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Social interactions are ubiquitous in nature and can shape the fitness of individuals through social selection. This type of selection arises when phenotypes of neighbors influence the fitness of a focal individual. Quantifying social selection is crucial to better characterize the overall selective landscape. For example, if intraspecific competition is strong, traits that are beneficial for an individual could be detrimental to competitors. In this study, we quantified social selection acting on three key ecological traits (body mass, wing length, and laying date) in wild Tree swallow (Tachycineta bicolor) females. We used reproductive success measured at three stages throughout the breeding season as fitness proxies to assess selection acting at those decisive moments. We also quantified the effects of environment on selection using measures of conspecifics' density, type of agricultural landscape, and presence of interspecific competitors. Overall, we found no strong evidence of social selection on these traits in our study system, although there were marginally nonsignificant selection gradients suggesting the positive effect of larger neighbors. Environmental variables affected reproductive success but did not strongly affect social selection gradients. Our study calls for more social selection estimates to be reported across environments to better understand its importance in wild populations. [ABSTRACT FROM AUTHOR]

Simple Summary: Abandoned underground coal mines collect ground water that eventually finds its way to the surface. A common way to treat pollutants and sediments from this mine water is to create passive treatment ponds that remove contaminates before the water enters a surface stream. Tree Swallows and many other birds and wildlife live and breed near these treatment ponds, with potentially detrimental effects. We monitored 63 nests over two breeding seasons (2022–2023) to determine if nests located next to the ponds had better or worse reproductive outcomes than nests farther away. We found that nests close to the ponds (<70 m) had higher numbers of young that survived to the age of fledging than nests that were built farther away from the ponds (>820 m). While this suggests that the treatment ponds provided meaningful resources for Tree Swallows to reproduce, the numbers of offspring were unusually low compared to what was found in studies by other investigators at other sites. More research will be needed to determine why. Abandoned mine drainage treatment ponds could have contrasting effects on the reproductive success of birds living in the vicinity. The ponds and associated vegetation may, like any other body of freshwater, provide beneficial habitats for the insects that the birds use to feed their young; or instead, the ponds may act as an ecological trap, attracting the birds to a habitat that is poor in quality and negatively impacting their productivity. We monitored nests of an aerial insectivore, the Tree Swallow (Tachycineta bicolor), to determine whether the distance between the ponds and the nests affected various reproductive parameters including clutch size, hatch rate, number of nestlings, nestling size and mass, number of fledglings, fledging rate, and fledge date. Data were collected over two breeding seasons (2022 and 2023) from a swallow population in southwestern Pennsylvania, USA. We found that the nests closest to the treatment ponds had significantly more nestlings and fledglings, earlier fledge dates, and a better fledging rate when compared to nests that were more distant from the ponds. However, all these parameters were well below previously published values, which suggests that the mine drainage ponds provide good nesting habitats relative to what is available in the region but that they do not represent high-quality habitats for this species overall. [ABSTRACT FROM AUTHOR]

Aerial insectivorous birds breeding in North America have experienced decades of population declines for reasons hypothesized to be related to changes in their insect prey. In agricultural landscapes, land management practices can affect insect communities, leading to concerns that ongoing trends toward more intensive cultivation could affect the ability of farmland-breeding aerial insectivores to forage and provision their offspring with aerial insect prey. To understand how differences in agricultural intensity may affect the foraging behavior of different aerial insectivore species, we used GPS tags to compare the movements and habitat use of 2 species with different foraging ecologies, Hirundo rustica (Barn Swallow) and Tachycineta bicolor (Tree Swallow), breeding at 17 sites in agricultural landscapes in Saskatchewan, Canada. Although we identified differences in foraging behavior consistent with each species' reported ecological traits, including T. bicolor foraging farther and over larger areas than H. rustica , overall foraging behavior was similar between species. Resource selection function analyses indicated that both species used wetlands disproportionately often relative to local wetland availability, especially when detected farther from their nests. Hirundo rustica and T. bicolor both also avoided cropped foraging habitat, using it proportionally less than it was locally available. In landscapes with greater wetland cover, both species selected for wetland habitat more strongly, and among T. bicolor , higher wetland density decreased maximum foraging distance and home range area. In contrast, we found no effect of crop cover on foraging habitat selection or foraging movements. These findings suggest that H. rustica and T. bicolor breeding in Saskatchewan agroecosystems share similar foraging strategies, with wetland habitats appearing to be highly important despite comprising only a small proportion of landscape area. Overall, these results indicate that protecting wetland habitats should be a priority for aerial insectivore conservation in the intensive agricultural landscapes such as the Canadian prairies. [ABSTRACT FROM AUTHOR]

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Copyright of Journal of Field Ornithology is the property of Resilience Alliance and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Competition for limited nest sites among secondary cavity-nesting bird species is intense and may result in loss of nests, physical conflict, injury, and occasionally death. The Prothonotary Warbler ( Protonotaria citrea ) is a secondary cavity-nesting species that has experienced a 38% population decline over the past five decades. In the northern portion of their range, Prothonotary Warblers are sympatric with two cavity-nesting species known for their nest usurpation behaviors: the House Wren ( Troglodytes aedon ) and Tree Swallow ( Tachycineta bicolor ). From 2017–2023 we monitored Prothonotary Warbler nests. House Wrens destroyed and usurped 38% of Prothonotary Warbler nests, which represented the greatest cause of nest failure, while Tree Swallows usurped only 1.5% of Prothonotary Warbler nests. We also documented two instances of adult Prothonotary Warblers likely killed by Tree Swallows. Interference competition from House Wrens is likely a significant factor limiting Prothonotary Warbler reproductive success where it is sympatric with these nest competitors.

Many bird species have advanced their first egg dates in response to recent milder winters and increases in spring temperatures. Tree Swallows ( Tachycineta bicolor ) begin egg laying earlier in warmer springs at most, but not all, study sites. We examined whether Tree Swallows that nested in boxes in west Michigan responded to an increase in spring temperatures from 1993 to 2018 by advancing their first egg dates. May, but not April, mean daily temperatures got significantly warmer from 1993 to 2018. We found that the first egg dates, but not mean first egg dates, of both second year (SY) and after second year (ASY) females got earlier between 1993 and 2018. The first egg dates of SY females did not get earlier in response to warmer April or May temperatures but got earlier when there were more days in May with measurable rain. The first egg dates of ASY females got earlier with warmer April and May temperatures. Overall, the relationships between weather conditions and first egg dates of both SY and ASY females were complex and varied yearly. The climatic conditions that influence Tree Swallow first egg dates are complex because stochastic rain and wind conditions interact with air temperatures to affect the availability of the aerial insect prey of swallows thereby influencing the ability of females to begin egg laying.

Savannah Sparrows (Passerculus sandwichensis) and Tree Swallows (Tachycineta bicolor) breed and forage in the same habitat on Kent Island, a boreal island in the Bay of Fundy, New Brunswick, but respond differently to the same weather conditions. The 2 passerines are similar in body size but because Tree Swallows depend upon small flying insects captured on the wing, they may be more sensitive to weather than Savannah Sparrows, which forage on insects and seeds on the ground and in shrubs and trees. To compare how reproductive success in the 2 species was affected by weather conditions, we took advantage of an 18-year dataset and used a model-building approach that controlled for year, adult sex and age, and field where they nested. We focused on 3 measures of reproductive success (hatching success, fledging success, and nestling condition) and different time periods (3- to 18-day time windows) before hatching or fledging. The responses of the 2 species differed in magnitude and direction. In Tree Swallows, adding weather variables to the basic model increased the explanatory power of fixed effects by 19.1%, illustrating the swallows' sensitivity to weather. In contrast, in Savannah Sparrows, the addition of weather variables only increased the model's explanatory power by 0.4% and the proportion of variation attributed to fixed factors by only 1.5%, which reflected the species' hardiness in the face of inclement weather. Our results suggest that how a bird species forages and the nature of its prey may influence its sensitivity to weather and indicate that increased rainfall, strong winds and other events associated with climate change may affect Tree Swallows and other aerial insectivores more than ground-foraging birds such as Savannah Sparrows. [ABSTRACT FROM AUTHOR]

Climate change predicts the increased frequency, duration, and intensity of inclement weather periods such as unseasonably low temperatures (i.e., cold snaps) and prolonged precipitation. Many migratory species have advanced the phenology of important life history stages and, as a result, are likely to be exposed to these periods of inclement spring weather more often, therefore risking reduced fitness and population growth. For declining avian species, including aerial insectivores, anthropogenic landscape changes such as agricultural intensification are another driver of population declines. These landscape changes may affect the foraging ability of food provisioning parents and reduce the survival of nestlings exposed to inclement weather through, for example, pesticide exposure impairing thermoregulation and punctual anorexia. Breeding in agro‐intensive landscapes may therefore exacerbate the negative effects of inclement weather under climate change. We observed that a significant reduction in the availability of insect prey occurred when daily maximum temperatures fell below 18.3°C, and thereby defined any day when the maximum temperature fell below this value as a day witnessing a cold snap. We then combined daily information on the occurrence of cold snaps and measures of precipitation to assess their impact on the fledging success of Tree Swallows (Tachycineta bicolor) occupying a nest box system placed across a gradient of agricultural intensification. Estimated fledging success of this declining aerial insectivore was 36.2% lower for broods experiencing 4 cold‐snap days during the 12 days post‐hatching period versus broods experiencing none, and this relationship was worsened when facing more precipitation. We further found that the overall negative effects of a brood experiencing periods of inclement weather was exacerbated in more agro‐intensive landscapes. Our results indicate that two of the primary hypothesized drivers of many avian population declines may interact to further increase the rate of declines in certain landscape contexts. [ABSTRACT FROM AUTHOR]

Anthropogenic noise pollution, such as that derived from traffic and industrial machinery, has been identified as an urgent conservation priority as it is often louder and more prevalent than natural acoustic stimuli, and can act as a stressor on wildlife. Research in avian systems has shown that anthropogenic noise can affect physiology and reproductive success of adult birds – but effects on juvenile birds have been less‐studied despite their being potentially more vulnerable during the nestling period. What studies have been done have shown remarkable variability in juvenile response to anthropogenic noise, suggesting that effects are highly context‐ and species‐specific. Here, we investigate the effects of gas compressor noise, an increasingly prevalent and biologically relevant noise stressor produced during natural gas production, on juvenile tree swallows (Tachycineta bicolor). Gas compressors generate considerable sound pressure as they work to pressurize gas pipelines for downstream distribution. We predicted that exposure to increased noise during incubation and the nestling period would result in smaller chicks in poorer body condition and with a dampened immune response. Surprisingly, we found no evidence for any of these predictions, providing further evidence that noise effects on juvenile birds is highly variable, and we explore ways in which individual birds may compensate for the effects of disturbance at the nest. [ABSTRACT FROM AUTHOR]

The historical rise of intensive agricultural practices is hypothesized to be related to declines of grassland and aerial insectivorous birds. Drivers of declines may also influence the overall abundance and spatial distribution of insects within agricultural landscapes. Subsequently, the food provisioning rate of birds breeding within more agro‐intensive landscapes may be impacted. Lower provisioning rates in agro‐intensive landscapes may lead not only to reduced growth rate, body condition, or fledging success of nestlings but also to diminished body condition of food provisioning adults. Results from a previous study supported this hypothesis as the fledging success and proxies of nestling body condition were lowest for an aerial insectivore breeding in more agro‐intensive landscapes. Of the multiple hypotheses put forward to explain these correlations, one mechanism may act through variation in food provisioning rates. In this study, we expounded on this hypothesis using data derived from the aforementioned study system and assessed if provisioning rates to nestlings and food provisioning behavior of adults varied across a gradient of agricultural intensification in a declining aerial insectivore, the Tree Swallow (Tachycineta bicolor). We found that the hourly provisioning rate was lower in agro‐intensive landscapes, and yet travel distances were longest within less agro‐intensive landscapes. Our results highlight that, in order to maximize long‐term average gain rates, Tree Swallows breeding within agro‐intensive landscapes must forage with greater intensity, perhaps at a cost to themselves, or else costs will transfer to growing broods. Our work provides further evidence that agricultural intensification on the breeding grounds can contribute to the declines of aerial insectivores in part through a trophic pathway. [ABSTRACT FROM AUTHOR]

Aerial insectivores show worldwide population declines coinciding with shifts in agricultural practices. Increasing reliance on certain agricultural practices is thought to have led to an overall reduction in insect abundance that negatively affects aerial insectivore fitness. The relationship between prey availability and the fitness of insectivores may thus vary with the extent of agricultural intensity. It is therefore imperative to quantify the strength and direction of these associations. Here we used data from an 11‐year study monitoring the breeding of Tree Swallows (Tachycineta bicolor) and the availability of Diptera (their main prey) across a gradient of agricultural intensification in southern Québec, Canada. This gradient was characterized by a shift in agricultural production, whereby landscapes composed of forage and pastures represented less agro‐intensive landscapes and those focusing on large‐scale arable row crop monocultures, such as corn (Zea mays) or soybean (Glycine max) that are innately associated with significant mechanization and agro‐chemical inputs, represented more agro‐intensive landscapes. We evaluated the landscape characteristics affecting prey availability and how this relationship influences the fledging success, duration of the nestling period, fledgling body mass, and wing length as these variables are known to influence the population dynamics of this species. Diptera availability was greatest within predominately forested landscapes, while within landscapes dominated by agriculture, it was marginally greater in less agro‐intensive areas. Of the measured fitness and body condition proxies, both fledging success and nestling body mass were positively related to prey availability. The impact of prey availability varied across the agricultural gradient as fledging success improved with increasing prey levels within forage landscapes yet declined in more agro‐intensive landscapes. Finally, after accounting for prey availability, fledging success was lowest, nestling periods were the longest, and wing length of fledglings were shortest within more agro‐intensive landscapes. Our results highlight the interacting roles that aerial insect availability and agricultural intensification have on the fitness of aerial insectivores, and by extension how food availability may interact with other aspects of breeding habitats to influence the population dynamics of predators. [ABSTRACT FROM AUTHOR]

Social status directly affects the health of humans and other animals. Low status individuals receive more antagonistic encounters, have fewer supportive relationships and have worse health outcomes. However, the physiological and cellular processes that mediate the relationship between the social environment and health are incompletely known. Epigenetic regulation of the hypothalamic-pituitary-adrenal (HPA) axis, the neuroendocrine pathway that activates in response to stressors, may be one process that is sensitive to the social environment. Here, we experimentally manipulated plumage, a key social signal in female tree swallows (Tachycineta bicolor) and quantified methylation of four genes in the HPA axis before and after treatment. We found that dulling the white breast plumage affected methylation in one gene, CRHR1; however, the effect depended on the original brightness of the bird. Methylation in this gene was correlated with baseline corticosterone levels, suggesting that DNA methylation of CRHR1 helps regulate glucocorticoid production in this species. Methylation in two other genes, FKBP5 and GR, changed over the course of the experiment, independent of treatment. These results show that methylation of these genes is labile into adulthood and suggest that epigenetic regulation of the HPA axis could help birds respond to current environmental conditions., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

The immune system can be modulated when organisms are exposed to acute or chronic stressors. Glucocorticoids (GCs), the primary hormonal mediators of the physiological stress response, are suspected to play a crucial role in immune modulation. However, most evidence of stress-associated immunomodulation does not separate the effects of glucocorticoid-dependent pathways from those of glucocorticoid-independent mechanisms on immune function. In this study, we experimentally elevated circulating corticosterone, the main avian glucocorticoid, in free-living female tree swallows (Tachycineta bicolor) for one to two weeks to test its effects on immune modulation. Natural variation in bacteria killing ability (BKA), a measure of innate constitutive immunity, was predicted by the interaction between timing of breeding and corticosterone levels. However, experimental elevation of corticosterone had no effect on BKA. Therefore, even when BKA is correlated with natural variation in glucocorticoid levels, this relationship may not be causal. Experiments are necessary to uncover the causal mechanisms of immunomodulation and the consequences of acute and chronic stress on disease vulnerability. Findings in other species indicate that acute increases in GCs can suppress BKA; but our results support the hypothesis that this effect does not persist over longer timescales, during chronic elevations in GCs. Direct comparisons of the effects of acute vs. chronic elevation of GCs on BKA will be important for testing this hypothesis. • The effects of glucocorticoids on constitutive innate immunity are unclear. • We tested this relationship in free-living tree swallows. • Natural variation in glucocorticoids predicted bacterial killing in some birds. • Late breeding birds with higher corticosterone had lower bacteria killing. • However, experimental glucocorticoid elevation did not affect bacteria killing. [ABSTRACT FROM AUTHOR]

Abstract Conditions during early life can have dramatic effects on adult characteristics and fitness. However, we still know little about the mechanisms that mediate these relationships. Telomere shortening is one possibility. Telomeres are long sequences of DNA that protect the ends of chromosomes. They shorten naturally throughout an individual's life, and individuals with short telomeres tend to have poorer health and reduced survival. Given this connection between telomere length (TL) and fitness, natural selection should favor individuals that are able to retain longer telomeres for a greater portion of their lives. However, the ability of natural selection to act on TL depends on the extent to which genetic and environmental factors influence TL. In this study, we experimentally enlarged broods of Tree Swallows (Tachycineta bicolor) to test the effects of demanding early‐life conditions on TL, while simultaneously cross‐fostering chicks to estimate heritable genetic influences on TL. In addition, we estimated the effects of parental age and chick sex on chick TL. We found that TL is highly heritable in Tree Swallow chicks, and that the maternal genetic basis for TL is stronger than is the paternal genetic basis. In contrast, the experimental manipulation of brood size had only a weak effect on chick TL, suggesting that the role of environmental factors in influencing TL early in life is limited. There was no effect of chick sex or parental age on chick TL. While these results are consistent with those reported in some studies, they are in conflict with others. These disparate conclusions might be attributable to the inherent complexity of telomere dynamics playing out differently in different populations or to study‐specific variation in the age at which subjects were measured.

The initial investment a female bird makes in an offspring is her production of its egg. The size of this investment can have important evolutionary consequences for both the female and her offspring. Between 2008 and 2016, we weighed 1977 tree swallow eggs freshly laid in nest boxes in west Michigan to investigate factors associated with egg mass. Breeding female age class was not associated with egg mass. Overall, eggs that hatched weighed significantly more than those that did not. An egg's mass was not associated with clutch size but increased with its position in the laying sequence. Females that bred multiple times showed high repeatability of egg mass. Mother–daughter narrow sense heritability of egg mass was low. There were statistically significant associations, both positive and negative, between female morphological characteristics and egg mass in some years but not others. Similarly, relationships between egg mass and weather conditions during egg formation were statistically significant in some years but not others. In summary, female characteristics and weather conditions were associated with tree swallow egg mass, but their influences varied yearly. These results reinforce the importance of long‐term studies for identifying the causes of selection that shape life‐history characteristics.

Natural gas compressor stations emit loud, low-frequency noise that travels hundreds of meters into undisturbed habitat. We used experimental playback of natural gas compressor noise to determine whether and how noise influenced settlement decisions and reproductive output as well as when in the nesting cycle birds were most affected by compressor noise. We established 80 nest boxes to attract Eastern Bluebirds (Sialia sialis) and Tree Swallows (Tachycineta bicolor) to locations where they had not previously nested and experimentally introduced shale gas compressor noise to half the boxes while the other 40 boxes served as controls. Our experimental design allowed us to control for the confounding effects of both physical changes to the environment associated with compressor stations as well as site tenacity or the tendency for birds to return to the specific locations where they had previously bred. We incorporated behavioral observations with video cameras placed within boxes to determine how changes in behavior might lead to any noted changes in fitness. Neither species demonstrated a preference for box type (quiet or noisy), and there was no difference in clutch size between box types. In both species, we observed a reduction in incubation time, hatching success, and fledging success (proportion of all eggs that fledged) between quiet and noisy boxes but no difference in provisioning rates. Nest success (probability of fledging at least one young; calculated from all nests that were initiated) was not affected by noise in either species suggesting that noise did not increase rates of either depredation or abandonment but instead negatively impacted fitness through reduced hatching and fledging success. Compressor noise caused behavioral changes that led to reduced reproductive success; for Eastern Bluebirds and Tree Swallows, gas infrastructure can create an equal-preference ecological trap where birds do not distinguish between lower and higher quality territories even when they incur fitness costs. [ABSTRACT FROM AUTHOR]

The initial investment a female bird makes in an offspring is her production of its egg. The size of this investment can have important evolutionary consequences for both the female and her offspring. Between 2008 and 2016, we weighed 1977 tree swallow eggs freshly laid in nest boxes in west Michigan to investigate factors associated with egg mass. Breeding female age class was not associated with egg mass. Overall, eggs that hatched weighed significantly more than those that did not. An egg's mass was not associated with clutch size but increased with its position in the laying sequence. Females that bred multiple times showed high repeatability of egg mass. Mother–daughter narrow sense heritability of egg mass was low. There were statistically significant associations, both positive and negative, between female morphological characteristics and egg mass in some years but not others. Similarly, relationships between egg mass and weather conditions during egg formation were statistically significant in some years but not others. In summary, female characteristics and weather conditions were associated with tree swallow egg mass, but their influences varied yearly. These results reinforce the importance of long‐term studies for identifying the causes of selection that shape life‐history characteristics. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The ecology of Pustulated Burying Beetle (Nicrophorus pustulatus, Coleoptera: Silphidae) appears distinct among Nicrophorus species, with evidence of it parasitizing snake eggs and foraging primarily above the ground and into the forest canopy. Here we document an extension of its aberrant ecology and behaviour: a case of N. pustulatus burying 2-day-old live and dead nestlings of Tree Swallow (Tachycineta bicolor, Passeriformes: Hirundinidae) under the nest, behaviour consistent with the early stages of breeding in N. pustulatus. Based on different levels of decomposition, we suspect that N. pustulatus responded to one dead swallow nestling in the brood of five and went on to bury all of the nestlings at the bottom of the nest box. The observation provides the first evidence, to our knowledge, of Nicrophorus burying live vertebrates. [ABSTRACT FROM AUTHOR]

1. Diverse assemblages of blood‐feeding parasitic arthropods occupy the nests of birds, and nest temperature and humidity can strongly influence the population dynamics of these ectoparasites, with important implications for parasite–host relationships. 2. This study used two types of nest box that differed in internal microclimates, one constructed of plywood and the other constructed of boles of aspen (Populus tremuloides Michx.), more closely replicating natural cavities, to examine how nest microclimate affects the prevalence and abundance of nest‐dwelling larval blow flies (Protocalliphora and Trypocalliphora spp.) in nests of tree swallows (Tachycineta bicolor Vieillot, 1808). 3. Based on known microclimatic differences between the box types and responses of larval blow flies to different temperatures, it was predicted that the microclimate of plywood boxes would be more favourable for growth and development of larval blow flies, and therefore have higher abundance, and possibly higher prevalence, of larval blow flies. 4. Plywood nest boxes had higher abundance, but not prevalence, of larval blow flies compared with aspen boxes at two different geographical locations in Canada. Nest composition also differed between box types, particularly at one site, where aspen boxes contained more nesting material (grass and feathers) than did plywood boxes. 5. Although it seems probable that microclimate was driving the differences between box types in abundance of larval blow flies, several additional explanations are discussed. These findings may have implications for conservation efforts, particularly those where nest boxes are used to aid in the recovery of declining bird populations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Extra‐pair paternity (EPP) is a widespread phenomenon in birds. Researchers have long hypothesized that EPP must confer a fitness advantage to extra‐pair offspring (EPO), but empirical support for this hypothesis is definitively mixed. This could be because genetic benefits of EPP only exist in a subset of environmental contexts to which a population is exposed. From 2013 to 2015, we manipulated perceived predator density in a population of tree swallows (Tachycineta bicolor) breeding in New York to see whether fitness outcomes of extra‐pair and within‐pair offspring (WPO) varied with predation risk. In nests that had been exposed to predators, EPO were larger, longer‐winged and heavier than WPO. In nonpredator nests, WPO tended to be larger, longer‐winged and heavier than EPO, though the effect was nonsignificant. We found no differences in age, morphology or stress physiology between extra‐pair and within‐pair sires from the same nest, suggesting that additive genetic benefits cannot fully explain the differences in nestling size that we observed. The lack of an effect of predator exposure on survival or glucocorticoid stress physiology of EPO and WPO further suggests that observed size differences do not reflect more general variation in intrinsic genetic quality. Instead, we suggest that size differences may have arisen through differential investment into EPO and WPO by females, perhaps because EPO and WPO represent different reproductive strategies, with each type of nestling conferring a fitness advantage in specific ecological contexts. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Young nest-bound birds often face a diversity of ectoparasites that typically feed on blood and can negatively affect nestling morphological and physiological traits, including hemoglobin concentration. While hemoglobin concentration can be correlated with nestling performance, such as body mass, it is unknown whether variation in hemoglobin is the direct proximate factor responsible for variation in morphology, or if nestling traits simply co-vary with hemoglobin concentration due to a number of similar factors influencing both traits. If hemoglobin concentration does directly influence the phenotype of nestlings, then the reduction in nestling hemoglobin concentration by ectoparasites may cause other negative effects commonly associated with parasitism. By experimentally reducing the hemoglobin concentration of nestling Tree Swallows (Tachycineta bicolor) using phenylhydrazine hydrochloride (PHZ), we tested whether reduced hemoglobin concentration could be the mechanism that causes changes in nestling morphology and behavior in response to increased parasitism. Parasite loads were manipulated in conjunction with the PHZ treatment. Nestlings injected with PHZ displayed no change in hemoglobin concentration 2 days post-injection, whereas control nestlings showed the typical increase that occurs during early development. By 6 days post-injection, the parasite, but not PHZ, treatment significantly affected hemoglobin concentration. Both treatments interacted to affect begging intensity, while size and growth rate of nestlings were only affected by the parasite load manipulation. This study demonstrates the potential use of PHZ in nestlings to tease apart the effects of parasitism and reduced hemoglobin, but the results suggest incorporating a second injection of PHZ to better replicate the pattern of hemoglobin reduction created by hematophagous ectoparasites. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Seasonal plasticity in aggression is likely to be shaped by the contexts in which aggression is beneficial, as well as the constraints inherent in its underlying mechanisms. In males, seasonal plasticity in testosterone (T) secretion is thought to underlie seasonal plasticity in conspecific aggression, but it is less clear how and why female aggression may vary across different breeding stages. Here, we integrate functional and mechanistic perspectives to begin to explore seasonal patterns of conspecific aggression in female tree swallows (Tachycineta bicolor), a songbird with intense female–female competition and T‐mediated aggression. Female tree swallows elevate T levels during early breeding stages, coinciding with competition for nest boxes, after which time T levels are roughly halved. However, females need to defend ownership of their nesting territory throughout the breeding season, suggesting it may be adaptive to maintain aggressive capabilities, despite low T levels. We performed simulated territorial intrusions using 3D‐printed decoys of female tree swallows to determine how their aggressive response to a simulated intrusion changes across the breeding season. First, we found that 3D‐printed decoys produce data comparable to stage‐matched studies using live decoys, providing researchers with a new, more economical method of decoy construction. Further, female aggressiveness remained relatively high through incubation, a period of time when T levels are quite low, suggesting that other mechanisms may regulate conspecific female aggression during parental periods. By showing that seasonal patterns of female aggression do not mirror the established patterns of T levels in this highly competitive bird, our findings provide a unique glimpse into how behavioural mechanisms and functions may interact across breeding stages to regulate plasticity. [ABSTRACT FROM AUTHOR]

Conditions during early life can have dramatic effects on adult characteristics and fitness. However, we still know little about the mechanisms that mediate these relationships. Telomere shortening is one possibility. Telomeres are long sequences of DNA that protect the ends of chromosomes. They shorten naturally throughout an individual's life, and individuals with short telomeres tend to have poorer health and reduced survival. Given this connection between telomere length (TL) and fitness, natural selection should favor individuals that are able to retain longer telomeres for a greater portion of their lives. However, the ability of natural selection to act on TL depends on the extent to which genetic and environmental factors influence TL. In this study, we experimentally enlarged broods of Tree Swallows (Tachycineta bicolor) to test the effects of demanding early‐life conditions on TL, while simultaneously cross‐fostering chicks to estimate heritable genetic influences on TL. In addition, we estimated the effects of parental age and chick sex on chick TL. We found that TL is highly heritable in Tree Swallow chicks, and that the maternal genetic basis for TL is stronger than is the paternal genetic basis. In contrast, the experimental manipulation of brood size had only a weak effect on chick TL, suggesting that the role of environmental factors in influencing TL early in life is limited. There was no effect of chick sex or parental age on chick TL. While these results are consistent with those reported in some studies, they are in conflict with others. These disparate conclusions might be attributable to the inherent complexity of telomere dynamics playing out differently in different populations or to study‐specific variation in the age at which subjects were measured. [ABSTRACT FROM AUTHOR]

It is widely recognized that female animals in a variety of taxa display ornamental traits, such as elaborate plumage, but elucidating whether such traits evolve by selection or genetic correlation remains a challenge because more ornamented females are often found to produce low‐quality offspring. While resource trade‐offs between the production of ornaments and offspring may underlie this negative relationship, it is not an adequate explanation for species where the timing of production of ornaments and offspring does not overlap. Instead, costs associated with engaging in agonistic interactions with conspecifics, which maintains the honesty of signals of quality, may also reduce resources available to invest in offspring. In this study, we enhanced and reduced the plumage brightness of female tree swallows (Tachycineta bicolor) relative to controls to test whether social costs associated with displaying bright plumage is a potential mechanism underlying the observation that more ornamented females produce low‐quality nestlings. Our results showed that nestlings reared by females in the enhanced plumage brightness treatment were structurally smaller, having shorter lengths of the combined head and bill than nestlings in the reduced plumage brightness treatment, and tended to grow their head and bills more slowly than nestlings in the reduced and control plumage brightness treatments. Nestlings in the enhanced plumage brightness treatment also tended to gain mass more slowly than nestlings in control treatment. Overall, that females with enhanced plumage brightness produced structurally smaller nestlings provides evidence that social costs paid by females may lead to the production of low‐quality offspring and should be considered in future studies. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Field Ornithology is the property of Resilience Alliance and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Latitudinal differences in timing of breeding are well documented but how such differences carry over to influence timing of events in the annual cycle of migratory birds is notwell understood. We examined geographical variation in timing of events throughout the year using light-level geolocator tracking data from 133 migratory tree swallows (Tachycineta bicolor) originating from 12 NorthAmerican breeding populations. As wallow's breeding latitude influenced timing of breeding, which then carried over to affect breeding ground departure. This resulted in subsequent effects on the arrival and departure schedules at autumn stopover locations and timing of arrival at non-breeding locations. This 'domino effect' between timing events was no longer apparent by the time individuals departed for spring migration. Our range-wide analysis demonstrates the lasting impact breeding latitude can have on migration schedules but also highlights how such timing relationships can reset when individuals reside at non-breeding sites for extended periods of time. [ABSTRACT FROM AUTHOR]

Nestlings of some aerial insectivores experience pre-fledging mass recession, possibly to achieve optimum wing loading at fledging. However, studies to date where mass recession was linked to wing loading at fledging have been limited to 2 species of swifts (Apodidae), and additional studies are needed to determine if factors contributing to prefledging mass recession vary among species. We examined factors contributing to pre-fledging mass recession by nestling Tree Swallows (Tachycineta bicolor). During the 2015 breeding season in Kentucky, nestling Tree Swallows in 29 broods were divided into half-weighted, full-weighted, and control treatment groups. Lead weights weighing either 2.5% (0.6 g) or 5% (1.2 g) of nestling mass were glued to the back feathers of half-weighted and full-weighted nestlings, respectively, between 9 and 11 days post-hatching. Video recordings were used to monitor provisioning and begging behavior. Treatment groups did not differ in mass at fledging, amount of mass lost, or wing loading at fledging, and adult provisioning rates and time spent begging by nestlings did not vary from day 11 to day 19 post-hatching. Thus, mass loss by nestling Tree Swallows prior to fledging was not due to changes in either parental or nestling behavior, but likely resulted from loss of water from maturing feathers and other tissues. In contrast, studies of 2 species of swifts (Apodidae) revealed that changes in nestling behavior influenced pre-fledging mass recession, with weighted nestlings losing more mass than control nestlings, apparently to optimize wing loading at fledging. This difference between swifts and Tree Swallows may be due to differences in the duration of nestling periods (longer for swifts) and wing loading (higher in swifts). With greater wing loading, optimum mass at fledging may be more critical for swifts than Tree Swallows. [ABSTRACT FROM AUTHOR]

Bird species around the world are threatened with extinction. In North America, aerial insectivores are experiencing particularly severe population declines. To conserve these species, we need to know which life stages have the largest influence on population growth. We monitored a box-nesting population of Tree Swallows (Tachycineta bicolor) from 1975 to 2017. From this long-term dataset, we derived estimates of 9 vital rates: clutch size, reproductive attempts, and overwinter return for 2 age classes of adult females, and hatching, fledging, and juvenile recruitment rates. We conducted a life-stage simulation analysis on this population based on a 3-stage, female-based population projection matrix to determine which of these vital rates had the greatest influence on overall population growth rate. We determined each vital rate's sensitivity (i.e. the effect of a small change in each vital rate on population growth), elasticity (i.e. the effect of a proportional change in each vital rate on population growth), and ability to explain variation in population growth rate. Juvenile recruitment, female return for both age classes, and fledging success determine population growth because they have high sensitivity, elasticity, and explained large amounts of variation in population growth rate. Contrary to expectations, the number of nesting attempts, clutch size, and hatch rate have little impact on population growth rate. To stem Tree Swallow decline, and potentially the declines we see across the aerial insectivores, fledging success or overwinter survival must increase. [ABSTRACT FROM AUTHOR]

The "good-genes" hypothesis to explain female extra-pair mating states that females benefit from this behavior by acquiring better genes for their offspring. Despite extensive research, results are mixed, and the predictions of the good-genes hypothesis have been met in fewer than half of published papers. One possible explanation for this lackofconsensusisthat the benefits of extra-pair copulation are context-dependent. Here we use chick size, the probability of fledging, and telomeres, the protective caps of chromosomes, as markers for individual quality. Telomere length (TelL) integrates across many stressors and covaries with probability of survival and reproductive success. To test whether benefits to extra-pair (EP) matings are context-dependent we look at the telomere length of extra-pair and within-pair offspring (EPO and WPO, respectively) reared either in experimentally enlarged broods or in broods left at their natural size. We predicted that EPO would have longer telomeres than WPO, and that this difference would be more pronounced among nutritionally limited nestlings reared in enlarged broods. Contrary to our predictions, EP status did not predict chick size or TelL of nestlings reared in either treatment group. EPO from enlarged broods had a higher probability of fledging than similarly reared WPO, but this effect was only seen after a separate analysis per group and not in the full model. Even though these results give mixed support to the good-genes hypothesis they also highlight the difficulty in choosing the proper metric and context. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Field Ornithology is the property of Resilience Alliance and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

That ornamental traits of females can act as signals of quality has gained empirical support, but whether and how such ornaments of females mediate social interactions with conspecifics remains less clear. Female Tree Swallows ( Tachycineta bicolor (Vieillot, 1808)) aggressively compete for and defend nest sites, and as such, nest site intrusions by conspecific females challenging ownership of a nest may prevent territory-owning females from dishonestly displaying ornamented plumage. We tested whether plumage brightness of female Tree Swallows influences nest site retention and reproductive success by experimentally enhancing or reducing their plumage brightness relative to controls prior to breeding. Females with reduced brightness were more likely to retain their nests sites and breed relative to control females and females with experimentally enhanced brightness. Females displaying enhanced brightness also tended to initiate clutches later than females with control and reduced brightness. Overall, lower nest site retention and reproductive success for females with enhanced brightness is consistent with social costs imposed on individuals dishonestly signalling high quality. Future studies in female birds should consider whether costs of losing a nest site to intruding conspecific females, especially in species where nest sites are limited, is a mechanism that maintains the honesty of signals of quality. [ABSTRACT FROM AUTHOR]

Climate change can drive population declines for many species, often through changes to their food supply. These changes can involve a mis-timing between periods of high food demand and peak food availability, typically from advances in breeding phenology, and/or an overall reduction in food availability. Aerial insectivores, birds that feed on insects caught in flight, are experiencing steep population declines possibly because of shifts in the timing and/or abundance of aerial insects. We determined whether changes in breeding performance over time could account for declines in Bank Riparia riparia, Barn Hirundo rustica, Cliff Petrochelidon pyrrhonota, and Tree Tachycineta bicolor Swallows, and if so, whether changes were related to shifts in breeding phenology and/or climate change. We compared breeding performance and phenology in Maritime Canada before (1962-1972) and after (2006-2016) the onset of steep population declines during the mid-1980s, to determine whether breeding performance was reduced or phenology was advanced. Then, we modeled relationships between temperature, precipitation, breeding phenology, and performance for Barn and Tree Swallows, the only species with sufficient data, from 1960 to 2016, to determine whether phenology and performance were related to climatic conditions. Between the two time periods, we found significantly lower performance in Bank Swallows, higher performance in Barn and Tree Swallows, and unchanged performance in Cliff Swallows. We also found clutch initiation dates advanced by 8-10 d for all species except Bank Swallows. On the breeding grounds, warmer winter temperatures for Tree Swallows and less winter precipitation for Barn and Tree Swallows in a given year were associated with earlier breeding, and for Tree Swallows, changes in nestling survival. Otherwise, Barn and Tree Swallow breeding performance was unaffected by winter temperature and precipitation. Our results suggest that in this region poorer breeding performance could contribute to population declines for Bank Swallows but not for the other three species. [ABSTRACT FROM AUTHOR]

Wastewater treatment plants (WWTPs) are an important source of anthropogenic chemicals, including organic flame retardants (FRs). Limited studies indicate birds can be exposed to FRs by feeding from waters receiving WWTP effluent or in fields receiving biosolids. Expanding on our earlier study, 47 legacy and 18 new FR contaminants were characterized in the eggs of insectivorous tree swallows ( Tachycineta bicolor ) feeding in water bodies receiving effluent from two WWTPs and compared to those from a reference site 19 km downstream of the nearest WWTP. Of the FRs measured, polybrominated diphenyl ethers (PBDEs) dominated the FR profile, specifically BDE-47, -99, -100, -153, -154, with considerably lower concentrations of hexabromocyclododecane (HBCDD), BDE-183 and BDE-209; each detected in 96–100% of the eggs overall except HBCDD (83%). FR concentrations were usually significantly greater in eggs from the secondary WWTP versus the tertiary WWTP and/or reference site. Despite low detection rates, concentrations of new FRs, specifically pentabromobenzyl acrylate (PBBA), 1,2,-bis-(2,4,6-tribromophenoxy)ethane (BTBPE), bis(2-ethylhexyl)-tetrabromophthalate (BEHTBP), tetrabromo- o -chlorotoluene (TBCT), hexabromobenzene (HBB), α- and β-1,2-dibromo-4-(1,2-dibromoethyl)-cyclohexane (DBE-DBCH), were greater than HBCDD or BDE-209. Additional evidence that WWTPs are an important source of exposure to new FR contaminants for birds utilizing associated water bodies is that only the WTTP eggs, not the reference eggs, had measureable concentrations of PBBA, TBCT, BEHTBP, HBB, α-DBE-DBCH, 2,2′,4,5,5′-pentabromobiphenyl (BB-101), pentabromoethyl benzene (PBEB), 2,4,6-tribromophenyl allyl ether (TBPAE), and tetrabromo- p -xylene ( p TBX). Our study suggests that WWTPs are an important source of legacy and new FR contaminants for birds consuming prey that are associated with WWTP out-flows. [ABSTRACT FROM AUTHOR]

Tree swallows (Tachycineta bicolor) have been a periodic bird-strike problem at John F. Kennedy International Airport (JFKIA), New York, New York, causing runway closures, flight delays, and damage to aircraft following the ingestion of bird flocks into engines. We examined 65 tree swallows collected at JFKIA in October 2001 to determine food sources that were attracting the birds to the airport. Digestive tracts of all 65 specimens contained northern bayberry fruits (Myrica pensylvanica), averaging 15.6 fruits per bird or 3.4% of the bird’s body mass in specimens where the entire tract was dissected. Bayberry fruits are a highly attractive food source for tree swallows, especially during fall migration when insects are limited. Beginning late in 2001, a bayberry removal program was instituted at JFKIA. We examined tree swallow strike reports from JFKIA before and after this program began and found a 75% reduction in the number of strikes after removal of bayberry bushes. Removal of bayberry from coastal airports like JFKIA may facilitate the dispersal of tree swallow flocks that use airports as resting sites during their migration and may reduce the risk to birds and dangerous encounters with aircraft, thus limiting problems caused by runway closures and flight delays.

Assessing the genetic variation and distribution of immune genes across heterogeneous environmental conditions in wild species is essential to further our understanding of the role of pathogen pressure and potential resistance or prevalence in hosts. Researchers have recently investigated β-defensin genes in the wild, because their variability suggests that they may play an important role in innate host defense. This study investigated the variation occurring at 6 innate immune genes of the β-defensin family in a declining population of tree swallows (Tachycineta bicolor) in southern Québec, Canada (N = 160). We found that all 6 genes showed synonymous and nonsynonymous single nucleotide polymorphisms (SNPs) within the exon coding for the mature peptide. These results indicated that this group of genes was diverse in tree swallows. Our results suggested a potential interaction of this group of genes with fluctuating pathogen diversity, however, we found no sign of positive or negative selection. We assessed whether or not the distribution of genetic diversity of β-defensin genes in our study population differed between 2 regions that strongly differ in their level of agricultural intensification. Adults are highly philopatric to their breeding sites and their immunological responses differ between these 2 regions. However, we found little evidence that the level and distribution of genetic variability differed between these heterogeneous environmental conditions. Further studies should aim to assess the link between genetic diversity of β-defensin genes and fitness-related traits in wild populations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

For organisms in seasonal environments, individuals that breed earlier in the season regularly attain higher fitness than their late-breeding counterparts. Two primary hypotheses have been proposed to explain these patterns: The quality hypothesis contends that early breeders are of better phenotypic quality or breed on higher quality territories, whereas the date hypothesis predicts that seasonally declining reproductive success is a response to a seasonal deterioration in environmental quality. In birds, food availability is thought to drive deteriorating environmental conditions, but few experimental studies have demonstrated its importance while also controlling for parental quality. We tested predictions of the date hypothesis in tree swallows ( Tachycineta bicolor) over two breeding seasons and in two locations within their breeding range in Canada. Nests were paired by clutch initiation date to control for parental quality, and we delayed the hatching date of one nest within each pair. Subsequently, brood sizes were manipulated to mimic changes in per capita food abundance, and we examined the effects of manipulations, as well as indices of environmental and parental quality, on nestling quality, fledging success, and return rates. Reduced reproductive success of late-breeding individuals was causally related to a seasonal decline in environmental quality. Declining insect biomass and enlarged brood sizes resulted in nestlings that were lighter, in poorer body condition, structurally smaller, had shorter and slower growing flight feathers and were less likely to survive to fledge. Our results provide evidence for the importance of food resources in mediating seasonal declines in offspring quality and survival. [ABSTRACT FROM AUTHOR]

Many songbirds are under increasing pressure owing to habitat loss, land-use changes, and rapidly changing climatic conditions. Using citizen science data collected from 1980 to 2014, we asked how local weather and regional climate influenced the breeding dynamics of Mountain Bluebirds ( Sialia currucoides (Bechstein, 1798)) and Tree Swallows ( Tachycineta bicolor (Vieillot, 1808)). Mountain Bluebird reproduction was strongly associated with local weather: number of nestlings and fledglings both decreased in years of high rainfall. Clutch size and number of fledglings also declined over the study period. Abundance of Mountain Bluebirds was higher in years of lower early-season snowfall and warmer local temperatures, as well as more negative Southern Oscillation Index (SOI) values, indicating a positive influence of El Niño conditions. Tree Swallow reproduction (clutch size, number of nestlings, and number of fledglings) was negatively associated with SOI values, and the number of Tree Swallow nestlings decreased in years of higher rainfall and warmer temperatures. Tree Swallows also showed a marked decline in abundance over the period of the study, consistent with recent range-wide declines. Together, our results demonstrate that local weather and regional climate differentially affect the reproductive dynamics of Mountain Bluebirds and Tree Swallows and highlight the importance of long-term citizen science data sets. [ABSTRACT FROM AUTHOR]

Immunity represents an important defense mechanism against pathogens and is intimately linked to fitness. Previous studies have found significant interindividual variation of immune responses in wild populations and have emphasized the importance of ecological factors in explaining this variability. A deterioration of environmental conditions, such as agricultural intensification, can modify resource availability and, as a result, alter immune functions. The aim of this study was to investigate the effect of agricultural intensification on innate immune functions in breeding adult tree swallows (Tachycineta bicolor) over 6 yr. We investigated the relationship between agricultural intensification and bacteria-killing ability (BKA) against a strain of E. coli. We also assessed how the presence and the number of bacteria on the surface of eggshells changed with agricultural intensification. Contrary to our expectations, we found a positive relationship between agricultural intensification and BKA, where individuals had higher BKA in intensive compared to nonintensive farmlands. While this trend was observed through the 6-yr study, we also found a tendency for a reduction of BKA over time. We found no relationships between the presence or number of different types of eggshell bacteria and agricultural intensification or an association between BKA of females and eggshell bacteria of their clutch. Our results suggest that differences in immune function observed between intensive and nonintensive farmlands could reflect genetic differences among individuals and/or trade-offs with other traits expressed among habitats within our study system. [ABSTRACT FROM AUTHOR]

Tree swallows, Tachycineta bicolor, were sampled across the Great Lakes basin in 2010 through 2015 to provide a systemwide assessment of current exposure to organic contaminants. The results provide information identified as critical by regulators to assess the "bird or animal deformity or reproductive problems" beneficial use impairment. Eggs were collected from 69 sites across all 5 Great Lakes, including 27 Areas of Concern (AOCs), some with multiple sites, and 10 sites not listed as an AOC. Concentrations of organic contaminants in eggs were quantified and compared with background and reproductive effect thresholds. Approximately 30% of AOCs had geometric mean concentrations of total polychlorinated biphenyls (PCBs) at or below average background exposure (0.34mg/g wet wt). Exposure to polybrominated diphenyl ethers (PBDEs) was minimal, and only 3 of 27 AOCs and 1 non-AOC had geometric mean concentrations that exceeded background for tree swallows (96 ng/g wet wt). Concentrations of both PCBs and PBDEs were 10 to 20 times below the lower limit associated with impaired hatching success. In contrast, geometric mean concentrations of polychlorinated dibenzo-p-dioxin and furan (PCDD-F) toxic equivalents (TEQs) at the Saginaw River and Bay AOC and Midland, Michigan, USA (a non-AOC site), exceeded the lower limit for hatching effects (181 pg/g PCDD-F TEQs). The rest of the sites had geometric mean concentrations of PCDD-F TEQs below background levels (87 pg/g PCDD-F TEQs). Other organic contaminants, including p,p0-dichlorodiphenyldichloroethylene, mirex, heptachlor, and chlordane, were at or below background or adverse effect concentrations. [ABSTRACT FROM AUTHOR]