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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.

The availability and appropriateness of nesting sites significantly influence the reproductive success and overall welfare of wild bees. Human‐induced factors contribute to the destruction of natural nesting habitats. To address these limitations, innovative solutions such as the development of artificial nests, offer alternative nest sites to support wild bee populations. We designed the Osmia3DNest, a 3D printed standardized nest tube for solitary cavity‐nesting bees, aiming to provide a safe for the environment, long‐life, time‐saving and biodegradable product that anyone can print. We proudly present the two Osmia3DNest models for mason bees—closed and open—using polylactic acid filament. We demonstrate the effectiveness of Osmia3DNest on mason bee reproduction parameters compared with traditional reed nests. Osmia3DNest can be an alternative to the other artificial nests, which people can customize for their necessity depending on their place of living (rural or urban area), and they can also be washed and reused several times and then decomposed. Osmia3DNest holds potential for wildlife biologists, management of pollinators, and educational outreach, offering adaptability for different bee species and experimental needs. Abstrakt Dostępność miejsc lęgowych oraz ich odpowiednie rozmiary znacząco wpływają na sukces reprodukcyjny i ogólny dobrostan dzikich pszczół. Czynniki wywołane działalnością człowieka takie jak urbanizacja czy fragmentacja siedlisk, przyczyniają się do niszczenia naturalnych siedlisk lęgowych. Aby opanować te zagrożenia, potrzebne są innowacyjne rozwiązania, na co wskazują najnowsze badania naukowe, takie jak tworzenie alternatywnych sztucznych gniazd w celu utrzymania populacji dzikich pszczół. Zaprojektowaliśmy gniazdo Osmia3DNest, wystandaryzowaną rurkę wydrukowaną na drukarce 3D, dla pszczół samotniczych w celu zapewnienia bezpiecznego dla środowiska, długotrwałego, biodegradowalnego produktu, który każdy może wydrukować oszczędzając przy tym czas. Prezentujemy dwa modele Osmia3DNest dla pszczół murarek—zamknięte i otwarte—wykonane z filamentu PLA. Wykazaliśmy skuteczność rurek Osmia3DNest w uzyskanych parametrach rozrodu murarek, porównując je z tradycyjnymi gniazdami trzcinowymi. Gniazdo Osmia3DNest stanowi alternatywę dla innych sztucznych gniazd, które każdy będzie mógł dostosować do swoich potrzeb w zależności m.in. od miejsca zamieszkania (wieś lub miasto), dodatkowo są wielokrotnego użytku, a z czasem ulegną rozkładowi. Model ten może potencjalnie być wykorzystywany przez biologów zajmujących się dziką przyrodą, hodowców komercyjnych oraz w celach edukacyjnych. Oferuje on możliwość dostosowania rozmiarów do różnych gatunków pszczół, a także na potrzeby eksperymentalne.

Birds select suitable nest sites for breeding to ensure their own and offspring's survival; however, they inevitably suffer some potential predation risk. We studied the breeding ecology of Daurian redstarts (Phoenicurus auroreus) by providing nest boxes for their breeding from March to August of 2022. We recorded the predation of both Daurian redstarts eggs or nestlings by Oriental magpie‐robins (Copsychus saularis) and tree sparrow (Passer montanus). Oriental magpie‐robin were recorded attacking a feeding female adult and depredating nestlings. After the nestling predation event, the Daurian redstarts abandoned the nest. This video evidence provide a better understanding of the potential predators of cavity‐nesting birds. The preying on the egg or nestling of Daurian redstarts by Oriental magpie‐robins (Copsychus saularis) and tree sparrow (Passer montanus) was recorded, of which the Oriental magpie‐robin attacking a feeding female adult and depredating the nestling of the Daurian redstarts.

Tree cavities are a critical multi-annual resource that can limit populations and structure communities of cavity-nesting vertebrates. We examined the regional and local factors influencing lifetime productivity (number and richness of occupants) of individual tree cavities across two divergent forest ecosystems: temperate mixed forest in Canada and subtropical Atlantic Forest, Argentina. We predicted that (1) species would accumulate more rapidly within cavities in the species-rich system (Argentina: 76 species) than the poorer system (Canada: 31 species), (2) cavity characteristics associated with nest-site selection in short-term studies would predict lifetime cavity productivity, and (3) species would accumulate more rapidly across highly used cavities than across cavities used only once, and in Argentina than in Canada. We monitored and measured nesting cavities used by birds and mammals over 22 breeding seasons (1995–2016) in Canada and 12 breeding seasons (2006–2017) in Argentina. Cavities were used an average of 3.1 times by 1.7 species in Canada and 2.2 times by 1.4 species in Argentina. Species richness within cavities increased with number of nesting events at similar rates in Canada and Argentina, in both cases much slower than expected if within-cavity species assemblages were random, suggesting that lifetime richness of individual cavities is more strongly influenced by local ecological factors (nest site fidelity, nest niche) than by the regional species pool. The major determinant of lifetime cavity productivity was the cavity’s life span. We found only weak or inconsistent relationships with cavity characteristics selected by individuals in short-term nest-site selection studies. Turnover among (vs. within) cavities was the primary driver of diversity at the landscape scale. In Canada, as predicted, species accumulation was fastest when sampling across high-use cavities. In Argentina, the rates of species accumulation were similar across high-and low-use cavities, and fastest when both high-and low-use cavities were pooled. These findings imply that biodiversity of cavity nesters is maintained by a mix of long-lived (highly productive, legacy trees) and many high-turnover (single-use, fast decaying) tree cavities. Conservation of both long-lasting and single-use cavities should be incorporated into decisions about stand-level forest management, regional land use policies, and reserve networks.

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.

Mosaics of agricultural land, forests, and other semi-natural areas represent landscapes providing valuable habitats and resources for various insect groups. We investigated the added value of agroforestry, the combination of crops or grasslands with woody elements, for important pollinating insects e.g. wild bees and associated pollination service potential at the landscape scale using a modelling approach. In a case study region in Switzerland, characterized by traditional grassland-cherry agroforestry, eight 1 km2 landscape test sites (LTS) with contrasting coverage of agroforestry were selected. Flowering resources and potential nesting habitats were mapped. The contribution of cherry trees floral resources was estimated by flower counts. Lonsdorf equations were used to assess the pollination service potential and were modelled at landscape scale for three scenarios: (A) agroforestry systems containing flowering cherry trees, (B) agroforestry systems with tree species that do not provide floral resources to wild bees and (C) replacement of agroforestry by grassland systems without trees. In total there was a higher proportion of flowering and nesting resources in LTS with agroforestry. The area of cherry flowers was, on average, a factor of 1 to 2.7 of the canopy area. Models predict enhanced wild bee habitat quality and tend to predict increased provision of pollination services by wild bees in landscapes with higher proportion of cherry tree agroforestry. Mainly cavity nesting species might potentially benefit from the agroforestry trees. Our findings highlight the potentially important role of traditional flowering fruit tree with grassland agroforestry in sustaining wild bees and associated delivery of pollination services in agroecosystems.

The number of wild bees and cavity‐nesting wasps is abundant in agricultural areas and they contribute significantly to ecosystem services. Due to their specialization in nesting sites and food sources, these groups are sensitive to habitat condition changes and they are therefore important indicators for environmental impact assessments. As semi‐natural habitats are steadily declining and often understudied, their significance for research is increasingly recognized. During this research, the role of wild bee species and cavity‐nesting Hymenopteran taxa as indicators was examined, along the unique combination of high nature value and traditional land use habitats in Eastern Europe, Transylvania. Transects and trap nests were used to test the diversity and abundance of wild bees and cavity‐nesting Hymenopterans to identify possible differences between highly protected and less protected areas. The differences in taxonomic groups between the sites and the potential effects of landscape structure on wild bees and cavity‐nesting Hymenopterans were also assessed. We detected a high diversity of wild bee species and a significant species replacement from one study year to another. Among the nest‐building Hymenopteran taxa, the majority of nests was built by Trypoxylon sp. during both study years, with a stronger dominance in the second year. The different taxonomic groups of wild bees and cavity‐nesting Hymenopterans showed differences in their habitat affinities. The majority of the sampled bumblebee species as well as Trypoxylon sp. had an affinity towards the study sites located within the highly protected study area. Altogether, we found different habitat preferences for different Hymenopteran groups (both wild bees and wasps) and conclude that these groups definitely have the potential to serve as indicators for differences in the intensity of land use. The role of wild bees and cavity‐nesting Hymenopteran species as indicators was examined, along the unique combination of high nature value and traditional land use habitats. The different taxonomic groups of wild bees and cavity‐nesting Hymenopterans showed differences in their habitat affinities. Landscape structure had no significant effects on the number of (occupied) brood cells for most of the cavity‐nesting Hymenopteran groups.

Some secondary cavity-nesting birds use nest material to cover their eggs when they are out foraging during the egg-laying stage. Egg covering presumably helps regulate nest temperature and/or prevents predation or parasitism. A recent study suggested that egg covering might prevent nest usurpation and therefore, we set up nest boxes with three different treatments to test this hypothesis: bottom of the nest box covered with moss containing two eggs covered with moss (type A); floor of the nest box covered with moss and two eggs exposed on top of the moss (Type B); and bare floor of the nest box, with two eggs added (Type C). The results showed the lowest egg predation rates in Type A nest boxes, which was significantly lower than those in type C boxes; the proportion of maritime striped squirrels (Tamiops maritimus), first appearing in the three types of nest box was not significantly different; however, the rate of first entry into Type A was significantly lower than that into Type C boxes. The rate of first entry and the time the squirrels spent in Type A boxes were significantly lower and shorter than those in Type C boxes. Our results suggest that the egg-covering behavior of secondary cavity-nesting birds delayed the entry of nest competitors and accelerated the departure of nest encroachers from the nest, thus provided experimental evidence for the usurpation hypothesis.Significance statementSeveral non-mutually exclusive hypotheses have been proposed to explain the function of egg covering by bird species. The present study showed that egg covering by secondary cavity-nesting birds delayed the entry of maritime striped squirrels and accelerated the departure of nest encroachers from the nest, suggesting that egg covering might reduce the cost of nest defense for birds and thus prevent nest encroachment by other species. We provided experimental evidence for the new hypothesis proposed by Slagsvold and Wiebe (2021a) that egg-covering behavior of birds deters nest encroachers from easily entering unfamiliar, poorly lit cavities due to fear, thereby effectively preventing nest usurpation by squirrels.

The ecological interactions of biota with natural ecosystems are still poorly understood. In Subtropical Dry forests, several stingless bees utilize cavities within trees for nesting. Due to their lack of morphological traits for creating these cavities, bees rely on other mechanisms to access and utilize hollow spaces. In the Argentinian Dry Chaco region, we set two main objectives: (1) Determine the richness of cavity-nesting bees and describe the characteristics of trees selected as substrates, and (2) identify the mechanisms employed by stingless bees in selecting trees with hollows. Observational records were used to identify bee-nesting sites, while standard vegetation inventory was conducted to assess preference. Structural equation models were employed to establish the selection mechanisms of tree species for nesting. We found 139 nests belonging to three species: Plebeia catamarcensis (n = 118), Plebeia molesta (n = 14), and Lestrimelitta (L.) chacoana (n = 2). Stingless bees, particularly smaller species like P. catamarcensis, specifically select Neltuma trees for nest installation. This preference is attributed to the presence of galleries and hollows within the heartwood, created by the larvae of Criodion angustatum beetle. Although the larval action may harm the mechanical structure of the trees and hasten their demise, it simultaneously creates suitable hollow spaces for the establishment of bee colonies. Further investigations into these species interactions within the forest are necessary to enhance management practices in this threatened ecosystem, recognizing the important ecological role of Neltuma genus as crucial for ensuring the availability of nesting substrates for these native stingless bees.

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.