Nest Cavities Research Articles

Barred Owl (<i>Strix varia</i>) activity and diet recorded with a camera trap at a natural cavity nest in Manitoba, Canada (2016–2017)

Camera trap images (n = 27 092) collected at a natural Barred Owl (Strix varia) nest site in Manitoba, Canada, 2016–2019, were used to quantify nesting behaviour and identify prey delivered to the nest. Adult Barred Owl activity increased prior to egg laying and again after incubation. Adults were mostly active at night, but daytime activity increased during the nestling period in 2016 and more so with a larger brood in 2017. Nestlings were active at the nest entrance both day and night for 8–9 days prior to fledging at ≤27–32 d old. Two of three nestling activity peaks (0400 and 2000 Central Daylight Time [CDT]) corresponded to prey delivery activity peaks whereas a third (1200 CDT) did not. Only 31/65 prey were identified to species, but 12 new prey taxa were documented for Barred Owl in Manitoba. Activity at the cavity during the non-breeding season before and after a nest predation event were documented; the nest site was abandoned after an American Black Bear (Ursus americanus) visited the nest cavity in May 2018. Factors affecting the quality and quantity of images, and hence data obtained from them, included camera position relative to the nest cavity entrance, light levels, camera trigger speed, non-target species, and the configuration and settings of motion detection sensors. Improved camera traps may overcome these limitations. This is the first published study on this owl species using this increasingly popular technology.

Sexual Offspring Production by Acorn Ant Temnothorax crassispinus Colonies Is Associated with the Colony Size but Not with the Volume of the Nest Cavity

Nest sites are important for ants, as the nests provide refuge against enemies and ensure optimal conditions for the brood development. As the construction of a nest is a time and energy consuming activity, many ant species dwell in ready-for-use cavities. For them, choosing a good nest site is important, as the quality of nest site could affect factors such as the energy allocation and production of sexual individuals. Ants of genus Temnothorax inhabit cavities in, e.g., acorns and twigs, and these ant colonies prefer larger cavities as nest sites. It was previously shown that colonies inhabiting more durable nest sites invested more resources in sexual production. The aim of this study was to find out whether the volume of a nest cavity influences the sexual offspring production of acorn ant Temnothorax crassispinus colonies. For this purpose, a three-month long laboratory experiment was performed. Colonies of the Temnothorax ant were kept in artificial nest cavities differing in volume. It was found that there was no correlation between the productivity per capita and the colony size. More populous colonies produced more sexual individuals; however, we found no statistical difference in the production of sexual individuals between the colonies that inhabited cavities of different volumes.

The Population Development of the Red Mason Bee, Osmia bicornis L., for Different Types of Nesting Materials.

Osmia bicornis L. is a widespread and valued pollinator species. It is considered to be easy to breed, provided that the nesting material in which the bees build their nests is of sufficient quality and quantity. The aim of this study was to test several different types of nesting materials: reeds and commercial structures, including wood, MDF (Medium Density Fibreboard), plastic, paper or polystyrene. The highest levels of nest cavity occupancy were found in reeds (90%) and grooved MDF (over 80%). We have shown that maintaining mason bee colonies in polystyrene leads to reproductive losses (occupancy only 2% of nesting holes). Mason bees built the most cells in MDF (8.02 cells/hole) and wood (7.34 cells/hole), slightly fewer in plastic (6.83 cells/hole) and reeds (6.74 cells/hole), and the fewest in paper (3.67 cells/hole). The most cocoons per nest were obtained from reed (average 5.47), MDF (4.84) and plastic (4.74). We observed the highest mortality in plastic (2 larvae/hole), and the lowest in reeds (0.92 larvae/hole). In nests made of wood, MDF and paper, large nesting losses were caused by the migration of Ch. osmiae mites along and through the nest holes. The most hygienic nesting material turned out to be reed and plastic forms.

Elucidating Collapse-Resistant Mechanisms of Pore Geometries in Fire Ant Nest Cavities.

Porous materials and structures, such as subterranean fire ant nests, are abundant in nature. It is hypothesized that these structures likely have evolved biological adaptations that enhance their collapse resistance. This research aims to elucidate the collapse-resistant mechanisms of pore geometries in fire ant nests. Finite Element Models of ant nests in soil were generated using X-ray CT imaging of aluminum castings of ant nests. Representative volume elements of the ant nests, representing porous structures at various depths, were analyzed under confined compression. This work on investigating fire ant (sp. Solenopsis Invicta) nests found them to be hierarchical and graded at various depths that affect how they resist loads and collapse. The top portion acts as a protective shield by distributing damage and absorbing energy. In contrast, the lower chambers localize stress, contributing to damage tolerance. This research provides evidence to suggest that ant nests have developed properties that allow them to resist collapse. These findings could inform the design of lightweight and durable cellular structures in various engineering fields.

Integrating arborists and birds: Habitat management options for birds in the tropical urban green space

Abstract Tropical urban areas have been known as excellent habitats for birds. Trees in urban areas are essential in supporting birds’ lives; they must be managed appropriately. This paper aims to formulate habitat and tree maintenance management options that could benefit birds in tropical urban areas. Previous bird observations from three urban green spaces formulated management options. Managing urban birds’ habitat mainly involved managing trees producing food (fruits, seeds, insects, nectars) and providing bird cover (as resting, roosting, and breeding sites). Trees can be planted in clumps or rows, creating bird habitat patches and corridors. Trees producing small-sized seeds/fruits attract insects, and having nectars from flowers is preferred by birds. Tall trees with thick canopies are excellent as cover. As some birds nest in tree cavities, old-decayed trees must also be maintained, which might conflict with arborists’ intentions. Other conflicting matters are snags, parasitic/epiphytic plants, pests, and thick litter, which are excellent for birds but unwanted by arborists. Management options for arborists need to be integrated and synergized with avian ecologists to maintain/increase bird diversity and number in the tropical urban green space.

Wood hardness drives nest-site selection in woodpeckers of the humid Chaco

Abstract Avian excavators (woodpeckers and other species) select nest sites based on characteristics of the nest patch, nest tree, and substrate. These characteristics could increase foraging opportunities or reduce the risk of predation, but there is also a potentially important role for wood hardness in restricting nest-site selection, a role that has been little explored and is expected to vary among species according to their ability to excavate. We examined patterns of nest-site selection in 8 woodpecker species in the humid Chaco of South America, where the dominant trees have extremely hard wood. We hypothesized that (1) wood hardness is the main factor driving selection of excavation sites, and (2) interspecific variation in body size and foraging behavior (traits frequently related to excavation ability) explain interspecific variation in the wood hardness of excavated nest substrates. From 2016 to 2019 in well-preserved forests of the Argentine Chaco, we compared nesting cavities excavated in wood (cases; n = 42) vs. potential wood substrates without cavities (matched controls) and made 187 focal observations of foraging woodpeckers. Woodpeckers selected nesting substrates with softer heartwood than potential substrates, regardless of any other characteristics of the tree or nest patch. Wood hardness around nest cavities increased with body size and the prevalence of chiseling during foraging, traits that were positively correlated. Woodpeckers often excavated in Prosopis spp. (Algarrobos) but rarely in Schinopsis balansae (Quebracho), a tree with exceptionally hard internal wood, in which cavity adopters frequently nest in non-excavated cavities. Wood hardness is critical to assessing the role of woodpeckers as cavity facilitators, understanding the costs and benefits of excavation, and interpreting excavation patterns across species and forests globally.

Sublethal fungicide-insecticide co-exposure affects nest recognition and parental investment in a solitary bee

Fungicides may interact synergistically with insecticides. However, our understanding of the impacts of sublethal insecticide-fungicide combinations on solitary bees is mostly restricted to laboratory studies, providing no information about potential consequences on behavior and reproductive success. We analyzed the effects of a fungicide application, alone and in combination with sublethal levels of an insecticide, on the nesting behavior and reproductive output of the solitary bee Osmia cornuta. We released individually-marked females into oilseed rape field cages, and subsequently sprayed the plants with four treatments: control (water), fungicide (tebuconazole), insecticide (acetamiprid at a sublethal concentration), and mixture (fungicide + insecticide). We recorded nesting activity before and after the sprays and assessed post-spray individual reproductive success. Bees of the single pesticide treatments were unaffected by the sprays and did not differ from control bees in any of the parameters measured. The longevity of bees of the mixture treatment was unaffected. However, these bees showed reduced foraging activity, shorter in-nest pollen-nectar deposition times, and increased difficulty recognizing their nesting cavity, leading to a decrease in provisioning rate, parental investment, and offspring production. Our study demonstrates that co-exposure to a fungicide with otherwise harmless levels of an insecticide caused behavioral effects with consequences on reproductive success. Because longevity was unaffected, these effects would not have been easily detected in a chronic laboratory test. Our results have important implications for bee risk assessment, which should account for exposure to multiple compounds and address behavioral effects and reproductive output under semi-field and/or field conditions.

Anatomy and Immunohistochemistry of Woodpecker Tail Muscles.

Woodpeckers (Order Piciformes) belong to a group of birds characterized by their hammering capabilities in which the bill is utilized as a tool to probe for food and to excavate nest cavities. They have numerous specializations for this behavior, including their bill and tongue, feet for gripping vertical tree trunks, and tail feathers with thickened shafts to provide stability as a postural appendage. We hypothesized that (1) woodpecker tail musculature is also modified for clinging behaviors with a heterogeneous distribution of fast and slow muscle fibers, and that (2) the tree-trunk foraging Hairy Woodpeckers would have more slow muscle fibers in their M. depressor caudae than Northern Flickers, which forage on the ground where they probe the substrate for insects. We performed immunohistochemistry to identify the fiber type distributions for tail muscles Mm. caudofemoralis pars caudalis, lateralis caudae, levator caudae, and depressor caudae in four Hairy Woodpeckers and five Northern Flickers. Our results show that these tail muscles in the two woodpecker species are comprised of a majority of fast muscle fibers common among dynamic locomotor muscles. Interestingly, we report a functionally-significant distribution of slow muscle fibers in M. depressor caudae predicted to be utilized in propping of the tail during tree climbing and support. Further, we found more slow fibers (13.80% ± 4.49%) in the trunk-foraging Hairy Woodpeckers compared with the ground-foraging Northern Flicker (7.40% ± 4.95%), which we interpret to be related to the trunk-foraging habits of Hairy Woodpeckers.

Orientation, thermal characteristics and structural dimensions of Mangrove Kingfisher Halcyon senegaloides nest cavities in arboreal termitaria in central Mozambique

The breeding ecology of the Mangrove Kingfisher Halcyon senegaloides (family Alcedinidae) remains poorly known. While the few nests recorded in southern and East Africa have been in tree hollows, a seasonal population in central Mozambique woodland breeds in cavities in arboreal termitaria. Despite this breeding strategy being widely recorded in many tropical kingfisher species, it has received little research attention in the Afrotropical realm. We report on the siting and structural characteristics of arboreal termitaria used as nesting sites by Mangrove Kingfishers in central Mozambique and document the thermal dynamics of a nesting cavity in an arboreal termitarium. Arboreal termitaria (average volume 40.1 ± 23.8 l) occurred at a density of 0.52 ± 0.22 termitaria ha−1 in large trees or shrubs, mostly of the families Fabaceae and Malvaceae. Termitaria containing nest cavities were situated 10.8 ± 3.1 m above the ground, and most nests (78.6%) faced north. Nest cavity temperatures averaged 31.4 ± 2.6 °C, which is warmer and more stable than the average ambient temperatures of 28.7 ± 4.0 °C. ‘Carton’ termitaria (comprising a mixture of faecal matter and wood fragments) are thus believed to confer a thermal advantage for summer-nesting Mangrove Kingfishers.

A descriptive study of the biometrics of the stingless bee Lepidotrigona flavibasis in northern Thailand

Stingless bees play a crucial role in tropical and subtropical ecosystems, contributing significantly to biodiversity and pollination services. The species Lepidotrigona flavibasis (Cockerell 1929) (Apidae: Meliponini), found in Southeast Asia, has attracted attention for its unique nesting habits and valuable honey production. The objective of this study was to compare colony size and productivity between different nesting cavities. Twelve colonies of L. flavibasis were collected in Chiang Mai province, Thailand, to study biometrical data. Six colonies were housed in hollowed logs, previously occupied by Apis cerana, and six in bamboo cavities. The colony ages ranged from 8 months to 5 years. This study found that log cavity colonies had larger populations and more brood cells than bamboo cavity colonies. Results show that log cavity colonies had an average number of workers (3,842.6 ± 2036), drones (288.2 ± 511), brood cells (5,914.5 ± 3026), honey pots (290.5 ± 210), and pollen pots (96.8 ± 90). The bamboo cavity colonies were found to have an average number of workers (1,628.2 ± 575), drones (64 ± 58), brood cells (2,333.7 ± 1875), honey pots (127.3 ± 95), and pollen pots (94.8 ± 57). Overall, the log cavity colonies demonstrated greater colony size and productivity regarding adult bees and brood.

Diapause, pollen ball incidence, and overwintering energetics in the alfalfa leafcutting bee, Megachile rotundata

IntroductionWarming summer temperatures have the potential to harm managed pollinators, impacting both summer performance and overwintering success. The alfalfa leafcutting bee, Megachile rotundata, is a solitary bee used for commercial pollination of alfalfa. M. rotundata undergoes facultative diapause in the prepupal stage. Prepupae that diapause early in the season are exposed to warm temperatures for a longer period of time than the individuals that start diapause closer to fall, which may reduce lipid reserves required for overwintering survival. Warm temperatures may also contribute to pollen ball incidence, which is when a provision is present but there is no sign of a larva in the brood cell. Our goal was to identify factors that regulate diapause and pollen ball incidence and examine effects of pre-wintering field conditions on post-overwintering energy reserves in M. rotundata.MethodsNest boxes were installed near Fargo, ND, Laramie, WY, and Las Cruces, NM, which exposed bees to different photoperiods and thermal regimes. Three nest boxes were placed at each site. We monitored nesting conditions and diapause and pollen ball incidence throughout the season. Lipids, sugars, and glycogen reserves were measured in adults after overwintering.Results and DiscussionOur models indicate that most of the variation in diapause incidence was explained by nest, with individuals within a nest tending to have the same diapause outcome. This suggests that the environmental conditions experienced by the mother, or genetic predisposition, influences offspring diapause. We also found evidence that high cavity temperatures can cause diapause aversion. In addition, our study is the first to link high nesting cavity temperatures to increased pollen ball incidence. Exposure to stressful temperatures during development and early diapause resulted in an increase in adult lipid reserves after overwintering. Adult sugar and glycogen reserves were not affected by exposure to warm temperatures during development and early diapause. In conclusion, maternal effects and temperature were important factors for diapause and pollen ball incidence in M. rotundata with macronutrient reserves similar for early and late season bees.

Ecology and conservation of cavity-nesting birds in the Neotropics: Recent advances, future directions, and contributions to ornithology

ABSTRACT About 35% of tree-cavity-nesting bird species inhabit the Neotropics, a region crucial to understanding their breeding ecology, conservation, and roles in social-ecological systems. Sixteen years ago, Cornelius et al. (2008) reviewed published knowledge and identified research priorities for Neotropical cavity-nesting birds. Advances since 2008 have not been synthesized and many remain excluded from dominant ornithology because of barriers that disproportionately affect people and ideas from the Global South. Here, we review recent advances in knowledge about Neotropical cavity-nesting birds, introduce the Special Feature series “Ecology and conservation of cavity nesters in the Neotropics,” and outline possible directions for future research. Research in the Neotropics has advanced knowledge of breeding biology, demonstrated that nest sites are limited and birds compete for cavities (mainly in humid forests), identified non-excavated cavities (formed by wood decay) as the main source of cavities and demonstrated the importance of understanding Indigenous and local community relationships to birds. With field studies across the Neotropics, the Special Feature series shows how environment, people’s common imaginaries, vegetation management, and behavior of avian excavators can interact to influence cavity availability, with ecological consequences for many cavity-using organisms. In the future, researchers should center ethno-knowledge and natural history to create an accurate list of cavity-nesting birds in the Neotropics, and integrate this knowledge into studies of population and community ecology. It is also important to study factors that influence cavity dynamics, especially using a social-ecological systems framework and especially in arid and semi-arid regions. We recommend expanding the concept of nest webs (ecological networks of cavity nesters) to incorporate additional cavity substrates (e.g., termitaria, cliffs), cavity alternatives (e.g., bulky enclosed stick nests of many Furnariidae), and cavity-using taxa beyond birds and mammals (e.g., social insects, snakes), which abound in the Neotropics but were not contemplated in the original nest web formulation. Translated versions of this article are available in Supplementary Material 1 (Spanish) and Supplementary Material 2 (Portuguese).

Ecosystem engineers show variable impacts on habitat availability for cavity nesters in South American temperate forests

Abstract Ecosystem engineers are organisms that impact their environment and co-existing species by creating or modifying habitats, and thus they play important roles as drivers of community assembly. We examined whether cavity characteristics and/or habitat attributes associated with cavities provided by 4 ecosystem engineers influence the presence of nests of 3 secondary cavity-nesting birds—Aphrastura spinicauda (Thorn-tailed Rayadito), Tachycineta leucopyga (Chilean Swallow), and Troglodytes aedon (Southern House Wren)—and whether these variations influence their reproductive success. We tested this by: (1) assessing nest presence in cavities supplied by ecosystem engineers and (2) quantifying the reproductive success of secondary cavity nesters as a function of cavity characteristics and habitat attributes supplied by ecosystem engineers. Between 2009 and 2022, we recorded 757 cavities in 546 trees in old-growth and second-growth forests in a Global Biodiversity Hotspot in the Andes of southern Chile. Insect/fungi and Pygarrhichas albogularis (White-throated Treerunner) play a key role as the primary producers of cavities. Insect/fungi generated the cavities for 82% of A. spinicauda nests and 95% of T. aedon nests; in contrast, 57% of T. leucopyga nests were cavities excavated by P. albogularis. Characteristics of cavities (size of cavity entrance, volume, and height above ground) were associated with nest presence of secondary cavity nesters and with reproductive success of A. spinicauda and T. aedon. Habitat attributes such as tree density and canopy cover influenced nest presence for A. spinicauda and T. leucopyga, but did not correlate with the reproductive success of any secondary cavity nester. Bamboo density and forest type were related to reproductive success of A. spinicauda and T. aedon. Diameter at Breast Height of trees was related to the reproductive success of T. leucopyga. This study contributes to understanding the importance of various ecosystem engineers for the conservation of secondary cavity-nesting birds in temperate forests and beyond.

Intrusion of birds into nest cavities depends on the presence of feathers in the cavity and not on species of nest owner

AbstractMost animals live and move in a landscape in which the risk of predation varies spatially and temporally, that is, a “landscape of fear” which may strongly affect their ecology and behaviour. Cavity‐nesting birds prospecting for nest sites are often forced to investigate unfamiliar, dark holes that may be dangerous to enter because they may conceal an aggressive nesting bird or a predator. The Fear of Feathers Hypothesis posits that some birds such as blue tits Cyanistes caeruleus, add large, conspicuous feathers on top of their own nest to exploit the fear of potential nest usurpers or brood parasites. Feathers may trigger fear in prospecting birds either because the feathers obstruct the view of the cavity interior, and/or because the feathers may be perceived as recent prey remains and suggest the predator will return. Here I studied the prospecting behaviour of unmated male pied flycatchers Ficedula hypoleuca by letting them choose between a dyad of nest boxes where one contained a nest of a great tit Parus major and one a nest of a blue tit. The objective was to test whether the presence of feathers would have a stronger repelling effect than the species that had built the nest. Great tits are larger than blue tits and may represent a greater threat to intruding flycatchers. However, blue tits but not great tits, often decorate their nest with large, conspicuous feathers. Consistent with the Fear of Feathers Hypothesis, flycatchers hesitated longer to enter blue tit than great tit nests but only if the blue tit nest contained feathers. The study has relevance to many species of birds that decorate their nest with feathers. It shows that a landscape may include aspects of fear that are important to animal behaviour although they may seem subtle and are easily overlooked.

Tree cavity density is a limiting factor for a secondary cavity nester in second-growth Andean temperate rainforests

ABSTRACT Cavity-nesting bird populations are most frequently limited by the number of tree cavities available in second-growth forests. However, this possible limitation of a key resource is less clear in old-growth forests. We compared forest attributes (i.e., basal area, density of larger trees, density of dead trees, and tree cavity density) in second-growth and old-growth stands in Andean temperate rainforests in southern Chile. To examine the role of nest-site availability in limiting the populations of Aphrastura spinicauda (Thorn-Tailed Rayadito), we monitored their populations in both forest types during a 5-year period (2008-2013), while we conducted an experiment in which nest boxes were added and then, after two years, removed by blocking cavity entrances. In old-growth forests, as compared to second-growth forests, we found a more than double basal area (99.6 vs. 43.7 m2 ha−1), a 3 times higher density of larger trees (88.2 vs. 36.4 trees ha−1), and a 1.5 times higher number of small cavities (25.9 vs. 10.3 cavities ha−1). The density of cavities also strongly increased with tree diameter and basal area. In second-growth forests, A. spinicauda showed a strong response to the addition, and later to the removal of nest boxes, with population abundance increasing by 13% and then decreasing by 50%, respectively. In contrast, we found no impact on old-growth stands. Our experiment emphasizes the importance of maintaining large and dead trees in second-growth, disturbed, and managed forests. These trees provide suitable cavities for A. spinicauda, and likely many other secondary cavity nesters, increasing their abundance in a Globally significant Biodiversity Hotspot in southern South America. A Spanish translation of this manuscript is available as Supplementary Material.

Distribution of brood of the acorn ant Temnothorax crassispinus in artificial nests after forced migration

Nest sites are important for social insects, as they provide refuge against enemies and ensure optimal conditions for the brood development. In large nests, the different chambers can be used for different reasons; for example, for food storage or as a brood chamber. Acorn ants from the genus Temnothorax dwell in small cavities in acorns and wood; however, even such small chambers can have a high degree of spatial heterogeneity. During this study, the distribution of brood items of the acorn ant Temnothorax crassispinus inside artificial nest cavities composed of three chambers in a linear system was analysed. 29 ant colonies were photographed 13 times during a period of approximately one month: during three consecutive days, and after forced migrations. I found that the distribution of the brood inside the nest cavity was similar during the consecutive days; however, after the forced migration, the distribution typically changed. Almost all the brood items were kept farther from the entrance. Keeping the brood farther from the entrance could be explained as a safer option.

Does Nesting Material Affect Wood Duck (Aix sponsa) Nest Box Selection, Reproduction, and Eggshell Bacteria?

Wood Ducks (Aix sponsa) are secondary cavity nesters that use natural cavities and artificial nest boxes, the latter of which has been attributed to the recovery of populations across the southeastern US. Continual use of these boxes results in a buildup of bacteria, parasites, and other pathogens. To avoid the accumulation of these deleterious organisms, best management practices include the occasional removal of old nesting material (i.e., wood shavings) and replacement with fresh wood shavings. No studies have been performed on the effects of shaving material on nest box selection, nest success, and bacterial growth. We monitored 142 and 111 nest boxes in Florida and Georgia, USA, respectively, and filled a random sample with aspen or cedar shavings. We then swabbed the surface of 144 and 150 eggs during 2020 and 2021, respectively, to screen for culturable bacteria. We detected no effect of shaving type on nest box selection, nest success, or egg surface bacterial growth. We found 3-8 bacterial colony types (1-123 colony-forming units [CFU]/box) and 1-8 bacterial colony types (3-382 CFU/box) among the Georgia and Florida samples, respectively. We detected no effect from shaving type on Wood Duck reproduction or bacterial growth in the sampled nest boxes. We concluded that both shaving types are suitable nesting materials for box-nesting Wood Duck populations and the continued use of either would be a reasonable decision for managers.

Diet and multi-taxa neo-taphonomy of Glaucidium nana (Aves, Strigiformes) from southeastern Patagonia and comparisons with G. brasilianum from Chaco forest and other owls

ABSTRACT The diet and neo-taphonomy of Glaucidium nana (Aves, Strigiformes), evaluated from pellets and leftover prey recovered in nest-boxes from a National Park of southeastern Patagonia are studied. Comparative evaluations are conducted with microvertebrate samples obtained from other raptors, particularly those of G. brasilianum from the Chaco forest in Argentina. The diet of G. nana reported here agrees with the generalist trophic behaviour of this species already documented, which feeds on invertebrate (insects and arachnids) and vertebrate prey (amphibian, reptiles, birds and mammals), mainly caviomorph rodents heavier than itself. The taphonomic attributes allow us to place the two species of Glaucidium in the moderate modification category. They could deposit their diet remains in several open-air sites, mainly in wooded and rocky areas, where the cavity nests are located. Later, their bone accumulation –composed of microvertebrates with evidence of moderate bone modifications and/or with articulated skulls and limb bones without digestive corrosion- might integrate into the lithosphere. Understanding the trophic interactions between predators and prey, and their taphonomic signatures, as well as identifying their nesting areas, is crucial for archaeology/palaeontology analysis and for developing effective conservation and management strategies within protected areas.

Conflicting cognitive decisions: Does egg retrieval modify egg rejection in a host of an obligate brood parasite?

AbstractEgg retrieval is an ancient behaviour displayed by birds in which a displaced egg is transferred back into the nest. Egg rejection, in contrast, is a recently evolved adaptation by hosts of brood parasites in which an egg is removed from a nest. These conflicting behaviours are both adaptive because they prevent reproductive losses, but egg retrieval may benefit brood parasites if hosts retrieve parasitic eggs into their nests. We examined these conflicting cognitive processes in the prothonotary warbler (Protonotaria citrea), a cavity‐nesting host of the brown‐headed cowbird (Molothrus ater). Eggs and nestlings are occasionally found on the rims of warbler nest cavities. We determined how this happened using video cameras and tested whether warblers retrieved their own eggs more often than cowbird eggs. We also determined if shape affects retrieval and rejection by placing cylinders inside nest cups or onto nest rims. We found that eggs were displaced by rapidly departing warblers whose nests are constantly prospected by nest competitors and brood parasites. Warblers retrieved their eggs (29%) and cowbird eggs (19%) at similar rates, and never rejected cowbird eggs after retrieval. Warblers removed most cylinders from nest rims and cups (89% and 78%, respectively), and never retrieved them. Warblers have retained egg retrieval at a low level and its expression is costly because they only retrieve a low level of their own eggs and also retrieve cowbird eggs, which benefits the brood parasite.

Nest site selection of cavity-nesting birds at Jahangirnagar University campus, Bangladesh

Understanding nest site selection by cavity-nesting birds is important for their conservation implications. We examined the preferences and characteristics of nesting trees and cavities used by cavity-nesting birds at Jahangirnagar University (JU) campus from January 2020 to October 2021. A total of 30 tree- cavity nests of 11 species of birds belonging to 4 orders and 7 families were recorded where 36% were primary excavators and 64% were secondary cavity-nesters. Out of 14 species of trees used in cavity-nesting, the most of the nests were built in Mahogany Swietenia mahagoni (n=8) followed by White siris Albizia procera (n=6) and Rain tree Samania saman (n=3). Diameter at breast height (DBH) of the nesting trees varied from 27 cm to 112 cm (52±23.2 cm). The highest mean DBH was recorded in Samania saman (85 cm) followed by Swietenia mahagoni (67 cm). Common Myna showed the widest selection of nesting tree species (n=9) followed by Black-rumped Flameback (n=4) and Lineated Barbet (n=4). Majority of the nesting trees (87%) were found in roadside (within 1-5 m) vegetation while 60% nesting trees located within 30 m from the nearby water bodies. The cavity-nesting species preferred to nest between 2 m to 12 m (5.2±2.6 m) height from the ground level. The entrance width and the depth of tree holes (n=30) used by cavity-nesters varied from 5 cm to 22 cm (7.5±3.5 cm) and 13 cm to 45 cm (23.2±6.5 cm), respectively. Suitable cavities are critical for reproductive success of cavity-nesting birds and our results highlight the conservation value of cavity-bearing large trees to maintain a healthy population of cavity-nesting birds at JU campus. Jahangirnagar University J. Biol. Sci. 12(1 & 2): 1-10, 2023 (June & December)