Aerial Insectivores Research Articles

Effect of mass ratio on thrust production of an elastic panel pitching or heaving near resonance

Flapping wings of aerial insects and undulating fins of fish typically experience significant elastic chordwise deformations, and such deformations have been shown in previous studies to be beneficial on force production and/or power efficiency for both types of animal locomotion. However, it is still not conclusive whether the resonant vibration plays a common role in these problems. For fish fins, passive deformations are predominantly due to the hydrodynamic force of the surrounding fluid, while for insect wings, the wing inertia becomes also important in driving the surface deformation in addition to the aerodynamic force. In the current study, we use a two-dimensional elastic panel pitching or heaving in a free stream as a model to represent the animal wings or fins. Bending rigidity of the panel and the flapping frequency are varied so that the panel flaps near or away from resonance of the coupled fluid–structure system. The results show that at low mass ratios where the fluid force is dominant over the panel inertia, or at intermediate mass ratios where the fluid force is comparable with the panel inertia, the system resonance significantly improves or maximizes the thrust force and also efficiency; in addition, thrust performance is improved around resonance for a wide range of flapping frequencies or Strouhal numbers. On the other hand, at high mass ratios where the panel inertia is dominant, the system resonance makes thrust production increasingly difficult and propulsion much less efficient. In conclusion, the role of resonant vibration in thrust production of flapping wings and fins depends on participation of the fluid inertia in the process.

Diet and Prey Selection of Barn Swallows (<i>Hirundo rustica</i>) at Vancouver International Airport

The Barn Swallow (Hirundo rustica) is the most widely distributed aerial insectivore in north America, but has declined appreciably in recent decades. reasons for these declines are largely unknown, though presumably relate mainly to changes in prey availability. To help inform conservation priorities for this species, we assessed their diet and prey selection using birds lethally struck by aircraft at Vancouver International Airport (YVR). Esophagi and gizzards of 31 Barn Swallows collected from june 2013 to october 2013 contained insects mainly from the orders Hymenoptera (mean across birds = 40% of insect numbers), Diptera (31%), Hemiptera (15%), and Coleoptera (12%). To assess prey selection, we compared the esophagi and gizzard contents of 20 swallows collected from July 2013 to September 2013 to populations of aerial insects we sampled during the same period using Malaise traps. Barn Swallows selected strongly for insects in the order Hymenoptera (mainly Formicidae, which comprised 29% of diet), and selected against insects in the orders Coleoptera, Diptera, and Lepidoptera. For all prey taxa combined, Barn Swallows displayed strong selection for insects of length 4−8 mm (body length excluding appendages). Conversely, they selected against smaller and larger insects, despite the fact that smaller insects comprised about 80% of all insects sampled in Malaise traps. Combined with past studies, our results suggest that Barn Swallows select among available aerial insects within local feeding sites for taxa that (i) are of intermediate size, (ii) occur at relatively high density, and (iii) have poor flight performance.

Correction to: Wind and rain are the primary climate factors driving changing phenology of an aerial insectivore.

You have accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Irons Rachel D., Scurr April Harding, Rose Alexandra P., Hagelin Julie C., Blake Tricia and Doak Daniel F. 2017Correction to: Wind and rain are the primary climate factors driving changing phenology of an aerial insectivoreProc. R. Soc. B.2842017116820171168http://doi.org/10.1098/rspb.2017.1168SectionYou have accessCorrectionCorrection to: Wind and rain are the primary climate factors driving changing phenology of an aerial insectivore Rachel D. Irons Rachel D. Irons Google Scholar Find this author on PubMed Search for more papers by this author , April Harding Scurr April Harding Scurr Google Scholar Find this author on PubMed Search for more papers by this author , Alexandra P. Rose Alexandra P. Rose Google Scholar Find this author on PubMed Search for more papers by this author , Julie C. Hagelin Julie C. Hagelin Google Scholar Find this author on PubMed Search for more papers by this author , Tricia Blake Tricia Blake Google Scholar Find this author on PubMed Search for more papers by this author and Daniel F. Doak Daniel F. Doak http://orcid.org/0000-0001-8980-3392 Google Scholar Find this author on PubMed Search for more papers by this author Rachel D. Irons Rachel D. Irons Google Scholar Find this author on PubMed Search for more papers by this author , April Harding Scurr April Harding Scurr Google Scholar Find this author on PubMed Search for more papers by this author , Alexandra P. Rose Alexandra P. Rose Google Scholar Find this author on PubMed Search for more papers by this author , Julie C. Hagelin Julie C. Hagelin Google Scholar Find this author on PubMed Search for more papers by this author , Tricia Blake Tricia Blake Google Scholar Find this author on PubMed Search for more papers by this author and Daniel F. Doak Daniel F. Doak http://orcid.org/0000-0001-8980-3392 Google Scholar Find this author on PubMed Search for more papers by this author Published:28 June 2017https://doi.org/10.1098/rspb.2017.1168This article corrects the followingResearch ArticleWind and rain are the primary climate factors driving changing phenology of an aerial insectivorehttps://doi.org/10.1098/rspb.2017.0412 Rachel D. Irons, April Harding Scurr, Alexandra P. Rose, Julie C. Hagelin, Tricia Blake and Daniel F. Doak volume 284issue 1853Proceedings of the Royal Society B: Biological Sciences26 April 2017Proc. R. Soc. B284, 20170412 (Published Online 26 April 2017) (doi:10.1098/rspb.2017.0412)The affiliations for the authors of Irons et al. 2017 [1] are incorrect as the two distinct institutions were conflated. The correct affiliations for the authors of this study are as follows:University of Colorado, Boulder: R. D. Irons, A. P. Rose and D. F. Doak.Alaska Department of Fish and Game, Threatened, Endangered and Diversity Program: R. D. Irons and J. C. HagelinAlaska Songbird Institute: A. Harding Scurr and T. Blake.Footnotes© 2017 The Author(s)Published by the Royal Society. All rights reserved.ReferencesReference1Irons RD, Harding Scurr AH, Rose AP, Hagelin JC, Doak DF. 2017Wind and rain are the primary climate factors driving changing phenology of an aerial insectivore. Proc. R. Soc. B 284, 20170412. (doi:10.1098/rspb.2017.0412) Link, ISI, Google Scholar Previous Article VIEW FULL TEXT DOWNLOAD PDF FiguresRelatedReferencesDetailsRelated articlesWind and rain are the primary climate factors driving changing phenology of an aerial insectivore26 April 2017Proceedings of the Royal Society B: Biological Sciences This Issue28 June 2017Volume 284Issue 1857 Article InformationDOI:https://doi.org/10.1098/rspb.2017.1168PubMed:28659454Published by:Royal SocietyOnline ISSN:1471-2954History: Published online28/06/2017Published in print28/06/2017 License:© 2017 The Author(s)Published by the Royal Society. All rights reserved. Citations and impact Subjectsecologyenvironmental science Large datasets are available through Proceedings B's partnership with Dryad

Subtle differences in birds detected between organic and nonorganic farms in Saskatchewan Prairie Parklands by farm pair and bird functional group

Abstract Organic farming may be more beneficial to biodiversity than nonorganic farming but the comparison is often confounded by regional within-farm and landscape differences. We compared breeding bird species composition and abundance on 10 farm pairs of each type matched at the site level for land cover in the prairie parklands of Saskatchewan, Canada in 1990. Land cover was measured around bird point counts at two extents; ‘site’ (6.3 ha area) and ‘field’ (16.3 ha area). We pooled species into functional groups; linear mixed models showed no significant differences between farm types for species richness but that all birds, migratory birds using crops and aerial insectivores were more abundant on organic farms. A permutational multivariate analysis of variance demonstrated that farm type did not have a significant overall effect on compositional similarity but that pairwise differences existed between about half of the farm pairs (the direction of differences in beta diversity was not consistent between organic and nonorganic farms according to tests for the homogeneity of multivariate dispersions). Farm-pair differences were more pronounced for all birds and for migratory bird species using crops, migratory birds consuming grains and ground feeders, but not grassland birds. nMDS ordinations suggested that there was more variation in species composition and abundance on organic farms than nonorganic ones but the difference was not significant. Distance-based redundancy analysis (dbRDA) was used to examine the main drivers of bird species composition and abundance and to see which extent was most important; land cover at the field extent was more important than land cover at the site extent or the farming practices measured. The most important field-extent land cover was the amount of native grassland, woodland (including shelterbelts) and wetlands. After controlling for significant field-extent land cover, seed treatment, herbicide use, and number of passes were significant. At the site extent, greater non-crop heterogeneity had a significantly positive effect on abundance and species richness of several groups (e.g., grassland birds, migratory granivores, ground feeders, ground nesters) but a negative effect on richness of woodland birds and abundance of aerial insectivores. Relationships with crop heterogeneity were mostly negative and non-significant. Overall land cover heterogeneity at the site level was positively related to the richness of grassland birds. In contrast at the field extent, non-crop heterogeneity did not have any significant effects on the richness and abundance of any functional group. Crop heterogeneity had a significantly negative effect on aerial insectivore richness and abundance. In the early 1990s, differences in birds between organic and nonorganic farms in Saskatchewan were evident but subtle and variable among farms, and apparently most related to land cover-bird assemblage interactions/relationships.

Integrated population models reveal local weather conditions are the key drivers of population dynamics in an aerial insectivore.

Changes to weather patterns under a warming climate are complex: while warmer temperatures are expected virtually worldwide, decreased mean precipitation is expected at mid-latitudes. Migratory birds depend on broad-scale weather patterns to inform timing of movements, but may be more susceptible to local weather patterns during sedentary periods. We constructed Bayesian integrated population models (IPMs) to assess whether continental or local weather effects best explained population dynamics in an environmentally sensitive aerial insectivorous bird, the tree swallow (Tachycineta bicolor), along a transcontinental gradient from British Columbia to Saskatchewan to New York, and tested whether population dynamics were synchronous among sites. Little consistency existed among sites in the demographic rates most affecting population growth rate or in correlations among rates. Juvenile apparent survival at all sites was stable over time and greatest in New York, whereas adult apparent survival was more variable among years and sites, and greatest in British Columbia and Saskatchewan. Fledging success was greatest in Saskatchewan. Local weather conditions explained significant variation in adult survival in Saskatchewan and fledging success in New York, corroborating the hypothesis that local more than continental weather drives the population dynamics of this species and, therefore, demographic synchrony measured at three sites was limited. Nonetheless, multi-population IPMs can be a powerful tool for identifying correlated population trajectories caused by synchronous demographic rates, and can pinpoint the scale at which environmental drivers are responsible for changes. We caution against applying uniform conservation actions for populations where synchrony does not occur or is not fully understood.

Dietary tracers and stomach contents reveal pronounced alimentary flexibility in the freshwater mullet (Myxus capensis, Mugilidae) concomitant with ontogenetic shifts in habitat use and seasonal food availability

We investigated ontogenetic and seasonal variations in the diet of the freshwater mullet (Myxus capensis) across a river–estuary interface using dietary tracer (stable isotopes and fatty acids) and stomach content analyses. Two hypotheses were tested: (A) the freshwater mullet diet shifts as individuals grow and migrate from the estuary to the river, and (B) the dominant food resources utilized by freshwater mullet vary through time, mainly as a function of the seasonal changes in the availability of preferred food items in each habitat. Both hypotheses were supported, as our results indicated broad dietary flexibility by M. capensis, with utilized food items ranging from benthic microalgae to insects depending on habitat and seasonal patterns in availability of resources. Given the unexpected importance of invertebrate-derived prey, including some of terrestrial origin (i.e. aerial or semi-aquatic insects), during the freshwater phase of the M. capensis life cycle, we also emphasize a need for a re-assessment of the trophic designation of this species (previously designated as a strict detritivore).

Forest conversion to cattle ranching differentially affects taxonomic and functional groups of Neotropical bats

Understanding the effects of land conversion for livestock grazing on species diversity and functional groups continues to be urgently needed to assess how ranching affects animal assemblages and provide guidelines for managing landscapes under this omnipresent type of land use. Given Neotropical bats' high diversity of feeding habits and flying abilities, and that they play multiple, important ecological roles in ecosystems, they are an ideal study system to address such a need. We investigated the effects of livestock ranching on Neotropical bat species and functional groups composition via meta-analyses of published information. We used the odds-ratio metric to compare the frequency of occurrence of bat species in old-growth forest vs. areas influenced by livestock. Our results show no effects when considering bats as a group. However, significant effects emerge when they are assessed separately, on the basis of taxonomic family, feeding habit, conservation status and flying ability, showing that considering bats as a black box mutes relevant patterns. Molossid and phyllostomid species with high movement ability or omnivorous habit showed an increased frequency in livestock areas. In contrast, frugivores and aerial insectivores with low movement ability, carnivores, gleaning insectivores, nectarivores, sanguivores and species considered under some degree of extinction risk were significantly more frequent in old-growth forest. Overall, our results support that areas converted for livestock production retain only a subset of the Neotropical bat functional diversity while most of the functional groups are negatively impacted. Such heterogeneity of responses seems critical for our understanding of the effects of land use change on animal communities.

Wind and rain are the primary climate factors driving changing phenology of an aerial insectivore.

While the ecological effects of climate change have been widely observed, most efforts to document these impacts in terrestrial systems have concentrated on the impacts of temperature. We used tree swallow (Tachycineta bicolor) nest observations from two widely separated sites in central Alaska to examine the aspects of climate affecting breeding phenology at the northern extent of this species' range. We found that two measures of breeding phenology, annual lay and hatch dates, are more strongly predicted by windiness and precipitation than by temperature. At our longest-monitored site, breeding phenology has advanced at nearly twice the rate seen in more southern populations, and these changes correspond to long-term declines in windiness. Overall, adverse spring climate conditions known to negatively impact foraging success of swallows (wet, windy weather) appear to influence breeding phenology more than variation in temperature. Separate analyses show that short windy periods significantly delay initiation of individual clutches within years. While past reviews have emphasized that increasing variability in climate conditions may create physiological and ecological challenges for natural populations, we find that long-term reductions in inclement weather corresponded to earlier reproduction in one of our study populations. To better predict climate change impacts, ecologists need to more carefully test effects of multiple climate variables, including some, like windiness, that may be of paramount importance to some species, but have rarely been considered as strong drivers of ecological responses to climate alteration.

Tracking the migration of a nocturnal aerial insectivore in the Americas

BackgroundPopulations of Eastern Whip-poor-will (Antrostomus vociferous) appear to be declining range-wide. While this could be associated with habitat loss, declines in populations of many other species of migratory aerial insectivores suggest that changes in insect availability and/or an increase in the costs of migration could also be important factors. Due to their quiet, nocturnal habits during the non-breeding season, little is known about whip-poor-will migration and wintering locations, or the extent to which different breeding populations share risks related to non-breeding conditions.ResultsWe tracked 20 males and 2 females breeding in four regions of Canada using geolocators. Wintering locations ranged from the gulf coast of central Mexico to Costa Rica. Individuals from the northern-most breeding site and females tended to winter furthest south, although east-west connectivity was low. Four individuals appeared to cross the Gulf of Mexico either in spring or autumn. On southward migration, most individuals interrupted migration for periods of up to 15 days north of the Gulf, regardless of their subsequent route. Fewer individuals showed signs of a stopover in spring.ConclusionsUse of the southeastern United States for migratory stopover and a concentration of wintering locations in Guatemala and neighbouring Mexican provinces suggest that both of these regions should be considered potentially important for Canadian whip-poor-wills. This species shows some evidence of both “leapfrog” and sex-differential migration, suggesting that individuals in more northern parts of their breeding range could have higher migratory costs.

Intensive agriculture and insect prey availability influence oxidative status and return rates of an aerial insectivore

AbstractBirds breeding in agricultural landscapes contend with potential reductions in prey availability that may alter behavior and incur physiological costs. Individuals may need to increase foraging intensity, producing elevated reactive oxygen species involved in oxidative damage. Food scarcity or low food quality may also reduce levels of diet‐derived antioxidants. Here, we tested whether short‐term changes in insect biomass on agricultural sites produce changes in the oxidative status of tree swallows (Tachycineta bicolor), with the potential to influence return rates. We sampled 368 adult and 374 nestling swallows at five agricultural cropland and grassland‐dominated sites over three years from 2012 to 2014. Blood plasma was assessed for antioxidant capacity (OXY) and reactive oxygen metabolites (ROMs), a marker for oxidative damage. Overall, males appeared to have higher oxidative damage and therefore oxidative stress (calculated as the ratio between ROMs and OXY) than females. Consistent with our hypothesis, aerial insect biomass was a strong predictor of oxidative status in swallows. Adult plasma antioxidants were higher with greater insect biomass, while nestling plasma antioxidants, oxidative damage, and oxidative stress exhibited negative relationships with insect biomass. Annual return rates of adults were predicted by site type, age, fledging success, and oxidative status. In 2013, adult return rates were higher at grassland sites (41%) than at cropland sites (25%) and birds with lower plasma antioxidants the previous year were more likely to return. In 2014, adults were more likely to return if they had fledged more nestlings the previous season and if they had lower levels of oxidative damage the previous year. We conclude that even subtle changes in insect prey availability in agricultural landscapes caused by pesticides, intense cropping, and natural habitat loss can play a key role in swallow oxidative status, with subsequent effects on local return rates.

Effects of habitat degradation and fragmentation on butterfly biodiversity in West Kotawaringin, Central Kalimantan, Indonesia

Harmonis, Saud OR. 2016. Effects of habitat degradation and fragmentation on butterfly biodiversity in West Kotawaringin, Central Kalimantan. Biodiversitasx 18: 500-506. The main purpose of this study was to examine the effects of degradation and fragmentation habitats to butterfly communities. To be specific, species diversity, taxonomy structure, main species in every study sites were observed to find out the effects and correlation of each parameters. Field study was carried out in 8 sites in Kotawaringin Barat, Central Kalimantan Province, Indonesia. The specimens were collected using aerial insect nets and baited traps in January-February 2016. From the result of the study, the total of 1085 individual in 130 species was successfully collected. Based on distribution analysis using Shannon-Wiener index, the diversity of butterfly was in the range of middle to high categories (H’ = 2.7-3.5). Of another parameter analysis, it showed that butterfly communities were affected by degradation habitat, while fragmentation habitat did not influence to the butterfly communities. Furthermore, the range of degradation level in the study sites did not correlate with the number of species and taxonomy structures, but the distribution of the special-group of main species showed in correlation. Lexias dirtea was only found in dense forests (site S-7), then Neptis hylas and Parantica agleoides appeared in shrub habitat (site S-5 and S-6). The finding indicated that green patches have valuable contribution to conserve the ecosystem as valuable germplasm for butterflies and also arthropods.

Migratory stopover timing is predicted by breeding latitude, not habitat quality, in a long-distance migratory songbird

The timing of migration can have important survival impacts, as birds must synchronize their movements with favourable environmental conditions to reach their destination. The timing of arrival at and duration of migratory stopover may be largely governed by environmental conditions experienced en route as well as by endogenous factors, but our understanding of these processes is limited. We used light-level geolocators to collect start-to-finish spatio-temporal migration data for a declining aerial insectivore, the Purple Martin (Progne subis), that travels seasonally between North and South America. Using data obtained for birds originating from range-wide breeding populations, our objectives were to test intrinsic and extrinsic hypotheses for migration stopover duration as well as to identify important stopover regions during fall migration. We examined whether breeding latitude, fall migration timing, age, sex or habitat quality at stopover sites (measured using Normalized Difference Vegetation Index) influenced the duration of stopovers. We found that most individuals rely on the eastern coast of the Yucatan Peninsula, Honduras, and Nicaragua for stopovers during fall migration, where duration ranged from 1 to 36 days (average 6.8 ± 8.2). Stopovers in these regions were later and of longer duration for more northern breeding populations. Only breeding latitude predicted stopover duration, and not habitat quality at stopovers, lending support to the hypothesis that duration is prescribed by endogenous factors. The important core stopover regions we documented could be targeted for conservation efforts, particularly for steeply-declining, more northern breeding populations that have greater stopover duration in these areas.

Determining fine‐scale migratory connectivity and habitat selection for a migratory songbird by using new GPS technology

Migratory aerial insectivores are among the fastest declining avian groups, but our understanding of these trends has been limited by poor knowledge of migratory connectivity and the identification of critical habitat across the vast distances they travel annually. Using new, archival GPS loggers, we tracked individual purple martins Progne subis from breeding colonies across North America to determine precise (< > 10 m) locations of migratory and overwintering roost locations in South America and to test hypotheses for fine‐scale migratory connectivity and habitat use. We discovered weak migratory connectivity at the roost scale, and extensive, fine‐scale mixing of birds in the Amazon from distant (> 2000 km) breeding sites, with some individuals sharing the same roosting trees. Despite vast tracts of contiguous forest in this region, birds occupied a much more limited habitat, with most (56%) roosts occurring on small habitat islands that were strongly associated with water. Only 17% of these roosts were in current protected areas. These data reflect a critical advance in our ability to remotely determine precise migratory connectivity and habitat selection across vast spatial scales, enhancing our understanding of population dynamics and enabling more effective conservation of species at risk.

Conversion efficiency of α-linolenic acid to omega-3 highly unsaturated fatty acids in aerial insectivore chicks.

Food availability and quality are both critical for growing young animals. In nature, swallows (Tachycineta bicolor) and other aerial insectivores feed on both aquatic insects, which are rich in omega-3 highly unsaturated fatty acids (HUFAs), and terrestrial insects, which contain considerably lower amounts of omega-3 HUFAs. Carnivorous mammals and fishes must obtain omega-3 HUFAs from their diet, as they have lost the capacity to convert the precursor omega-3 α-linolenic acid (ALA) into omega-3 HUFAs. Thus, the relative value of aquatic versus terrestrial insects depends not only on the fatty acid composition of the prey but also on the capacity of consumers to convert ALA into omega-3 HUFAs. We used a combination of stable-isotope-labeled fatty acid tracers to ask whether, and how efficiently, tree swallows can deposit newly synthesized omega-3 HUFAs into tissue. Our data show for the first time that tree swallows can convert ALA into omega-3 HUFAs deposited in liver and skeletal muscle. However, high tree swallow demand for omega-3 HUFAs combined with low ALA availability in natural terrestrial foods may strain their modest conversion ability. This suggests that while tree swallows can synthesize omega-3 HUFAs de novo, omega-3 HUFAs are ecologically essential nutrients in natural systems. Our findings thus provide mechanistic support for our previous findings and the importance of omega-3 HUFA-rich aquatic insects for tree swallows and most likely other aerial insectivores with similar niches.

Combined analysis of roadside and off-road breeding bird survey data to assess population change in Alaska

ABSTRACT Management interest in North American birds has increasingly focused on species that breed in Alaska, USA, and Canada, where habitats are changing rapidly in response to climatic and anthropogenic factors. We used a series of hierarchical models to estimate rates of population change in 2 forested Bird Conservation Regions (BCRs) in Alaska based on data from the roadside North American Breeding Bird Survey (BBS) and the Alaska Landbird Monitoring Survey, which samples off-road areas on public resource lands. We estimated long-term (1993–2015) population trends for 84 bird species from the BBS and short-term (2003–2015) trends for 31 species from both surveys. Among the 84 species with long-term estimates, 11 had positive trends and 17 had negative trends in 1 or both BCRs; negative trends were primarily found among aerial insectivores and wetland-associated species, confirming range-wide negative continental trends for many of these birds. Three species with negative trends in the contiguous Unit...

Variation in developmental trajectories of physiological and somatic traits in a common songbird approaching fledging.

In avian species, little is known about the development of physiological traits in the days preceding fledging, a critical life history transition marked by a high mortality rate. Developmental trajectory during this period may be flexible based on ecological context or hardwired, with potential costs for variation in growth in the form of oxidative stress. Patterns in development are likely to relate to variation in life history, for which seabirds and aerial insectivores have been well studied, while our focal species is a grassland ground forager, the European starling (Sturnus vulgaris). We show that changes in haematocrit, body mass and wing length are independent of year and brood quality, while changes in haemoglobin concentration are higher in low-quality broods. Moreover, we also identify higher oxidative stress in low-quality year and second broods, a potential cost for maintaining a hardwired developmental trajectory in a lower quality environment. Finally, we experimentally test the effects of food supplementation on development and maturity of chicks at fledging to show that although food increases body mass early in development, it does not change the trajectory or final maturity of chicks at fledging. Collectively this study demonstrates that some developmental changes prior to fledging may be hardwired, but may have long-term oxidative costs in low-quality environments.

No effect of insect abundance on nestling survival or mass for three aerial insectivores

Imlay, T. L., H. A. R. Mann, and M. L. Leonard. 2017. No effect of insect abundance on nestling survival or mass for three aerial insectivores. Avian Conservation and Ecology 12(2):19. https://doi.org/10.5751/ACE-01092-120219

Assessing the relative use of clearcuts, burned stands, and wetlands as breeding habitat for two declining aerial insectivores in the boreal forest

Fires are an ecological process essential for species dependent on early successional habitat in forested landscapes. In a wildlife context, clearcut forestry practices can mimic forest fires through the creation of early successional forest clearings, however, evidence that clearcuts provide the same ecological value as fire is mixed. In temperate deciduous/hardwood forests, many species that depend on early successional habitat are known to use clearcuts, including Eastern Whip-poor-wills (Antrostomus vociferous) and Common Nighthawks (Chordeiles minor), two threatened aerial insectivorous birds. However, the relative importance of recent clearcuts as breeding habitat relative to other more naturally open habitat types in the boreal forest is unknown. In May-July 2015 we studied occupancy and detectability of these two species in the boreal forest of northwestern Ontario. We first determined whether occupancy differed among three open habitats: burned stands, recent clearcuts, and open wetlands, and whether it differed in relation to the size of clearcut patches. We also examined how detectability of each species varied with time of day, season and weather conditions. Site occupancy for the Eastern Whip-poor-will and Common Nighthawk averaged 0.413 and 0.437, respectively. We found no significant difference in occupancy of either species in relation to burned stands, recent clearcuts, or open wetlands, although Eastern Whip-poor-will occupancy tended to be higher in burned stands. Occupancy did not show a linear relationship with patch size but neither species was found in the smallest open patches (<3ha), perhaps indicating a minimum size threshold, although further study is needed. The detection of each species was positively correlated with the occurrence of the other species, suggesting that they were both selecting similar site characteristics. Detectability for Eastern Whip-poor-will was highest after sunset and increased over the course of the breeding season, while for Common Nighthawk, detectability was similar during and after sunset and decreased over the season. Our results suggest that Eastern Whip-poor-will and Common Nighthawk show similar preference for natural and managed open sites and that recent clearcuts may provide early successional habitat in the absence of burned stands. Our results also extend the known breeding range of Eastern Whip-poor-will, which further emphasizes the need for future research on these poorly studied species in the boreal forest.

Convergent evolution in social swallows (Aves: Hirundinidae).

Behavioral shifts can initiate morphological evolution by pushing lineages into new adaptive zones. This has primarily been examined in ecological behaviors, such as foraging, but social behaviors may also alter morphology. Swallows and martins (Hirundinidae) are aerial insectivores that exhibit a range of social behaviors, from solitary to colonial breeding and foraging. Using a well‐resolved phylogenetic tree, a database of social behaviors, and morphological measurements, we ask how shifts from solitary to social breeding and foraging have affected morphological evolution in the Hirundinidae. Using a threshold model of discrete state evolution, we find that shifts in both breeding and foraging social behavior are common across the phylogeny of swallows. Solitary swallows have highly variable morphology, while social swallows show much less absolute variance in all morphological traits. Metrics of convergence based on both the trajectory of social lineages through morphospace and the overall morphological distance between social species scaled by their phylogenetic distance indicate strong convergence in social swallows, especially socially foraging swallows. Smaller physical traits generally observed in social species suggest that social species benefit from a distinctive flight style, likely increasing maneuverability and foraging success and reducing in‐flight collisions within large flocks. These results highlight the importance of sociality in species evolution, a link that had previously been examined only in eusocial insects and primates.

High Accuracy Acquisition of 3-D Flight Trajectory of Individual Insect Based on Phase Measurement.

Accurate acquisition of 3-D flight trajectory of individual insect could be of benefit to the research of insect migration behaviors and the development of migratory entomology. This paper proposes a novel method to acquire 3-D flight trajectory of individual insect. First, based on the high range resolution synthesizing and the Doppler coherent processing, insects can be detected effectively, and the range resolution and velocity resolution are combined together to discriminate insects. Then, high accuracy range measurement with the carrier phase is proposed. The range measurement accuracy can reach millimeter level and benefits the acquisition of 3-D trajectory information significantly. Finally, based on the multi-baselines interferometry theory, the azimuth and elevation angles can be obtained with high accuracy. Simulation results prove that the retrieval accuracy of a simulated target’s 3-D coordinates can reach centimeter level. Experiments utilizing S-band radar in an anechoic chamber were taken and results showed that the insects’ flight behaviors and 3-D coordinates’ variation matched the practical cases well. In conclusion, both the simulated and experimental datasets validate the feasibility of the proposed method, which could be a novel measurement way of monitoring flight trajectory of aerial free-fly insects.