Habitat selection responses of parents to offspring predation risk: an experimental test

The ability of nest predation to influence habitat settlement decisions in birds is widely debated, despite its importance in limiting fitness. Here, we experimentally manipulated nest predation risk across a landscape and asked the question, do migratory birds assess and respond to variation in nest predation risk when choosing breeding habitats? We examined habitat preference by quantifying the density and settlement date of eight species of migratory passerines breeding in areas with and without intact nest predator communities. We found consistently more individuals nesting in areas with reduced nest predation than in areas with intact predator assemblages, although predation risk had no influence on settlement or breeding phenology. Additionally, those individuals occupying safer nesting habitats exhibited increased singing activity. These findings support a causal relationship between habitat choice and nest predation risk and suggest the importance of nest predation risk in shaping avian community structure and breeding activity.     

Nest Predation Deviates from Nest Predator Abundance in an Ecologically Trapped Bird

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.     

Testing ecological and behavioral correlates of nest predation

Variation in nest predation rates among bird species are assumed to reflect differences in risk that are specific to particular nest sites. Theoretical and empirical studies suggest that parental care behaviors can evolve in response to nest predation risk and thereby differ among ecological conditions that vary in inherent risk. However, parental care also can influence predation risk. Separating the effects of nest predation risk inherent to a nest site from the risk imposed by parental strategies is needed to understand the evolution of parental care. Here we identify correlations between risks inherent to nest sites, and risk associated with parental care behaviors, and use an artificial nest experiment to assess site-specific differences in nest predation risk across nesting guilds and between habitats that differed in nest predator abundance. We found a strong correlation between parental care behaviors and inherent differences in nest predation risk, but despite the absence of parental care at artificial nests, patterns of nest predation risk were similar for real and artificial nests both across nesting guilds and between predator treatments. Thus, we show for the first time that inherent risk of nest predation varies with nesting guild and predator abundance independent of parental care.     

Do alien predators pose a particular risk to duck nests in Northern Europe? Results from an artificial nest experiment

Several alien predator species have spread widely in Europe during the last five decades and pose a potential enhanced risk to native nesting ducks and their eggs. Because predation is an important factor limiting Northern Hemisphere duck nest survival, we ask the question, do alien species increase the nest loss risk to ground nesting ducks? We created 418 artificial duck nests in low densities around inland waters in Finland and Denmark during 2017–2019 and monitored them for seven days after construction using wildlife cameras to record whether alien species visit and prey on the nests more often than native species. We sampled various duck breeding habitats from eutrophic agricultural lakes and wetlands to oligotrophic lakes and urban environments. The results differed between habitats and the two countries, which likely reflect the local population densities of the predator species. The raccoon dog (Nyctereutes procyonoides), an alien species, was the most common mammalian nest visitor in all habitats and its occurrence reduced nest survival. Only in wetland habitats was the native red fox (Vulpes vulpes) an equally common nest visitor, where another alien species, the American mink (Neovison vison), also occurred among nest visitors. Although cautious about concluding too much from visitations to artificial nests, these results imply that duck breeding habitats in Northern Europe already support abundant and effective alien nest predators, whose relative frequency of visitation to artificial nests suggest that they potentially add to the nest predation risk to ducks over native predators.

     

Understanding avian nest predation: why ornithologists should study snakes

Despite the overriding importance of nest predation for most birds, our understanding of the relationship between birds and their nest predators has been developed largely without reliable information on the identity of the predators. Miniature video cameras placed at nests are changing that situation and in six of eight recent studies of New World passerine birds, snakes were the most important nest predators. Several areas of research stand to gain important insights from understanding more about the snakes that prey on birds' nests. Birds nesting in fragmented habitats often experience increased nest predation. Snakes could be attracted to habitat edges because they are thermally superior habitats, coincidentally increasing predation, or snakes could be attracted directly by greater prey abundance in edges. Birds might reduce predation risk from snakes by nesting in locations inaccessible to snakes or in locations that are thermally inhospitable to snakes, although potentially at some cost to themselves or their young. Nesting birds should also modify their behavior to reduce exposure to visually orienting snakes. Ornithologists incorporating snakes into their ecological or conservation research need to be aware of practical considerations, including sampling difficulties and logistical challenges associated with quantifying snake habitat use.     

Nesting patterns of European hedgehogs (Erinaceus europaeus) under northern conditions

Little information exists on the nesting of hedgehogs (Erinaceus europaeus) in the harsh northern environment, although this aspect has specific importance for the species’ survival in this region. We studied the nest types and nesting site selection of radio tagged hedgehogs in urban areas in Eastern Finland. Altogether, four different nest types were discovered and one of them (the pre-hibernation nest) is described here for the first time. Hedgehogs preferred residential areas for nesting during the mating and post-mating seasons while in the pre-hibernation season and hibernation period nesting was more common in forest areas. Nest constructions were closely related to materials found in the nest vicinity. During the active period, males used on average 24 nests and changed them 30 times, whereas females used 17 nests and changed them 26 times. The number of female nests and frequency of nest change increased from post-mating to pre-hibernation seasons, while in males both decreased. In general, female and male nests were situated within their established long-term home range, but in the pre-hibernation season over 30 % of male nests were situated outside of it. In post-mating and pre-hibernation seasons, females avoided other individuals of the same sex; this was demonstrated by the lack of nests in other female core areas. Hedgehogs hibernate for around 223 days, which is the longest reported hibernation period for this species. The results of the present study emphasise the importance of forest and diverse residential areas including forest patches for the hedgehog’s nesting habitat.     

Facultative nest patch shifts in response to nest predation risk in the Brewer’s sparrow: a “win-stay, lose-switch” strategy?

Facultative shifts in nesting habitat selection in response to perceived predation risk may allow animals to increase the survival probability of sessile offspring. Previous studies on this behavioral strategy have primarily focused on single attributes, such as the distance moved or changes in nesting substrate. However, nest site choice often encompasses multiple habitat elements at both the nest site and nest patch scales. We studied the within-season re-nesting strategy of a multi-brooded songbird, the Brewer’s sparrow (Spizella breweri), to determine whether pairs utilized a “win-stay, lose-switch” decision rule with respect to inter-nest distance, nest substrate and/or nest patch characteristics in response to previous nest fate. Pairs moved sequential nest sites slightly farther following nest predation versus success. When inter-nest distance was controlled, however, pairs changed nest patch attributes (shrub height, potential nest shrub density) associated with probability of nest predation to a greater extent following nest predation than success. The strategy appeared to be adaptive; daily nest survival probability for previously depredated pairs increased with greater Euclidian habitat distances between attempts, whereas previously successful pairs were more likely to fledge second attempts when nest sites were similar to those of previous attempts. Our results suggest that nesting birds can use prior information and within-season plasticity in response to nest predation to increase re-nesting success, which may be a critical behavioral strategy within complex nest predator environments. Re-nesting site selection strategies also appeared to integrate multiple habitat components and inter-nest distances. The consideration of such proximate, facultative responses to predation risk may clarify often unexplained variation in habitat preferences and requirements.     

Artificial nest and seed predation experiments on tropical southeast Asian islands

Southeast Asia is rapidly losing native habitats and the consequences of this are poorly understood. Because habitat loss and disturbance can affect avian and seed survivorship, we conducted artificial nest and seed predation experiments on tropical southeast Asian islands. Data among islands and fragments or different forest types (e.g. primary versus exotic forest) within the islands are compared. On Singapore Island, predation among different forest types (primary, secondary and woodland) did not differ. Only at one of the sites, nest predation was higher at 75 m from the forest edge than at 25 m. In other sites, predation did not differ in relation to the distance from the forest edge. Predation among 10 small (0.8–1026 ha) Singaporean islands differed. However, none of the environmental variables (e.g. island area) could explain the predation differences. The lowest predation of both nests and seeds was recorded in the primary forest areas of a contiguous forest (25 500 ha) in central Java (Linggoasri). Small mammals were the main predators on Singapore and other surrounding islands. However, the index of potential predator abundance, overall, did not correlate with predation. While larger and more pristine forests may be better for avian and seed survivorship, pinpointing variables affecting both artificial nest and seed predation may be difficult.     

Nest-site selection by Common Black-Hawks in southwestern New Mexico

ABSTRACT.   Despite the interest of resource managers and conservationists in the status of Common Black-Hawk ( Buteogallus anthracinus ) populations in the southwestern United States, little is known about their nesting success and habitat requirements. Because such information is essential for effective population and habitat management, I examined the nesting success and nest-site selection of Common Black-Hawks in southwestern New Mexico during 2000 and 2001. Of the 37 nesting attempts in 21 territories, ≥1 young fledged from 25 nests (68%). Comparison of nest-sites and nonused sites suggested that breeding Common Black-Hawks selected nest-sites in areas with a sparser and shorter subcanopy tree layer and in trees with a smaller trunk diameter and a greater minimum crown diameter. These differences appear to be related to variation in forest ages within territories, with nonused sites having fewer, but older, canopy trees than nest-sites. Sites with younger, smaller subcanopy trees may provide forest structure for more effective foraging, whereas the characteristics of younger nest tree canopies may reduce the risk of nest predation or offer more protection from inclement weather. Due to the limited range of this species in the southwestern United States, efforts to encourage the establishment and maturation of riparian forests in Common Black-Hawk breeding areas could be important in sustaining available nesting habitat and, in turn, maintaining or expanding current population levels.     

Nest predation and habitat change interact to influence Siberian jay numbers

We studied Siberian jays, breeding in northern Sweden, to examine the potential for interactions between nest predation and reduced vegetation heterogeneity around nest sites to cause a decrease in jay numbers. Parent behaviour and nests are highly cryptic in the species. Our 12-year data showed, however, that nests had a probability of only 0.46 to be successful and produce at least one nestling. Nest predation was intense and a main cause of nest failure. All predators that could be identified were visually oriented hunters, mostly other corvids able to colonize taiga forest only close to human settlements. Consistent with the idea that predators used visual cues, nest predation increased with parental activity, which suggests that predators used parental provisioning trips to locate nests. Furthermore, a reduction in daily nest survival rates with decreasing amount of nesting cover was more pronounced in areas with high corvid activity as predicted when cover mediates the hunting efficiency of visual oriented predators. Declining temperatures interacted with the effects of habitat characteristics to further reduce daily nest survival rates suggesting that parents were not able to increase nest visitation rates to satisfy the higher energy demands of their nestlings without endangering the nest. Our results identify a mechanism through which predation and human-induced reduction in nesting cover on a larger scale may interact to cause a reduction in Siberian jay numbers larger than expected from habitat loss alone.     

Nesting failure in Finnish Northern Goshawks Accipiter gentilis: incidence and cause

Habitat composition is an important factor influencing nesting failure probability in birds. However, although various habitat effects such as fragmentation and edge density are known to have clear negative effects on the breeding success of passerines, the role that habitat composition plays in shaping nesting failure patterns among other avian groups is less well known. We studied nesting failure in a large forest raptor, the Northern Goshawk Accipiter gentilis , during the period 1999–2003 in Finland. Illegal human persecution was found to constitute a major cause of failure among nests where cause could be determined accurately (comprising c . 60% of all failed nesting attempts). Egg predation by corvids and nestling predation by Eagle Owls Bubo bubo were also common. However, the exact cause of nesting failure could not be inferred in every case. Overall, the degree of initial parental investment (clutch size and egg volume) was significantly smaller in nests that failed than in nesting attempts that were successful. This did not apply to nests that were destroyed by humans, in which investment was at a level equal to nests that were successful. Although the probability that a nesting attempt would fail was also related to small-scale nest concealment, nesting failure probability was not associated with main prey density or several measures describing territorial habitat composition at larger scales. Small initial parental investment, not habitat composition, is thus the major correlate of nesting failure in Goshawks.     

Prevalence of nest predators in a sub-Arctic ecosystem

High nest loss is an important driver of gallinaceous bird population dynamics. Identifying factors determining the spatial distribution of potential nest predators and thereby indirectly risk of nest losses is therefore essential. The aim of this 1-year study was to estimate relative predation rates on artificial ground nests in willow ptarmigan (Lagopus lagopus) habitats, along replicate altitudinal gradients (transects, n?=?60) spanning from sub-Arctic birch forest to the low-alpine tundra in three locations in northern Norway. In each transect, one artificial nest (track board) was placed in three different habitats: (1) birch forest, (2) edge between birch forest and low-alpine tundra and (3) low-alpine tundra. Total predation rates over all habitats within locations ranged from 47.4% to 77.5% and did not vary systematically in space and time. The average predation rate by avian predators was consistently high (58%), and mammalian predation rate was consistently low (5.6%). The consistently high level of predation inflicted by birds was mainly due to omnipresent corvids, especially the hooded crow (Corvus cornix). Analysis of species-specific predation rates showed that habitat and location effects were insignificant for all species, except for raven (Corvus corax) that showed clearly higher predation in one of the locations. The results indicate that from the perspective of the spatial distribution of potential nest predators in sub-Arctic birch forest, ground nesting birds like willow ptarmigan should not be expected to be selective with respect to nesting habitat in the ecotone between birch forest and the low-alpine tundra.     

Landscape and habitat affect frequency of artificial duck nest predation by native species,but not by an alien predator

Annual Finnish breeding duck surveys over the last 30 years show declining abundance among several species and greater declines on eutrophic waters than oligotrophic lakes. It has been suggested that habitat-related differences in the rate of increase in predation pressure is a potential explanation for contrasting duck population trajectories between habitats. We assessed potential duck nest predation risk and predator presence in various duck breeding habitats in Finland and Denmark by monitoring 333 artificial duck nests with wildlife cameras during 2017–2019. Predation rates differed between landscapes and habitats: nest predation rate and predator diversity were lowest in forested and highest in agricultural landscapes. Forest nests further from water bodies survived better than nests around shorelines of permanent lakes. Of the 16 different predator species detected, the most common were Eurasian magpie (Picapica), hooded crow (Corvus corone) and raccoon dog (Nyctereutes procyonoides). While predation by specific native predator species was typically associated with particular habitats and landscapes, the alien raccoon dog appeared to be a true habitat generalist, ubiquitous and common across all habitats and landscapes. Based on these results, the higher duck nest predation pressure along shorelines, especially in agricultural landscape lakes, due to increased diversity and abundance within the predator community, may contribute to the declining population trends of ducks.     

Nesting habitat characteristics of Marbled Murrelets occurring in near‐shore waters of the Olympic Peninsula,Washington

Marbled Murrelets (Brachyramphus marmoratus) are listed as threatened in the portion of their range extending from British Columbia to California due to loss of nesting habitat. Recovery of Marbled Murrelet populations requires a better understanding of the characteristics of their nesting habitat in this part of their range. Our objective, therefore, was to describe their nesting habitat in Washington State and Vancouver Island, British Columbia. We captured Marbled Murrelets from 2004 to 2008, fitted them with radio transmitters, and followed them to nests (N = 20). We used Cohen's unbiased d effect size to assess differences between forest plots surrounding nest sites and nearby control sites (N = 18). Nest sites had less canopy cover of the dominant conifers and fewer, but larger, trees than control sites. Nest sites also had greater percentages of trees with platforms >10 cm diameter and >15 cm diameter, and more platforms of these sizes than control sites. The mean diameter at breast height of nest trees was 136.5 cm (range = 84–248 cm) and all but one nest was in dominant or co‐dominant tree species. At the landscape scale, we used vegetation maps derived from remotely sensed data and found greater canopy cover, higher density of mature trees, more platforms >10 cm/ha, and more old‐growth habitat at nest sites than at random sites. Our findings suggest that, at the site scale, nesting Marbled Murrelets selected the most suitable features of forest structure across expansive potentially suitable habitat. Our landscape‐scale analysis showed that habitat features in nesting stands differed from those features in available stands in the murrelet's range in Washington. We also found that stands with nests were less fragmented than available forest across murrelet range. All nest sites of radio‐tagged birds in Washington were in protected areas in mostly undisturbed forest habitat. Conservation of these areas of inland nesting habitat will be critical to the recovery of Marbled Murrelet populations.     

Ability to assess nest predation risk in secondary hole-nesting birds: an experimental study

Because nest predation is the major source of nesting mortality in birds, site-specific predation risk may play an important role in determining birds' ability to select nest sites that reduce predation risk. This possibility has not been adequately tested. Here we report on 5-year experiments by which we studied, independently from birds' earlier experience with specific nest boxes, both the selection and predation risk of nest sites in the common goldeneye (Bucephala clangula). New, previously unoccupied nest boxes were erected in two habitat types on three study areas. Experimentally measured predation risk in the nest boxes varied between 0 and 1.0, i.e. goldeneye females could select a nest site along a wide gradient of possible predation-risk values. We did not find a difference in predation risk between occupied and unoccupied nest boxes, nor was the order of nest box occupation associated with predation risk. A power analysis revealed that our test had reasonably high power to reject a false null hypothesis. Our results suggest that common goldeneye females likely have not evolved an ability to assess predation risk of new, previously unoccupied nest sites.     

Nest predation in forest birds: influence of predator type and predator's habitat quality

We used the introduction of a generalist nest predator, the red squirrel Tamiasciurus hudsonicus, and of a large herbivore, the Sitka black-tailed deer Odocoileus hemionus sitkensis, to the islands of Haida Gwaii (Queen Charlotte Islands, British Columbia, Canada) to study how predator assemblage and habitat quality and structure influenced nest predation in forest birds. We compared losses of natural nests to predators on islands with and without squirrels. We selected nine islands with or without squirrel or deer and used 506 artificial nests put on the ground or in shrubs to further analyse variation of nest predation with predator assemblage and habitat quality for the predators. For both natural and artificial nests predation risk was higher in presence of squirrels. But predation risk varied within island categories. In presence of squirrels it was highest in stands with mature conifers where it fluctuated from year to year, in response to fluctuations in squirrel abundance. Vegetation cover around the nest had little effect on nest predation by squirrels. Where squirrels were absent, nest predation concentrated near predictable food sources for corvids, the main native predators, and increased with decreasing vegetation cover, suggesting that removal of the vegetation by deer increased the risk of predation by native avian nest predators that use visual cues. Predation risk in these forests therefore varies in space and time with predator composition and with quality of the habitat from the predators' perspective. This temporal and spatial variation in predation risk should promote trade-offs in the response of birds to nest predation, rather than fine-tuned adaptations to a given predation pattern.     

Are house sparrow populations limited by the lack of cavities in urbanized landscapes? An experimental test

Current urban policies are associated with deep changes in urban structures, which may impoverish urban biodiversity. A major concern is the disappearance of nesting sites for wild vertebrate species living in urban areas. New urban structures without any cracks or cavities may especially preclude cavity nesters from breeding in cities and they may cause population declines. In that context, we experimentally investigated this question in an urban exploiter bird species (the house sparrow Passer domesticus), which is dramatically declining in most European cities. To test if the lack of cavities is limiting house sparrow populations in urban areas, we equipped 11 sites along an urbanization gradient with nest boxes and we then evaluated the rate of occupancy of these nest‐boxes. This urbanization gradient was characterized by very rural places (isolated farms) and moderately urbanized areas (town of medium size, i.e. 60 000 inhabitants). Surprisingly, rural nest boxes were more occupied than urban ones, suggesting that cavity availability is probably more constraining in rural areas relative to urban ones. Therefore, our study suggests that urban house sparrow populations are probably not constrained by a lack of nesting sites in medium size cities with urban designs similar to our city of interest (Niort, western France). This hypothesis definitely needs now to be tested in further urban landscapes (e.g. large cities and urban landscapes with other architecture and management policies).     

Nesting success and within-season breeding dispersal in the Orange-breasted Sunbird Anthobaphes violacea

Nest predation is a primary cause of nesting mortality for many bird species, particularly passerines. Nest location can affect predation, and it has also been demonstrated that predation risk can alter nest site selection. Birds can limit predation risk by selecting specific habitat characteristics; by changing nest site characteristics between attempts; and by dispersing between nesting events. Here we report breeding data from a population of Orange-breasted Sunbirds Anthobaphes violacea (L.), for a single breeding season in the Jonkershoek Nature Reserve, South Africa. Neither shrub type nor nest height was found to affect the outcome of a nest. For subsequent breeding attempts, birds were not more likely to change the type of shrub in which they nested after a predation event than when the attempt was successful, nor did they change the height of their nest. However, we found that the distance between a nest and the subsequent one was significantly shorter after a successful nest than after an unsuccessful one. We interpret this as an adaptive strategy to avoid predation.     

Nesting Habitat Creation Enhances Recruitment in a Predator‐Free Environment: Malaclemys Nesting at the Paul S. Sarbanes Ecosystem Restoration Project

Aquatic turtles worldwide are plagued with habitat loss due to development and shoreline alteration that destroys the terrestrial–aquatic linkage which they must cross to reproduce successfully. Furthermore, nesting habitat loss can concentrate nesting, increasing nest predator efficiency. We describe how the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island created nesting habitat for Malaclemys terrapin (Diamondback Terrapin), and document nesting success in response to construction progress and the absence of raccoons and foxes, the primary nest predators. We monitored terrapin nests throughout the nesting seasons from 2002 to 2011 to determine overall and within‐nest survivorship. Female terrapins began nesting on the restoration project within 1 year but planned construction during the study eliminated some nesting areas and opened previously inaccessible areas. Overall, nest survivorship was considerably higher than mainland nesting areas due to the absence of raccoons and foxes on the island and within‐nest survivorship was similar. Egg size, hatchling size, and the frequency of shell scute anomalies were similar to other terrapin populations, suggesting normal developmental conditions on the island. We documented annual variation in hatchling size that correlated negatively with mean air temperature during the incubation season. Our results indicate that restored or created isolated island habitat can be located rapidly by terrapins and can become an important source of recruitment in regions where nesting habitat is limited and predation is high. Poplar Island illustrates how habitat loss and restoration can affect turtle populations by revealing the changes in nesting patterns and success in newly created, predator‐free habitat.     

Bluehead chub nesting activity: a potential mechanism of population persistence in degraded stream habitats

Aquatic biodiversity continues to decline as humans modify the landscape, mainly because of stream habitat alterations and loss caused by urban development. Bluehead chubs may mitigate some effects of instream habitat degradation by providing clean gravel substrate via their spawning nests. We used path analysis, an extension of multiple linear regression, to explore the relationships among instream habitat degradation, adult chub abundance, chub nesting activity, and chub reproductive performance. Age-0 chub abundance was best explained by small adult abundance and nest abundance. Habitat disturbance indirectly and negatively influenced age-0 chub abundance through adult chubs and nest abundance. Percentages of pool and run habitat also had indirect negative effects on age-0 chub abundance. Several metrics of chub nesting activity (nest density [proportion of substrate occupied by nests], average nest size, and number of nests) were explained by both adult chub abundance and nesting site conditions. Variability among stream systems described significant variation in adult chub abundance and nesting characteristics and, if unaccounted for, would have resulted in large unexplained variability. Chub nesting activity served as a link between habitat degradation, adult chub abundance, and their reproductive performance. Our study provides preliminary evidence that bluehead chubs’ nesting activity may be a mechanism of their persistence in degraded stream reaches. We recommend confirmatory studies through in-stream manipulative experiments.