Tree Swallows Research Articles

Mercury exposure to swallows breeding in Canada inferred from feathers grown on breeding and non-breeding grounds.

Aerial insectivorous birds such as swallows have been the steepest declining groups of birds in North America over the last 50 years but whether such declines are linked to contaminants has not been examined. We sampled feathers from five species of swallow at multiple locations to assess total mercury [THg] exposure for adults during the non-breeding season, and for juveniles on the breeding grounds. We assessed Hg exposure to juvenile birds in crop- and grass-dominated landscapes to determine if land-use practices influenced feather [THg]. We assayed feathers for stable isotopes (δ2H, δ13C, δ15N) as proxies for relative habitat use and diet to determine their potential influence on feather [THg]. Feather [THg] was highest in adult bank swallows (Riparia riparia) and purple martins (Progne subis) from Saskatchewan and adult cliff swallows (Petrochelidon pyrrhonota) from western regions, indicating differential exposure to Hg on the non-breeding grounds. Juvenile bank, barn (Hirundo rustica) and tree (Tachycineta bicolor) swallows had lower feather [THg] in crop-dominated landscapes than grass-dominated landscapes in Saskatchewan, potentially resulting from lower use of wetland-derived insects due to wetland drainage and intensive agriculture. Feather [THg] was related to juvenile feather stable isotopes for several species, suggesting complex interactions with diet and environmental factors. Many individuals had feather [THg] values >2 µg/g, a threshold at which deleterious effects may occur. Our findings indicate differential Hg exposure among species of swallow, regions and land-uses and highlight the need for additional research to determine dietary and finer-scale land-use impacts on individual species and populations.

Full lifetime perspectives on the costs and benefits of lay-date variation in tree swallows.

Animals must balance various costs and benefits when deciding when to breed. The costs and benefits of breeding at different times have received much attention, but most studies have been limited to investigating short-term season-to-season fitness effects. However, breeding early, versus late, in a season may influence lifetime fitness over many years, trading off in complex ways across the breeder's lifespan. In this study, we examined the complete life histories of 867 female tree swallows (Tachycineta bicolor) breeding in Ithaca, New York, between 2002 and 2016. Earlier breeders outperformed later breeders in short-term measures of reproductive output and offspring quality. Though there were weak indications that females paid long-term future survival costs for breeding early, lifetime fledgling output was markedly higher overall in early-breeding birds. Importantly, older females breeding later in the season did not experience compensating life history advantages that suggested an alternative equal-fitness breeding strategy. Rather, most or all of the swallows appear to be breeding as early as they can, and differences in lay dates appear to be determined primarily by differences in individual quality or condition. Lay date had a significant repeatability across breeding attempts by the same female, and the first lay date of females fledged in our population was strongly influenced by the first lay date of their mothers, indicating the potential for ongoing selection on lay date. By examining performance over the entire lifespan of a large number of individuals, we were able to clarify the relationship between timing of breeding and fitness and gain new insight into the sources of variability in this important life history trait.

Yearly variation in factors associated with local recruitment of Tree Swallows

Yearly variation in factors associated with local recruitment of Tree Swallows

Effect of noise on development of call discrimination by nestling tree swallows, Tachycineta bicolor

Anthropogenic noise is increasing in intensity and scope, raising concern over its effects on wildlife populations. Laboratory studies suggest that exposure to elevated noise can interfere with the development of a young animal's ability to process social signals and, ultimately, its ability to communicate as an adult. Whether such effects occur in nature is unknown, however. Here, we present the first field experiments examining whether elevated noise affects the development of the ability to discriminate the vocalizations of different conspecifics. We exposed nestling tree swallows to white noise during development, and then tested, in both quiet and noisy conditions, whether they could discriminate their parents' provisioning calls and their nestmates' begging calls from those of other individuals. We predicted that noise would interfere with discrimination, because previous work showed that it decreased nestling detection of adult calls, ostensibly an easier task. Instead, noise had no discernible effect on discrimination of parental and nestmate calls, even though it reduced overall responses to adult calls, as shown previously. While our results show no long-term disruptive effect of noise on development, they also show no adjustments to sustained noise that might help nestlings better cope with noisy conditions.

Swallow mums push metabolic limits when they can keep cool

![Figure][1] Male tree swallow ( Tachycineta bicolor ) sitting on a birdhouse. Photo credit: Mykola Swarnyk [CC BY-SA ( )] Parenting is not for the faint hearted. Dedicated tree swallow mums and dads commit themselves to 16 h of exertion

Statistical Inference on Tree Swallow Migrations with Random Forests

SummaryBird species’ migratory patterns have typically been studied through individual observations and historical records. In recent years, the eBird citizen science project, which solicits observations from thousands of bird watchers around the world, has opened the door for a data-driven approach to understanding the large-scale geographical movements. Here, we focus on the North American tree swallow (Tachycineta bicolor) occurrence patterns throughout the eastern USA. Migratory departure dates for this species are widely believed by both ornithologists and casual observers to vary substantially across years, but the reasons for this are largely unknown. In this work, we present evidence that maximum daily temperature is predictive of tree swallow occurrence. Because it is generally understood that species occurrence is a function of many complex, high order interactions between ecological covariates, we utilize the flexible modelling approach that is offered by random forests. Making use of recent asymptotic results, we provide formal hypothesis tests for predictive significance of various covariates and also develop and implement a permutation-based approach for formally assessing interannual variations by treating the prediction surfaces that are generated by random forests as functional data. Each of these tests suggest that maximum daily temperature is important in predicting migration patterns.

Occurrence of anthropogenic litter in nestling Tree Swallows (<i>Tachycineta bicolor</i>)

While undertaking a study of the effects of strontium-90 on Tree Swallow (Tachycineta bicolor) near Chalk River, Ontario, we noticed the presence of anthropogenic litter (pieces of metal, glass, and plastic, and paper, plastic, and foil wrappers, >1 mm in size) in the nestlings. Although combustible litter (pieces of plastic and wrappers) were not quantified before the nestlings were incinerated in 2014 and 2015, gizzards were dissected in 2016. Litter (>1 mm diameter) was found in 30% of the 74 nestlings examined. This material is most likely provided to nestlings, along with food (insects) and natural grit (sand, stones, and mollusc shells), which we also found, by parent birds; however, it could lead to internal injuries and/or harmful substances being absorbed by the young birds.

Florida's Strategic Position for Collaborative Automated Telemetry Tracking of Avian Movements Across the Americas

Florida's Strategic Position for Collaborative Automated Telemetry Tracking of Avian Movements Across the Americas

Impacts of environmental heterogeneity on natural selection in a wild bird population.

Natural selection has been studied for several decades, resulting in the computation of thousands of selection estimates. Although the importance of environmental conditions on selection has often been suggested, published estimates rarely take into account the effects of environmental heterogeneity on selection patterns. Here, we estimated linear and nonlinear viability selection gradients on morphological traits of 12-day old nestlings in a wild population of tree swallows (Tachycineta bicolor) across a large-scale heterogeneous study system in southern Québec, Canada. We assessed the environmental drivers of nestling survival and evaluated their effects on strength and direction of selection gradients. Separate analyses of environmental variables showed that high temperatures and heavy rainfall caused stronger positive linear selection on morphological traits. Weaker linear selection was also measured in more extensively cultivated areas. Both strength and shape of nonlinear quadratic and correlational components of selection were modified by environmental variables. Considering all environmental variables revealed that precipitation since hatching affected patterns of linear selection on traits, while temperatures since hatching shaped nonlinear selection patterns. Our study underlines the importance of quantifying linear and nonlinear natural selection under various environmental conditions and how the evolutionary response of traits may be affected by ongoing human-induced environmental changes.

Population decline in tree swallows (Tachycineta bicolor) linked to climate change and inclement weather on the breeding ground.

Population decline and the threat of extinction are realities currently facing many species. Yet, in most cases, the detailed demographic data necessary to identify causes of population decline are unavailable. Using 43years (1975-2017) of data from a box-nesting population of tree swallows (Tachycineta bicolor), we identified reduced survival of offspring as a probable demographic cause of population decline. Poor fledging success was associated with increased predation and poor weather conditions during early nestling development. Low juvenile survival and subsequent recruitment was linked to poor weather conditions during the post-fledging period and may also be linked to conditions on the wintering grounds. Regional weather conditions during critical stages of breeding (early nestling and post-fledging) have become progressively worse over the 43-year study period. None of the other factors linked to offspring survival have similarly deteriorated. Overall, our results suggest tree swallows should be added to the growing list of species challenged by climate change, and that other species of aerial insect specialists may face similar impacts of climate change.

Rainfall and nest site competition delay Mountain Bluebird and Tree Swallow breeding but do not impact productivity

Abstract Optimizing breeding phenology, an important aspect of fitness, is complex for migratory species as they must make key timing decisions early, and remotely, from breeding sites. We examined the role of weather (locally and cross-seasonally), cavity availability, and competitive exclusion in determining among-year variation in breeding phenology over 17 yr for 2 migratory, cavity-nesting birds: Mountain Bluebirds (Sialia currucoides; n = 462 nests) and Tree Swallows (Tachycineta bicolor; n = 572) using natural tree cavities in British Columbia, Canada. We assessed weather effects within the winter and migratory range and at our study sites. We quantified competition as the proportion of cavities occupied by European Starlings (Sturnus vulgaris) (for both species) and Mountain Bluebirds (for Tree Swallow only) in each year. For 229 bluebird and 177 swallow nests with known fates, we tested whether late years resulted in reduced productivity. Although the effects were small, heavy rainfall and strong diurnal westerly winds during migration were associated with breeding delays for Mountain Bluebirds. However, cavity availability (earlier breeding with increases) had a 5–8 × greater effect on timing than migratory conditions. There was no evidence that starling competition delayed bluebirds. In Tree Swallows, greater local daily rainfall was associated with delayed breeding, as was starling abundance (the effect of starlings was 1.4 × smaller than that of rainfall). Neither bluebird abundance nor cavity availability changed swallow phenology. Neither species showed reduced productivity in late breeding years. In both species, individuals that bred late relative to conspecifics within-year had smaller clutches and greater probability of nest failure. We conclude that breeding ground conditions, particularly cavity limitation and local rainfall (for swallows), are important drivers of breeding phenology for our focal species, but that the productivity cost of late years, at least for Tree Swallows, is minimal.

Interspecific Density Influences the Adaptive Significance of Provisioning Coordination Between Breeding Partners

Cooperation between parents in species with biparental care can reduce sexual conflict and increase reproductive success. If parents cooperate in a conditional way- that is, alternate feeding visits to offspring- this should equalize parental investment and may improve nestling growth. Environmental variation, including competition for limited resources, may influence the need for, and benefits of, parental cooperation. We measured the benefits of partner coordination in offspring provisioning behavior among eastern bluebird partners (Sialia sialis) in which the strength of interspecific density varied spatially. Tree swallows (Tachycineta bicolor) are a recent (<40 years) arrival in our study area, are aggressive nestbox competitors with eastern bluebirds, and their density varies across the field site. Nesting among higher densities of tree swallows led to reduced parental feeding rates and reproductive success of bluebirds. Partner alternation, however, did not vary with tree swallow density. Additionally, alternation level and provisioning rate only influenced nestling growth in areas of high swallow density. It may be that the benefits of parental coordination may only be apparent when environmental conditions are poor. This study provides an important new perspective on the resolution of negotiations between breeding partners; environmental variation could influence the benefits of parental cooperation in a wide variety of animals.

Nestling tree swallows (Tachycineta bicolor) alter begging behaviour in response to odour of familiar adults, but not their nests

AbstractCommunication using chemical cues is important for many taxa, including birds, but the use of olfaction for intraspecific communication has been investigated only recently in passerines and is understudied in nestlings. To address this knowledge gap, we explored whether nestling tree swallows (Tachycineta bicolor) would recognize and respond to chemical cues of conspecifics, specifically testing begging responses to familiar and unfamiliar nest and adult odours. For the nest odour experiment, nests were treated with either orange essential oil or distilled water to create scented and unscented (control) odour environments, respectively. For the adult odour experiment, adults attending the nestlings were considered “familiar adults” and adults attending a different brood in the population were considered “unfamiliar adults.” We found that begging responses of nestlings did not differ in response to orange oil odour or water, but nestlings begged significantly longer and more intensely in response to odours of a familiar than an unfamiliar adult, regardless of adult sex. This provides evidence that tree swallows use chemical cues to alter their behaviour and opens up many exciting avenues of future research.

Cloacal bacterial communities of tree swallows (Tachycineta bicolor): Similarity within a population, but not between pair-bonded social partners.

Host-associated microbial communities can influence the overall health of their animal hosts, and many factors, including behavior and physiology, can impact the formation of these complex communities. Bacteria within these communities can be transmitted socially between individuals via indirect (e.g., shared environments) or direct (e.g., physical contact) pathways. Limited research has been done to investigate how social interactions that occur in the context of mating shape host-associated microbial communities. To gain a better understanding of these interactions and, more specifically, to assess how mating behavior shapes an animal’s microbiome, we studied the cloacal bacterial communities of a socially monogamous yet genetically polygynous songbird, the North American tree swallow (Tachycineta bicolor). We address two questions: (1) do the cloacal bacterial communities differ between female and male tree swallows within a population? and (2) do pair-bonded social partners exhibit more similar cloacal bacterial communities than expected by chance? To answer these questions, we sampled the cloacal microbiome of adults during the breeding season and then used culture-independent, 16S rRNA gene amplicon sequencing to assess bacterial communities. Overall, we found that the cloacal bacterial communities of females and males were similar, and that the communities of pair-bonded social partners were not more similar than expected by chance. Our results suggest that social monogamy does not correlate with an increased similarity in cloacal bacterial community diversity or structure. As social partners were not assessed at the same time, it is possible that breeding stage differences masked social effects on bacterial community diversity and structure. Further, given that tree swallows exhibit high variation in rates of extra-pair activity, considering extra-pair activity when assessing cloacal microbial communities may be important for understanding how these bacterial communities are shaped. Further insight into how bacterial communities are shaped will ultimately shed light on potential tradeoffs associated with alternative behavioral strategies and socially-transmitted microbes.

Does blood loss explain higher resting metabolic rates in nestling birds with hematophagous ectoparasites?

Nestlings of many bird species are hosts to hematophagous ectoparasites. Parasitism of nestlings is usually sub‐lethal, but its effects can extend into the fledgling and adult stages. Nestling hosts lose enough blood to become anemic, but the effects of reduced oxygen‐carrying capacity on metabolic rate are poorly understood. This study examined the consequences of parasitism by larval blow flies Protocalliphora sialia for nestling tree swallows Tachycineta bicolor. We found that nestlings with more parasites had higher whole‐animal RMR. We evaluated the role of increased erythropoiesis as a potential mechanism explaining increased RMR by drawing blood from some birds. However, we found no evidence that blood loss, as a proxy for hematophagous parasitism, increased metabolic rate. Future work should examine the metabolic costs of upregulation of immunity and how elevated RMR due to ectoparasites affects nestlings as they develop into independent adults.

Benefits of an anti-parasite treatment are influenced by within-brood size variation in Tree Swallows (Tachycineta bicolor)

AbstractIn all animals, susceptibility to parasites can differ among individuals. Young, nest-bound birds are exposed to a diversity of nest-dwelling ectoparasites that typically feed on their blood. Within broods, hatching asynchrony creates size hierarchies that result in morphological and physiological variation among nest mates, and susceptibility to parasites also may vary predictably with this size hierarchy. Our objective was to use a broad-spectrum, anti-parasite drug, ivermectin (IVM), to treat individual nestling Tree Swallows (Tachycineta bicolor) and assess how nestling susceptibility to parasites varied both within and among broods. Broods were either assigned to an IVM group, where half of the nestlings in a brood received IVM injections and half received control injections of pure sesame oil, or to a control group, where all nestlings received oil injections. We found that the IVM treatment reduced parasite loads for broods as a whole, thereby benefiting all nestlings in IVM broods and suggesting our treatment resulted in herd immunity. Specifically, nestlings from IVM broods had higher hemoglobin concentrations, regardless of whether they received injections with IVM or oil, and greater fledging success, than nestlings from control broods. On the contrary, IVM treatment did not strongly affect nestling morphology, with only marginal effects on the growth rate of ninth primary feathers, and the effects of the treatment on 2 other morphological traits depending on temporal factors. Variation in size within broods, however, influenced the chance of an individual fledging, which increased with relative size within a brood, but only under lower parasite loads (i.e. IVM broods). By experimentally manipulating nestling susceptibility to parasites, we have demonstrated variation in nestling response to an anti-parasite treatment both within and among broods, and future studies should investigate the underlying mechanism for why certain nestlings along the brood size hierarchy are more susceptible to parasites.

Do songbirds in wetlands show higher mercury bioaccumulation relative to conspecifics in non-wetland habitats?

Environmental conditions in wetlands facilitate favorable biogeochemical conditions for the conversion of inorganic mercury into methylmercury. For this reason, wetlands are increasingly classified as mercury hotspots, places where biota exhibit elevated mercury concentrations. While it is clear that wetlands play an important role in methylmercury production, factors such as geographic variation in mercury deposition, wetland type, and trophic dynamics can cause variation in mercury dynamics and bioaccumulation in biota occupying wetlands or connected to wetland trophic systems. Here, we use songbirds as bioindicators in a two-pronged approach aimed at evaluating the state of our understanding of mercury bioaccumulation by songbirds in wetland ecosystems. First, we use a case study in southeast Missouri to compare blood mercury concentrations in tree swallows (Tachycineta bicolor) and eastern bluebirds (Sialia sialis) occupying wetland and non-wetland habitats to test the hypothesis that songbirds in wetlands will have higher mercury bioaccumulation than those in non-wetlands. Adult tree swallows in wetlands had significantly higher blood mercury concentrations than those in non-wetlands; however, no difference between ecosystems was detected in eastern bluebirds. Second, we present a review of the current literature on mercury in songbirds in wetland ecosystems across North America. Mercury concentrations in songbirds varied among wetland types and with geographic location, often in an unpredictable manner. Mercury concentrations in songbird blood varied 3-10 fold at locations separated only by ~10 to several hundred kilometers. This magnitude of difference in blood mercury concentrations among wetlands exceeds documented differences between wetland and non-wetland ecosystems. Therefore, we caution against the automatic assumption that songbirds occupying wetlands will have higher mercury bioaccumulation than conspecifics living in other habitats.

Expanding our view of Bartonella and its hosts: Bartonella in nest ectoparasites and their migratory avian hosts

BackgroundBartonella is a genus of Gram-negative facultative intracellular Alphaproteobacteria of public health importance. Although they are known to mainly infect mammalian hosts with some blood-feeding arthropods having been confirmed as vectors, there is some evidence of Bartonella association with non-mammalian hosts including birds.MethodsHere we used high-throughput sequencing of 16S rRNA and Sanger sequencing of the citrate synthase (gltA) genes to test for the presence of Bartonellaceae in the blood of three migratory cavity nesting bird species, purple martins (Progne subis), tree swallows (Tachycineta bicolor) and eastern bluebirds (Sialia sialis) and their most prevalent and abundant nest ectoparasites, Dermanyssus prognephilus (mite), Ceratophyllus idius (flea) and Protocalliphora sialia (bird blow fly larva). We constructed maximum likelihood phylogenetic trees to verify the placement of the resulting sequences in the Bartonellaceae.ResultsWe found evidence of Bartonella in all three bird species and all three arthropod species tested. We report multiple instances of identical Bartonella sequences in both birds and parasites, leading to the likely hypothesis that these ectoparasites are potential vectors of Bartonella. Our phylogenetic analysis suggests that ‘avian Bartonella’ may form its own sub-clade within the genus Bartonella.ConclusionsTo the best of our knowledge, we provide the first confirmation of overlapping Bartonella strains among bird hosts and various species of nest-associated ectoparasites from the same system, suggesting a possible Bartonella host–vector relationship between these arthropods and a non-mammalian host. Our study adds to the growing appreciation of the Bartonellaceae as a phylogenetically diverse group with a wide range of hosts.

Short-term exposure to unmanned aerial vehicles does not alter stress responses in breeding tree swallows.

Recent studies suggest that visual and acoustic anthropogenic disturbances can cause physiological stress in animals. Human-induced stress may be particularly problematic for birds as new technologies, such as drones, increasingly invade their low-altitude air space. Although professional and recreational drone usage is increasing rapidly, there is little information on how drones affect avian behavior and physiology. We examined the effects of drone activity on behavior and physiology in adult, box-nesting tree swallows (Tachycineta bicolor). Specifically, we monitored bird behavior during drone flights and in response to a control object and measured telomere lengths and corticosterone levels as indicators of longer-term physiological stress. We predicted that drone-exposed tree swallows would habituate behaviorally after multiple flights, but that telomeres would shorten more quickly and that baseline corticosterone levels would be altered. One significant and two strong, non-significant trends in behavioral assays indicated that adult swallows acted more aggressively towards drone presence compared to a control object, but were slower to approach the drone initially. Swallows were also more reluctant to use nest boxes during drone activity. Tree swallows habituated to drone presence as expected, although the rate of habituation often did not differ between drone-exposed and control groups. Contrary to our prediction, drone activity did not affect telomere length, corticosterone levels, body mass or fledging rates. Overall, our results indicate that a small number of short, targeted, drone flights do not impact tree swallow health or productivity differently than a non-invasive control object. Minor behavioral differences suggest that increasing the frequency of drone use could impact this species. We provide some of the first results addressing how drone activity alters behavioral, physiological and molecular responses to stress in songbirds. A better understanding of these impacts will allow ecologists to make more informed decisions on the use and regulation of new drone technologies.

Heat dissipation capacity influences reproductive performance in an aerial insectivore.

Climatic warming is predicted to increase the frequency of extreme weather events, which may reduce an individual's capacity for sustained activity because of thermal limits. We tested whether the risk of overheating may limit parental provisioning of an aerial insectivorous bird in population decline. For many seasonally breeding birds, parents are thought to operate close to an energetic ceiling during the 2-3 week chick-rearing period. The factors determining the ceiling remain unknown, although it may be set by an individual's capacity to dissipate body heat (the heat dissipation limitation hypothesis). Over two breeding seasons we experimentally trimmed the ventral feathers of female tree swallows (Tachycineta bicolor) to provide a thermal window. We then monitored maternal and paternal provisioning rates, nestling growth rates and fledging success. We found the effect of our experimental treatment was context dependent. Females with an enhanced capacity to dissipate heat fed their nestlings at higher rates than controls when conditions were hot, but the reverse was true under cool conditions. Control females and their mates both reduced foraging under hot conditions. In contrast, male partners of trimmed females maintained a constant feeding rate across temperatures, suggesting attempts to match the feeding rate of their partners. On average, nestlings of trimmed females were heavier than controls, but did not have a higher probability of fledging. We suggest that removal of a thermal constraint allowed females to increase provisioning rates, but additionally provided nestlings with a thermal advantage via increased heat transfer during maternal brooding. Our data provide support for the heat dissipation limitation hypothesis and suggest that depending on temperature, heat dissipation capacity can influence reproductive success in aerial insectivores.