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Predators can significantly limit the amount of available habitat for vulnerable prey. Encouraging spatial segregation of predators and prey through habitat management prescriptions may be a useful tool to increase productivity and abundances of prey species of conservation concern. We estimated the total area of low‐risk nesting habitat by interacting predator habitat selection models with northern bobwhite (Colinus virginianus) nest‐site selection models. We used trail cameras, transect sampling, spotlighting transects, and incidental tracking to survey and map occurrences of mesopredators at a site in western Oklahoma, USA. We created broad‐scale resource selection function models for bobwhite nest‐site and mesopredator habitat selection using generalized linear models to create maps of occurrence probability in ArcGIS. Bobwhite nests were more likely to be depredated in areas of high selection by coyotes (Canis latrans) and striped skunks (Mephitis mephitis) compared to areas with low mesopredator selection. Approximately 392 ha of bobwhite nesting habitat (17%) had low probabilities of selection by both coyotes and striped skunks. Our results demonstrate the need for incorporating species' interactions into estimations of available habitat. Based on the total area of highly selected cover by northern bobwhite, approximately 29% of the study area would have been deemed suitable for nesting. However, only 5% of that area is predicted to have a low predation risk.

Alexander Skutch hypothesized that increased parental activity can increase the risk of nest predation. We tested this hypothesis using ten open-nesting bird species in Arizona, USA. Parental activity was greater during the nestling than incubation stage because parents visited the nest frequently to feed their young during the nestling stage. However, nest predation did not generally increase with parental activity between nesting stages across the ten study species. Previous investigators have found similar results. We tested whether nest site effects might yield higher predation during incubation because the most obvious sites are depredated most rapidly. We conducted experiments using nest sites from the previous year to remove parental activity. Our results showed that nest sites have highly repeatable effects on nest predation risk; poor nest sites incurred rapid predation and caused predation rates to be greater during the incubation than nestling stage. This pattern also was exhibited in a bird species with similar (i.e. controlled) parental activity between nesting stages. Once nest site effects are taken into account, nest predation shows a strong proximate increase with parental activity during the nestling stage within and across species. Parental activity and nest sites exert antagonistic influences on current estimates of nest predation between nesting stages and both must be considered in order to understand current patterns of nest predation, which is an important source of natural selection.

Increasing nest survival by excluding predators is a goal of many bird conservation programs. However, new exclosure projects should be carefully evaluated to assess the potential risks of disturbance. We tested the effectiveness of predator exclosure fences (hereafter, fences) for nests of critically endangered Florida Grasshopper Sparrows (Ammodramus savannarum floridanus) at a dry prairie site (Three Lakes; 2015-2018) and a pasture site (the Ranch; 2015-2016) in Osceola County, Florida, USA. We installed fences at nests an average of 8 days after the start of incubation, and nest abandonment after fence installation was rare (2 of 149 installations). Predation was the leading cause of failure for unfenced nests at both sites (48-73%). At Three Lakes, nest cameras revealed that mammals and snakes were responsible for 61.5% and 38.5% of predation events, respectively, at unfenced nests. Fences reduced the daily probability of predation (0.016 for fenced nests vs. 0.074 for unfenced nests). The probability that a fenced nest would survive from discovery to fledging was more than double that of unfenced nests (60.4% vs. 27.7%). However, we found no difference in daily nest survival at the Ranch between the year before nests were fenced (2015; 0.874) and the year when all but one nest were fenced (2016; 0.867) because red imported fire ants (Solenopsis invicta) were responsible for 86% of predation events at fenced nests at the Ranch. The use of cameras at fenced nests revealed that site-specific differences in nest predators explained variation in fence efficiency between sites. Our fence design may be useful for other species of grassland birds, but site-specific predator communities and species-specific response of target bird species to fences should be assessed before installing fences at other sites. Incrementar la supervivencia de los nidos mediante la exclusión de depredadores es uno de los objetivos de muchos programas de conservación de aves. Sin embargo, nuevos proyectos de exclusión deben ser evaluados cuidadosamente para determinar el riesgo potencial del disturbio. Evaluamos la efectividad de cercas excluyentes de depredadores (cercas de aquí en adelante) para nidos del críticamente amenazado Ammodramus savannarum floridianus en un sitio de pradera seca (Three Lakes; 2019-2018) y un sitio de potrero (the Ranch; 2015-2016) en el condado de Osceola, Florida, USA. Instalamos cercas en los nidos en promedio ocho días después del inicio de la incubación y el abandono del nido después de la instalación del acerca fue raro (2 de 149 instalaciones). Depredación fue la causa principal de fracaso de los nidos sin cercas en los dos sitios (60.4% vs. 27.7%). Sin embargo, no encontramos diferencias en la supervivencia diaria de los nidos en \"the Ranch\" entre los años anteriores a la instalación de las cercas (2016; 0.874) y el año en el que todos los nidos excepto uno fueron cercados (2016; 0.867), debido a que las hormigas de fuego (Solenopsis invicta) no nativas fueron responsables por el 86% de los eventos de depredación en \"the Ranch\". El uso de cámaras en nidos cercados revelaron que las diferencias especificas al sitio en los depredadores de nidos explican la variación en la eficiencia de las cercas entre los sitios. Nuestro diseño de las cercas puede ser útil para otras especies de aves de pastizales, pero comunidades de depredadores especificas a los sitios y respuestas especificas a las especies que son objetivo para la instalación de cercas deben ser determinadas previo a la instalación de las cercas en otros sitios.

Visible sign produced by nesting turtles has been suggested to be a cue used by foraging raccoons (Procyon lotor) to locate nests. Experiments investigating the potential for reducing turtle nest predation by eliminating these surface markings by broom sweeping nesting areas were conducted at 2 Graptemys nesting sites along the lower Wisconsin River in Iowa County, Wisconsin, during 2013 and 2014. Ninety-five percent of the natural nests in unswept control areas (n = 20) and all of the nests in swept treatment areas (n = 16) were depredated by raccoons within 24 hrs. Supplemental artificial nests with refilled manufactured cavities but lacking potential olfactory turtle- or egg-related cues were also excavated by raccoons within similar time lines (97% within 24 hrs) and at high rates both when unswept (100%, n = 20) and when swept (95%, n = 19). However, artificial facsimiles of the surface markings left by nesting turtles, lacking cavities, were disturbed less frequently (26%, n = 19). Findings suggest that broom sweeping was ineffective because the location cues used by raccoons to find newly constructed nests are not primarily visual but olfactory and related to soil profile disturbance, possibly via the microbial metabolite geosmin.

Summary Nest structure is thought to provide benefits that have fitness consequences for several taxa. Traditionally, reduced nest predation has been considered the primary benefit underlying evolution of nest structure, whereas thermal benefits have been considered a secondary or even non‐existent factor. Yet, the relative roles of these factors on nest structures remain largely unexplored. Enclosed nests have a constructed or natural roof connected to sides that allow a restricted opening or tube entrance that provides cover in all directions except the entrance, whereas open nests are cups or platforms that are open above. We show that construction of enclosed nests is more common among songbirds (Passeriformes) in tropical and southern hemisphere regions than in north temperate regions. This geographic pattern may reflect selection from predation risk, under long‐standing assumptions that nest predation rates are higher in southern regions and that enclosed nests reduce predation risk compared with open cup nests. We therefore compared nest predation rates between enclosed vs. open nests in 114 songbird species that do not nest in tree holes among five communities of coexisting birds, and for 205 non‐hole‐nesting species from the literature, across northern temperate, tropical, and southern hemisphere regions. Among coexisting species, enclosed nests had lower nest predation rates than open nests in two south temperate sites, but not in either of two tropical sites or a north temperate site. Nest predation did not differ between nest types at any latitude based on literature data. Among 319 species from both our field studies and the literature, enclosed nests did not show consistent benefits of reduced predation and, in fact, predation was not consistently higher in the tropics, contrary to long‐standing perspectives. Thermal benefits of enclosed nests were indicated based on three indirect results. First, species that built enclosed nests were smaller than species using open nests both among coexisting species and among species from the literature. Smaller species lose heat fastest and thereby may gain important thermal benefits from reduced convective cooling. Second, eggs were warmed by parents for less time in species with enclosed nests, as can be expected if egg cooling rates are slower. Finally, species using enclosed nests exhibited enhanced growth of mass and wings compared with species using open nests, suggesting reduced thermoregulatory costs allowed increased energy for growth. Enclosed nests may therefore provide more consistent thermal than nest predation benefits, counter to long‐standing perspectives. A lay summary is available for this article. Lay Summary

Many birds add anthropogenic material to the nest. This may increase the probability of total failure because the nest may be more easily located by enemies. However, the material may also induce a threat response in predators sceptical to new objects (the Neophobia Hypothesis). We presented artificial nests on the ground each with two quail eggs, in territories of Eurasian magpies Pica pica in spring. Some nests were decorated with pieces of white plastic while others were not (control). When nests of both types were presented simultaneously on a magpie territory and only a meter apart, depredation started later for nests with plastic than for control nests, supporting the Neophobia Hypothesis. When a trial was repeated on the same territory later in the season, predation started sooner. However, this was probably caused by habituation to the experimental set up (wildlife camera and artificial nests) and not to the plastic itself because in the repeated trials, the eggs in the nests with plastic were still depredated later than the eggs in the control nests. The nests were not depredated sooner if similar experiments had been conducted on the same territory in the previous year. The onset of depredation was no sooner in territories that initially contained plastic close to the magpie nest than in territories containing no plastic. Finally, when only a single nest was presented on a magpie territory, the time lag until depredation was similar for decorated and control nests, suggesting that the increased detectability caused by decoration outweighed the fear response to the plastic. We conclude that the Neophobia Hypothesis may be relevant to natural cases including birds nesting in habitats containing anthropogenic material and to circumstances with repeated visits by corvids to bird nests, such as in a bird colony. Many birds add anthropogenic material to the nest. We presented artificial nests on the ground in spring, each with two quail eggs and half of them decorated with pieces of white plastic. The plastic induced a neophobic response in territorial European magpies, reducing the rate of nest predation.

Many animals build new nests every breeding season instead of saving time by reusing old ones. One hypothesis is that nest reuse leads to increased predation risk if predators memorize nest locations and revisit these sites. Here we examine patterns in the prevalence of facultative nest reuse. Further, we relate nest reuse and timing of breeding to nest predation risk, clutch size and nestling survival. We analyse 1570 breeding attempts of the Eurasian sparrowhawk (Accipiter nisus) from Denmark (1977–1997) and from two sites in Norway (1985–2017). The probability of reuse varied between study areas, increased in replacement clutches, and was lower in adults compared to 1-year-old breeders. Pairs reusing nests laid their first egg on average 2.6 ± 1.0 SE days later than those building new nests, suggesting they are compensating for an already late breeding schedule. Indeed, reuse increased nest predation risk, but we discovered no other productive effects of reuse. In non-predated nests, late breeders had both smaller clutches and lower nestling survival. We propose that nest predation is a contributing driver to the behaviour of building a new nest each year, whereas nest reuse is a strategy to compensate for delayed onset of breeding, mainly used by inexperienced males.

1. Landscape composition around bird nests can strongly influence nest predation, a major cause of reproductive failure for many species. Understanding this relationship may improve the effectiveness of management actions aimed at reducing predation. Despite attempts to link landscape composition to nest predation, consistent patterns have proven elusive, likely because studies often examine only one landscape scale, thereby overlooking scale-specific interactions between predators and landscape features. 2. To demonstrate the value of incorporating scale-dependence when connecting nest predation to landscape composition, we identified predators and analysed predator-specific patterns among land cover types at four scales (200 m, 500 m, 1 km, 2.5 km). We video monitored 468 nests of 22 shrub-nesting bird species, documented 212 predation events, and modelled relationships between landscape composition and predation by seven common predators. 3. The direction and strength of predator-specific relationships varied among land cover types and scales. No single scale best predicted predation by all predators, though effects appeared to be stronger at larger scales. Two ecologically similar predators (fox snakes [Pantherophis vulpinus] and black ratsnakes [P. obsoletus]) showed contrasting relationships with different land cover types and one commonly cited predator (raccoon [Procyon lotor]) showed positive and negative links to developed cover across scales. 4. Synthesis and applications. Our results illustrate that elucidating the complex relationships between different nest predator species and the landscape composition surrounding nests requires the incorporation of scale-dependence. Although such an undertaking may involve intensive nest monitoring to identify predators, it can provide managers with a more complete understanding of the linkages between predation and the landscape surrounding nests. With this knowledge, managers could employ structured decision making in an adaptive management framework to identify optimal strategies that address nest predation and allow them to confront potentially unexpected changes in predation patterns following management actions. Ultimately, by acknowledging that predator species differ in their relationships with landscape composition among different landscape scales, and incorporating this fact into future research, we can improve our ability to focus management on the habitats and scales most likely to impact predators of interest.

The alternative prey hypothesis (APH) states that temporally synchronous population fluctuations of microtine rodents and other small herbivores are caused by generalist predators that show functional and numerical responses to the abundance of microtines. This would lead to an increased predation of alternative prey in the low phase of the microtine population fluctuations. One candidate for such a predator is the tree-climbing pine marten (Martes martes), which includes bird eggs in its diet, among them eggs of the cavity-nesting boreal owl (Aegolius funereus). I used long-term data to test whether pine marten predation of boreal owl eggs in nest boxes varied as predicted by the APH. The probability of predation of owl nests situated < 45 km from a site where microtines were trapped in spring during four decades increased with microtine trapping index, which is opposite to the prediction from the APH. As the data set was limited to one nest per box, I extended it spatially and temporally using the clutch size of each boreal owl nest as a proxy for the actual microtine abundance at the site. The probability of nest predation increased with clutch size. However, the effects of microtine index and owl clutch size became non-significant when I controlled for habitat, and in particular cavity age, which had an overriding effect. The increase in predation probability with cavity age suggests that the long-term spatial memory of pine marten is an important factor in the pattern of its nest predation in tree cavities.

Predation is the main cause of nest failure among birds and, therefore, a strong selective agent. To fully understand patterns of nest predation, determining the identities of nest predators is crucial. Information about nest predators in the Neotropics, however, is largely anecdotal and not easily accessible in the literature. Our objective was to search the literature and compile a list of the known predators of nests in the Neotropics. We identified 256 species belonging to 67 families of birds, reptiles, mammals, and arthropods as nest predators. Families with at least 10 species of identified nest predators included Colubridae, Accipitridae, Corvidae, Ramphastidae, Falconidae, Furnariidae, Icteridae, and Didelphidae. Species in the first five of these families, plus the family Cebidae, predated nests of at least 30 species of birds. Many species not included on our list are also likely nest predators, e.g., 79 species identified as nest predators in the Nearctic that also occur in the Neotropics, but have not yet been confirmed as predators there. Increased use of video technology in the future should lead to an increase in the numbers of nest predators identified, particularly those that are nocturnal. By determining which species on our list occur in a given study area, researchers can now consider the likely nest predators in their study areas when designing hypotheses and conservation plans. Depredación es la principal causa de fracaso de nido en las aves y por lo tanto es un fuerte agente de selección. Para comprender completamente los patrones de depredación de nidos, es crucial determinar la identidad de los depredadores. La información sobre los depredadores de nidos en el Neotrópico, sin embargo, es principalmente anecdótica y de difícil acceso en la literatura. Nuestro objetivo fue realizar una búsqueda en la literatura y compilar una lista de depredadores de nidos conocidos en el Neotrópico. Identificamos 256 especies pertenecientes a 67 familias de aves, reptiles, mamíferos y artrópodos como depredadores de nidos. Las familias con al menos 10 especies identificadas como depredadores de nidos incluyeron Colubridae, Accipitridae, Corvidae, Ramphastidae, Falconidae, Furnariidae, Icteridae y Didelphidae. Las especies en las primeras cinco de estas familias más la familia Cebidae, fueron responsables por la depredación de nidos de al menos 30 especies de aves. Muchas especies no incluidas en nuestra lista son probablemente también depredadores de nidos, por ejemplo, 79 especies identificadas como depredadores en el Neártico que también ocurren en el Neotrópico pero que no han sido confirmados como depredadores en esta región. El incremento en el uso de tecnología de video en el futuro debería promover un incremento en el número de depredadores identificados, particularmente aquellos que son nocturnos. Mediante la determinatión de las especies de nuestra lista que ocurren en un área de estudio en particular, los investigadores pueden ahora considerar probables depredadores de nidos en sus áreas de estudio en el momento del diseiño de hipótesis y planes de conservación.