Bumble bees strategically use ground level linear features in navigation

Bumble bee movement ecology: foraging and dispersal across castes and life stages

Movement is a dynamic process that changes with ontogeny, physiological state, and ecological context. The results of organismal movement impact multiple dimensions of fitness, population dynamics, and functional interactions. As such, the study of movement is critical for understanding and conserving species. Bumble bees (Apidae: Bombus spp.) offer a powerful system to study multiple complexities of movement within a functionally important clade. Their life history includes distinct social and solitary phases, substantial intraspecific variation in body size, and multiple modes of movement behavior. These traits allow investigations of diverse concepts at multiple scales and during contrasting behavioral and motivational states-from individuals, to colonies, to populations, and among species. Despite extensive study as model organisms of fine-scale movements and optimal foraging theory, understanding of landscape-scale movements is more limited. This knowledge gap is especially troubling given global pollinator declines because such dispersive movements fundamentally affect how populations respond to landscape transformation, climate change, and restoration efforts. To build toward a refined understanding of the bumble bee movement, inform research, and assist conservation programs, we review foraging and dispersal movement across life stages and castes. Using an ontogenetic approach, we compare the movement motivation and capacity of individuals throughout colony development. Despite the growth in recent literature, much remains to be learned about the bumble bee movement, especially dispersive life stages. Focused effort on how movement varies with individual state such as nutrition and age, and comparative studies of species would all fill knowledge gaps with high potential to improve bee conservation and research.

Bumblebees increase their learning flight altitude in dense environments

Bumblebees rely on visual memories acquired during the first outbound flights to relocate their nest. While these learning flights have been extensively studied in sparse environments with few objects, little is known about how bees adapt their flight in more dense, cluttered, settings that better mimic their natural habitats. Here, we investigated how environmental complexity influences the first outbound flights of bumblebees. In a large arena, we tracked the bees' 3D positions to examine the flight patterns, body orientations and nest fixations across environmental conditions characterised by different object constellations around the nest entrance. In cluttered environments, bees prioritised altitude gain over horizontal distance, suggesting a strategy to overcome obstacles and visual clutter. Body orientation patterns became more diverse in dense environments, indicating a balance between nest-oriented learning and obstacle avoidance. Notably, bees consistently preferred to fixate the location of the nest entrance from elevated positions above the dense environment across all conditions. Our results reveal significant changes in 3D flight structure, body orientation and nest fixation behaviours as object density increases. This highlights the importance of considering 3D space and environmental complexity in understanding insect navigation.

Bee-Mediated Pollen Transport Across Five Urban Landscape Features: Buildings Are Important Barriers

Urbanization alters insect pollinator diversity and foraging ranges, while also providing novel pollinator habitats. Common urban landscape features, such as roads and buildings, may alter the ability of insect pollinators to move and forage throughout the urban landscape. In this study, we aimed to quantify the effects of common urban landscape features on insect pollinator movement. We focused on roads, buildings, forest fragments, lawns, and community gardens. We studied five community garden sites and the landscape features surrounding them in Raleigh, North Carolina, USA. To measure pollinator movement across each feature, we placed clusters of potted cucumber plants on either side of a feature and added fluorescent dye powder to the stamens of the flowers. After 7 h, we collected and counted the number of fluorescent dye powder grains transferred to each cucumber stigma. We conducted 10-min visitation observations at each cluster to assess the pollinator community and to assess whether low visitation was linked to low dye transfer. Buildings had the lowest estimated dye transfer, roads and gardens were intermediate, and lawns and forest fragments had the highest estimated dye transfer. Although plants associated with buildings also had low visitation rates, visitation overall was a poor predictor of dye transfer. The most common visitors observed were Apis mellifera, Bombus spp., and Xylocopa virginica, indicating our results are likely primarily representative of these large, generalist bee species. Our study highlights the heterogeneity of urban spaces to pollinators. We demonstrate which features facilitate and inhibit movements of pollinators and thereby provide an empirical basis to map and assess functional landscape connectivity. This information can help cities identify and create connected networks of habitat for essential pollinators using geospatial methods, and can inform research about resource accessibility and foraging energetics for urban pollinators.

Flight behaviour and short-distance homing by nomadic grey-headed flying-foxes: a pilot study

BACKGROUND

The ability to navigate is crucial to the survival of many flying animals. Though relatively much less is known about the navigational abilities of bats versus birds, recent progress has been made in understanding the navigational abilities of cave roosting bats, but little is known about those of arboreal roosting flying-foxes, despite their extreme mobility.

METHODS

We use extremely high spatiotemporal resolution GPS tracking to examine the flight behaviour of 11 grey-headed flying-foxes (Pteropus poliocephalus) displaced 16.8 km from their roost. We examined flight metrics of the resulting high-resolution traces to understand whether the displaced animals were aware their location with respect to the roost of capture. We use 7 grey-headed flying-foxes tracked from the roost of capture-as part of a separate, concurrent study-to aid in this comparison.

RESULTS

Ten of 11 displaced individuals were detected at the roost of capture within four days of release, but all displaced individuals roosted for at least one night away from the roost of capture. Six individuals returned 'home' the next day, and four roosted away from 'home' for ≥ one further night. Prior to their return 'home', displaced individuals on average flew 2.7 times further and stopped 1.7 more times than reference individuals or displaced animals that had already returned 'home'. This indicates that displaced individuals expended more effort each night than non-displaced individuals. This suggests that these individuals were attempting to return 'home', rather than choosing not to return due to a lack of motivation to home. Flight segments of displaced individuals were higher, less straight, and less likely to be oriented. Flight segments that ended in a point that an individual had previously visited were faster, higher, and straighter than those not known to end in a point previously visited.

CONCLUSIONS

Our findings suggest that approximately half of the displaced animals were aware of where they were with respect to 'home' the night after release, whereas other individuals took at least a further night to orient themselves. While our results are consistent with previous work suggesting that non-echolocating bats may use a large-scale navigational map based on vision, sensory manipulations would be needed to confirm this.

Roads are partial barriers to foraging solitary bees in an urban landscape

Understanding how animals navigate novel heterogeneous landscapes is key to predicting species responses to land-use change. Roads are pervasive features of human-altered landscapes, known to alter movement patterns and habitat connectivity of vertebrates like small mammals and amphibians. However, less is known about how roads influence movement of insects, a knowledge gap that is especially glaring in light of recent investments in habitat plantings for insect pollinators along roads verges and medians. In this study, we experimentally investigate behavioral avoidance of roads by a solitary bee and explore whether landscape factors are associated with bee movement in urban Massachusetts, USA. Using mark-recapture surveys, we tracked individual solitary bee (Agapostemon virescens) foraging movements among floral patches separated by roads or grass lawn. We found that roads acted as partial barriers to movements of foraging bees, with road crossings nearly half as likely as along-road movements (36% vs. 64%). Movement probabilities were negatively associated with distance and the proportion of roadway between patches, and positively associated with higher floral resource density at the destination patch. Importantly, our findings also suggest that while roads impede bee movement, they are not complete barriers to dispersal of bees and/or transfer of pollen in urban landscapes. In the context of green space design, our findings suggest that prioritizing contiguous habitat and ensuring higher floral densities along road edges may enhance resource access for pollinators and mitigate the risk of ecological traps.

Bumblebees mediate landscape effects on a forest herb's population genetic structure in European agricultural landscapes

Spatially isolated plant populations in agricultural landscapes exhibit genetic responses not only to habitat fragmentation per se but also to the composition of the landscape matrix between habitat patches. These responses can only be understood by examining how the landscape matrix influences among-habitat movements of pollinators and seed vectors, which act as genetic linkers among populations. We studied the forest herb Polygonatum multiflorum and its associated pollinator and genetic linker, the bumblebee Bombus pascuorum, in three European agricultural landscapes. We aimed to identify which landscape features affect the movement activity of B. pascuorum between forest patches and to assess the relative importance of these features in explaining the forest herb's population genetic structure. We applied microsatellite markers to estimate the movement activity of the bumblebee as well as the population genetic structure of the forest herb. We modelled the movement activity as a function of various landscape metrics. Those metrics found to explain the movement activity best were then used to explain the population genetic structure of the forest herb. The bumblebee movement activity was affected by the cover of maize fields and semi-natural grasslands on a larger spatial scale and by landscape heterogeneity on a smaller spatial scale. For some measures of the forest herb's population genetic structure, that is, allelic richness, observed heterozygosity and the F-value, the combinations of landscape metrics, which explained the linker movement activity best, yielded lower AICc values than 95% of the models including all possible combinations of landscape metrics. Synthesis: The genetic linker, B. pascuorum, mediates landscape effects on the population genetic structure of the forest herb P. multiflorum. Our study indicates, that the movement of the genetic linker among forest patches, and thus the pollen driven gene flow of the herb, depends on the relative value of floral resources in the specific landscape setting. Noteworthy, the population genetic structure of the long-lived, clonal forest herb species correlated with recent land-use types such as maize, which have been existing for not more than a few decades within these landscapes. This underscores the short time in which land-use changes can influence the evolutionary potential of long-lived wild plants.

Interspecific interactions disrupted by roads

Roads have pervasive impacts on wildlife, including habitat loss and fragmentation, road mortality, habitat pollution and increased human use of habitats surrounding them. However, the effects of roads on interspecific interactions are less understood. Here we provide a synthesis of the existing literature on how species interactions may be disrupted by roads, identify knowledge gaps, and suggest avenues for future research and conservation management. We conducted a systematic search using the Web of Science database for each species interaction (predation, competition, mutualism, parasitism, commensalism and amensalism). These searches yielded 2144 articles, of which 195 were relevant to our topic. Most of these studies focused on predation (50%) or competition (24%), and less frequently on mutualism (17%) or, parasitism (9%). We found no studies on commensalism or amensalism. Studies were biased towards mammals from high-income countries, with most conducted in the USA (34%) or Canada (18%). Our literature review identified several patterns. First, roads disrupt predator-prey relationships, usually with negative impacts on prey populations. Second, new disturbed habitats created in road corridors often benefit more competitive species, such as invasive species, although some native or endangered species can also thrive there. Third, roads degrade mutualistic interactions like seed dispersal and pollination. Fourth, roads can increase parasitism rates, although the intensity of the alteration is species specific. To reduce the negative impacts of roads on interspecific interactions, we suggest the following management actions: (i) verges should be as wide and heterogenous as possible, as this increases microhabitat diversity, thus enhancing ecosystem services like pollination and seed dispersal; (ii) combining different mowing regimes can increase the complexity of the habitat corridor, enabling it to act as a habitat for more species; (iii) the use of de-icing salts should be gradually reduced and replaced with less harmful products or maintenance practices; (iv) wildlife passes should be implemented in groups to reduce animal concentrations inside them; (v) periodic removal of carcasses from the road to reduce the use of this resource by wildlife; and (vi) implementation of traffic-calming schemes could enhance interspecific interactions like pollination and avoid disruption of predator-prey relationships.

Assessing habitat connectivity of rare species to inform urban conservation planning

Urbanization is commonly associated with biodiversity loss and habitat fragmentation. However, urban environments often have greenspaces that can support wildlife populations, including rare species. The challenge for conservation planners working in these systems is identifying priority habitats and corridors for protection before they are lost. In a rapidly changing urban environment, this requires prompt decisions informed by accurate spatial information. Here, we combine several approaches to map habitat and assess connectivity for a diverse set of rare species in seven urban study areas across southern Michigan, USA. We incorporated multiple connectivity tools for a comprehensive appraisal of species-habitat patterns across these urban landscapes. We observed distinct differences in connectivity by taxonomic group and site. The three turtle species (Blanding's, Eastern Box, and Spotted) consistently had more habitat predicted to be suitable per site than other evaluated species. This is promising for this at-risk taxonomic group and allows conservation efforts to focus on mitigating threats such as road mortality. Grassland and prairie-associated species (American Bumble Bee, Black and Gold Bumble Bee, and Henslow's Sparrow) had the least amount of habitat on a site-by-site basis. Kalamazoo and the northern Detroit sites had the highest levels of multi-species connectivity across the entire study area based on the least cost paths. These connectivity results have direct applications in urban planning. Kalamazoo, one of the focal urban regions, has implemented a Natural Features Protection (NFP) plan to bolster natural area protections within the city. We compared our connectivity results to the NFP area and show where this plan will have an immediate positive impact and additional areas for potential consideration in future expansions of the protection network. Our results show that conservation opportunities exist within each of the assessed urban areas for maintaining rare species, a key benefit of this multi-species and multi-site approach.

The potential underlying mechanisms during learning flights

Hymenopterans, such as bees and wasps, have long fascinated researchers with their sinuous movements at novel locations. These movements, such as loops, arcs, or zigzags, serve to help insects learn their surroundings at important locations. They also allow the insects to explore and orient themselves in their environment. After they gained experience with their environment, the insects fly along optimized paths guided by several guidance strategies, such as path integration, local homing, and route-following, forming a navigational toolkit. Whereas the experienced insects combine these strategies efficiently, the naive insects need to learn about their surroundings and tune the navigational toolkit. We will see that the structure of the movements performed during the learning flights leverages the robustness of certain strategies within a given scale to tune other strategies which are more efficient at a larger scale. Thus, an insect can explore its environment incrementally without risking not finding back essential locations.

A Sublethal Concentration of Sulfoxaflor Has Minimal Impact on Buff-Tailed Bumblebee (Bombus terrestris) Locomotor Behaviour under Aversive Conditioning

Pesticide exposure has been cited as a key threat to insect pollinators. Notably, a diverse range of potential sublethal effects have been reported in bee species, with a particular focus on effects due to exposure to neonicotinoid insecticides. Here, a purpose-built thermal-visual arena was used in a series of pilot experiments to assess the potential impact of approximate sublethal concentrations of the next generation sulfoximine insecticide sulfoxaflor (5 and 50 ppb) and the neonicotinoid insecticides thiacloprid (500 ppb) and thiamethoxam (10 ppb), on the walking trajectory, navigation and learning abilities of the buff-tailed bumblebee (Bombus terrestris audax) when subjected to an aversive conditioning task. The results suggest that only thiamethoxam prevents forager bees from improving in key training parameters (speed and distanced travelled) within the thermal visual arena. Power law analyses further revealed that a speed-curvature power law, previously reported as being present in the walking trajectories of bumblebees, is potentially disrupted under thiamethoxam (10 ppb) exposure, but not under sulfoxaflor or thiacloprid exposure. The pilot assay described provides a novel tool with which to identify subtle sublethal pesticide impacts, and their potential causes, on forager bees, that current ecotoxicological tests are not designed to assess.

Generalization of navigation memory in honeybees

Flying insects like the honeybee learn multiple features of the environment for efficient navigation. Here we introduce a novel paradigm in the natural habitat, and ask whether the memory of such features is generalized to novel test conditions. Foraging bees from colonies located in 5 different home areas were tested in a common area for their search flights. The home areas differed in the arrangements of rising natural objects or their lack, and in the existence or lack of elongated ground structures. The test area resembled partly or not at all the layout of landmarks in the respective home areas. In particular, the test area lacked rising objects. The search flights were tracked with harmonic radar and quantified by multiples procedures, extracting their differences on an individual basis. Random search as the only guide for searching was excluded by two model calculations. The frequencies of directions of flight sectors differed from both model calculations and between the home areas in a graded fashion. Densities of search flight fixes were used to create heat maps and classified by a partial least squares regression analysis. Classification was performed with a support vector machine in order to account for optimal hyperplanes. A rank order of well separated clusters was found that partly resemble the graded differences between the ground structures of the home areas and the test area. The guiding effect of elongated ground structures was quantified with respect to the sequence, angle and distance from these ground structures. We conclude that foragers generalize their specific landscape memory in a graded way to the landscape features in the test area, and argue that both the existence and absences of landmarks are taken into account. The conclusion is discussed in the context of the learning and generalization process in an insect, the honeybee, with an emphasis on exploratory learning in the context of navigation.