Search

Copyright of Journal of Caribbean Ornithology is the property of Society for the Conservation & Study of Caribbean Birds 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.)

Hosts of brood parasitic Brown-headed Cowbirds (Molothrus ater) have acquired a suite of behavioral responses against them, including egg rejection and nest defense. Several cavity-nesting species have been shown to exhibit egg rejection, including the Mountain Bluebird (Sialia currucoides). Previous work reported egg rejection rates as low as 20%, under the assumption that they may instead be relying heavily on aggressive interactions to defend their nests from parasitism. In the present study, we evaluated the egg rejection and aggression behaviors of a population of Mountain Bluebirds in western Montana. Results indicate a higher rate of rejection than previously documented, with model cowbird eggs rejected in over 40% of trials (n = 37), compared with 5% rejection of mimetic eggs. In contrast, we found little aggressive response by Mountain Bluebirds toward both an adult cowbird model and a nonthreatening American Goldfinch (Carduelis tristis) model. Aggression patterns were consistent between sexes, with the most common behaviors including sitting and watching from within 5 m and flying past the models (n = 21). Hovering above the model was observed on a few occasions, and physical contact by bluebirds happened on only 3 occasions toward the goldfinch model. In summary, Mountain Bluebirds in western Montana showed relatively high rates of cowbird egg rejection but little aggressive response toward adult heterospecific nest intruders. [ABSTRACT FROM AUTHOR]

Much attention has been given to the topic of bird phenology in response to climate change. While strong evidence supports a general pattern of advancement in spring migrants' arrival dates with warming temperatures, the mechanisms underlying these changes are not clearly understood. We summarize the spring arrival of the Mountain Bluebird (Sialia currucoides) in central Alberta from 58 years of data and examine the influence of temperature and snow cover on the patterns of arrival. We hypothesized that a significant advance in the Mountain Bluebird's first arrival date was related to weather variables. In central Alberta, March temperatures increased, and first arrival dates for the Mountain Bluebird advanced 0.33 days per year from 1961 to 2018 or 19 days over the 58 years. However, temperatures on the date of arrival have cooled slightly (2.8 °C) over the study period, and snow depth on the date of arrival decreased slightly (1.5 cm) over the study period, which may influence early migrants' opportunities for foraging. Although Mountain Bluebirds have arrived at our central Alberta study area considerably earlier over the past decades, temperatures and snow depth have been highly variable, suggesting that the species is likely responding to multiple cues that influence its arrival dates. Given the Mountain Bluebird's migratory nature, environmental and behavioral stimuli en route to breeding areas likely exert considerable influence on arrival dates. [ABSTRACT FROM AUTHOR]

Clearcutting of forests results in habitats that structurally resemble grasslands and so may act as ecological traps for grassland birds. Several studies have implicated predation as the factor that decreases the number of offspring, but few have examined performance at other breeding stages. Consistent with a passive ecological trap, Mountain Bluebirds (Sialia currucoides (Bechstein, 1798)) that settled in clearcuts in central British Columbia did not differ in age or quality from adults in grasslands. Nest building and laying date of the first egg did not differ between habitats, suggesting an equal propensity for settling in each habitat. In clearcuts, however, the body condition of female parents was lower, and they abandoned their nests more often in harsh weather. This higher total clutch loss in clearcuts meant that seasonal production of fledglings per female was 13% less in clearcuts. Furthermore, fledglings in grasslands weighed 4% more and female fledglings had plumage with shorter (UV-shifted) wavelengths (hence greater ornamentation) than those in clearcuts, suggesting that they were also of better quality. Thus, predation rates were not the cause of reduced reproduction in clearcuts; rather, our results suggest that lower prey abundance was linked to nest abandonment in harsh weather and reduced both the number and quality of offspring in those habitats. [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.)

The article offers information on the radio tracking of mountain bluebirds visiting neighbors' nests. Topics include, North American bluebirds are secondary cavity nesters that readily accept nest boxes; documenting of cooperative breeding, prospecting for the future requires marked breeding pairs; and monitoring of mountain bluebirds by using RFID technology (Radio frequency identification systems).

Copyright of Avian Conservation & Ecology 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.)

Both weather and parental care can influence avian reproductive success, yet few studies have investigated these 2 factors simultaneously. Examining these factors under a common framework is informative because they may interact to influence overall productivity; for example, weather could directly influence nestling survival or could act indirectly by influencing rates of provisioning. To tease apart these possibilities, we used piecewise structural equation modeling and path analysis to assess the relative influence of local weather (temperature and rainfall) and rates of provisioning on the fledging success of Mountain Bluebirds (Sialia currucoides) breeding in nest boxes. Both ambient temperature during the nestling period and provisioning rates influenced fledging success, but this finding was dependent on nest box entrance type. Bluebirds nesting in boxes with a hole-shaped entrance had higher overall fledging success than those using boxes with a slot-shaped entrance and exhibited a positive association between fledging success and provisioning rates but a negative association with temperature. Bluebirds nesting in boxes with a slot-shaped entrance experienced reduced fledging success, and success was only weakly associated with provisioning rates. Reduced fledging success for birds nesting in slot boxes may be due to increased exposure and higher susceptibility to stochastic events (e.g., storms), which may also mask any effects of parental effort on success rates. Based on these findings, we recommend the use of nest boxes with hole-shaped rather than slot-shaped entrances when managers and conservation groups establish new bluebird routes or replace existing boxes. Les conditions météorologiques ainsi que l'approvisionnement parentale peuvent influencer le succès reproducteur aviaire; peu d'études, cependant, ont exploré ces deux facteurs simultanément. L'examen de ces facteurs dans le cadre d'un même programme d'étude est informatif puisque ces facteurs peuvent interagir de façon à influencer la productivité totale; par exemple, les conditions météorologiques pourraient directement influencer la survie des oisillons ou agir indirectement en influençant le taux d'approvisionnement. Pour distinguer ces influences directes et indirectes, nous avons employé une modélisation par équation structurelle séquentielle ainsi que l'analyse des trajectoires, permettant de déterminer l'influence des conditions météorologiques locales (température et précipitation) et de l'approvisionnement sur le succès d'envol de merlebleus azurés (Sialia currucoides) utilisant des nichoirs. La température ambiante pendant la période de nidification de même que le taux d'approvisionnement ont influencé le succès d'envol, mais le résultat variait selon le type de nichoir. Les merlebleus utilisant des nichoirs avec trou d'entrée circulaire avaient un succès d'envol plus élevé que ceux utilisant des nichoirs avec trou d'entrée en forme de fente verticale, et le succès d'envol était positivement lié au taux d'approvisionnement mais négativement lié à la température. Les merlebleus utilisant des nichoirs avec entrée en forme de fente avaient un succès d'envol réduit, et le succès d'envol était faiblement lié au taux d'approvisionnement. Le succès d'envol inférieur observé parmi les oiseaux utilisant les nichoirs avec entrée en forme de fente était possiblement dû à une plus grande exposition et sensibilité du nid aux événements stochastiques (e.g. tempêtes), ce qui pourrait également masquer les effets de l'approvisionnement parentale sur le taux de succès d'envol. Compte tenu de ces résultats, nous recommandons de munir les nichoirs d'une entrée circulaire plutôt que d'une entrée en forme de fente verticale lorsque gestionnaires et groupes de conservation cherchent à créer de nouveaux sentiers de nichoirs ou veulent remplacer des nichoirs existants. Mots-clés: approvisionnement, conditions météorologiques, envol, merlebleu azuré, nichoir, soins parentaux. [ABSTRACT FROM AUTHOR]

Determining the functional significance of ornamental traits and whether they are shaped by sexual selection requires understanding how they vary among individuals, and their relationship with other measures of quality. Conspicuous eggshell coloration is a trait that may have evolved through sexual selection as a signal of female quality. This hypothesis is based on the possibility that the pigment used to colour blue-green eggs is limited and potentially costly to allocate to eggshells. We investigated the signalling potential of blue-green eggshell colour by quantifying patterns of within- and among-clutch colour variation in Mountain Bluebirds (Sialia currucoides) to determine if pigment was limited and if egg colour traits are intrinsic to individual females. We also explored relationships over two breeding seasons between eggshell colour and other female traits and investment in eggs. Eggshell colour was highly repeatable within clutches for most measures, and relatively consistent between breeding events in different years, indicating that eggshell colour is an intrinsic trait. Eggs in second clutches within a season had less saturated blue-green colour than in first clutches, and within clutches, later-laid eggs were brighter but generally less blue-green in colour than earlier laid eggs, providing evidence of pigment limitation. However, associations between eggshell colour and other female traits and investment in eggs were less clear, and inconsistent among study years. Our findings suggest that there is potential for blue-green egg colour to function as a signal of female quality, but further study is needed to determine if blue-green eggshell colour is a truly informative signal. [ABSTRACT FROM AUTHOR]

Clear-cutting of forests results in early successional stages that resemble grasslands, and grassland birds such as Mountain Bluebirds (Sialia currucoides) may settle in these anthropogenically created habitats to breed. Our objective was to determine if parent bluebirds provisioned offspring differently, in terms of amount and quality of prey, in clear-cuts versus grasslands, and how this related to fledgling production. We placed microcameras inside 92 nestboxes during two breeding seasons to film parental food deliveries at sites in central British Columbia. At the young nestling stage (< 5 d old), there were no significant differences in terms of provisioning rate or the type of prey delivered. Neither the abundance of perches in the habitat nor parental traits such as age or plumage brightness were associated with provisioning. When nestlings were older, parents in clear-cuts delivered slightly larger prey and diets with proportionately more larvae and spiders, the most nutritious taxa. However, delivery rates were 21% higher in grasslands than in clear-cuts. Fledglings in clear-cuts had lighter body mass than those in grasslands, suggesting that the high nutrient content of prey in clear-cuts could not compensate for the lower deliveries. Thus, parents in grasslands seem more able to meet the energy demands of large nestlings by incorporating diverse insect taxa into their diet.

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.)

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]

Birds breeding in heterogeneous landscapes select nest sites by cueing in on a variety of factors from landscape features and social information to the presence of natural enemies. We focus on determining the relative impact of anthropogenic noise on nest site occupancy, compared to amount of forest cover, which is known to strongly influence the selection process. We examine chronic, industrial noise from natural gas wells directly measured at the nest box as well as site-averaged noise, using a well-established field experimental system in northwestern New Mexico. We hypothesized that high levels of noise, both at the nest site and in the environment, would decrease nest box occupancy. We set up nest boxes using a geospatially paired control and experimental site design and analyzed four years of occupancy data from four secondary cavity-nesting birds common to the Colorado Plateau. We found different effects of noise and landscape features depending on species, with strong effects of noise observed in breeding habitat selection of Myiarchus cinerascens, the Ash-throated Flycatcher, and Sialia currucoides, the Mountain Bluebird. In contrast, the amount of forest cover less frequently explained habitat selection for those species or had a smaller standardized effect than the acoustic environment. Although forest cover characterization and management is commonly employed by natural resource managers, our results show that characterizing and managing the acoustic environment should be an important tool in protected area management. [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.)

Sex allocation theory predicts that females should bias the sex ratio of their offspring in response to differences in the reproductive value of sons versus daughters. Consistent with this prediction, females of many species appear to bias offspring sex ratios in response to mate attractiveness and condition. Male mountain bluebirds (Sialia currucoides) display full body UV-blue structural plumage colouration, which is associated with attractiveness, condition, and reproductive success. Over four breeding seasons, we found females paired with more colourful males produced increasingly male-biased broods and provisioned offspring at a higher rate. Surprisingly, however, we also found females with duller plumage and those mated to first-year males produced more malebiased broods. These results provide support for sex allocation in mountain bluebirds and suggest female reproductive decisions may be influenced by the attractiveness of her mate. However, this system is clearly complex and more work is needed to understand the roles of male age and female colouration in the signalling systems of mountain bluebirds. [ABSTRACT FROM AUTHOR]

Understanding inter- and intraspecific variation in parental care has been an important focus in studies of avian behaviour and evolution. Unfortunately, typical methods for quantifying parental care, such as field observation and video recordings, can be extremely time-consuming. Here, we demonstrate that utilizing behavioural analysis software, such as EthoVision XT, can reduce time required for video data extraction by 37−69 %. This method is highly accurate; results and error rates did not differ from those of manual observation. We suggest this method could be beneficial and time-saving for studies analyzing large amounts of video recordings. [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.)

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.)

The article discusses the challenges encountered in identifying male and female warm-colored Mountain Bluebirds. Topics discussed include bluebird molt strategy, the typical female Mountain Bluebirds and relevance of molt timing. Also mentioned is the juvenal plumage obtained by bluebirds in their first plumage cycle.

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.)

Annual reproductive success in many species is influenced by the number of breeding attempts within a season. Although previous studies have shown isolated effects of female quality, food, and timing of breeding on the probability of female birds producing second broods, to our knowledge, none have tested the relative importance of multiple factors and their interactions using simultaneous manipulations within populations of free-living birds. In this study, we show that individual quality and timing of breeding interact to affect the probability of double-brooding in female mountain bluebirds ( Sialia currucoides). High-quality females (those that naturally initiated clutches early in the season) were more likely to double-brood, regardless of whether their hatching date was advanced or delayed, whereas later breeding, lower quality females were much less likely to double-brood when their first attempt was delayed. This indicates that annual fecundity of poorer quality (or younger) female bluebirds may be more sensitive to seasonal variation in environmental conditions. In addition, birds that were provided with supplemental food throughout first breeding attempts were more likely to double-brood in one of the study years, suggesting that female bluebirds may be energetically limited in their capacity to initiate a second brood. Females that had their first brood delayed also had a shorter inter-brood interval and were moulting fewer feathers during second broods compared to controls, while females in better condition showed more advanced moult in second breeding attempts. Taken together, our results demonstrate the combined effects of age- or individual quality-mediated energetic trade-offs between current and future reproduction, and between investments in offspring and self-maintenance, on annual fecundity of female birds. [ABSTRACT FROM AUTHOR]

Male reproductive success in socially monogamous birds is influenced to varying degrees by within-pair fertilization (WPF) and extrapair fertilization (EPF). In many species, males of higher phenotypic quality (e.g., plumage color) are more likely to obtain EPFs; however, predictors of WPF success have been less consistently identified. Moreover, few studies have examined the influence of ecological variables on patterns of paternity, even though environmental conditions are known to affect mating behavior of male and female birds. In this study, we examined phenotypic and ecological factors influencing patterns of paternity in broods of mountain bluebirds, Sialia currucoides. We show that brighter, bluer males were more likely to obtain EPFs in first broods but that plumage color did not predict the ability of males to maintain paternity in their own nest. We then examined the effect of food availability in first broods on the probability of males losing paternity in second broods within the same season. Females that were provided with supplemental food throughout first breeding attempts were less likely to produce extrapair offspring in second broods, and we suggest that supplemented females may have been less likely to seek extrapair mating opportunities because they perceived their social mates to be of higher quality under conditions of enhanced food availability. Our results demonstrate that ecological variables such as food availability can influence patterns of paternity and suggest that consideration of environmental context will be important for future research investigating mate choice and sexual selection in socially monogamous species. [ABSTRACT FROM PUBLISHER]

Asynchronous hatching of eggs in avian clutches produces a size hierarchy among nestlings that may lead to variation within broods in resistance to pathogens or parasites. In this study, we tested several predictions regarding variation in immunocompetence and distribution of parasites within avian broods by combining parasite removal and carotenoid supplementation treatments in nests of mountain bluebirds Sialia currucoides. Last-hatched nestlings were less likely to invest carotenoids in an induced cell-mediated immune response, suggesting they may be more susceptible to parasites; however, parasite removal disproportionately benefited middle-ranked nestlings. This supports the hypothesis that some avian ectoparasites balance host resistance against nutritional benefits by preferentially parasitizing nestlings of intermediate quality and immunocompetence. We found no evidence that males positioned last in the hatching sequence were differentially affected by ectoparasites, and, contrary to some previous studies in other passerines, last-hatched nestlings in asynchronously hatching broods were not less immunocompetent than their nest mates. In fact, junior nestlings exhibited weaker immune responses than their siblings in more synchronously hatching broods, and we suggest this may reflect environment-dependent maternal effects that warrant further investigation. Overall, our results highlight the importance of understanding the feeding and host selection behaviour of ectoparasites, as well as the fitness consequences thereof, since many predictions related to within-brood distribution of parasites require that parasites are able to discern the relative quality of available hosts. [ABSTRACT FROM AUTHOR]

Sexual selection theory posits that ornamental traits can evolve if they provide individuals with an advantage in securing multiple mates. That male ornamentation occurs in many bird species in which males pair with a single female is therefore puzzling. It has been proposed that extra-pair mating can substantially increase the variance in reproductive success among males in monogamous species, thus increasing the potential for sexual selection. We documented the frequency of extra-pair paternity and examined its effect on variation in male reproductive success in the mountain bluebird Sialia currucoides, a socially monogamous songbird in which males possess brilliant plumage ornamentation. Extra-pair paternity was common in our Wyoming study population, with 72% of broods containing at least one extra-pair offspring. The standardized variance in actual male reproductive success (i.e., the total number of within-pair and extra-pair offspring sired) was more than seven times higher than the variation in apparent success (i.e., success assuming that no extra-pair mating occurred). Success at siring within-pair and extra-pair offspring both contributed to the variation in overall male reproductive success. Within-pair success, however, did not predict a male's level of extra-pair success, suggesting that males do not sacrifice within-pair paternity to gain extra-pair paternity. Calculation of the sexual selection (Bateman) gradient showed that males sire approximately two additional offspring for each extra-pair mate that we identified. Thus, in this sexually dichromatic species, extra-pair mating increases the variance in male reproductive success and provides the potential for sexual selection to act. [ABSTRACT FROM AUTHOR]

Ornamental traits are thought to evolve because they give individuals an advantage in securing multiple mates. Thus, the presence of ornamentation among males in many monogamous bird species presents something of a conundrum. Under certain conditions, extra-pair paternity can increase the variance in reproductive success among males, thus increasing the potential for sexual selection to act. We addressed this possibility in the mountain bluebird ( Sialia currucoides), a socially monogamous songbird in which males possess brilliant ultraviolet (UV)-blue plumage. Specifically, we asked whether a male’s success at siring offspring within his own nest and within the nests of other males was related to his coloration. In pairwise comparisons, males that sired extra-pair offspring were not more colorful than the males that they cuckolded. However, males that sired at least one extra-pair offspring were, on average, brighter and more UV-blue than males that did not sire extra-pair offspring. Brighter, more UV-blue males sired more offspring both with their own mate and tended to sire more offspring with extra-pair mates and thus sired more offspring overall. Our results support the hypothesis that the brilliant UV-blue ornamental plumage of male mountain bluebirds evolved at least in part because it provides males with an advantage in fertilizing the eggs of multiple females. [ABSTRACT FROM AUTHOR]

Resource selection plasticity and behavioral dominance may influence the ability of a species to respond to changes in resource availability, particularly if dominant species have highly specialized resource requirements. We examined the response of several dominant and subordinate cavity-nesting species to a reduction in the availability of an essential resource (nesting cavities) using the novel experimental approach of blocking the entrances to high-quality cavities. We monitored nest abundance on seven treatment and 13 control sites (aspen groves in a grassland matrix) in British Columbia, Canada, for two years pretreatment (2000-2001), two years during treatment (2002-2003), and two years posttreatment (cavities reopened; 2004-2005). At the community level, nest abundance declined by 50% on treatment sites following cavity blocking and returned to pretreatment levels following cavity reopening. Nest abundance of European Starlings (Sturnus vulgaris), a dominant secondary cavity-nester (SCN), declined by 89% and failed to recover posttreatment. Conversely, nest abundance of Mountain Bluebirds (Sialia currucoides; a subordinate SCN) increased following cavity blocking and remained high following reopening. Tree Swallows (Tachycineta bicolor) were unaffected by cavity blocking. We suggest that starlings, while being the dominant SCN, may be limited by availability of suitable nest sites, whereas bluebirds may be limited by starling abundance. We propose that plasticity in nest site preferences of subordinate cavity-nesters may enable them to contend with natural variation in availability of critical resources, such as nest cavities and food, in addition to coping with interspecific competition. This is the first community-level, multiyear study involving manipulation of nest site availability via experimental cavity blocking. [ABSTRACT FROM AUTHOR]

1. Trade-offs between growth and immunity of nestling birds can be influenced by parasites, but the magnitude of these effects may depend on availability of critical dietary nutrients. Owing to their importance for both immune system function and growth, dietary carotenoids have the potential to mediate parasite-induced developmental strategies of avian hosts. 2. The effects of ectoparasitic blow flies Protocalliphora spp. and dietary carotenoids (lutein and zeaxanthin) on immune function and patterns of growth in nestling mountain bluebirds Sialia currucoides were investigated by combining parasite removal and carotenoid supplementation treatments in a 2 × 2 design. 3. Supplemental carotenoids enhanced nestlings’ T-cell-mediated immune response following intradermal injection of phytohaemagglutinin. 4. The effect of carotenoid supplementation on rate of mass gain depended on whether broods were exposed to parasites: among parasitized broods, those receiving supplemental carotenoids gained mass more rapidly than nonsupplemented broods, whereas there was no effect of supplemental carotenoids on growth of mass in broods that had parasites removed. This suggests that additional dietary carotenoids allowed nestlings to compensate for the otherwise detrimental effects of parasites on mass gain. For length of the eighth primary feather at fledging, early and late broods differed in their response to parasitism: early broods showed an increase in feather length when parasites were removed, while nestlings in late broods had shorter feathers in the absence of parasites. We suggest that this may reflect within-season variation in parasite-mediated growth strategies of nestlings. 5. Maternal condition was positively associated with mass, condition and rate of feather growth of offspring under all conditions, and also influenced nestling immunocompetence, but only in the absence of parasites. 6. We conclude that dietary carotenoids alleviate some of the detrimental effects of parasites on nestling birds; however, parasites also appear to specifically influence other growth and resource allocation strategies, and possibly constrain maternal or genetic effects on offspring phenotype, irrespective of dietary carotenoid availability. [ABSTRACT FROM AUTHOR]

Indicator models of sexual selection suggest that costly ornaments signal reliable information regarding an individual's quality to potential mates. In species that produce altricial offspring, the amount of parental care provided by both males and females can impact reproductive success. The Good Parent Hypothesis proposes that ornamentation in biparental species can act as an honest signal of parental ability to potential mates. We tested this hypothesis using the mountain bluebird ( Sialia currucoides), a sexually dichromatic, socially monogamous species in which both sexes have structurally based ornamental plumage coloration. A male's plumage color predicted neither the rate at which it provisioned nestlings nor brood growth rate. The same was true for females. We also found no indication of assortative mating by color or body condition. Feeding rates within pairs were positively correlated, which we suggest may be due to pairs responding similarly to the perceived needs of nestlings or to local area prey availability. In sum, our results do not support the Good Parent Hypothesis as an explanation for the evolution of ornamental plumage color in mountain bluebirds. We suggest alternative hypotheses for the evolution of ornamental plumage color in this species. [ABSTRACT FROM AUTHOR]

Nest-site selection is an important determinant of individual fitness in birds. Understanding what information individuals use to choose nest sites is therefore important for understanding the evolution of nest-site selection, the dynamics of populations, and the conservation of species. We used five years of mark-recapture data for Mountain Bluebirds (Sialia currucoides) to examine how dispersal probability and nest-site selection vary with potential cues of nest-site quality. Dispersal distance between breeding seasons and nest-site selection were modeled as a function of personal reproductive success, conspecific density, conspecific reproductive success, and habitat type. Between years, the dispersal probability was related to personal reproductive success, not conspecific information, and individuals fledging fewer young dispersed longer distances. For dispersing individuals, the probability that a nest site was selected in year i was negatively related to distance from the nest site selected in year i — 1 for all age and sex classes, and positively related to conspecific density and reproductive success in year i — 1 for both second-year (SY) and after-hatch-year (AHY) females. However, nest-site selection in year i was more strongly related to conspecific density in year i — 1 for hatch-year (HY) females and was much more strongly related to the reproductive success of conspecifics in year i — 1 for AHY females. Nest-site selection of HY and AHY males was not consistently related to the metrics of conspecific information, but we suspect that relationships were obscured by competitive interactions. We found no evidence indicating that individuals respond differently to conspecific information at longer distances, suggesting that individuals limit dispersal to areas where they have prior knowledge. We predict that these patterns of nest-site selection will allow birds to loosely track nest-site quality and maintain an ideal free distribution, where average fitness is equal in all habitat types. [ABSTRACT FROM AUTHOR]

Male investment of time and energy in caring for offspring varies substantially both between and within bird species. Explaining this variation is of long-standing interest to ornithologists. One factor that may affect male care is breeding site altitude, through its effects on climate. The harsher, less predictable abiotic conditions at higher altitudes are hypothesized to favour increased male investment of time and energy in offspring care. We tested this hypothesis by comparing male parental behaviour in Mountain Bluebirds ( Sialia currucoides) nesting at 1500 and 2500 m a.s.l. in the Bighorn Mountains of Wyoming, USA. We compared rates of prey delivery to nestlings at these two altitudes at two times: 1–2 days after hatching, when females spend much of their time brooding young, and 12–13 days later, when brooding has ended and nestling energy demands are peaking. High-altitude males fed nestlings 18 and 28% more often than low-altitude males early and later in the nestling stage, respectively, but only the difference in late-stage feeding rates were significant. Like males, females at the high site also fed nestlings significantly more often than females at the low site later in the nestling stage (45% difference in feeding rates). Consequently, the proportion of all feeding trips made by males at the high site (40%) did not differ significantly from that at the low site (44%). Parents at the high altitude may feed nestlings more often to compensate for their greater thermoregulatory costs. Parents may also be attempting to assist nestlings in storing fat and/or attaining a large size and effective homeothermy as quickly as possible to enhance nestling ability to survive bouts of severe weather which are common at high altitudes. [ABSTRACT FROM AUTHOR]

Few studies have examined how avian life-history traits vary within populations as elevation increases and climate becomes more severe. We compared egg and clutch sizes of Mountain Bluebirds (Sialia currucoides) nesting at two elevations (1500 m and 2500 m above sea level) in the Bighorn Mountains of Wyoming over two years. Eggs laid by females at the high-elevation site were, on average, significantly (6%) smaller in volume than eggs laid by their lower-elevation counterparts. Across elevations, egg size showed a significant positive correlation with female body condition (weight relative to size), and high-elevation females had significantly lower indices of condition than low-elevation females. Temperatures during clutch formation were colder at the high- elevation site, and egg size was negatively related to temperature after controlling for the effects of female condition. Clutches of females at high elevations were, on average, marginally smaller (by 5%, ∼0.3 eggs) than clutches of low-elevation females. Unlike egg size, clutch size was unrelated to either female condition or temperature during clutch formation. This suggests that, when under energetic or nutritional stress at high elevations, females sacrifice egg size before sacrificing clutch size. [ABSTRACT FROM AUTHOR]

An important question in ecology is how mechanistic processes occurring among individuals drive large-scale patterns of community formation and change. Here we show that in two species of bluebirds, cycles of replacement of one by the other emerge as an indirect consequence of maternal influence on offspring behavior in response to local resource availability. Sampling across broad temporal and spatial scales, we found that western bluebirds, the more competitive species, bias the birth order of offspring by sex in a way that influences offspring aggression and dispersal, setting the stage for rapid increases in population density that ultimately result in the replacement of their sister species. Our results provide insight into how predictable community dynamics can occur despite the contingency of local behavioral interactions. [ABSTRACT FROM AUTHOR]

The dates of "first observed arrivals" of Mountain Bluebirds, Sialia currucoides, and Tree Swallows, Tachycineta bicolor, have been recorded for approximately 40 years near Lacombe, Alberta, Canada. Examinations of trends of these returns with average monthly temperatures for March and April, respectively, suggest trends for earlier returns and warmer temperatures, consistent with theories of climate warming. [ABSTRACT FROM AUTHOR]

Presents information on a study that presented data of egg rejection in Mountain Bluebirds. Methods of the study; Results of the study; Discussion.