase in nest predation is often attributed to an increase in nest predators, we suggest that in our study, it may be caused by altered predator activity resulting from increased activity of the primary prey, invertebrates, rather than activity of the red‐capped larks. Our results emphasize the need to conduct more studies in Afro‐tropical regions because proximate mechanisms explaining nest predation can be different in the unpredictable and highly variable environments of the tropics compared with the relatively predictable seasonal changes found in temperate regions. Such studies will aid in better understanding of the environmental influences on life‐history variation and population dynamics in birds.

Mismatches between habitat preferences and risk avoidance for birds in intensive Mediterranean farmland

Land use intensification may create habitats that organisms perceive as suitable, but where reproduction or survival is insufficient to maintain self-sustaining populations. Such conditions may qualify as ecological traps, but their existence is often hard to prove. Here, we provide a practical framework to evaluate a potential ecological trap resulting from mismatch between habitat preferences and predation risk, focusing on ground-nesting farmland birds of conservation concern. The framework is based on species-specific associations with safe or unsafe habitat types (i.e. field and landscape types with high or low nest survival), and the occurrence of risk avoidance (i.e. negative responses to predator abundances or to nest failure rates after controlling for habitat effects). Bird densities were far more influenced by field characteristics than landscape context. Corn bunting and fan-tailed warbler were associated with tall swards (safe habitats), and did not show risk avoidance. Tawny pipit and and Galerida larks were associated with short swards (unsafe habitats), with the former avoiding fields with high nest predation rates, and the later avoiding high mongoose abundances. Short-toed lark was associated with fields with short swards and low nest trampling rates. Results suggest that short-toed lark may be the most vulnerable to ecological trapping, because it nests on unsafe habitats and did not show predation risk avoidance. Our approach provides a practical first step to infer vulnerability to a potential ecological trap, though further research is needed to confirm this effect. Management actions increasing nest survival in short sward fields will likely favour grassland bird conservation in intensive Mediterranean farmland.

Fitness Consequences of Interspecific Nesting Associations among Cavity-Nesting Birds.

Interspecific aggregations of prey may provide benefits by mitigating predation risk, but they can also create costs if they increase competition for resources or are more easily detectable by predators. Variation in predation risk and resource availability may influence the occurrence and fitness effects of aggregating in nature. Yet tests of such possibilities are lacking. Cavity-nesting birds provide an interesting test case. They compete aggressively for resources and experience low nest predation rates, which might predict dispersion, but across 19 years of study we found that they commonly aggregate by sharing nest trees. Tree sharing was more common when aspen were more abundant and was somewhat more common in years with higher nest predation risk. Nest success was higher in shared trees when nest predation risk was higher than average. Ultimately, the costs and benefits of aggregating (nest tree sharing) varied across years, and we outline hypotheses for future studies.

Ecological determinants ofTyrannusflycatcher nestling growth at north- and south-temperate latitudes

ABSTRACT An organism's life history strategy is made up of a suite of physiological, behavioral, and ecological traits, which vary at both the interspecific and intraspecific levels in accordance with selective pressures operating on individuals. For birds, 2 primary ecological factors have been proposed to explain intraspecific and interspecific variation in nestling growth: nest predation and food availability. Individual nestling growth rates have important consequences for overall fitness because growth speed could influence subsequent reproductive performance and survival. We studied the relationship between ecological factors (i.e. precipitation level and predation rate) and nestling growth patterns of 2 New World flycatcher species (Tyrannidae) of the genus Tyrannus (Fork-tailed Flycatcher [T. savana] and Scissor-tailed Flycatcher [T. forficatus]) breeding at south- and north-temperate latitudes. We tested the hypothesis that nestling growth rates are driven by nest predation rates and predicted th...

Seasonal variation in nest predation rates in boreal forests

Nest predation is the most important factor causing reproductive failure in open-cup nesting birds. Therefore, it represents a strong selection agent shaping reproductive strategies. To understand how predation affects avian populations, it is crucial to understand how predation effects on nesting success vary in space and time, and which ecological factors determine variation in predation rates. Artificial nests are commonly used to evaluate nest predation rates, but their use is criticised for not providing predation rates comparable with natural nests, either because timing of predation or predator species targeting the nests differ. However, use of artificial nests allows us to standardize nest characteristics between sites and across time, even outside the breeding season of most birds. Here, we present data on 576 artificial nests gathered over several years that explore how nest predation rates vary over the year. We found that predation rates on artificial nests show seasonal variation where rates are high during the bird breeding season and low outside the breeding season. Avian and mammalian predators tend to display different nest predation behaviours. The frequency of predation events by avian predators follows a similar seasonal pattern as predation rates, whereas mammalian predators show elevated, but stable, frequency of predation events across the breeding season. Our study supports the commonly reported temporal variation in nest predation rates, indicating that avian predators actively search for bird nests as food during the bird breeding season, while mammalian predators seem to prey on bird nests incidentally.

Predation and nutrients drive population declines in breeding waders.

Allee effects are defined as a decline in per capita fitness at low population density. We hypothesized that predation reduces population size of breeding waders and thereby the efficiency of predator deterrence, while total nitrogen through its effects on primary and secondary productivity increases population size. Therefore, nest predation could have negative consequences for population size because nest failure generally results in breeding dispersal and hence reduced local population density. To test these predictions, we recorded nest predation in five species of waders for 4,745 nests during 1987-2015 at the nature reserve Tipperne, Denmark. Predation rates were generally negatively related to conspecific and heterospecific population density, but positively related to overall population density of the entire wader community. Nest predation and population density were related to ground water level, management (grazing and mowing), and nutrients. High nest predation with a time lag of one year resulted in low overall breeding population density, while high nutrient levels resulted in higher population density. These two factors accounted for 86% of the variance in population size, presumably due to effects of nest predation on emigration, while nutrient levels increased the level of vegetation cover and the abundance of food in the surrounding brackish water. These findings are consistent with the hypothesis that predation may reduce population density through negative density dependence, while total nitrogen at adjacent shallow water may increase population size. Nest predation rates were reduced by high ground water level in March, grazing by cattle and mowing that affected access to and susceptibility of nests to predators. These effects can be managed to benefit breeding waders.

Short-Term Resilience of New Jersey Tidal Marshes to Hurricane Sandy

Hurricane Sandy made landfall in the USA on October 29, 2012 and had devastating impacts on human-dominated landscapes in the mid-Atlantic and New England states, but its effects on tidal marsh habitats remain largely undescribed. We evaluated the short-term resilience (a resistance to change or a rapid return to pre-storm conditions) of tidal marshes on Edwin B. Forsythe National Wildlife Refuge, New Jersey by comparing vegetation cover/composition, meadow vole (Microtus pennsylvanicus) relative abundance, and predation rates on artificial bird nests, from three to six months pre-hurricane with seven to 11 months post-hurricane. These three metrics show a high degree of resilience to Hurricane Sandy. Vegetation cover/composition remained similar pre- and post-hurricane, except for five site-specific changes. Although meadow voles were significantly less abundant following the hurricane, we detected a rapid increase from June to July 2013, indicating resiliency via rapid recovery in the population. We also did not observe widespread changes in nest predation rates on artificial nests. Our findings indicate that management actions intended to recover vegetation, small mammals, and nest predators following a large hurricane disturbance may be of less importance than long-term strategies to avoid gradual changes that can reduce ecosystem resilience.

Small between-year variations in nest predation rates are not related with between-year differences in predator identity

ABSTRACTNest predation is one of the most important causes of nest failure in breeding birds and can vary extensively between sites and years. Different mechanisms governing predation rates may dominate in different years and this annual variation should therefore be evaluated directly. Here we document year-to-year variation in nest predation rates in two ecosystems (forest and salt meadows) within the mid-boreal forest zone to evaluate whether annual variation in nest predation rates are linked with annual variation in predator identity or the ratio between predator types. Year-to-year variation in predation rates was low in all experiments (non-significant differences in experiments 1 and 2), with a significant decrease only from 2005 (0.90%) to 2008 (0.70%), 2009 (0.65%) and 2010 (0.72%) in experiment 3. In addition, random intercept estimates indicated that two sites from experiment 1 showed higher predation rates in year 2 than in year 1. None of these differences were related with differences in apparent predator community structure or predator identity. This suggests that low between-year variation in nest predation rates may be common in areas where the predator communities are stable, and the existing variation cannot be explained by variation in predator identity alone.

Agroforestry system as a buffer zone in a Brazilian Atlantic Forest conservation unit: an artificial nest predation perspective

Abstract Here we inferred about the effectiveness of a buffer zone composed by an Agroforestry System (AS) for providing reproductive conditions for Atlantic Forest birds by comparing artificial nest predation rates between a buffer zone, a primary forest area, and a set of small and isolated Atlantic Forest fragments. We have used 237 nests throughout the three areas, of which 100 (42.2%) were depredated. Predation frequencies were 28.6% in the continuous forest, 100% in the AS, and 51.9% in the fragments, differing significantly. We could detect nest predators in 48 of the 100 depredated nests (48%) using camera traps. Differences between areas may be attributed to changes in nest predator species. We support previous evidences that the conservation of bird communities may not rely on buffer zones as an extension of their breeding habitats.

Predation on artificial and natural nests in the lowland rainforest of Papua New Guinea

ABSTRACTCapsule: Although survival of nests was similar between forest fragments and continuous forest, the range of predators differed. Artificial nests provide an under-estimate of nest predation by snakes.Aims: To estimate the natural nest predation rate in continuous primary forest, compare it with predation rates in forest fragments. To assess the reliability of nest survival rates determined by the use of artificial nests with clay eggs and identify the main nest predators.Methods: We observed survival of natural nests during the incubation period in continuous primary forest in Papua New Guinea. Some nests were monitored with infrared cameras. We also used artificial nests deployed with clay eggs to identify predators.Results: There was a predation rate of 50% for natural nests and snakes were major predators of nest contents. Clutch daily survival rates (DSRs) differed among nest types. The DSR of artificial nests (0.977) was not significantly different to that of natural cup nests (0.969). Survival rates of artificial nests were similar in forest fragments and continuous forest. Forest fragments had, however, a higher proportion of avian predators than continuous forest.Conclusion: Although, we observed similar survival rates in artificial and natural nests, the composition of nest predators was different between natural and artificial nests. Artificial nests were not suitable for estimating the real predation caused by reptiles. Nevertheless, we find that participation of avian nest predators can be estimated correctly with the use of artificial nests.

Reproductive success of Common Ravens influences nest predation rates of their prey: implications for egg-oiling techniques

Reproductive success of Common Ravens influences nest predation rates of their prey: implications for egg-oiling techniques