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Cavity-nesting birds and mammals exhibit species-specific nest-site selection for tree characteristics and cavity dimensions. Although trees and their cavities change as they age, with trees becoming softer and cavities becoming larger, it is not known how their value as nesting resources varies with age. In the context of wildlife and forest management, we investigated the relative value of generating a supply of fresh cavities, which are thought to be of high quality, versus protecting cavities as they age and expand in interior volume. For 21 years (1995-2016), we monitored the formation and occupancy of tree cavities used by >30 species of birds and mammals in interior British Columbia, Canada. Cavity occupancy by secondary users was highest 1 year post-excavation (53%), then declined to 40% after 2 years, remained at 33 ± 7% (SD) between 3 and 16 years of age, and increased to 50% use from 17–20 years post-excavation. Excavators that reused cavities (woodpeckers [Picidae], nuthatches [Sitta spp.]) strongly selected 1- and 2-year-old cavities, large-bodied non-excavators (ducks, raptors, squirrels) selected mid-aged cavities, and mountain bluebirds (Sialia currucoides) and tree swallows (Tachycineta bicolor) selected most strongly for the oldest cavities. Cavities created in living aspen trees (Populus spp.), especially those excavated by northern flickers (Colaptes auratus), maintained high occupancy by secondary users across cavity age, and provided the bulk of cavities used in this system. Altogether, these results show that a diverse excavator community is needed to generate a supply of fresh cavities in the ecosystem, and retention of the mid-aged and older cavities will help support larger species.

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.

1. Nesting birds can be vulnerable to predation. Wildlife managers sometimes manipulate predator communities to enhance avian productivity and abundance. Managers need to know the predation risk from different predator species responsible for nest failures to maximize success. This issue is especially important when considering reductions in only a part of the predator community in complex ecosystems. 2. We conducted a 7-year crossover experiment at four study sites to examine the effect of mesomammalian predator control on nest success of northern bobwhite Colinus virginianus in the southeastern USA. Nests were monitored using 24-h near-infrared video. We hypothesized that nest failures caused by different predator guilds may not be independent and may lead to compensation by other predators as one predator guild was reduced. 3. We compared levels of bobwhite nest predation by mesomammals, snakes and other predators in years with and without mesomammal control. 4. Control of mesomammal predators reduced the levels of mesomammal nest predation, but predation levels by snakes and other predators increased such that total nest mortality was not reduced. Nest mortality among predator groups was best described as compensatory, and total nest mortality differed among sites. 5. Synthesis and applications. Our findings suggest that reductions in predation risk from one predator guild can be compensated by an increased risk from other predators in complex ecosystems. Predator removal within one group may not translate to additive increases in overall nest success, but rather results in shifts in the identity of predators responsible for nest failures. Management efforts focused on manipulating predator communities to enhance avian reproduction are encouraged to examine cause-specific nest fates to determine the effectiveness of predator reduction programmes.

ABSTRACT Environmental DNA (eDNA) has transformed biodiversity monitoring, especially in aquatic environments; yet, its application in terrestrial habitats remains limited. In arid regions, artificial waterbodies, such as farm dams and water troughs, serve as essential resources for wildlife and offer a promising but underutilised opportunity for eDNA‐based detection. Here, we designed and validated a highly sensitive, species‐specific quantitative PCR (qPCR) assay to detect the nationally threatened southern squatter pigeon (Geophaps scripta scripta). We validated the qPCR assay in the field by successfully detecting the target species at extremely low DNA concentrations (1 × 10−7 ng/μL; r2 = 0.992) using both active syringe and passive filtration methods across multiple farm dams and water troughs on a 20,000‐ha cattle property in northern Australia. To complement eDNA analysis, we also undertook standardised 20‐min, 2‐ha bird surveys at these sites. Positive detections were recorded at both trough and dam sites during the austral tropical dry season. Notably, whilst eDNA detections and visual bird counts aligned in terms of the number of occupied sites, their exact locations did not always coincide, highlighting the complementary nature of these two monitoring techniques. This assay represents a significant advancement in the conservation of this threatened ground‐nesting species, demonstrating that eDNA sampling at artificial waterpoints is a viable tool for monitoring terrestrial fauna in remote, semi‐arid landscapes.

Assumptions that populations of cavity-nesting birds are limited by access to nest sites have largely been based on anecdotal reports or correlative data. Nest-box-addition experiments or tree-cavity-blocking experiments are potentially rigorous ways to investigate how densities of breeding birds are affected by access to nest cavities. Experimental evidence indicates that natural tree holes are limited in human-altered landscapes, but the possibility that cavity nests are limited in old growth (unmanaged) forests is less clear. I reviewed 31 nest-cavityremoval or addition experiments conducted with 20 species of cavity-nesting birds in mature forests. Of these 31 experiments conducted with a variety of different species of birds, only 19% reported statistically significant changes in breeding densities. However, none of these studies included data about the reproductive history of individuals colonizing the boxes (i.e., whether birds using the boxes would have otherwise been floaters or that birds excluded from blocked cavities on the plots did not simply move elsewhere), so they provided no strong evidence that the number of breeding pairs was limited by availability of nest sites at the population scale. Although some studies indicate that nest sites are limited at local (plot) scales in old growth forests, there is still little empirical evidence for nest-site limitation at the population- and landscape-level in mature, unmanaged forests. I review the challenges in designing and interpreting box-addition experiments and highlight the main gaps in knowledge that should be targeted in the future. El asumir que poblaciones de aves que anidan en cavidades están limitadas por el acceso a lugares para anidar ha estado basado mayormente en informes anecdóticos o datos correlativos. Los experimentos en donde se suplen cajas para anidar o se obstruyen cavidades en árboles son formas potenciales y rigurosas para determinar como la densidad de aves reproductivas es afectada por el acceso a cavidades para el anidamiento. La evidencia experimental indica que las cavidades naturales para anidar están limitadas en paisajes alterados por los humanos, pero la posibilidad que las mismas están limitadas en bosques maduros esta menos clara. Revisé 31 experimentos donde se proveían o se removían cavidades, llevados a cabo en 20 especies de aves que anidan en cavidades en bosques maduros. De estos 31 experimentos, llevados a cabo con una gran variedad de especies, solo el 19% informaron cambios estadísticamente significativos en la densidad reproductiva. Sin embargo, ninguno de estos estudio incluyó información sobre la historia reproductiva de individuos colonizando cajas de anidamiento (ej. si las aves utilizando dichas cajas eran individuos flotadores o si las aves excluidas de cavidades no se movían a áreas nuevas), y no proveyeron evidencia contundente de que el número de parejas reproductivas estuviera limitada por la disponibilidad de lugares para anidar a escala poblacional. Aunque algunos estudios indican que los lugares de anidamiento están limitados a nivel local o en parcelas particulares, en bosques maduros todavía existe poca evidencia empírica referente a limitación de lugares de anidamiento al nivel poblacional o del paisaje en bosques maduros no manejados. Revise los retos en el diseño e interpretación de experimentoas donde se añaden cajas de anidamiento y señale las lagunas principales en la documentación que debe ser el objetivo de estudios futuros.

Tree cavities are a vital multi-annual resource used by cavity-nesting birds and mammals for nesting and shelter. The abundance of this resource will be influenced by the rates at which cavities are created and destroyed. We applied the demographic concepts of survival and longevity to populations of tree holes to investigate rates of loss for cavities in three tree species, as well as how characteristics of nest trees, habitat type, and species of excavator affected the persistence of tree cavities in trembling aspen, Populus tremuloides (95% of cavities were in aspen trees), in interior British Columbia, Canada. By modeling survival of 1635 nesting cavities in aspen over a time span of 16 years, we found that the decay stage of the nest tree was the most important factor determining cavity longevity. Cavities in trees with advanced decay had a relatively short median longevity of 7 years (95% CI 6-9 years), whereas those in living trees had a median longevity of more than 15 years. We found that cavity longevity was greater in continuous forest than in aspen grove habitat. Interestingly, cavities formed by weak excavators survived as long as those created by Northern Flickers ( Colaptes auratus ), despite occurring in more decayed tree stems. Thus, weak excavators may be selecting for characteristics that make a tree persistent, such as a broken top. Our results indicate that retention of cavities in large, live aspen trees is necessary to conserve persistent cavities, and that cavity longevity will have a large effect on the structure and function of cavity-using vertebrate communities.

The nests of ground‐nesting birds rely heavily on camouflage for their survival, and predation risk, often linked to ecological changes from human activity, is a major source of mortality. Numerous ground‐nesting bird populations are in decline, so understanding the effects of camouflage on their nesting behavior is relevant to their conservation concerns. Habitat three‐dimensional (3D) geometry, together with predator visual abilities, viewing distance, and viewing angle, determine whether a nest is either visible, occluded, or too far away to detect. While this link is intuitive, few studies have investigated how fine‐scale geometry is likely to help defend nests from different predator guilds. We quantified nest visibility based on 3D occlusion, camouflage, and predator visual modeling in northern lapwings, Vanellus vanellus, on different land management regimes. Lapwings selected local backgrounds that had a higher 3D complexity at a spatial scale greater than their entire clutches compared to local control sites. Importantly, our findings show that habitat geometry—rather than predator visual acuity—restricts nest visibility for terrestrial predators and that their field habitats, perceived by humans as open, are functionally closed with respect to a terrestrial predator searching for nests on the ground. Taken together with lapwings' careful nest site selection, our findings highlight the importance of considering habitat geometry for understanding the evolutionary ecology and management of conservation sites for ground‐nesting birds. We used 3D scanning and color‐calibrated images to investigate the effects of local geometry on ground‐nesting bird site selection and camouflage. We found that lapwings, Vanellus vanellus, locally select for more 3D variable areas and that the scale and shape of their nests restrict visibility more than predator visual acuity, with crop fields and wet grassland acting more like a closed habitat from the viewing angles of natural predators.

Repeated prescribed fire can create and maintain areas with sparse overstory tree cover and a dense grass-forb-shrub understory, providing habitat for northern bobwhite (Colinus virginianus; hereafter, bobwhite). Despite potential benefits of prescribed fires for conserving bobwhite habitat, burning during the nesting season may destroy bobwhite nests and reduce available nesting cover. We monitored radio-transmittered bobwhite (n = 104) from 2016 to 2018 to describe nest-site selection and determine the risk of nest destruction on a 17,000-ha North Carolina military installation, Fort Bragg, managed with rotational growing-season and dormant-season prescribed fires on an approximate 3-year return interval. We located 48 nests, of which 8 (16%) were in areas burned the same year, 9 (19%) were in one-year post fire, 25 (52%) were in 2-years post fire, and 6 (13%) were in ≥3-years post fire areas. We compared vegetation composition and structure at nests to nearby random locations and determined bobwhite selected nest sites with greater woody understory and wiregrass cover, lower basal areas of pines and hardwoods, and less distance to the nearest road. Two nests (6.7%) were destroyed during prescribed fires, but success of incubated nests was high (67%). We calculated the overall risk of nest destruction by prescribed fire as the proportion of active nests in areas with ≥3 years since last fire multiplied by the proportion of the study area burned each week. Overall, 11% (weekly x̄ = 0.75%, range = 0–3%) of the study area was burned during the 2016 nesting season (3 June to 3 September), 4% (weekly x̄ = 0.31%, range 0–2%) of the study area was burned during the 2017 nesting season (5 June to 2 September), and 7.5% (weekly x̄ = 0.58%, range 0–5%) of the study area was burned during the 2018 nesting season (3 June to 31 August). We estimated that no more than 0.75% of bobwhite nests across the study site were exposed to fire annually. Most growing-season fires occurred before the bobwhite nesting season, which limited direct effects of prescribed fire on bobwhite nest survival. However, shifting prescribed fires to later in the growing season to better match the historical lightning season (i.e., after 1 June) would increase the risk of nest destruction. Because bobwhite used older roughs (i.e. areas 2 years since fire) for nesting, shortening the fire return interval to less than 3 years would increase the proportion of nests exposed to fire. Additionally, a shortened fire return interval would decrease available nesting cover, especially in regions with low soil fertility where vegetation change following fire is less rapid than on more productive soils.

Humans have long provided nest boxes in a widespread and popular effort to augment nesting sites for cavity-nesting birds. Nest boxes, however, may provide easy access for predators and thereby create ecological traps for nesting birds. Predator exclusion techniques are often deployed at nest boxes to reduce nest predation, but few studies have tested their performance. For the first time, we test the effectiveness of predator guards in promoting the nesting success of multiple species of birds at a large spatial scale (United States and Canada). We used nest fate data from 24,114 nest records submitted from 2014 to 2016 to NestWatch, a citizen-science program focused on quantifying nesting success, to determine whether installing predator guards on nest boxes is an effective management technique. Across all species, top models predicting daily nest survival rates suggest a positive influence of predator guards, with a nearly 7% increase in nest success for attempts in boxes with guards versus attempts in boxes without guards. At the species level, nest survival was greater for individuals nesting in boxes with guards in 7 of 9 species, with no effect in the remaining 2 species. Although all types of guards were correlated with improved nesting success, birds nesting in boxes with cone-type baffles, stovepipe baffles, or entrance hole extenders were most likely to result in successful nesting. Further, birds nesting in boxes with multiple predator guards were more successful, on average, than birds nesting in boxes with only a single guard. Our results can help managers of cavity-nesting birds incorporate science-based evidence into decision-making and allocate resources more effectively.

Comparative studies of egg recognition and rejection between various sympatric hosts provide insight into the coevolutionary history of the hosts and parasites, as well as the degree of antagonism between the species. Although buntings are widely considered to be a suitable host taxon for cuckoos, there has been relatively little research on this example of parasitism and host antiparasitic behaviour. Here we provided the first report on brood parasitism and egg recognition in three sympatric ground‐nesting bunting hosts of the common cuckoo ( Cuculus canorus ), namely the yellow‐throated bunting ( Emberiza elegans ), south rock bunting ( E. yunnanensis ), and crested bunting ( E. lathami ). The results show that for the five breeding seasons during 2018–2022, the parasitism rate by common cuckoos was 0.87% and 0.45% in yellow‐throated buntings and south rock buntings, respectively, whereas the parasitism rate by an unidentified parasite was 4% during 2018–2023 in the crested bunting. The rejection rates of the three bunting hosts for blue non‐mimetic eggs were 89.3%, 88.9%, and 100% for yellow‐throated buntings, south rock buntings, and crested buntings, respectively. The rejection rates for red non‐mimetic eggs by yellow‐throated buntings and south rock buntings were lower at 76.9% and 82.4%, respectively. All three sympatric bunting hosts examined had high levels of egg recognition and egg rejection, suggesting that it may have been subjected to high parasitic history and that egg recognition ability was retained after the loss of parasitism, which needs to be further verified by future experiments.