Aerial Insectivores Research Articles

EDITOR'S CHOICE: Enhancing gardens as habitats for flower‐visiting aerial insects (pollinators): should we plant native or exotic species?

Summary Domestic gardens typically consist of a mixture of native and non‐native plants which support biodiversity and provide valuable ecosystem services, particularly in urban environments. Many gardeners wish to encourage biodiversity by choosing appropriate plant taxa. The value of native and non‐native plants in supporting animal biodiversity is, however, largely unknown. The relative value of native and non‐native garden plants to invertebrates was investigated in a replicated field experiment. Plots (deliberately akin to garden borders) were planted with one of three treatments, representing assemblages of plants based on origin (native, near‐native and exotic). Invertebrates and resource measurements were recorded over four years. This paper reports the abundance of flower‐visiting aerial insects (‘pollinators’) associated with the three plant assemblages. For all pollinator groups on all treatments, greater floral resource resulted in an increase in visits. There was, however, a greater abundance of total pollinators recorded on native and near‐native treatments compared with the exotic plots. Short‐tongued bumblebees followed the same pattern whilst more hoverflies were recorded on the native treatment than the other treatments, and more honeybees on the near‐native treatment. There was no difference between treatments in abundance of long‐tongued bumblebees or solitary bees. The lack of difference in solitary bee abundance between treatments was probably due to a third of individuals from this group being recorded on one exotic plant species. The number of flower visitors corresponded to the peak flowering period of the treatments, that is there were fewer flower visitors to the exotic treatment compared with the other treatments in early summer but relatively more later in the season. Synthesis and applications. This experiment has demonstrated that utilizing plants from only a single region of origin (i.e. nativeness) may not be an optimal strategy for resource provision for pollinating insects in gardens. Gardens can be enhanced as a habitat by planting a variety of flowering plants, biased towards native and near‐native species but with a selection of exotics to extend the flowering season and potentially provide resources for specialist groups.

Change Points in the Population Trends of Aerial-Insectivorous Birds in North America: Synchronized in Time across Species and Regions.

North American populations of aerial insectivorous birds are in steep decline. Aerial insectivores (AI) are a group of bird species that feed almost exclusively on insects in flight, and include swallows, swifts, nightjars, and flycatchers. The causes of the declines are not well understood. Indeed, it is not clear when the declines began, or whether the declines are shared across all species in the group (e.g., caused by changes in flying insect populations) or specific to each species (e.g., caused by changes in species’ breeding habitat). A recent study suggested that population trends of aerial insectivores changed for the worse in the 1980s. If there was such a change point in trends of the group, understanding its timing and geographic pattern could help identify potential causes of the decline. We used a hierarchical Bayesian, penalized regression spline, change point model to estimate group-level change points in the trends of 22 species of AI, across 153 geographic strata of North America. We found evidence for group-level change points in 85% of the strata. Change points for flycatchers (FC) were distinct from those for swallows, swifts and nightjars (SSN) across North America, except in the Northeast, where all AI shared the same group-level change points. During the 1980s, there was a negative change point across most of North America, in the trends of SSN. For FC, the group-level change points were more geographically variable, and in many regions there were two: a positive change point followed by a negative change point. This group-level synchrony in AI population trends is likely evidence of a response to a common environmental factor(s) with similar effects on many species across broad spatial extents. The timing and geographic patterns of the change points that we identify here should provide a spring-board for research into the causes behind aerial insectivore declines.

Effects of area size, heterogeneity, isolation, and disturbances on urban park avifauna in a highly populated tropical city

We assessed bird diversity and nesting activity in 54 urban parks in the core of a highly populated East-Asian tropical city to investigate the effects of area, isolation, habitat heterogeneity, and human disturbances on avifauna. Tree density and heterogeneity were lower while isolation was greater in small than in large or medium-sized parks. Yet, park features were often interrelated, with isolation variables negatively correlated to each other, heterogeneity positively correlated to area, and habitat variables mostly positively correlated with one another but variously to disturbances; whereas pedestrian densities wee positively correlated with green area proportions (ISO3) but negatively with the distances to large green areas (ISO2). Park size played a primary role by positively affecting species richness and numbers of nesting species, thus contributing to higher total and nesting species heterogeneity, and determining the occurrence of a greatest number of species. Pedestrian density, canopy cover, and ground heterogeneity played secondary roles, whereas isolation appeared less influential at the community level. Omnivores, granivores, and aerial insectivores appeared more abundant but were dominated by several common species. Nesting was restricted to even fewer species. While species varied in the occupancy responses to these factors, tree heterogeneity positively affected the nesting of Zosterops japonicus and cavity-nesting birds, and predator density negatively affected those of Lonchura punctulata and Streptopelia doves. Improved urban land use planning and park management incorporating these effects should be implemented to enhance breeding and avoid compositional homogenization for long-term sustainability of urban avian diversity.

A Continent-Wide Migratory Divide in North American Breeding Barn Swallows (Hirundo rustica)

Populations of most North American aerial insectivores have undergone steep population declines over the past 40 years but the relative importance of factors operating on breeding, wintering, or stopover sites remains unknown. We used archival light-level geolocators to track the phenology, movements and winter locations of barn swallows (Hirdundo rustica; n = 27) from populations across North America to determine their migratory connectivity. We identified an east-west continental migratory divide for barn swallows with birds from western regions (Washington State, USA (n = 8) and Saskatchewan, Canada (n = 5)) traveling shorter distances to wintering areas ranging from Oregon to northern Colombia than eastern populations (Ontario (n = 3) and New Brunswick (n = 10), Canada) which wintered in South America south of the Amazon basin. A single swallow from a stable population in Alabama shared a similar migration route to eastern barn swallows but wintered farther north in northeast Brazil indicating a potential leap frog pattern migratory among eastern birds. Six of 9 (67%) birds from the two eastern populations and Alabama underwent a loop migration west of fall migration routes including around the Gulf of Mexico travelling a mean of 2,224 km and 722 km longer on spring migration, respectively. Longer migration distances, including the requirement to cross the Caribbean Sea and Gulf of Mexico and subsequent shorter sedentary wintering periods, may exacerbate declines for populations breeding in northeastern North America.

Food habits and resource partitioning in a guild of Neotropical swifts

ABSTRACT The Coastal Cordillera of Venezuela has a rich avifauna including swifts. The aerial arthropod prey of three species found there, Gray-rumped Swift (Chaetura cinereiventris), Vaux’s Swift (Chaetura vauxi), and White-tipped Swift (Aeronautes montivagus), included spiders plus nine orders and 110 families of insects. Diptera and Hymenoptera were the most numerous prey taxa (>60%) taken by all three swifts. Prey size ranged from 0.5–17.9 mm body length, and averaged 2.69 mm for Gray-rumped Swifts, 2.91 mm for Vaux’s Swifts, and 5.52 mm for White-tipped Swifts. Niche breadth was similar in Gray-rumped and Vaux’s Swifts (2.4 and 3.13), and niche overlap was also high (0.98). Niche breadth was higher in White-tipped Swifts (8.49) and niche overlap was <60 with both Gray-rumped and Vaux’s swifts. Observed elevational differences in foraging habitat and altitudinal foraging zones are proposed as resource partitioning mechanisms for this guild of sympatric aerial insectivores.

Observations on Fecal Sac Consumption and Near-ground Foraging Behavior in the Olive-sided Flycatcher (Contopus cooperi)

We present details on parental care and foraging behavior of Olive-sided Flycatchers (Contopus cooperi) in central Alaska. We document the first evidence of fecal sac consumption in this species. Both sexes exhibited this behavior while tending chicks less than one week old. Adults with older nestlings (1.5–2 weeks) removed fecal sacs only. The general pattern of reduced fecal sac consumption with chick age is consistent with other passerines and may supplement parental nutrition. Near-ground foraging behavior in C. cooperi is rarely reported, as birds typically sally for aerial insects near or above the canopy. Two breeding females fed multiple times from 1–3 m perches, hovering over, flying directly above or disappearing into low vegetation (<0.5 m) for up to 15 secs. Low stumps and saplings in a wood cutting area and in undisturbed forest provided access to patches of flowering vegetation that appeared to concentrate pollinator prey during cool or inclement weather. Given the conservation concerns for this species, its low productivity, dietary specialization, and hypothesized early-season reliance on insect prey, flowering vegetation presents a testable visual stimulus that may govern settlement behavior of breeding adults.

Short-term changes in summer and winter resident bird communities following a high severity wildfire in a southern USA mixed pine/hardwood forest

High severity forest fires are increasing in large areas of the southern and western United States as the climate becomes warmer and drier. Given their strong roles in ecosystem dynamics, documenting the response of bird communities to wildfires is important for improving our understanding and management of post-wildfire ecosystems. However, because wildfires are unplanned events, relatively few studies have been conducted to assess local-scale impacts on forest bird communities. In this study, we had the opportunity to use a before-after, control-impact (BACI) approach to assess the response of resident birds to high severity wildfires that occurred in the Lost Pines ecoregion of Texas in September and October 2011. We replicated a previous study using point count surveys to assess summer and winter bird community changes ca. 1year after the wildfires. We found that total number of detected individuals did not change following the wildfires, but winter bird species richness increased in burned habitat. Changes were apparent at the foraging guild-level for the winter bird community, with an increase in aerial insectivores and decrease in bark insectivores. Summer and winter bird community composition changes were apparent at the species-level and generally agreed with species-specific habitat preferences. For example, species such as eastern bluebirds and chipping sparrows that prefer open woodlands were positively associated with burned habitat. Our results provide quantitative evidence that high severity forest fires increased habitat suitability for many resident bird species. At the landscape-scale, fire-induced increases in habitat heterogeneity could result in higher bird diversity in the Lost Pines ecoregion. We expect bird community composition will be dynamic in the Lost Pines ecoregion over the next few decades as the burned habitat continues to change through successional processes and post-fire management actions.

Bird population responses to wildfire and planned burns in foothill forests of Victoria, Australia

Fires and people have helped shape forest ecosystems. Planned burns can be used to reduce social or ecological risks from wildfires, but we need a better understanding of the ecological effects of planned burns and wildfire over various temporal and spatial scales. Here, two approaches were used to answer various questions about responses of diurnal birds to fire regimes in mixed eucalypt forests in the foothills of Victoria, Australia: what are the effects of planned burns (at two different frequencies and seasons) when applied systematically over many years, and what are the short-term effects of severe wildfire? A long-term experiment examined planned burns in two seasons and at two frequencies on 25 sites in Wombat State Forest in 1984. An opportunistic study compared bird abundance in 33 burnt and 33 unburnt sites in the year after an extensive severe wildfire in Bunyip State Park in 2009. Brief reference is also made to a retrospective study, which provided a longer-term perspective by examining bird abundances at 113 sites in eastern Victoria that had been subject to different regimes over the past 40+ years, addressing questions about the impacts of different fire frequencies and times since fire. This paper considers data from snapshot surveys in 2009–2012. Data from Wombat State Forest showed significant effects of fire treatments for just four of the 27 species analysed (p < 0.05). In frequently burnt sites, Brown Thornbills Acanthiza pusilla (shrub foraging insectivores) and Scarlet Robins Petroica boodang (open-ground insectivores) were least common, and Rufous Whistlers Pachycephala rufiventris (canopy-foraging insectivores) and Australian Magpies Cracticus tibicen (open-ground insectivores) were most common. There was weak evidence that three species were advantaged by burning in autumn rather than spring, and one of them (White-winged Chough Corcorax melanorhamphos, an open-ground insectivore) was rarely recorded except in sites burnt in autumn. Data from Bunyip State Park showed that birds were 77 % less numerous on burnt than unburnt sites in the winter after severe bushfire, but some redistribution had occurred by the next spring, along with an unprecedented spring influx of White-browed Woodswallows Artamus superciliosus (aerial insectivores) to burnt sites from inland Australia. The study shows that planned burns can be conducted in spring or autumn every 3–10 years with only small effects on common forest birds, at least when they are conducted on small areas in a forest with a history of disturbance. Wildfires can have much more dramatic short-term effects on bird populations. The retrospective study suggested that these effects may be short-lived, as such dramatic contrasts were not found between sites burned at different times beyond 3 years. Multiple approaches will be needed to answer key questions about longer-term effects of planned burns and wildfires in order to help reduce risk and conserve biodiversity.

Assessing costs of carrying geolocators using feather corticosterone in two species of aerial insectivore

Assessing costs of carrying geolocators using feather corticosterone in two species of aerial insectivore

Assessing costs of carrying geolocators using feather corticosterone in two species of aerial insectivore.

Despite benefits of using light-sensitive geolocators to track animal movements and describe patterns of migratory connectivity, concerns have been raised about negative effects of these devices, particularly in small species of aerial insectivore. Geolocators may act as handicaps that increase energetic expenditure, which could explain reported effects of geolocators on survival. We tested this ‘Energetic Expenditure Hypothesis’ in 12 populations of tree swallows (Tachycineta bicolor) and barn swallows (Hirundo rustica) from North America and Europe, using measurements of corticosterone from feathers (CORTf) grown after deployment of geolocators as a measure of physiology relevant to energetics. Contrary to predictions, neither among- (both species) nor within-individual (tree swallows only) levels of CORTf differed with respect to instrumentation. Thus, to the extent that CORTf reflects energetic expenditure, geolocators apparently were not a strong handicap for birds that returned post-deployment. While this physiological evidence suggests that information about migration obtained from returning geolocator-equipped swallows is unbiased with regard to levels of stress, we cannot discount the possibility that corticosterone played a role in reported effects of geolocators on survival in birds, and suggest that future studies relate corticosterone to antecedent factors, such as reproductive history, and to downstream fitness costs.

Variable contribution of functional prey groups in diets reveals inter- and intraspecific differences in faecal concentrations of essential and non-essential elements in three sympatric avian aerial insectivores: A re-assessment of usefulness of bird faeces in metal biomonitoring

Aerial insectivores through their insect diet can contribute to biotransfer of elements across habitats. We investigate the relationship between dietary composition as expressed by the contributions of six functional invertebrate prey groups (primarily of agriculturally subsidised invertebrates characteristic of agricultural areas in temperate regions of Europe) and concentrations of essential (Na, K, Ca, Mg, Fe, Cu, Zn, Mn, Co) and non-essential (As, Cd, Pb) elements of environmental concern in the faeces of nestlings of three species of avian aerial insectivores – Common Swift Apus apus, Barn Swallow Hirundo rustica and House Martin Delichon urbicum – which breed sympatrically and use apparently similar resources of flying insect prey. There were significant differences between the species for 7 of the 12 elements (Ca, Zn, Cu, Co, As, Pb, Cd); these differences were attributable to the variable dietary composition, even though the concentrations of the elements varied enormously between the faecal samples from the individual species. Partial correlation analysis between the biomass (expressed in mg dry weight) of the six functional prey groups and faecal concentrations of elements showed the highest number of significant relationships for toxic metals (As, Pb and Cd). The results of the General Regression Model explaining faecal element concentrations revealed the different explanatory power of the effects of PCA (of six functional prey groups) dietary scores. A significant fit of GRM was obtained for 7 elements (Na, Mg, Fe, Mn, As, Pb, Cd) for Barn Swallows, 2 elements (Cu, As) for House Martins and 1 element (Mn) for Common Swifts. Overall, the results confirmed our predictions that the biomass of consumed coprophilous taxa and insects from crop habitats was positively correlated with the faecal concentrations of toxic elements. Unexpectedly, however, the faecal samples (primarily those of Common Swifts) that contained many oil-seed rape insect pests had lower Ca, Pb and Cd levels and a higher As level. Our study implies that the cross-boundary transfer of contaminants, primarily non-essential elements, by aerially foraging birds through the considerable accumulation of their faeces has potential consequences for the local biogeochemical cycle and environmental quality.

Rapid detection of Fusarium circinatum propagules on trapped pine beetles

SummaryPitch canker is a destructive disease of pine caused by the fungus Fusarium circinatum. This taxon is listed as a quarantine fungus for several regional plant protection organizations throughout the world. Whereas long‐distance spread of the disease is made possible through the trade of infected pine seeds, local spread is caused by aerial dispersion or insect transportation of the fungal conidia. Developing a reliable and efficient tool to detect of F. circinatum in insects would be very useful to monitor the local spread of the pathogen. This tool would also provide the means to assess the range of insect species that could serve as potential vector of the fungus. A DNA extraction protocol was optimized and combined with a real‐time PCR test to detect F. circinatum on pine beetles. Using artificially contaminated Ips sexdentatus, it was shown that the test was able to detect down to 10 F. circinatum conidia per individual, and 20 conidia per batch of 10 insects, which is below the lowest inoculum load occurring in nature. With this technique, several batches of up to 10 insects may be analysed simultaneously, with a timescale for analysis reduced to &lt;5 h and without the need for expertise in Fusarium taxonomy. This tool may be useful to monitor potential spread of the pathogen across regions. Using this method, to date, despite F. circinatum foci occurred in Northern Spanish regions across the border in France, the pathogen was not found on I. sexdentatus.

Functional invertebrate prey groups reflect dietary responses to phenology and farming activity and pest control services in three sympatric species of aerially foraging insectivorous birds.

Farming activity severely impacts the invertebrate food resources of farmland birds, with direct mortality to populations of above-ground arthropods thorough mechanical damage during crop harvests. In this study we assessed the effects of phenological periods, including the timing of harvest, on the composition and biomass of prey consumed by three species of aerial insectivorous birds. Common Swifts Apus apus, Barn Swallows Hirundo rustica and House Martins Delichon urbica breed sympatrically and most of their diet is obtained from agricultural sources of invertebrate prey, especially from oil-seed rape crops. We categorized invertebrate prey into six functional groups, including oil-seed rape pests; pests of other arable crops; other crop-provisioned taxa; coprophilous taxa; and taxa living in non-crop and mixed crop/non-crop habitats. Seasonality impacted functional groups differently, but the general direction of change (increase/decrease) of all groups was consistent as indexed by prey composition of the three aerial insectivores studied here. After the oil-seed rape crop harvest (mid July), all three species exhibited a dietary shift from oil-seed rape insect pests to other aerial invertebrate prey groups. However, Common Switfts also consumed a relative large quantity of oil-seed rape insect pests in the late summer (August), suggesting that they could reduce pest insect emigration beyond the host plant/crop. Since these aerially foraging insectivorous birds operate in specific conditions and feed on specific pest resources unavailable to foliage/ground foraging avian predators, our results suggest that in some crops like oil-seed rape cultivations, the potential integration of the insectivory of aerial foraging birds into pest management schemes might provide economic benefits. We advise further research into the origin of airborne insects and the role of aerial insectivores as agents of the biological control of crop insect pests, especially the determination of depredation rates and the cascading effects of insectivory on crop damage and yield.

Linking Population Declines with Diet Quality in Vaux's Swifts

Over the past 50 years, a range of environmental stressors has resulted in aerial insectivores throughout North America experiencing sharp population declines. Vaux’s swifts (Chaetura vauxi) are small, long-distance migratory birds that are currently experiencing range-wide population declines, especially at the their northern range limit. Many studies attribute the Vaux’s swift’s population decline to a loss in nesting habitat; however, other potentially exacerbating factors, such as changes in insect composition and diet, remain unstudied. Here, we examine a ~26 year dietary archive of Vaux’s swift guano to ask whether diet composition has changed over time. Vaux’s swifts roost communally at the same roost sites each year when migrating, often within decommissioned brick chimneys. As a result, guano accumulates at the base of these roost sites, providing a chronostratified snapshot of the bird’s historic diet. We obtained a vertical core sample from a Vaux’s swift guano deposit in a chimney on Vancouver Island, BC, Canada. We symmetrically stratified the guano and assessed diet composition by visually analyzing egested arthropod exoskeletons, identifying them to order, and measuring δ15N signatures at each layer. Our 26-year data set revealed an increase in the ratio of Hemiptera to Coleoptera corresponding with an increase in δ15N, suggesting a possible decline in diet quality through time because Hemipterans tend towards higher trophic status than Coleopterans, but are of less caloric value per capita. In addition, δ15N was significantly negatively correlated with an annual population index (Breeding Bird Survey). We suggest a reduction in diet quality may be contributing to the decline of Vaux’s swift populations, and could be contributing to more declines in other aerial insectivore species.

Barn SwallowHirundo rusticaparents work harder when foraging conditions are good

In altricial birds, the great effort involved in supplying food to nestlings can create trade‐offs in the allocation of resources between the current brood and parental self‐maintenance. In poor foraging conditions, parents have to adjust their energy expenditure in relation to the increased foraging costs. However, intra‐specific variation in parental energy expenditure has rarely been evaluated in the context of these trade‐offs. Here, we quantified the daily energy expenditure (DEE) of parent Barn SwallowsHirundo rusticaduring the nestling period in relation to foraging conditions while controlling for differences in brood size and nestling age. DEE varied substantially with environmental conditions, increasing by 10 kJ/day per 5 °C in ambient temperature, and by 11 kJ/day per hour in day length. Parent birds did not compensate for a poor aerial insect supply on cool days, but reduced their DEE. Parents only slightly buffered a negative energy balance during chick provisioning with stored body reserves. They did not sacrifice their own energy demands to keep up a high energy flow to the brood when foraging conditions were poor. Instead they worked harder when foraging conditions allowed a surplus intake, fully compensating for their additional efforts, and made maximum use of the rich food supply, allowing the brood to accrue body reserves to compensate for low food intake on cold days. This strategy of energy management may have evolved in the context of the adaptation to the aerial foraging mode and to the ephemeral nature of aerial food resources.

Severe recent decrease of adult body mass in a declining insectivorous bird population.

Migratory bird species that feed on air-borne insects are experiencing widespread regional declines, but these remain poorly understood. Agricultural intensification in the breeding range is often regarded as one of the main drivers of these declines. Here, we tested the hypothesis that body mass in breeding individuals should reflect habitat quality in an aerial insectivore, the tree swallow (Tachycineta bicolor), along a gradient of agricultural intensity. Our dataset was collected over 7 years (2005-2011) and included 2918 swallow captures and 1483 broods. Analyses revealed a substantial decline of the population over the course of the study (-19% occupancy rate), mirrored by decreasing body mass. This trend was especially severe in females, representing a total loss of 8% of their mass. Reproductive success was negatively influenced by intensive agriculture, but did not decrease over time. Interestingly, variation in body mass was independent of breeding habitat quality, leading us to suggest that this decline in body mass may result from carry-over effects from non-breeding areas and affect population dynamics through reduced survival. This work contributes to the growing body of evidence suggesting that declines in migratory aerial insectivores are driven by multiple, complex factors requiring better knowledge of year-round habitat use.

Phototaxis and polarotaxis hand in hand: night dispersal flight of aquatic insects distracted synergistically by light intensity and reflection polarization

Based on an earlier observation in the field, we hypothesized that light intensity and horizontally polarized reflected light may strongly influence the flight behaviour of night-active aquatic insects. We assumed that phototaxis and polarotaxis together have a more harmful effect on the dispersal flight of these insects than they would have separately. We tested this hypothesis in a multiple-choice field experiment using horizontal test surfaces laid on the ground. We offered simultaneously the following visual stimuli for aerial aquatic insects: (1) lamplit matte black canvas inducing phototaxis alone, (2) unlit shiny black plastic sheet eliciting polarotaxis alone, (3) lamplit shiny black plastic sheet inducing simultaneously phototaxis and polarotaxis, and (4) unlit matte black canvas as a visually unattractive control. The unlit matte black canvas trapped only a negligible number (13) of water insects. The sum (16,432) of the total numbers of water beetles and bugs captured on the lamplit matte black canvas (7,922) and the unlit shiny black plastic sheet (8,510) was much smaller than the total catch (29,682) caught on the lamplit shiny black plastic sheet. This provides experimental evidence for the synergistic interaction of phototaxis (elicited by the unpolarized direct lamplight) and polarotaxis (induced by the strongly and horizontally polarized plastic-reflected light) in the investigated aquatic insects. Thus, horizontally polarizing artificial lamplit surfaces can function as an effective ecological trap due to this synergism of optical cues, especially in the urban environment.

An Assessment of Nestling Diet Composition in the Violet-Green Swallow (Tachycineta thalassina)

Aerial insectivores have undergone marked population declines in recent decades, including members of the Hirundinidae (swallows), which have long served as sentinels of environmental change. In contrast to other swallow species that breed in North America, we have a poor understanding of most aspects of the basic ecology and life history of the violetgreen swallow (Tachycineta thalassina), a widespread species found throughout the Pacific Northwest. In this study, we investigated the diet composition of violet-green swallow nestlings to document the consumption of food resources by offspring during adult feeding visits. We identified arthropods from 13 taxonomic orders in feeding boluses and found that representation of taxonomic groups was highly uneven and dominated by Diptera and Hemiptera. Although swallows did provision some large prey, the great majority (i.e., 92.6% of 1047) of food items were < 5 mm in length. Feeding boluses collected from the congeneric tree swallow (T. bicolor) at the same study area and during the same time period revealed similar patterns of size and taxonomic representation of diet composition of violet-green nestlings, raising questions as to how these species partition critical resources in areas of sympatry.

Historical decline and probable extinction of the Jamaican Golden SwallowTachycineta euchrysea euchrysea

SummaryThe endemic Jamaican subspecies of the Golden SwallowTachycineta euchrysea euchryseahas been rare and locally distributed since its discovery in 1847. By the 1950s, its geographic range had contracted to a small region along the northern frontier of Cockpit Country. The last unequivocal sight records occurred in the early 1980s, raising strong concern about the swallow’s conservation status. I conducted an island-wide search for the swallow from 1994 through 2012. Standardised censuses of aerial insectivores at 1,281 sites, including the last redoubts of the Golden Swallow in Trelawny Parish, revealed no evidence of the species. These surveys and the absence of documented sight records during the past three decades suggest that the Jamaican race of the Golden Swallow is close to extinction if not already extinct. The cause of the population decline is unknown but is most likely linked to chronic predation by introduced mammalian predators, particularly the arboreal black ratRattus rattus.

Ecological Energetics of an Abundant Aerial Insectivore, the Purple Martin

The atmospheric boundary layer and lower free atmosphere, or aerosphere, is increasingly important for human transportation, communication, environmental monitoring, and energy production. The impacts of anthropogenic encroachment into aerial habitats are not well understood. Insectivorous birds and bats are inherently valuable components of biodiversity and play an integral role in aerial trophic dynamics. Many of these insectivores are experiencing range-wide population declines. As a first step toward gaging the potential impacts of these declines on the aerosphere’s trophic system, estimates of the biomass and energy consumed by aerial insectivores are needed. We developed a suite of energetics models for one of the largest and most common avian aerial insectivores in North America, the Purple Martin ( Progne subis ). The base model estimated that Purple Martins consumed 412 (± 104) billion insects*y-1 with a biomass of 115,860 (± 29,192) metric tonnes*y-1. During the breeding season Purple Martins consume 10.3 (+ 3.0) kg of prey biomass per km3 of aerial habitat, equal to about 36,000 individual insects*km-3. Based on these calculations, the cumulative seasonal consumption of insects*km-3 is greater in North America during the breeding season than during other phases of the annual cycle, however the maximum daily insect consumption*km-3 occurs during fall migration. This analysis provides the first range-wide quantitative estimate of the magnitude of the trophic impact of this large and common aerial insectivore. Future studies could use a similar modeling approach to estimate impacts of the entire guild of aerial insectivores at a variety of temporal and spatial scales. These analyses would inform our understanding of the impact of population declines among aerial insectivores on the aerosphere’s trophic dynamics.