The potential function of post-fledging dispersal behavior in first breeding territory selection for males of a migratory bird

One possible hypothesis for the function of post-fledging dispersal is to locate a suitable future breeding area. This post-fledging period may be particularly important in migratory species because they have a limited period to gather information prior to autumn migration, and in protandrous species, males must quickly acquire a territory after returning from spring migration to maximize their fitness. Here we use color-ring resightings to investigate how the post-fledging dispersal movements of the Cyprus wheatear Oenanthe cypriaca, a small migratory passerine, relate to their first breeding territory the following year when they return from migration. We found that males established first breeding territories that were significantly closer to their post-fledging location than to their natal sites or to post-fledging locations of other conspecifics, but these patterns were not apparent in females. Our findings suggest that familiarity with potential breeding sites may be important for juveniles of migratory species, particularly for the sex that acquires and advertises breeding territories. Exploratory dispersal prior to a migrant’s first autumn migration may contribute toward its breeding success the following year, further highlighting the importance of early seasonal breeding on fitness and population dynamics more generally.     

Does the migration programme constrain dispersal and range sizes of migratory birds?

Aim  It is generally believed that the migration programme constrains the dispersal and hence range sizes of migratory bird species. This conclusion is based on analyses of breeding ranges of migratory versus non-migratory (resident) terrestrial bird species, and rests on the assumption that there are no ecological or evolutionary constraints on extending the non-breeding range. To investigate this assumption, the abilities of migrant and resident terrestrial species to colonize new wintering areas were compared.
Location  Three major wintering regions of long-distance migrants: South America, sub-Saharan Africa and the Indian Subcontinent.
Methods  It was determined whether the relative numbers of residents and short- and long-distance migrants were the same in those species that have dispersed to a novel wintering region as in the source species pools.
Results  At the species level, long-distance migratory species are more likely to have non-breeding ranges that include more than one of the above regions than resident species. This indicates that the dispersal of migratory species is less constrained than that of resident species. The pattern holds irrespective of the inclusion or exclusion of species associated with coastal, freshwater and wetland habitats, and also holds for ecological groups such as aerial feeders. The pattern is most pronounced between the regions separated by the strongest dispersal barriers (South America and sub-Saharan Africa).
Main conclusions  It is unlikely that the migration programme per se constrains dispersal, but rather that difficulties in establishing new non-breeding areas prevent range expansions in migrant species.     

Size and accumulation of fuel reserves at stopover predict nocturnal restlessness in a migratory bird

Early arrival at the breeding site positively affects the breeding success of migratory birds. During migration, birds spend most of their time at stopovers. Therefore, determining which factors shape stopover duration is essential to our understanding of avian migration. Because the main purpose of stopover is to accumulate fat as fuel for the next flight bout, fuel reserves at arrival and the accumulation of fuel are both expected to affect stopover departure decisions. Here, we determined whether fuel reserves and fuel accumulation predict a bird''s motivation to depart, as quantified by nocturnal migratory restlessness (Zugunruhe), using northern wheatears (Oenanthe oenanthe) that were captured and temporarily contained at spring stopover. We found that fuel reserves at capture were positively correlated with Zugunruhe, and negatively correlated with fuel accumulation. This indicates that fat birds were motivated to depart, whereas lean birds were set on staying and accumulating fuel. Moreover, the change in fuel reserves was positively correlated with the concurrent change in Zugunruhe, providing the first empirical evidence for a direct link between fuel accumulation and Zugunruhe during stopover. Our study indicates that, together with innate rhythms and weather, the size and accumulation of fuel reserves shape stopover duration, and hence overall migration time.     

Climate warming,ecological mismatch at arrival and population decline in migratory birds

Climate is changing at a fast pace, causing widespread, profound consequences for living organisms. Failure to adjust the timing of life-cycle events to climate may jeopardize populations by causing ecological mismatches to the life cycle of other species and abiotic factors. Population declines of some migratory birds breeding in Europe have been suggested to depend on their inability to adjust migration phenology so as to keep track of advancement of spring events at their breeding grounds. In fact, several migrants have advanced their spring arrival date, but whether such advancement has been sufficient to compensate for temporal shift in spring phenophases or, conversely, birds have become ecologically mismatched, is still an unanswered question, with very few exceptions. We used a novel approach based on accumulated winter and spring temperatures (degree-days) as a proxy for timing of spring biological events to test if the progress of spring at arrival to the breeding areas by 117 European migratory bird species has changed over the past five decades. Migrants, and particularly those wintering in sub-Saharan Africa, now arrive at higher degree-days and may have therefore accumulated a ‘thermal delay’, thus possibly becoming increasingly mismatched to spring phenology. Species with greater ‘thermal delay’ have shown larger population decline, and this evidence was not confounded by concomitant ecological factors or by phylogenetic effects. These findings provide general support to the largely untested hypotheses that migratory birds are becoming ecologically mismatched and that failure to respond to climate change can have severe negative impacts on their populations. The novel approach we adopted can be extended to the analysis of ecological consequences of phenological response to climate change by other taxa.     

Estimability of migration survival rates from integrated breeding and winter capture–recapture data

Long‐distance migration is a common phenomenon across the animal kingdom but the scale of annual migratory movements has made it difficult for researchers to estimate survival rates during these periods of the annual cycle. Estimating migration survival is particularly challenging for small‐bodied species that cannot carry satellite tags, a group that includes the vast majority of migratory species. When capture–recapture data are available for linked breeding and non‐breeding populations, estimation of overall migration survival is possible but current methods do not allow separate estimation of spring and autumn survival rates. Recent development of a Bayesian integrated survival model has provided a method to separately estimate the latent spring and autumn survival rates using capture–recapture data, though the accuracy and precision of these estimates has not been formally tested. Here, I used simulated data to explore the estimability of migration survival rates using this model. Under a variety of biologically realistic scenarios, I demonstrate that spring and autumn migration survival can be estimated from the integrated survival model, though estimates are biased toward the overall migration survival probability. The direction and magnitude of this bias are influenced by the relative difference in spring and autumn survival rates as well as the degree of annual variation in these rates. The inclusion of covariates can improve the model's performance, especially when annual variation in migration survival rates is low. Migration survival rates can be estimated from relatively short time series (4–5 years), but bias and precision of estimates are improved when longer time series (10–12 years) are available. The ability to estimate seasonal survival rates of small, migratory organisms opens the door to advancing our understanding of the ecology and conservation of these species. Application of this method will enable researchers to better understand when mortality occurs across the annual cycle and how the migratory periods contribute to population dynamics. Integrating summer and winter capture data requires knowledge of the migratory connectivity of sampled populations and therefore efforts to simultaneously collect both survival and tracking data should be a high priority, especially for species of conservation concern.     

河北省东亚飞蝗发生动态及未来灾变趋势分析

80年代以来 ,尤其进入 90年代 ,由于受异常气候、农业生态及人为因素的影响 ,河北省东亚飞蝗Locustamigratoriamanilensis (Meyen)出现了暴发频次增加、发生期提前、秋蝗发生加重、潜在和隐伏蝗区突发等特点。作者分析了 5 0年来影响河北省东亚飞蝗发生动态的 5种因素 :气象因素、生态因素、湖库水位因素、河泛流量因素、人为因素等。并对河北省东亚飞蝗未来灾变趋势做了展望。     

Reconstruction of a beech population bottleneck using archival demographic information and Bayesian analysis of genetic data

Range expansion and contraction has occurred in the history of most species and can seriously impact patterns of genetic diversity. Historical data about range change are rare and generally appropriate for studies at large scales, whereas the individual pollen and seed dispersal events that form the basis of geneflow and colonization generally occur at a local scale. In this study, we investigated range change in Fagus sylvatica on Mont Ventoux, France, using historical data from 1838 to the present and approximate Bayesian computation (ABC) analyses of genetic data. From the historical data, we identified a population minimum in 1845 and located remnant populations at least 200 years old. The ABC analysis selected a demographic scenario with three populations, corresponding to two remnant populations and one area of recent expansion. It also identified expansion from a smaller ancestral population but did not find that this expansion followed a population bottleneck, as suggested by the historical data. Despite a strong support to the selected scenario for our data set, the ABC approach showed a low power to discriminate among scenarios on average and a low ability to accurately estimate effective population sizes and divergence dates, probably due to the temporal scale of the study. This study provides an unusual opportunity to test ABC analysis in a system with a well-documented demographic history and identify discrepancies between the results of historical, classical population genetic and ABC analyses. The results also provide valuable insights into genetic processes at work at a fine spatial and temporal scale in range change and colonization.     

Exploring an efficient habitat index for predicting population and abundance of migratory birds in Poyang Lake Wetland,South China

Poyang Lake wetland is an important wintering habitat of migratory birds with a complexity of coupled nature and human systems. Reported studies suggested that habitat indices were mostly developed based on single-class factors and scale-dependent. Therefore the indices might not be sufficient and applicable to predict regional changes for population and abundance of migratory birds (PMB and AMB) in Poyang Lake wetland at watershed and basin scales. In order to explore an efficient habitat index for predicting PMB and AMB, an integrated and scale-independent habitat index was proposed by integration of landscape and environmental temperature variables at basin and watershed scales. The landscape index and environmental temperature index based on single-class dominant factors, were also evaluated by weighted additive method. Multi-source data, including multi-spatial and temporal remote sensing images and field survey data, was used in this study. Results indicated that the average 10-night temperature in July (TN-Jul.) had dominant influence on PMB and the environmental temperature index was a better predictor for predicting PMB; AMB was influenced by both landscape and temperature variables and the proposed integrated habitat index was better for prediction of AMB in Poyang Lake wetland. The proposed integrated habitat index is a supplement of the single-class habitat index, which provides a more scientific technique for the study of biodiversity.     

Apparent breeding success drives long-term population dynamics of a migratory swan

The ability of a species to adapt to environmental change is ultimately reflected in its vital rates – i.e. survival and reproductive success of individuals. Together, vital rates determine trends in numbers, commonly monitored using counts of species abundance. Rapid changes in abundance can give rise to concern, leading to calls for research into the biological mechanisms underlying variations in demography. For the northwest European population of Bewick's swan Cygnus columbianus bewickii, there have been major changes in the population trends recorded during nearly five decades of monitoring (1970–2016). The total number of birds increased to a maximum of ca 30 000 in 1995 and subsequently decreased to about 18 000 individuals in 2010. Such large fluctuation in population numbers is rare in long-lived species and understanding the drivers of this population change is crucial for species management and conservation. Using the integrated population model (IPM) framework, we analysed three demographic datasets in combination: population counts, capture–mark–resightings (CMR) and the proportion of juveniles in winter over a period of ~50 years. We found higher apparent breeding success in the years when the population had a positive growth rate compared to years with a negative growth rate. Moreover, no consistent trend in adult and yearling survival, and an increasing trend in juvenile survival was found. A transient life-table response experiment showed that apparent breeding success and adult survival contributed most to the variation in population trend. We explored possible explanatory variables for the different demographic rates and found a significant association between juvenile survival both with the water level in lakes during autumn migration, which affects food accessibility for the swans, and with summer temperatures. Such associations are important for understanding the dynamics of species with fluctuating population sizes, and thus for informing management and conservation decisions.     

Spatial and temporal variation in population trends in a long‐distance migratory bird

Aim Over the past three decades, evidence has been growing that many Afro‐Palaearctic migratory bird populations have suffered sustained and severe declines. As causes of these declines exist across both the breeding and non‐breeding season, identifying potential drivers of population change is complex. In order to explore the roles of changes in regional and local environmental conditions on population change, we examine spatial and temporal variation in population trajectories of one of Europe’s most abundant Afro‐Palaearctic summer migrants, the willow warbler, Phylloscopus trochilus. Location Britain and Ireland. Methods We use national survey data from Britain and Ireland (BBS: BTO/RSPB/JNCC Breeding Bird Survey and CBS: BWI/NPWS/Heritage Council Countryside Breeding Survey) from 1994 to 2006 to model the spatial and temporal variation in willow warbler population trends. Results Across Britain and Ireland, population trends follow a gradient from sharp declines in the south and east of England to shallow declines and/or slight increases in parts of north and west England, across Scotland and Ireland. Decreasing the spatial scale of analysis reveals variation in both the rate and spatial extent of population change within central England and the majority of Scotland. The rates of population change also vary temporally; declines in the south of England are shallower now than at the start of the time series, whereas populations further north in Britain have undergone periods of increase and decline. Main conclusion These patterns suggest that regional‐scale drivers, such as changing climatic conditions, and local‐scale processes, such as habitat change, are interacting to produce spatially variable population trends. We discuss the potential mechanisms underlying these interactions and the challenges in addressing such changes at scales relevant to migratory species.     

Altered light conditions during spring: effects on timing of migration and reproduction in migratory redheaded bunting (Emberiza bruniceps)

Photoperiod is the most consistent environmental cue, and therefore, any change in anticipated light environment may affect subsequent response under long days. To test this hypothesis, photosensitive migratory redheaded buntings (Emberiza bruniceps) were exposed to altered photoperiods for 4 weeks [short days (SP, 8L:16D, group 1; control), short days alternated with constant dim light (SP/LL_dim; group 2), constant dim light (LL_dim; group 3) and constant bright light (LL_bright; group 4)] before being transferred to long days (LP; 16L:8D) for 15 weeks. Group differences in long-day-induced responses were observed. The onset of migratory restlessness (Zugunruhe) was earliest in LL_bright but persisted for maximum period in LL_dim group. The LL_dim group attained peak testis size significantly delayed and had more food consumption under long days. The results suggest that the altered photoperiodic exposure during photosensitive stage affects the seasonal phenotypes such as migration and reproduction in migratory buntings.     

Ecological conditions during winter predict arrival date at the breeding quarters in a trans-Saharan migratory bird

We studied variation in arrival date to the breeding colonies in Italy of a trans‐Saharan migratory bird, the barn swallow Hirundo rustica, in relation to variation in ecological conditions, as reflected by the normalized difference vegetation index (NDVI), in the winter quarters. Arrival date of old but not young individuals captured during consecutive breeding seasons was earlier after winters with favourable conditions. Change in arrival date in relation to change in NDVI was similar in the two sexes. Change in arrival date significantly and positively predicted change in breeding date. As a result of increased frequency of second broods determined by earlier arrival, the number of fledged offspring per season was larger after African winters with good in comparison to poor ecological conditions for barn swallows. This is the first study demonstrating phenotypic plasticity in migration phenology of a long‐distance migratory bird in relation to ecological conditions during wintering.     

Potential age differences in the migratory behaviour of a nocturnal songbird migrant during autumn and spring

In migratory songbirds, older individuals are thought to be more efficient migrants than younger individuals. Age‐specific differences in migratory efficiency have been reported mainly in respect of arrival timing, energy stores, rate of energy accumulation, departure behaviour, and departure direction. Yet, these traits were rarely assessed simultaneously in a single species. We further lack information whether age‐specific differences in behavioural traits present in autumn still manifest to the same degree in spring. Here we used the northern wheatear Oenanthe oenanthe, a long‐distance nocturnal songbird migrant, and investigated age‐specific differences in energy stores at capture (autumn: 1059 birds/spring: 803 birds), rate of energy accumulation (168/147), nocturnal departure timing (126/105), and departure direction (94/77) for both seasons. We found that in autumn, young northern wheatears departed significantly later in the night than older birds. This difference was not observed in spring. The resulting advance in nocturnal departure timing by young birds from autumn to spring may be due to learning based on experience gained during autumn, and/or to selective disappearance of those young individuals showing late departure times during autumn. We found no age‐specific difference in any of the other migratory traits investigated. To get a better understanding of age effects in songbird migrants, we need to study the potential adjustments of migratory behaviour within the individual over its life time. By individually tracking songbirds throughout their lifetime, we could start estimating whether a certain migratory decision (fuelling, departure, orientation) translates into higher (or lower) fitness, and whether individuals adjust their migratory behaviour based on learning from ‘wrong decisions’.     

Local and regional weather patterns influencing post‐breeding migration counts of soaring birds at the Strait of Gibraltar,Spain

Migration is a significant event in the annual cycle of many avian species. During migration birds face many challenges, including unfamiliar foraging and refuge habitats, resulting in a much higher rate of mortality during migration than during other seasons of the year. Weather may significantly affect a bird's decision to initiate migration, the course and pace of migration, and its survival during migration. Each of these influences may impact the counts of migrating birds at geographical convergence zones or bottlenecks. It is important to quantify the effect of short‐term weather on these counts to appropriately interpret and use such counts in other analyses. To this end, we aim to assess the effects of local and regional weather conditions on the migration counts of soaring birds at the Strait of Gibraltar during post‐breeding migration. We used information‐theoretic approaches to analyse the influence of local weather and weather in northern Spain on the migration counts of five soaring bird species from two count sites near the Strait of Gibraltar. Migration counts were higher on days with local northerly and westerly winds, often following a day of easterly winds, on days with local high pressure systems, and often following a day of lower pressure. Weather conditions in northern Spain influenced migration counts at the Strait of Gibraltar, but the effects were much weaker than local weather conditions. We confirm that short‐term weather conditions, locally and regionally, can influence migration counts and should thus be considered when these counts are used in other analyses.     

Genomic inference accurately predicts the timing and severity of a recent bottleneck in a nonmodel insect population

The analysis of molecular data from natural populations has allowed researchers to answer diverse ecological questions that were previously intractable. In particular, ecologists are often interested in the demographic history of populations, information that is rarely available from historical records. Methods have been developed to infer demographic parameters from genomic data, but it is not well understood how inferred parameters compare to true population history or depend on aspects of experimental design. Here, we present and evaluate a method of SNP discovery using RNA sequencing and demographic inference using the program δaδi, which uses a diffusion approximation to the allele frequency spectrum to fit demographic models. We test these methods in a population of the checkerspot butterfly Euphydryas gillettii. This population was intentionally introduced to Gothic, Colorado in 1977 and has as experienced extreme fluctuations including bottlenecks of fewer than 25 adults, as documented by nearly annual field surveys. Using RNA sequencing of eight individuals from Colorado and eight individuals from a native population in Wyoming, we generate the first genomic resources for this system. While demographic inference is commonly used to examine ancient demography, our study demonstrates that our inexpensive, all‐in‐one approach to marker discovery and genotyping provides sufficient data to accurately infer the timing of a recent bottleneck. This demographic scenario is relevant for many species of conservation concern, few of which have sequenced genomes. Our results are remarkably insensitive to sample size or number of genomic markers, which has important implications for applying this method to other nonmodel systems.     

Challenging claims in the study of migratory birds and climate change

Recent shifts in phenology in response to climate change are well established but often poorly understood. Many animals integrate climate change across a spatially and temporally dispersed annual life cycle, and effects are modulated by ecological interactions, evolutionary change and endogenous control mechanisms. Here we assess and discuss key statements emerging from the rapidly developing study of changing spring phenology in migratory birds. These well‐studied organisms have been instrumental for understanding climate‐change effects, but research is developing rapidly and there is a need to attack the big issues rather than risking affirmative science. Although we agree poorly on the support for most claims, agreement regarding the knowledge basis enables consensus regarding broad patterns and likely causes. Empirical data needed for disentangling mechanisms are still scarce, and consequences at a population level and on community composition remain unclear. With increasing knowledge, the overall support (‘consensus view’) for a claim increased and between‐researcher variability in support (‘expert opinions') decreased, indicating the importance of assessing and communicating the knowledge basis. A proper integration across biological disciplines seems essential for the field's transition from affirming patterns to understanding mechanisms and making robust predictions regarding future consequences of shifting phenologies.     

Challenging a 15‐year‐old claim: The North Atlantic Oscillation index as a predictor of spring migration phenology of birds

Many migrant bird species that breed in the Northern Hemisphere show advancement in spring arrival dates. The North Atlantic Oscillation (NAO) index is one of the climatic variables that have been most often investigated and shown to be correlated with these changes in spring arrival. Although the NAO is often claimed to be a good predictor or even to have a marked effect on interannual changes in spring migration phenology of Northern Hemisphere breeding birds, the results on relations between spring migration phenology and NAO show a large variety, ranging from no, over weak, to a strong association. Several factors, such as geographic location, migration phase, and the NAO index time window, have been suggested to partly explain these observed differences in association. A combination of a literature meta‐analysis, and a meta‐analysis and sliding time window analysis of a dataset of 23 short‐ and long‐distance migrants from the constant‐effort trapping garden at Helgoland, Germany, however, paints a completely different picture. We found a statistically significant overall effect size of the NAO on spring migration phenology (coefficient = ?0.14, SE = 0.054), but this on average only explains 0%–6% of the variance in spring migration phenology across all species. As such, the value and biological meaning of the NAO as a general predictor or explanatory variable for climate change effects on migration phenology of birds, seems highly questionable. We found little to no definite support for previously suggested factors, such as geographic location, migration phenology phase, or the NAO time window, to explain the heterogeneity in correlation differences. We, however, did find compelling evidence that the lack of accounting for trends in both time series has led to strongly inflated (spurious) correlations in many studies (coefficient = ?0.13, SE = 0.019).     

The interacting effects of food,spring temperature,and global climate cycles on population dynamics of a migratory songbird

Although long‐distance migratory songbirds are widely believed to be at risk from warming temperature trends, species capable of attempting more than one brood in a breeding season could benefit from extended breeding seasons in warmer springs. To evaluate local and global factors affecting population dynamics of the black‐throated blue warbler (Setophaga caerulescens), a double‐brooded long‐distance migrant, we used Pradel models to analyze 25 years of mark–recapture data collected in New Hampshire, USA. We assessed the effects of spring temperature (local weather) and the El Niño Southern Oscillation index (a global climate cycle), as well as predator abundance, insect biomass, and local conspecific density on population growth in the subsequent year. Local and global climatic conditions affected warbler populations in different ways. We found that warbler population growth was lower following El Niño years (which have been linked to poor survival in the wintering grounds and low fledging weights in the breeding grounds) than La Niña years. At a local scale, populations increased following years with warm springs and abundant late‐season food, but were unaffected by spring temperature following years when food was scarce. These results indicate that the warming temperature trends might have a positive effect on recruitment and population growth of black‐throated blue warblers if food abundance is sustained in breeding areas. In contrast, potential intensification of future El Niño events could negatively impact vital rates and populations of this species.