Journal of Avian Biology最新文献

Airspace habitat is essential foraging space for tree swallows Tachycineta bicolor, which rely on flying insects as their main source of food. Insect availability can change quickly from hour-to-hour or day-to-day, however, it is unclear whether insectivores primarily respond to changing atmospheric dynamics, resource dynamics, or a combination. Rapidly changing conditions are common in high-elevation areas – an understudied portion of the tree swallow's breeding range. To explore the relationship between food availability and high-elevation weather conditions as related to female provisioning, we deployed a mobile radar unit to collect insect abundance data during the 2022 and 2023 summer breeding seasons at a high-elevation site in Colorado's Rocky Mountains. We monitored 41 active nest boxes using radio-frequency identification (RFID) technology to track female provisioning behavior. We deployed three models to assess 1) how strongly swallow provisioning rates correlated with insect traffic rates, 2) how well swallow provisioning rates were explained by insect traffic rates and weather conditions, and 3) how insect traffic rates were related to weather conditions. Although there remains substantial unexplained variation in tree swallow provisioning rates, we found a significant positive relationship with insect traffic rate, a negative relationship with precipitation, and curvilinear relationships with temperature and wind speed. Weather variables and time of day explained nearly 80% of the variation in insect traffic rate, and the strength of these relationships suggests weather conditions serve as a good proxy of airborne insect activity. This research presents a link between our vast airspace habitat and animal ecology, advancing our understanding of how flying organisms respond to rapidly changing conditions in aerial environments and how multiple factors contribute to variation in provisioning rates in an aerial insectivore.

In consideration of current global climate change, ecophysiological research on wild birds has increased its emphasis on approaches related to thermal tolerance. Many studies have investigated how desert specialists are adapted physiologically to the hot and xeric conditions they live in. Our aim was to test whether migratory passerines from temperate areas also have physiological adaptations to cope with heat stress and whether such adaptations may be related to habitat or migration distance. Using video recording and flow-through respirometry, we measured temperatures of panting onset (T_PANT) of 113 individuals of 14 different species, exposed to increasing ambient temperature. Our study species differed in size, migration type (short-distance migrants vs. trans-Saharan migrants) and habitat preferences (woodland, farmland, reeds). We found that trans-Saharan migrants started panting at higher ambient temperatures (T_A) than short-distance migrants of similar size, but no difference between species from different habitats. This finding suggests that migrants facing a desert crossing may have adaptations to decrease the risk of dehydration while maintaining body temperature below the critical range. According to this, we suggest that there may be selection on traits related to the modulation of respiratory water loss in birds that cross the Sahara Desert during migration. Flexibility in these traits will be of crucial importance in a warmer future.

Egg color polymorphism and egg mimicry are important adaptations in the game process between hosts and brood parasites at the egg stage. The ability of hosts to recognize and reject parasitic eggs based on effective egg characteristics is a crucial factor in determining the outcome of this arms race. The evolution of linear markings on eggs has been identified in several parasitic systems of common cuckoos Cuculus canorus, yet little is known about the functional adaptation of this egg characteristic. Here, we examined the recognition and utilization methods of maculation signals of eggs in the common cuckoo hosts, south rock bunting Emberiza yunnanensis, which lays eggs with linear mimetic spots, and yellow-throated bunting Emberiza elegans, which lays eggs with dotted mimetic spots. The results demonstrated that both species of bunting hosts show moderate recognition and rejection levels towards interspecific eggs (spotted versus streaked). Moreover, during recognition, they utilized the contrast between the maculation and the egg background rather than the contrast between the maculations themselves. Our study is the first to demonstrate that two species of open-nesting buntings use achromatic contrast (not chromatic contrast) between pattern features and egg background color to identify and reject foreign eggs. However, whether other differences in pattern features, such as pattern density, distribution, and proportion are utilized by the hosts requires further verification.

Bird migration, as an energy-demanding activity, is expected to generate allocation trade-offs between important biological processes. For example, long-distance migratory flights may require redirection of resources from immune response and promote temporal immunosuppression. Individuals in high body condition may have the capacity to cope with the costs of migration while maintaining adequate levels of immune activity. Here, we investigated the covariation of immune response and two measures of condition in a short-distance migratory shorebird, the common snipe Gallinago gallinago. We captured and experimentally induced immune response using phytohaemagglutinin (PHA) in 148 snipes during the autumn migration. We found a positive relationship of PHA-induced immune response with indices of body condition reflecting aerobic capacity (total blood haemoglobin concentration) and the level of accumulated energy reserves (size-corrected body mass). The results provided evidence for a condition-dependent immune response in migrating snipes, indicating that high-quality individuals are capable of sustaining immune response during migration. We suggest that abundant food resources at high-quality stopover sites may help individuals rapidly replenish body reserves essential for the effective functioning of the immune system. It also seems likely that the maintenance of adequate immune function or its upregulation may confer significant adaptive advantages under ecological conditions of increased pathogenic exposure during migration.

While it is well known that the overall timing of avian breeding in northern latitudes has generally advanced due to climate change, it is still unclear how climate warming has affected the beginning, end, and duration of the breeding period and reproductive success of birds. This is because changes in the phenological breeding metrics have often been studied using ringing data that are based on successful nests only and impacts of local factors such as nest predation have not been analysed simultaneously. This study used both successful and failed nesting attempts to estimate the annual timing and duration of breeding in common goldeneyes Bucephala clangula. There was strong evidence that the beginning of breeding has advanced during 1995‒2022 but only weak evidence that the end of breeding has advanced. Consequently, the duration of the breeding period lengthened, although statistical evidence for the trend was only weak. The relative importance of climate change and nest predation in affecting the timing and duration of breeding as well as breeding success was also studied. Among-year variation in the beginning of breeding was mainly governed by the timing of ice breakup, an indicator of climate change, whereas nest predation rate in the previous year was the main driver of the end of breeding, the duration of breeding being affected by both the timing of ice breakup and nest predation rate. Annual nest-stage success was best explained by nest predation rate. However, final reproductive success (proportion of nest-left ducklings that survived until independence) decreased with advancing timing of ice breakup, suggesting that climate change has negatively affected the production of independent offspring in the study population. The findings of this study underline the importance of also considering local ecological factors when analysing climate change impacts on phenological breeding metrics and breeding success of birds.

Cryptic genetic differentiation is being increasingly documented in birds and other organisms using genome-wide variation. A recent example of cryptic genetic differentiation in a widespread species with conserved morphology is the northern house wren Troglodytes aedon. We found that, despite extremely similar morphology and no documented vocal differences, the two subspecies of the northern house wren, T. a. aedon (eastern) and T. a. parkmanii (western), exhibited both nuclear and mitochondrial genomic differentiation. Individuals present along the Front Range of the Colorado Rocky Mountains possessed nuclear genetic variation intermediate between T. a. aedon and T. a. parkmanii; additionally, both divergent mitochondrial lineages, corresponding to the western and eastern northern house wren populations, occur in Colorado. However, the dynamics of this putative contact zone (i.e. amount of hybridization or introgression) and the degree of differentiation between the two subspecies remain uncharacterized. To expand our understanding of northern house wren population genetic differentiation and explore the possibility of hybridization, we used a double digest restriction-site associated (ddRAD) approach and sequenced 127 northern house wrens, including 109 individuals from across Colorado and Wyoming, as well as nine individuals each from eastern and western allopatric regions. Our results highlight that T. a. aedon occur significantly further west than previously thought, and provide evidence for weak population structure within the northern house wren, while generally setting the stage for future investigations of northern house wren population genomics and the genetic basis of cryptic speciation.

Animal sounds contain important information used in intra- and inter-species communication. For species exhibiting elaborate and energetically expensive signals such as aerial displays accompanied by a call, the nature of the message being transmitted is honest and usually reflects individual fitness. Display events that combine flight and calls and are executed during the breeding season have traditionally been associated with two main functions: repelling rivals and/or attracting mates. In waders, the distinction between the two may rely on the timing of the breeding season at which displays occur, but also on the frequency at which displays occur in relation to local breeding density. Here, we investigated the function of display behaviour in the Icelandic whimbrel throughout the breeding season and along a breeding density gradient. We used a site-based approach in the southern lowland plain in Iceland where whimbrel breeding density and display frequency were recorded for two years. Although whimbrels showed display behaviour throughout the entire season, display frequency was higher at low densities during pre-incubation but similar at different densities during incubation and post-incubation. Our results indicate that this behaviour is context-dependent and multi-functional, supporting the importance of mate attraction at low conspecific density during pre-incubation, while other functions such as resource defence may be important throughout the breeding season.

MicroRNAs (miRNAs) are highly conserved small noncoding RNAs that regulate gene expression post-transcriptionally. Circulating miRNAs – miRNAs that have been released from cells and circulate in the bloodstream – are relatively stable and interesting molecules for wildlife research, where they may form a proxy for gene expression as a function of the animal's state under a variety of environmental challenges. Aiming at providing initial baseline data on the circulating miRNAome in avian wildlife, we assessed the miRNA profiles of wild ruddy turnstones Arenaria interpres on their Australian non-breeding grounds. The ruddy turnstone is a long-distant migrant and a significant reservoir species for low pathogenic avian influenza virus (LPAIV). We therefore investigated both LPAIV-infected and uninfected individuals for their specific miRNA profiles to potentially elucidate the species' molecular mechanisms underlying its response to LPAIV infection. De novo miRNA characterisation in the ruddy turnstone genome identified 161 conserved and two novel, bird-specific miRNAs, with liver-enriched miRNA-122 being the most abundant. Z chromosome-linked miR-2954-3p was significantly more abundant in serum from males (ZZ) than from females (ZW). Furthermore, we found a sex- and age-associated effect of LPAIV infection on miRNA abundance in serum samples, including one novel miRNA. This circulating miRNA signature may reflect sex- and age-specific differences in the host response, indicating that circulating miRNAs could serve as a valuable non-destructive analytical tool for enhancing our understanding of avian infections in a wildlife context and should be explored further.

Ground nesting birds are sensitive to habitat structure, so understanding this relationship is fundamental to managing habitat to maintain or enhance bird populations. We used an existing long-term, large-scale experiment with routine monitoring of meadow pipit territories to assess the capability of drone-based remote sensing as a means of capturing relevant habitat information. Normalised Difference Vegetation Index (NDVI) captured differences in stocking density between treatments, and autumn-measured NDVI was well correlated to field measurements of vegetation height and density. Spring and autumn NDVI were negatively correlated due to dominant tussock-forming species dying back over winter. Meadow pipit apparent territory size was positively correlated to autumn NDVI and to the difference between autumn and spring NDVI. Apparent territory size was larger where there was more tussocky vegetation that comprise the areas least preferred for foraging. The long-lived nature of tussocks likely constrains the effect of the grazing treatments on meadow pipit breeding apparent territory size. Drone-based remote sensing of habitat characteristics appears to be a powerful way forward to understand bird–habitat associations.

Seasonal migration is highly labile from an evolutionary perspective and known to rapidly evolve in response to selective pressures. However, long-distance migratory birds rely partially on innate genetic programs and may be constrained in their ability to alter their migratory behavior. We take advantage of recent advances in our ability to genotype historical DNA samples to examine the temporal stability of migratory connections between breeding and nonbreeding populations (i.e. migratory connectivity) and population-level nonbreeding distributions in the Wilson's warbler Cardellina pusilla, a long-distance migratory songbird. By assigning historical and contemporary samples collected across the nonbreeding range to genetically distinct breeding clusters, we suggest that broad-scale population-level nonbreeding distributions within this species have remained largely consistent within Mexico from the mid-1900s to the present day. These findings support the idea that the nonbreeding distributions of long-distance migrants may remain stable over long time scales, even in the face of rapid environmental change.