Geographic Variation and Its Climatic Correlates in the Sex Ratio of Eastern-Wintering Dark-Eyed Juncos (Junco Hyemalis Hyemalis)

Temporal increase in migratoriness and increasing male bias among residents in partially migrating Swedish sparrowhawks Accipiter nisus

Article

Full-text available

Dec 2024
ORNIS FENNICA

Partial migrants have populations consisting of both migratory and resident individuals. These migrants and residents experience unequal ecological conditions during winter and the underlying factors driving their decision to stay on their breeding grounds or to migrate remain debated—both from the viewpoint of populations and individuals. Here, we studied partial migration in a small raptor, the Eurasian Sparrowhawk (Accipiter nisus), from two different but interconnected perspectives: 1) explaining the patterns and variation in the ratio of migrants to residents (migratoriness) at the population level and 2) revealing how age and sex may affect the individual decision to be migratory or resident. We used citizen observation data over four decades to explore the temporal and spatial variation in the age and sex ratio of wintering resident sparrowhawks in Sweden. We found that the migratoriness unexpectedly increased with higher annual temperatures and showed long-term trend across the study period. Also, this migrant-to-resident ratio increased with smaller winter prey abundance. The average winter sex ratio was male-biased and became increasingly so over the years. We suggest that residency benefits territory-establishing males as early presence gives a competitive advantage in obtaining high-quality territories. Moreover, the distribution of overwintering individuals (regardless of sex) moved gradually northwards as the winter progressed, suggesting that smaller-scale migration occurs among the resident fraction of the population. These results provide suggestions for the underlying drivers and regulation of partial migration.

Impacts of a warming climate on the non-breeding distribution of a classic differential migrant

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Full-text available

Nov 2024

Many changes in species’ geographic distributions have been attributed to recent climate warming. One understudied phenomenon is the effect of climate change on differential migrants, species in which the sexes differ in distance migrated to and from the breeding range. We evaluated the impact of climate change on differential migration in the dark-eyed junco (Junco hyemalis) by assessing temporal and geographic changes in overall population abundance throughout the winter range over the past 60 years. We also compared the abundance of females in two wintering populations studied 15 years ago with historical abundances studied 45 years ago We observed a northward movement of the population as a whole and an increase in female abundance at higher latitudes that correlated with recent changes in winter climate. These findings suggest that climate change has reduced distance migrated in this species and increased the proportion of females wintering at higher latitudes, providing new insights into the impact of climate warming on migratory distance and winter distributions.

The underlying causes of differential migration: assumptions, hypotheses, and predictions

Article

Nov 2024

Mechanisms governing the migratory decisions of birds have long fascinated ecologists and sparked considerable debate. Identifying factors responsible for variation in migration distance, also known as differential migration, has been a popular approach to understanding the mechanisms underlying migratory behaviour more generally. However, research progress has been slowed by the continued testing of overlapping, non‐mechanistic, and circular predictions among a small set of historically entrenched hypotheses. We highlight the body size hypothesis and suggest that the predictions commonly tested have impeded progress because body size relationships with migration distance are predictions made by several distinct hypotheses with contrasting mechanisms. The cost of migration itself has not been adequately accounted for in most hypotheses, and we propose two flight efficiency hypotheses with time‐ and energy‐minimizing mechanisms that allow individuals to mitigate the risks inherent to longer migrations. We also advance two conceptual versions of the social dominance hypothesis based on two distinct underlying mechanisms related to distance minimization and food maximization that will help clarify the role of competition in driving migratory decisions. Overall, we describe and refine 12 mechanistic hypotheses proposed to explain differential migration (along with several other special‐case hypotheses), seven of which have underlying mechanisms related to food limitation as past research has identified this to be an important driver of differential migration. We also thoroughly reviewed 145 publications to assess the amount of support for 10 critical assumptions underlying alternative hypotheses for differential migration in birds. Our review reveals that surprisingly few studies explicitly evaluate assumptions within a differential migration context. Generating and testing strong predictions and critical assumptions underlying mechanisms of alternative hypotheses will improve our ability to differentiate among these explanations of differential migration. Additionally, future intraspecific progress will be greatest if investigators continue to focus on mechanisms underlying variation in migration distance within rather than among demographic classes, as previous research has found differing mechanisms to be responsible for differential migration among demographic classes. Interspecifically, a thorough comparative analysis that seeks to explain variation in migration distance among species would broaden both our understanding of the mechanisms regulating current differential migration patterns and those that led to the evolution of migration more generally. Collectively, we provide a framework that, together with advances in animal‐borne tracking and other technology, can be used to advance our understanding of the causes of differential migration distance, and migratory decisions more generally.

Sex and size shape the ontogeny of partial migration

Article

Jan 2024
J ANIM ECOL

The arrival‐time hypothesis of partial seasonal migration proposes that over‐winter residence is driven by reproductive benefits of early presence on the breeding grounds. Thus, it predicts increased occurrence of residence at reproductive age. In contrast, the body size hypothesis proposes age‐independent benefits of residence for large individuals, who should exhibit greater winter tolerance. Despite different expectations in age patterns for the two hypotheses in long‐lived partially migrant species, there is little empirical work investigating the ontogeny of migratory phenotypic expression, that is the expression of residence or migration. We investigated the influence of age, sex and body size on migratory phenotype throughout ontogeny (from first year to early adulthood) in a long‐lived partially migrant species, the red kite Milvus milvus . We GPS‐tracked 311 individuals tagged as juveniles and 70 individuals tagged as adults over multiple years, yielding 881 observed annual cycles. From this data, we estimated age‐dependent probabilities of the transition to residence and of survival in migrants and residents using a Bayesian multistate capture‐recapture model, as well as the probability of resuming migration once resident. We then calculated the resulting proportion of residents per age class. In both sexes, almost all juveniles migrated in their first winter, after which the probability of becoming resident gradually increased with age class to approximately 0.3 in adults (>3 calendar years). A size effect in third calendar year females suggests that large females adopt residence earlier in life than small females. The transition from residence back to migration only occurred with a probability of 0.15 across all resident individuals. In addition, survival was notably reduced in adult male migrants compared to adult male residents. These results are largely consistent with the arrival‐time and body size hypotheses, simultaneously. Our results reveal a plastic, yet primarily directional within‐individual change in migratory phenotype towards more residence with increasing age, varying between sexes and between individuals of different size. This study highlights that different individual characteristics can jointly shape the ontogeny of migratory behaviour and result in complex within‐population patterns and persistence of migratory phenotypes.

Drivers of partial migration in the reddish egret Egretta rufescens

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Sep 2023
J AVIAN BIOL

The reddish egret Egretta rufescens is North America's rarest Ardeidae and is listed as ‘Near Threatened' by the IUCN, as endangered in Mexico, and as a species of conservation concern throughout much of its range in the United States. Little is known about the migratory behavior of the reddish egret. Individuals that were banded during the breeding season in Texas, USA, have been resighted away from breeding areas; however, records are limited and the extent of migration is unknown. Using GPS transmitters, we found reddish egrets breeding in southern Texas exhibited a partial migration strategy, with 39% of the marked population migrating from breeding sites. We assessed the dominance, body size, and arrival time hypotheses to better understand the drivers of partial migration. We did not find support for the body size hypothesis and found mixed support for the dominance hypothesis; both males and females migrated, and migratory status of individuals did not change across the years of study. Long‐distance migrants were also larger than resident individuals. We found some support for the arrival time hypothesis; residents began breeding earlier than long‐distance migrants and had moderately greater nest success. However, within long‐distance migrants, an earlier arrival to breeding areas did not necessarily equate to earlier nesting or greater nest success. This study is the first to examine the migratory behavior of adult reddish egrets and assesses the dominance, body size, and arrival time hypotheses as explanations for partial migration in this species. Further, the results of this study emphasize the need for international conservation efforts.

Migration Strategy in the Chaffinch, Fringilla coelebs

Article

Full-text available

Jan 2020

Birds have developed morphological and behavioural adaptations as migratory strategies. A comparative study of morphology and demography between the Chaffinches' (Fringilla coelebs) sedentary gengleri and migratory coelebs races was conducted using a ringing dataset collected on Lundy between 1972 and 2017. Migratory individuals were significantly and proportionately longer winged and had greater body weight. The migrant sex and age ratios were skewed towards females and first-year birds and were responsive to annual climatic variations. The results support the species' status as a differential migrant and present the potential of Lundy's extensive ringing efforts in contributing to studies on avian migration.

Sex, body size, and winter weather explain migration strategies in a partial migrant population of American Kestrels

Article

Apr 2023

Given increasing evidence that climate change affects the annual cycles of birds, it is important to understand the mechanisms underlying individual migration strategies and population-level patterns in partial migrants. In this study, we found that thermoregulation (body size and winter temperatures) was a key driver of American Kestrel (Falco sparverius) migration decisions. The annual proportion of migrants in the population, however, was not explained by winter weather and may be the result of differential survival. We measured stable hydrogen isotope values (δD) of talon tissues collected from 501 breeding and overwintering birds to distinguish migrant from resident kestrels in a partially migratory population of American Kestrels in southwestern Idaho in 2013–2021. We then evaluated drivers of migration decisions by assessing potential correlates of migration strategies, whether individuals switched migration strategies between years, and whether the proportion of migrants in the population changed over time or was correlated with winter weather. Male kestrels were 1.6 times more likely to migrate than females, and in colder than average winters, smaller birds of both sexes were more likely to migrate than larger birds. Only 27% of 26 recaptured individuals showed evidence of switching their migration strategies on an annual basis. There was no temporal trend in the proportion of migrants in the population, but proportions varied between years. Interestingly, there was no association between winter minimum temperature anomalies and annual migrant proportions in the population, suggesting that differential over-winter survival, or other stochastic processes, may play an important role in population composition. As winters continue to warm, fewer kestrels may migrate and more may remain resident on breeding grounds. However, it is unclear how changes in migration strategies might affect population-level patterns and resilience to climate change.

Sex-dependent migration of eastern great bustard (Otis tarda dybowskii) in Northeast Asia

Preprint

Full-text available

Jun 2022

Background The great bustard (Otis tarda) holds the distinction of the heaviest bird to undergo migration as well as the greatest degree of sexual size dimorphism among living birds. Though the migration of the species has been widely discussed in the literature, researchers know little about the migration patterns of the subspecies in Asia (Otis tarda dybowskii), especially the males. Methods In 2018 and 2019, we captured six O. t. dybowskii (five males and one female) at their breeding sites in eastern Mongolia and tagged them with GPS-GSM satellite transmitters. This constitutes the first time that male great bustards of the eastern subspecies have been tracked. We combined the tracking data of our only female with other three females from central Mongolia, which was published in previous study for analysis. Results We found notable differences between the sexes: 1) males started migration later but arrived early than females in the spring, but not in autumn; 2) males had 1/3 of the migration duration of females (16.44 ± 14.68 days vs. 49.34 ± 21.28 days); 3) males migrated about 1/2 the distance of females (945.13 ± 79.00 km vs. 1922.88 ± 87.08 km). Additionally, we found bustards exhibited high fidelity to their breeding, post-breeding and wintering sites. Indeed, most of the wintering sites found by GPS tracking in this study were also utilized 70 years earlier, according to previous work. For conservation, we found only 22.20% of GPS location fixes of bustards were within protected areas and less than 5.0% for wintering sites and during migration. Conclusions Our findings suggest that the migration patterns of eastern great bustards are sex-specific and more conservation effort is needed for the Asian populations of this threatened species.

Simulating selection and evolution at the community level using common garden data

Article

Full-text available

Mar 2022

A key issue in evolutionary biology is whether selection acting at levels higher than the individual can cause evolutionary change. If it can, then conceptual and empirical studies must consider how selection operates at multiple levels of biological organization. Here, we test the hypothesis that estimates of broad-sense community heritability, H C 2 , can be used to predict the evolutionary response by community-level phenotypes when community-level selection is imposed. Using an approach informed by classic quantitative genetics, we made three predictions. First, when we imposed community-level selection, we expected a significant change in the average phenotype of arthropod communities associated with individual tree genotypes [we imposed selection by favoring high and low NMDS (nonmetric multidimensional scaling) scores that reflected differences in arthropod species richness, abundance and composition]. Second, we expected H C 2 to predict the magnitude of the community-level response. Third, we expected no significant change in average NMDS scores with community-level selection imposed at random. We tested these hypotheses using three years of common garden data for 102 species comprising the arthropod communities, associated with nine clonally replicated Populus angustifolia genotypes. Each of our predictions were met. We conclude that estimates of H C 2 account for the resemblance among communities sharing common ancestry, the persistence of community composition over time, and the outcome of selection when it occurs at the community level. Our results provide a means for exploring how this process leads to large-scale community evolutionary change, and they identify the circumstances in which selection may routinely act at the community level.

Drivers and consequences of partial migration in an alpine bird species

Article

Full-text available

Mar 2022

Partial migration, where a portion of the population migrates between winter and summer (breeding) areas and the rest remain year‐round resident, is a common phenomenon across several taxonomic groups. Several hypotheses have been put forward to explain why some individuals migrate while others stay resident, as well as the fitness consequences of the different strategies. Yet, the drivers and consequences of the decision to migrate or not are poorly understood. We used data from radio‐tagged female (n = 73) willow ptarmigan Lagopus lagopus in an alpine study area in Central Norway to test if (i) the decision to migrate was dependent on individual state variables (age and body weight), (ii) individuals repeated migratory decisions between seasons, and (iii) the choice of migratory strategy was related to reproductive success. Partially supporting our prediction that migratory strategy depends on individual state, we found that juvenile birds with small body sizes were more likely to migrate, whereas large juveniles remained resident. For adult females, we found no relationship between the decision to migrate or stay resident and body weight. We found evidence for high individual repeatability of migratory decision between seasons. Migratory strategy did not explain variation in clutch size or nest fate among individuals, suggesting no direct influence of the chosen strategy on reproductive success. Our results indicate that partial migration in willow ptarmigan is related to juvenile body weight, and that migratory behavior becomes a part of the individual life history as a fixed strategy. Nesting success was not affected by migratory strategy in our study population, but future studies should assess other traits to further test potential fitness consequences.

Temporal and spatial variation in reproductive benefits in a partial migrant

Article

Full-text available

Oct 2024
ECOLOGY

In partial migrant systems, where residents and migrants coexist within a population, residents are commonly predicted to gain a reproductive advantage over migrants through priority access to high‐quality territories and an earlier breeding start. Annual variation in reproductive benefits has been suggested to be important for the coexistence of both strategies in a population, as differences in wintering conditions experienced by the two strategies may result in a periodic reproductive advantage for migrants. However, the importance of spatial environmental variation for reproductive output in partially migrant populations remains largely unexplored. We investigated variation in the reproductive output of migrants and residents in a population of Swiss red kites (Milvus milvus) both temporally, across and within years, and spatially, along an elevational gradient. We gathered 4 years of reproductive data combined with 183 GPS‐derived full annual cycles from individuals breeding in the Swiss Alpine foothills. At low, but not high, elevations, residents produced more fledglings than migrants. We also found evidence for annual variation in the reproductive advantage of the two strategies. Furthermore, while reproductive output did decline with a later breeding start, there was no difference in the start of breeding between the two migration strategies. The results of this study suggest that differences in reproductive output between migrants and residents in partial migrant populations can vary both due to the use of spatially distinct overwintering grounds and because the strategies are differently affected by spatial variables in the breeding area, such as elevation. The study emphasizes that spatial and temporal variation in reproductive benefits must be considered when predicting how migratory species will respond to future environmental change.

Ontogeny of migration destination, route and timing in a partially migratory bird

Article

Full-text available

Jul 2024
J ANIM ECOL

In migratory animals, the developmental period from inexperienced juveniles to breeding adults could be a key life stage in shaping population migration patterns. Nevertheless, the development of migration routines in early life remains underexplored. While age‐related changes in migration routes and timing have been described in obligate migrants, most investigations into the ontogeny of partial migrants only focused on age‐dependency of migration as a binary tactic (migrant or resident), and variations in routes and timing among individuals classified as ‘migrants’ is rarely considered. To fill this gap, we study the ontogeny of migration destination, route and timing in a partially migratory red kite (Milvus milvus) population. Using an extensive GPS‐tracking dataset (292 fledglings and 38 adults, with 1–5 migrations tracked per individual), we studied how nine different migration characteristics changed with age and breeding status in migrant individuals, many of which become resident later in life. Individuals departed later from and arrived earlier at the breeding areas as they aged, resulting in a gradual prolongation of stay in the breeding area by 2 months from the first to the fifth migration. Individuals delayed southward migration in the year prior to territory acquirement, and they further delayed it after occupying a territory. Migration routes became more direct with age. Individuals were highly faithful to their wintering site. Migration distance shortened only slightly with age and was more similar among siblings than among unrelated individuals. The large gradual changes in northward and southward migrations suggest a high degree of plasticity in temporal characteristics during the developmental window. However, the high wintering site fidelity points towards large benefits of site familiarity, prompting spatial migratory plasticity to be expressed through a switch to residency. The contrasting patterns of trajectories of age‐related changes between spatial and temporal migration characteristics might reflect different mechanisms underlying the expression of plasticity. Investigating such patterns among species along the entire spectrum of migration tactics would enable further understanding of the plastic responses exhibited by migratory species to rapid environmental changes.

Effects of short-term experimental manipulation of captive social environment on uropygial gland microbiome and preen oil volatile composition

Article

Full-text available

Jan 2023

Introduction Avian preen oil, secreted by the uropygial gland, is an important source of volatile compounds that convey information about the sender’s identity and quality, making preen oil useful for the recognition and assessment of potential mates and rivals. Although intrinsic factors such as hormone levels, genetic background, and diet can affect preen oil volatile compound composition, many of these compounds are not the products of the animal’s own metabolic processes, but rather those of odor-producing symbiotic microbes. Social behavior affects the composition of uropygial microbial communities, as physical contact results in microbe sharing. We experimentally manipulated social interactions in captive dark-eyed juncos (Junco hyemalis) to assess the relative influence of social interactions, subspecies, and sex on uropygial gland microbial composition and the resulting preen oil odor profiles. Methods We captured 24 birds at Mountain Lake Biological Station in Virginia, USA, including birds from two seasonally sympatric subspecies – one resident, one migratory. We housed them in an outdoor aviary in three phases of social configurations: first in same-sex, same-subspecies flocks, then in male-female pairs, and finally in the original flocks. Using samples taken every four days of the experiment, we characterized their uropygial gland microbiome through 16S rRNA gene sequencing and their preen oil volatile compounds via GC-MS. Results We predicted that if social environment was the primary driver of uropygial gland microbiome composition, and if microbiome composition in turn affected preen oil volatile profiles, then birds housed together would become more similar over time. Our results did not support this hypothesis, instead showing that sex and subspecies were stronger predictors of microbiome composition. We observed changes in volatile compounds after the birds had been housed in pairs, which disappeared after they were moved back into flocks, suggesting that hormonal changes related to breeding condition were the most important factor in these patterns. Discussion Although early life social environment of nestlings and long-term social relationships have been shown to be important in shaping uropygial gland microbial communities, our study suggests that shorter-term changes in social environment do not have a strong effect on uropygial microbiomes and the resulting preen oil volatile compounds.

Thermal adaptation best explains Bergmann’s and Allen’s Rules across ecologically diverse shorebirds

Article

Full-text available

Aug 2022

Bergmann’s and Allen’s rules state that endotherms should be larger and have shorter appendages in cooler climates. However, the drivers of these rules are not clear. Both rules could be explained by adaptation for improved thermoregulation, including plastic responses to temperature in early life. Non-thermal explanations are also plausible as climate impacts other factors that influence size and shape, including starvation risk, predation risk, and foraging ecology. We assess the potential drivers of Bergmann’s and Allen’s rules in 30 shorebird species using extensive field data (>200,000 observations). We show birds in hot, tropical northern Australia have longer bills and smaller bodies than conspecifics in temperate, southern Australia, conforming with both ecogeographical rules. This pattern is consistent across ecologically diverse species, including migratory birds that spend early life in the Arctic. Our findings best support the hypothesis that thermoregulatory adaptation to warm climates drives latitudinal patterns in shorebird size and shape.

BIRD MIGRATION: A NECESSARY BEHAVIORAL ADAPTATION

Chapter

Full-text available

Nov 2024

Bird migration is a remarkable phenomenon that captures the essence of nature's ingenuity and resilience. Millions of birds embark on incredible journeys yearly, traversing vast distances across continents, oceans, and landscapes. Birds are the most mobile creatures on the earth. Birds migrate seasonally from an unfavorable location to some favorable location to breed, feed and raise the young ones. Not all birds migrate. About 40% of the world's total bird species perform migration. Birds migrate for food, shelter, reproduction, predator avoidance, and to avoid climate extremes. Seasonal photoperiodic cues also trigger migratory behavior. There are certain centers in the brain which are integrated with the external stimulus and the secretion of hormones takes place which triggers the migration. It often occurs along a flyway. It is a to & fro movement between breeding and non-breeding grounds and vice-versa. It is an instinctive behavior. Migration began to evolve when individuals who moved from one area to another ultimately produced younger ones than those who remained in one location. Birds use celestial cues, smell, landmarks, and magnetic cues for navigation during the migration. Over 300 species of migratory birds visit India annually. India forms a part of the Central Asian Flyway. Habitats of migratory birds should be conserved, especially wetlands. Birds are an important part of the ecosystem; they are the bioindicators of the ecosystem.

Influence of Human Hunting Strategies and Large Carnivore Presence on Population Dynamics of European Facultative Scavengers

Article

Full-text available

Nov 2024

Ungulates serve as the primary carrion source for facultative scavengers in European ecosystems. In the absence of large carnivores, such as wolves (Canis lupus), human hunting leftovers are the main source of carrion for these scavengers. Additionally, wild boars (Sus scrofa) are heavily culled in many ecosystems and are both a significant prey species for wolves as well as a key scavenger. Nowadays, wolves and wild boars are re‐establishing their historical home ranges. However, it remains unclear how their presence influences the population dynamics of facultative scavengers under different scenarios of human hunting strategies. We simulated the biomass densities of all states in the trophic web including European scavengers and wolves using an ordinary differential equations (ODE) model. The presence of wolves led to a positive trend in scavenger biomass in general. However, in general, we found that plant‐based resources were more important for scavenger dynamics than carrion, regardless of whether the carrion originated from human hunting or wolf predation. Only when wolves were absent but boars present, the human hunting strategy became important in determining scavenger dynamics via carrion supply. In conclusion, our model indicates that population dynamics of facultative scavengers are not mainly driven by the availability of carrion, but rather by the presence of and competition for vegetation. Furthermore, our simulations highlight the importance of adapting human hunting strategies in accordance with the re‐establishment of wolf and boar as these can cause fluctuating population patterns over the years.

High variability in the migratory behaviour of a tropical seabird

Article

Full-text available

Oct 2024

We investigated the non-breeding movements and distribution of West African Crested terns (Thalasseus albididorsalis) breeding in one of the largest colonies of the species, in Guinea-Bissau. Through GPS tracking of six individuals, we show that half of the birds performed long-distance migrations to non-breeding sites located up to 5039 km south of the colony, mostly in Nigeria and Angola. The other half performed short-distance migrations to areas within 340 km of the breeding colony, mainly in Guinea. These results show high variability on the migratory strategies of the West African Crested Tern and suggest low migratory connectivity within the studied population. Regardless of their migratory strategy, all tracked birds visited at least one additional breeding colony both after and before the breeding season. This behaviour might be particularly relevant for species breeding in unstable environments, which is the case of the studied species, nesting in highly dynamic coastal sandbanks. During the non-breeding season West African Crested terns used coastal areas falling within 18 different jurisdictions, highlighting the need for concerted action between all coastal countries of Western Africa, from Senegal to Angola, for the conservation of this species.

Natural Selection after Severe Winter Favors Larger and Duller Bluebirds

Article

Oct 2024

Extreme cold events, which have become more frequent, can revert the direction of long-term responses to climate change. In 2021, record snowstorms swept the United States, causing wildlife die-offs that may have been associated with rapid natural selection. Our objective was to determine whether the snowstorms caused natural selection in Eastern Bluebirds (Sialia sialis). To test which mechanism most influenced their survival, we measured the morphology and coloration of fatalities and survivors at three sites. Survival was associated with a longer tarsus and with a wider, longer, and deeper beak, in support of the starvation and thermal endurance hypotheses. Additionally, bluebirds with more-ornamented plumage were less likely to have survived, perhaps because of an early energy investment in mate and site acquisition. As bluebirds encounter increasingly warm summer conditions, the longer extremities favored during the snowstorms may continue to be favored through their thermoregulatory benefits. However, the dull plumage coloration favored by natural selection during the snowstorms may be opposed by sexual selection benefits of more-ornamented plumage. Overall, responses to extreme events are difficult to predict from responses to long-term climate change, and responses to one event, such as the 2021 snowstorms, may not predict responses to a future extreme event.

The intensity of supplementary feeding in an urban environment impacts overwintering Mallards (Anas platyrhynchos) as wintering conditions get harsher

Article

Full-text available

Aug 2024

Sex-specific migration strategies and underlying physiology contribute to spring arrival protandry in a songbird

Article

Full-text available

Aug 2024
BEHAV ECOL SOCIOBIOL

In spring, many migrating songbirds exhibit protandry (the phenomenon whereby males precede females in arrival at breeding sites). The reed bunting (Emberiza schoeniclus) is a short-distance European migrant which expresses a high degree of protandry and combines both nocturnal and diurnal movements during migrations. In experimental conditions, we studied the proximate mechanisms of protandry and compared locomotor behavior between spring and autumn migrations. We assumed that captive behavior is a proxy for the behavior that birds demonstrate in the wild. Combined, the analysis of seasonal patterns and circadian dynamics of locomotor activity suggested that male reed buntings depart from wintering grounds by daytime flights approximately two weeks earlier than females. Later, they develop nocturnal activity, take off shortly before dawn and continue their flight for several hours in the morning. We argue that such behavior allows males to benefit from both the advantage of nocturnal flight and an efficient start of foraging, thereby reducing the stopover duration (by minimizing search/settling costs) and increasing the total migration speed. In contrast, females express predominantly nocturnal migratory activity in spring. We observed that in spring males had lower fat reserves compared to females. We suggest that males can forage during diurnal movements and therefore do not need to store large energetic reserves. In contrast, in autumn, both sexes display similar patterns of locomotor activity and fat reserves. Overall, our results describe unique sex-specific migratory behaviour and physiology in reed buntings in spring, which, we assume, contribute to spring arrival protandry in this species.

Migration patterns of the Japanese sardine in the Sea of Japan by combining the microscale stable isotope analysis of otoliths and an ocean data assimilation model

Article

Full-text available

Jun 2024

The Japanese sardine (Sardinops sagax melanostictus) is a small pelagic fish found in the Sea of Japan, the marginal sea of the western North Pacific. It is an important species for regional fisheries, but their dispersal and migration patterns during early life stages remain unclear. In this study, we analyzed the stable oxygen isotope ratios of otoliths of young-of-the-year (age 0) Japanese sardines collected from the northern offshore and southern coastal areas of the Sea of Japan in 2015 and 2016. The ontogenetic shifts of the geographic distribution were estimated by comparing the profiles of life-long isotope ratios and temporally varying isoscape, which was calculated using the temperature and salinity fields produced by an ocean data assimilation model. Individuals that were collected in the northern and southern areas hatched and stayed in the southern areas (west offshore of Kyushu) until late June, and thereafter, they can be distinguished into two groups: one that migrated northward at shallow layer and one that stayed around the southern area in the deep layer. A comparison of somatic growth trajectories of the two groups, which was reconstructed based on otolith microstructure analysis, suggested that individuals that migrated northward had significantly larger body lengths in late June than those that stayed in the southern area. These results indicate that young-of-the-year Japanese sardines that hatched in the southern area may have been forced to choose one of two strategies to avoid extremely high water temperatures within seasonal and geographical limits. These include migrating northward or moving to deeper layers. Our results indicate that the environmental variabilities in the southern area could critically impact sardine population dynamics in the Sea of Japan.

Proximate drivers of migration propensity: a meta-analysis across species

Preprint

Apr 2024

Animal migration is multifaceted in nature, but the relative strength of different cues that trigger resulting patterns of migration is not well understood. Partially migratory populations offer an opportunity to test hypotheses about migration more broadly by comparing trait differences of migrants and residents. We quantitatively reviewed 45 studies that statistically modeled migration propensity, extracting132 effect sizes for internal and external proximate drivers across taxa. Our meta-analysis revealed that internal and external drivers had medium (Cohen’s d > 0.3) and large (Cohen’s d > 0.5) effect sizes on migration propensity respectively. Predator abundance and predation risk had a large effect, as did individual behaviour (e.g., personality). The abiotic environment and individual physiology had a medium effect on migration propensity. Of the studies that examined genetic divergence between migrants and residents, 64% found some genetic divergence between groups. These results clarify broad proximate drivers of migration and offer generalities across taxa.

Hit Snooze: An Imperiled Hibernator Assesses Spring Snow Conditions to Decide Whether to Terminate Hibernation or Reenter Torpor

Article

Full-text available

Jan 2024

Determinants of spring migration departure dates in a New World sparrow: Weather variables reign supreme

Article

Full-text available

Feb 2024

Numerous factors influence the timing of spring migration in birds, yet the relative importance of intrinsic and extrinsic variables on migration initiation remains unclear. To test for interactions among weather, migration distance, parasitism, and physiology in determining spring departure date, we used the Dark‐eyed Junco ( Junco hyemalis ) as a model migratory species known to harbor diverse and common haemosporidian parasites. Prior to spring migration departure from their wintering grounds in Indiana, USA, we quantified the intrinsic variables of fat, body condition (i.e., mass ~ tarsus residuals), physiological stress (i.e., ratio of heterophils to lymphocytes), cellular immunity (i.e., leukocyte composition and total count), migration distance (i.e., distance to the breeding grounds) using stable isotopes of hydrogen from feathers, and haemosporidian parasite intensity. We then attached nanotags to determine the timing of spring migration departure date using the Motus Wildlife Tracking System. We used additive Cox proportional hazard mixed models to test how risk of spring migratory departure was predicted by the combined intrinsic measures, along with meteorological predictors on the evening of departure (i.e., average wind speed and direction, relative humidity, and temperature). Model comparisons found that the best predictor of spring departure date was average nightly wind direction and a principal component combining relative humidity and temperature. Juncos were more likely to depart for spring migration on nights with largely southwestern winds and on warmer and drier evenings (relative to cooler and more humid evenings). Our results indicate that weather conditions at take‐off are more critical to departure decisions than the measured physiological and parasitism variables.

Himalayan birds that show the greatest elevational shifts remain within the narrowest thermal regimes

Article

Sep 2023
GLOBAL ECOL BIOGEOGR

Aim Elevational migration is a globally ubiquitous animal behaviour. Understanding the mechanisms that drive variation in elevational movement can help explain the evolution of this widespread animal behaviour and its role in shaping montane life history. We examine the role of thermal regime (the intra‐annual variation in temperature experienced by a species), dispersal ability and diet in explaining the extent of elevational movements. Location Eastern and Western Himalayas. Time Period 2011–2022. Major Taxa Studied Birds. Methods We used community science data from eBird to acquire checklist‐based observations of birds and used comprehensive data cleaning procedures and randomization tests to produce estimates of seasonal elevational shifts for 302 species of Himalayan birds. Using these data, we ran phylogenetic least squares regressions (PGLS) to test if the extent of elevational shift is driven by thermal regime, dispersal ability and diet. Results Most Himalayan birds (up to 65%) showed downslope shifts in the winter, although some (5%‐10%) low elevation species shifted upslope. Elevational shift was negatively associated with a species' thermal regime. Species that showed the greatest elevational shifts in both eastern and western Himalayas moved within the narrowest intra‐annual temperature regimes, but did not match their breeding range temperatures as closely as possible. Diet influenced elevational shift in both eastern and western Himalayas, while dispersal ability did not drive elevational shifts. Main Conclusions Species that show the biggest elevational shifts track thermal regimes most closely. However, in addition to tracking thermal regimes, diet and potentially habitat availability/preferences may drive seasonal elevational shifts. Our results show convergent evolution of elevational shifts across clades. Low elevation habitats are important not only for conserving low elevation birds but also for conserving wintering sites of most high elevation breeders.

Wintering Artemisiospiza sparrows: patterns of segregation between Sagebrush Sparrow ( A. nevadensis ) and Mojave Bell's Sparrow ( A. belli canescens ) across Lower Colorado Desert vegetation assemblages, with evidence for differential migration in Mojave Bell's Sparrow

Article

Full-text available

Jan 2023
J FIELD ORNITHOL

Geographic variation in the altitudinal migration patterns, body size, oxidative status and exploratory behavior in a neotropical bird

Article

Full-text available

Mar 2023

To cope with life in the mountains, populations of the same species can exhibit sub- stantial variability in their altitudinal migration patterns and phenotypes in response to local weather conditions. Studying such variability can provide valuable insights into how local populations respond to environmental challenges, and this informa- tion can be useful for conservation efforts in mountain ecosystems. Here, we used δ2H values of feathers and blood to evaluate latitudinal variation in altitudinal migra- tion patterns and its possible links with body size, oxidative status, and exploratory behavior in 72 individuals of rufous-collared sparrow (Zonotrichia capensis) that breed at low and high elevations in the center (~33°) and south (~38°) of Chile. Our results show that both altitudinal migration patterns and oxidative status were significantly influenced by the latitude of breeding sites, while exploratory behavior was associ- ated with elevation. Notably, we found that fast-explorer birds inhabiting low eleva- tions in central Chile displayed higher levels of oxidative damage than slow-explorer birds. These outcomes underscore the possibility of local adaptations in response to diverse local environmental conditions in the Andes. We discuss the implications of latitude, elevation, and environmental temperature in shaping the observed patterns and highlight the significance of identifying local adaptations in mountain birds for better predicting their response to climate change and other challenges stemming from anthropogenic activities

The effect of the temperature on local differences in the sex ratio of Mallards Anas platyrhynchos wintering in an urban habitat

Article

Mar 2023
ACTA OECOL

In Mallard, as in other ducks of the northern hemisphere, males outnumber females in wintering flocks and the temperature seems to be one of the most important factors shaping the sex ratio at a given site. In this study, we checked the influence of winter harshness on the sex ratio of Mallards overwintering in urban waterbodies with an emphasis on differences at the local scale within a single town. Our study shows that in harsh winter seasons, there was a lower share of males among wintering Mallards. It seems that females, despite their smaller body size and higher specific metabolic rate, found favourable conditions in the urban area during cold weather. Towns are characterized by a milder winter climate than rural areas, moreover birds profit from the supplementary feeding by humans. In severe weather conditions, females remained in urban waterbodies together with their paired mate, whereas unpaired males possibly left the town in search of sites with less competition, as they occupy a lower position in the flock hierarchy than paired individuals. We also found such differences on a local scale, with the proportion of males decreasing with decreasing temperature. Obtained results suggest that the sex- and status-dependent response to even a slight temperature change during the winter period is probably the most important factor shaping the variation in the proportion of male and female Mallards in flocks, at least in areas with a high abundance of anthropogenic food, which is likely to weaken competition between the sexes for resources.

Abundance and timing of non-raptorial diurnal landbird migrants passing through Khao Dinsor, southern Thailand, in autumn 2015–2018

Article

Full-text available

Dec 2022

Systematic observations at Khao Dinsor, Chumphon province, Thailand, in the overland diurnal migrant 'bottleneck' of the Thai-Malay Peninsula during 2015-2018 recorded 619,075 individuals of 86 non-raptorial bird species considered non-breeding visitors. Data on the southward migration timing and patterns of 16 regular diurnal migrants are presented, including less-studied species such as the Pacific Swift Apus pacificus, Oriental Pratincole Glareola maldivarum, Oriental Dollarbird Eurystomus orientalis, Ashy Minivet Pericrocotus divaricatus and Asian House Martin Delichon dasypus. In nine species, the seasonal totals of southbound migrants exceeded one thousand individuals, including the White-throated Needletail Hirundapus caudacutus, previously regarded as little more than a vagrant in the Thai-Malay Peninsula. The regular passage of the Common Swift Apus apus, a transcontinental species thought to winter only in Africa, was also recorded. Future studies of passage migrant monitoring at the Kra Isthmus and nearby areas should extend the autumn count period from August to December for better coverage, and should involve observers trained to be highly vigilant of flight calls. There should also be more efforts to determine differences in the proportion and timing of different sex/age classes within species when practical, to explore and better understand the migratory strategies of specific groups.

Autumnal migration patterns of hoverflies (Diptera: Syrphidae): interannual variability in timing and sex ratio

Article

Full-text available

Dec 2022

Background The migration of hoverflies (Diptera: Syrphidae) is a well-known phenomenon, with growing interest due to the ecosystem services provided by migrants. However, we still lack fundamental data on species composition, timing of migration, or sex ratio of migrants. To address this gap, we focused on the southward autumnal migration of hoverflies through central Europe. Methods To recognize migrating individuals from resident ones, we used a pair of one-side-blocked Malaise traps, exposed in a mountain pass in the Jeseníky mountains, Czech Republic, where a mass migration of hoverflies takes place annually. Traps were set for 4 years, from August to October. Results In total, we recorded 31 species of migrating hoverflies. The timing of migration differed between the years, taking place from the beginning of September to the end of October. Differences in phenology were observed in the four most common migrant species, where larger species seemed to migrate earlier or at the same time compared to the smaller ones. The sex ratio was strongly asymmetrical in most common species Episyrphus balteatus , Eupeodes corollae , and Sphaerophoria scripta , and varied between years for each species. Weather conditions strongly influenced the migration intensity at ground-level: hoverflies migrate mainly during days with south wind, high temperature, high atmospheric pressure, and low precipitation.

Flyway‐scale GPS tracking reveals migratory routes and key stopover and non‐breeding locations of lesser yellowlegs

Article

Full-text available

Nov 2022

Many populations of long‐distance migrant shorebirds are declining rapidly. Since the 1970s, the lesser yellowlegs (Tringa flavipes) has experienced a pronounced reduction in abundance of ~63%. The potential causes of the species' decline are complex and interrelated. Understanding the timing of migration, seasonal routes, and important stopover and non‐breeding locations used by this species will aid in directing conservation planning to address potential threats. During 2018–2022, we tracked 118 adult lesser yellowlegs using GPS satellite tags deployed on birds from five breeding and two migratory stopover locations spanning the boreal forest of North America from Alaska to Eastern Canada. Our objectives were to identify migratory routes, quantify migratory connectivity, and describe key stopover and non‐breeding locations. We also evaluated predictors of southbound migratory departure date and migration distance. Individuals tagged in Alaska and Central Canada followed similar southbound migratory routes, stopping to refuel in the Prairie Pothole Region of North America, whereas birds tagged in Eastern Canada completed multi‐day transoceanic flights covering distances of >4000 km across the Atlantic between North and South America. Upon reaching their non‐breeding locations, lesser yellowlegs populations overlapped, resulting in weak migratory connectivity. Sex and population origin were significantly associated with the timing of migratory departure from breeding locations, and body mass at the time of GPS‐tag deployment was the best predictor of southbound migratory distance. Our findings suggest that lesser yellowlegs travel long distances and traverse numerous political boundaries each year, and breeding location likely has the greatest influence on migratory routes and therefore the threats birds experience during migration. Further, the species' dependence on wetlands in agricultural landscapes during migration and the non‐breeding period may make them vulnerable to threats related to agricultural practices, such as pesticide exposure. Since the 1970s, the lesser yellowlegs (Tringa flavipes) has experienced a pronounced reduction in abundance of ~63%. The potential causes of the species’ decline are complex and interrelated and understanding the timing of migration and seasonal routes used by this species will aid in directing conservation planning to address potential threats. Our objectives were to identify migratory routes, quantify migratory connectivity and describe key stopover and non‐breeding locations.

Migration patterns and conservation status of Asian Great Bustard (Otis tarda dybowskii) in northeast Asia

Article

Full-text available

Nov 2022

The Great Bustard (Otis tarda) holds the distinction of the heaviest bird to undertake migration as well as the greatest degree of sexual size dimorphism among living birds. Though the migration of the species has been widely discussed in the literature, researchers know little about the migration patterns of the subspecies in Asia (Otis tarda dybowskii), especially the males. In 2018 and 2019, we captured six O. t. dybowskii (five males and one female) at their breeding sites in eastern Mongolia and tagged them with GPS-GSM satellite transmitters. This constitutes the first time that the Great Bustards of the eastern subspecies have been tracked in eastern Mongolia. We found sex differences in migration patterns: males started migration later but arrived earlier than the female in the spring; males had 1/3 of the migration duration and migrated about 1/2 the distance of the female. Additionally, Great Bustards exhibited high fidelity to their breeding, post-breeding, and wintering sites. For conservation, only 22.51% of GPS location fixes of bustards were within protected areas, and less than 5.0% for wintering sites and during migration. Within two years, half of the Great Bustards we tracked died at their wintering sites or during migration. We recommend establishing more protected areas at wintering sites and rerouting or undergrounding powerlines in areas where Great Bustards are densely distributed to eliminate collisions.

The effects of powerlines on bustards: how best to mitigate, how best to monitor?

Article

Full-text available

Sep 2022

Bustards comprise a highly threatened family of birds and, being relatively fast, heavy fliers with very limited frontal visual fields, are particularly susceptible to mortality at powerlines. These infrastructures can also displace them from immediately adjacent habitat and act as barriers, fragmenting their ranges. With geographically ever wider energy transmission and distribution grids, the powerline threat to bustards is constantly growing. Reviewing the published and unpublished literature up to January 2021, we found 2,774 records of bustard collision with powerlines, involving 14 species. Some studies associate powerline collisions with population declines. To avoid mortalities, the most effective solution is to bury the lines; otherwise they should be either routed away from bustard-frequented areas, or made redundant by local energy generation. When possible, new lines should run parallel to existing structures and wires should preferably be as low and thick as possible, with minimal conductor obstruction of vertical airspace, although it should be noted that these measures require additional testing. A review of studies finds limited evidence that 'bird flight diverters' (BFDs; devices fitted to wires to induce evasive action) achieve significant reductions in mortality for some bustard species. Nevertheless , dynamic BFDs are preferable to static ones as they are thought to perform more effectively. Rigorous evaluation of powerline mortalities, and effectiveness of mitigation measures, need systematic carcass surveys and bias corrections. Whenever feasible, assessments of displacement and barrier effects should be undertaken. Following best practice guidelines proposed with this review paper to monitor impacts and mitigation could help build a reliable body of evidence on best ways to prevent bustard mortality at powerlines. Research should focus on validating mitigation measures and quantifying, particularly for threatened bustards, the population effects of powerline grids at the national scale, to account for cumulative impacts on bustards and establish an equitable basis for compensation measures.

Ajustements phénotypiques en réponse aux contraintes associées à l'hiver, la migration et la reproduction chez le plectrophane des neiges

Thesis

Full-text available

Aug 2021

Audrey Le Pogam

Organisms are confronted with multiple environmental constraints to which they can respond through phenotypic adjustments that can potentially lead to physiological trade-offs. Contrary to species living only in temperate environments, the mechanisms underlying the phenotypic adjustments of species confronted with cold temperatures during most of the year are still poorly understood. My thesis focuses on the phenotypic adjustments of snow bunting's (Plectrophenax nivalis), a migratory passerine that winters in temperate zones (between 40° and 60°N) and migrates in spring to Arctic regions to breed. More specifically, I was interested in the variations of body composition (body mass, lipid and lean mass, pectoral muscle thickness), oxygen transport capacity (hematocrit) and metabolic performance (physiological maintenance costs - BMR and thermogenic capacity - Msum) among the winter, migratory and reproductive stages. For this, I conducted measurements from 2013 to 2019 on individuals either (1) held captive in an outdoor aviary in Rimouski (QC, 48°N), (2) on wild individuals captured on their wintering grounds in Rimouski and (3) wild birds captured at the northernmost point of their breeding range in Alert, Nunavut (82°N). In Chapter 1, I studied the winter phenotypic adjustments of buntings held captive in the temperate zone. The objective was to determine if the pattern of adjustments for this cold-associated species conformed to that of resident species at the same latitudes. Increases in body and lipid mass, pectoral muscle thickness, hematocrit, and Msum observed between summer and winter suggest that the phenotypic flexibility of traits associated with thermal acclimation in northern species is comparable to that of temperate resident passerines and thus that these adjustments are not constrained by life in a cold environment. However, lean mass declined and BMR remained stable over the winter, suggesting that buntings may also minimize the energetic costs of living in cold environments. In Chapter 2, I analyzed the phenotypic adjustment patterns of captive buntings during periods corresponding to migration and reproduction and compared them to the winter phenotype. The objective was to see if, and by what mechanism, traits associated with winter cold acclimation could be transferred to later stages of the annual cycle. The results show that although body mass, lipid mass and BMR increase for migration, traits related to cold endurance do not change in parallel since they are already elevated at the end of winter. This is the first direct demonstration that phenotypic traits associated with winter acclimation can transfer to the migratory phenotype and even be maintained during the breeding season. Through Chapter 3, I compared the phenotype of free-living buntings caught during winter at Rimouski and during pre-breeding at Alert. The objective was to determine whether cold endurance and associated traits could be maintained at a winter level during migration and pre-breeding. Results indicate that despite a decline in muscle thickness and hematocrit between winter and pre-breeding, cold endurance and energy reserves were maintained. These results support the hypothesis that migratory cold specialist species could maintain their cold endurance at a winter level until pre-breeding. Finally, in Chapter 4, I examined the change in phenotype between the pre-breeding and chick provisioning periods at Alert to determine how the transition between life stages on the breeding grounds, in interaction with spring thermal conditions, could influence cold endurance. Results show that buntings maintain a high thermogenic capacity as long as temperatures remain below 0-2°C, whether or not they actively reproduce. These observations therefore suggest that buntings likely experience a double physiological cost in late spring, when reproductive activities (i.e., egg production and incubation) begin and air temperatures are still below 0-2°C. Overall, this study demonstrates that not all thermal acclimation mechanisms established to date are generalizable to Arctic species. It therefore provides a reference point for future comparative research. Les organismes sont confrontés à de multiples contraintes environnementales auxquelles ils peuvent répondre par des ajustements phénotypiques menant potentiellement à des compromis physiologiques. Contrairement aux espèces vivant uniquement en milieux tempérés, les mécanismes sous-jacents aux ajustements phénotypiques des espèces confrontées au froid la majeure partie de l'année sont encore mal compris. Ma thèse porte sur les ajustements phénotypiques du plectrophane des neiges (Plectrophenax nivalis), un passereau migrateur qui hiverne en zone tempérée (entre 40° et 60°N) et migre au printemps vers les régions arctiques pour se reproduire. Plus particulièrement, je me suis intéressée aux variations de composition corporelle (masse corporelle, lipidique et maigre, épaisseur des muscles pectoraux), de capacité de transport de l'oxygène (hématocrite) et de performance métabolique (coûts de maintenance physiologiques - BMR et de capacité thermogénique - Msum) au cours de l'hiver, de la migration et de la reproduction. Pour cela, j'ai effectué de 2013 à 2019, des mesures (1) sur des individus maintenus captifs en volière extérieure à Rimouski (QC, 48°N), (2) sur des individus capturés sur leur aire d'hivernage à Rimouski et (3) à l'extrême nord de leur aire de reproduction, à Alert au Nunavut (82°N). Dans le chapitre 1, j'ai étudié les ajustements phénotypiques hivernaux des plectrophanes maintenus captifs en zone tempérée. L'objectif était de déterminer si le patron d'ajustements de cette espèce associée au froid la majeure partie de sa vie se conformait à celui des espèces résidentes aux mêmes latitudes. Les augmentations de masse corporelle et lipidique, d'épaisseur des muscles pectoraux, d'hématocrite et de Msum observées entre l'été et l'hiver suggèrent que la flexibilité phénotypique des traits associés à l'acclimatation thermique chez les espèces nordiques est comparable à celle des passereaux résidents des zones tempérées et donc que ces ajustements ne sont pas contraints par la vie dans un environnement froid. Toutefois, le déclin de masse maigre et la stabilité du BMR observés au cours de l'hiver suggèrent que les plectrophanes peuvent aussi minimiser les coûts énergétiques de la vie en milieux froids. Au chapitre 2, j'ai analysé les patrons d'ajustements phénotypiques de plectrophanes maintenus captifs au cours des périodes correspondant à la migration et la reproduction et je les ai comparées au phénotype hivernal. L'objectif était de voir si et par quel mécanisme, les traits associés à l'acclimatation au froid hivernal pouvaient être transférés aux stades ultérieurs du cycle annuel. Les résultats montrent que, bien que la masse corporelle, la masse lipidique et le BMR augmentent pour la migration, les traits liés à l'endurance au froid ne changent pas en parallèle puisqu'ils sont déjà élevés à la sortie de l'hiver. Il s'agit de la première démonstration directe que des traits phénotypiques associés à l'acclimatation hivernale peuvent se transférer au phénotype migratoire et même se maintenir en période de reproduction. Au travers du chapitre 3, j'ai comparé le phénotype de plectrophanes capturés en milieu naturel en hiver à Rimouski et en pré-reproduction à Alert. L'objectif était de déterminer si l'endurance au froid et les traits associés pouvaient se maintenir à un niveau hivernal durant la migration et la pré-reproduction. Les résultats indiquent que malgré un déclin d'épaisseur des muscles et d'hématocrite, l'endurance au froid et les réserves énergétiques étaient maintenues. Ces résultats confirment l'hypothèse selon laquelle les espèces migratrices spécialistes du froid pourraient maintenir leur endurance au froid à un niveau hivernal jusqu'à la pré-reproduction. Enfin dans le Chapitre 4, j'ai examiné l'évolution du phénotype entre la période de pré-reproduction et d'approvisionnement des oisillons à Alert afin de déterminer comment la transition entre les stades de vie sur les aires de reproduction, en interaction avec les conditions thermiques printanières, pouvait influencer l'endurance au froid. Les résultats montrent que les plectrophanes maintiennent une capacité thermogénique élevée tant que les températures demeurent inférieures à 0-2°C, qu'ils se reproduisent activement ou non. Ces observations suggèrent donc que les plectrophanes subissent probablement un double coût physiologique à la fin du printemps, lorsque les activités de reproduction (c.-à-d., production et incubation des œufs) commencent alors que les températures sont encore inférieures à 0-2°C. De manière générale, cette étude démontre que les mécanismes d'acclimatation thermique établis jusqu'à maintenant ne sont pas tous généralisables aux espèces arctiques. Elle constitue donc un point de référence pour de futures recherches comparatives.

The role of context in elucidating drivers of animal movement

Article

Full-text available

Jul 2022

Despite its consequences for ecological processes and population dynamics, intra-specific variability is frequently overlooked in animal movement studies. Consequently, the necessary resolution to reveal drivers of individual movement decisions is often lost as animal movement data are aggregated to infer average or population patterns. Thus, an empirical understanding of why a given movement pattern occurs remains patchy for many taxa, especially in marine systems. Nonetheless, movement is often rationalized as being driven by basic life history requirements, such as acquiring energy (feeding), reproduction, predator-avoidance, and remaining in suitable environmental conditions. However, these life history requirements are central to every individual within a species and thus do not sufficiently account for the high intra-specific variability in movement behavior and hence fail to fully explain the occurrence of multiple movement strategies within a species. Animal movement appears highly context dependent as, for example, within the same location, the behavior of both resident and migratory individuals is driven by life history requirements, such as feeding or reproduction , however different movement strategies are utilized to fulfill them. A systematic taxa-wide approach that, instead of averaging population patterns, incorporates and utilizes intra-specific variability to enable predictions as to which movement patterns can be expected under a certain context, is needed. Here, we use intra-specific variability in elasmobranchs as a case study to introduce a stepwise approach for studying animal movement drivers that is based on a context-dependence framework. We examine relevant literature to illustrate how this context-focused approach can aid in reliably identifying drivers of a specific movement pattern. Ultimately, incorporating behavioral variability in the study of movement drivers can assist in making predictions about behavioral responses to environmental change, overcoming tagging biases, and establishing more efficient conservation measures.

Do Nearctic hover flies (Diptera: Syrphidae) engage in long‐distance migration? An assessment of evidence and mechanisms

Article

Full-text available

Jul 2022
ECOL MONOGR

Long‐distance insect migration is poorly understood despite its tremendous ecological and economic importance. As a group, Nearctic hover flies (Diptera: Syrphidae: Syrphinae), which are crucial pollinators as adults and biological control agents as larvae, are almost entirely unrecognized as migratory despite examples of highly migratory behavior among several Palearctic species. Here, we examined evidence and mechanisms of migration for four hover fly species (Allograpta obliqua, Eupeodes americanus, Syrphus rectus, and Syrphus ribesii) common throughout eastern North America using stable hydrogen isotope (δ²H) measurements of chitinous tissue, morphological assessments, abundance estimations, and cold‐tolerance assays. Although further studies are needed, nonlocal isotopic values obtained from hover fly specimens collected in central Illinois support the existence of long‐distance fall migratory behavior in Eu. americanus, and to a lesser extent S. ribesii and S. rectus. Elevated abundance of Eu. americanus during the expected autumn migratory period further supports the existence of such behavior. Moreover, high phenotypic plasticity of morphology associated with dispersal coupled with significant differences between local and nonlocal specimens suggest that Eu. americanus exhibits a unique suite of morphological traits that decrease costs associated with long‐distance flight. Finally, compared with the ostensibly nonmigratory A. obliqua, Eu. americanus was less cold tolerant, a factor that may be associated with migratory behavior. Collectively, our findings imply that fall migration occurs in Nearctic hover flies, but we consider the methodological limitations of our study in addition to potential ecological and economic consequences of these novel findings.

Dancing drives evolution of sexual size dimorphism in manakins

Article

Full-text available

May 2022

Body size mediates life history, physiology and inter- and intra-specific interactions. Within species, sexes frequently differ in size, reflecting divergent selective pressures and/or constraints. Both sexual selection and differences in environmentally mediated reproductive constraints can drive sexual size dimorphism, but empirically testing causes of dimorphism is challenging. Manakins (Pipridae), a family of Neotropical birds comprising approximately 50 species, exhibit a broad range of size dimorphism from male- to female-biased and are distributed across gradients of precipitation and elevation. Males perform courtship displays ranging from simple hops to complex aerobatic manoeuvres. We tested associations between sexual size dimorphism and (a) agility and (b) environment, analysing morphological, behavioural and environmental data for 22 manakin species in a phylogenetic framework. Sexual dimorphism in mass was most strongly related to agility, with males being lighter than females in species performing more aerial display behaviours. However, wing and tarsus length dimorphism were more strongly associated with environmental variables, suggesting that different sources of selection act on different aspects of body size. These results highlight the strength of sexual selection in shaping morphology—even atypical patterns of dimorphism—while demonstrating the importance of constraints and ecological consequences of body size evolution.

A high-quality genome assembly and annotation of the dark-eyed junco Junco hyemalis , a recently diversified songbird

Article

Full-text available

Apr 2022

The dark-eyed junco (Junco hyemalis) is one of the most common passerines of North America, and has served as a model organism in studies related to ecophysiology, behavior and evolutionary biology for over a century. It is composed of at least six distinct, geographically structured forms of recent evolutionary origin, presenting remarkable variation in phenotypic traits, migratory behavior and habitat. Here we report a high-quality genome assembly and annotation of the dark-eyed junco generated using a combination of shotgun libraries and proximity ligation ChicagoTM and Dovetail Hi-CTM libraries. The final assembly is ∼1.03 Gb in size, with 98.3% of the sequence located in 30 full or nearly full chromosome scaffolds, and with a N50/L50 of 71,3 Mb/5 scaffolds. We identified 19,026 functional genes combining gene prediction and similarity approaches, of which 15,967 were associated to GO terms. The genome assembly and the set of annotated genes yielded 95.4% and 96.2% completeness scores, respectively, when compared with the BUSCO avian dataset. This new assembly for J. hyemalis provides a valuable resource for genome evolution analysis, and for identifying functional genes involved in adaptive processes and speciation.

Winter space use and sex ratios of Chestnut-collared Longspurs (Calcarius ornatus) in Oklahoma

Article

Apr 2022

As grasslands have become the most threatened ecosystem in North America, so too have many migratory obligate grassland birds. Chestnut-collared Longspurs (Calcarius ornatus) are a great example, as they have experienced an 89% population decline during the last 5 decades. We captured and tracked individuals during the winters of 20182019 and 20192020 and calculated their home ranges as both minimum convex polygons (MCP) and fixed kernel density estimates (KDE). Across the 2 winters, we captured and banded 116 longspurs (75% males), fitting 90 of them with VHF radio-transmitters. The winter (5 Dec8 Mar) mean home ranges defined by MCP were 128.8 ha, while the 95% KDE indicated a mean of 29.87 ha. Wintering longspurs used larger areas and displayed higher nomadism than reported for other grassland bird species. Therefore, management for the species scales up beyond the relatively small areas that longspurs aggregate into flocks within and will require landscape-level coordination to maintain habitat adequate for effective winter population.

Seeing Is Be-Leaving: Perception Informs Migratory Decisions in Sierra Nevada Bighorn Sheep (Ovis canadensis sierrae)

Article

Full-text available

Feb 2022

Seasonal migration is a behavioral response to predictable variation in environmental resources, risks, and conditions. In behaviorally plastic migrants, migration is a conditional strategy that depends, in part, on an individual’s informational state. The cognitive processes that underlie how facultative migrants understand and respond to their environment are not well understood. We compared perception of the present environment to memory and omniscience as competing cognitive mechanisms driving altitudinal migratory decisions in an endangered ungulate, the Sierra Nevada bighorn sheep (Ovis canadensis sierrae) using 1,298 animal years of data, encompassing 460 unique individuals. We built a suite of statistical models to partition variation in fall migratory status explained by cognitive predictors, while controlling for non-cognitive drivers. To approximate attribute memory, we included lagged attributes of the range an individual experienced in the previous year. We quantified perception by limiting an individual’s knowledge of migratory range to the area and attributes visible from its summer range, prior to migrating. Our results show that perception, in addition to the migratory propensity of an individual’s social group, and an individual’s migratory history are the best predictors of migration in our system. Our findings suggest that short-distance altitudinal migration is, in part, a response to an individual’s perception of conditions on alterative winter range. In long-distance partial migrants, exploration of migratory decision-making has been limited, but it is unlikely that migratory decisions would be based on sensory cues from a remote target range. Differing cognitive mechanisms underpinning short and long-distance migratory decisions will result in differing levels of behavioral plasticity in response to global climate change and anthropogenic disturbance, with important implications for management and conservation of migratory species.

Breeding Dark-eyed Junco (Junco hyemalis hyemalis) subspecies in western Massachusetts has not changed over previous 80 years

Article

Apr 2024

Sex-specific migration strategies and underlying physiology contribute to spring arrival protandry in a songbird

Preprint

Full-text available

Feb 2024

In spring, many migrating songbirds exhibit protandry (the phenomenon whereby males precede females in arrival at breeding sites). The reed bunting ( Emberiza schoeniclus ) is a short-distance migrant which expresses a high degree of protandry and combines both nocturnal and diurnal movements during migrations. In experimental conditions, we studied the proximate mechanisms of protandry and compared locomotor behavior between spring and autumn migrations. We assumed that captive behavior is a proxy for the behavior that birds demonstrate in the wild. Combined, the analysis of seasonal patterns and circadian dynamics of locomotor activity suggested that male reed buntings depart from wintering grounds by daytime flights approximately two weeks earlier than females. Later, they develop nocturnal activity, take off shortly before dawn and continue their flight for several hours in the morning. We argue that such behavior allows males to benefit from both the advantage of nocturnal flight and an efficient start of foraging, thereby reducing the stopover duration (by minimizing search/settling costs) and increasing the total migration speed. In contrast, females migrate predominantly at night in spring. Sex-related variation in behavior was accompanied by differences in energetic conditions; males in spring had, on average, lower fat reserves. However, leukocyte profile parameters were similar in males and females. In contrast, in autumn, both sexes display similar levels/dynamics of locomotor activity and fat reserves. Overall, our results describe unique sex-specific migratory behaviour and physiology in reed buntings in spring, which, we assume, contribute to spring arrival protandry in this species.

Sex and age differences in migration

Chapter

Jan 2024

Ian Newton

Migratory control mechanisms

Chapter

Jan 2024

Ian Newton

Migration

Chapter

Nov 2023

Gary Ritchison

About half of the approximately 10,000 species of birds are classified as migrants. Ideas about the origins of avian migration are discussed in this chapter and, for present-day birds, the distances, routes, and heights that migrants fly are explained. In mountainous regions, many species of birds are altitudinal migrants and the reasons why birds exhibit such behavior are discussed. The reasons why some migrants follow loop and figure-eight migration routes are also explained. Also discussed is the importance of stopover sites for migrants. Other topics covered in this chapter include bird migration in the Neotropics and seasonal differences in the speed of migration. Many migratory species exhibit protandry, with males arriving in breeding areas before females and factors contributing to such behavior are discussed. Reasons why birds migrate during the day versus at night are explained, and the chapter closes with a discussion of the possible effects of climate change on bird migration.

Elevational differences in migration phenology of Lazuli Buntings do not support selection-based hypotheses for protandry

Article

Jun 2023

Documenting and understanding sex-specific variation in migratory phenology is important for predicting avian population dynamics. In spring, males often arrive on the breeding grounds before females (protandry), though whether these patterns result from fitness benefits versus sex-specific constraints on arrival timing remains poorly understood. Sex-specific variation in the timing of fall migration is less well-documented than in spring, in part because documenting fall departures is often limited by cryptic behaviors, lower vocalization rates, and shifting territory boundaries during this time of year. We used 2 years of high-resolution encounter data from radio-frequency identification (RFID)-equipped bird feeders to monitor the daily presence of male and female Lazuli Buntings (Passerina amoena) throughout the breeding season at a high and a low-elevation site in Cache County, Utah, USA. These encounter data were used to estimate daily arrival and departure probabilities and to investigate possible differences in migration timing in relation to sex and elevation. At low elevation, male arrival (n = 15) preceded female arrival (n = 16) by ~1 week, consistent with previous research that has documented protandry in other migratory songbirds. At high elevation, however, no significant differences were found between male (n = 19) and female arrival (n = 6). In fall, we found little difference in departure dates between elevation or sex, or between years. Our observations are most consistent with constraint-based hypotheses explaining protandry, possibly relating to sex-specific constraints operating during the nonbreeding period. We additionally emphasize the need for quantifying uncertainty in phenological estimates and importance of addressing potential differences across demographic groups.

Why hibernate? Tests of four hypotheses to explain intraspecific variation in hibernation phenology

Article

Full-text available

May 2023
FUNCT ECOL

Hibernation is a remarkable behaviour deployed by a diverse array of endotherms within many clades that greatly reduces metabolic need, but also has somatic costs. Hibernation in modern endotherms is often assumed to be an adaptation allowing animals to avoid extreme thermal conditions or food shortages in seasonal environments. However, many animals hibernate when foraging conditions are energetically profitable, suggesting other causal factors influence hibernation behaviour. Understanding the selection pressures responsible for intraspecific variation in the timing and duration of hibernation can help elucidate the relative evolutionary influences of the ultimate ecological causes of hibernation. We tested four previously proposed mechanistic hypotheses to explain intraspecific variation in hibernation phenology in the federally threatened northern Idaho ground squirrel (Urocitellus brunneus): (1) thermal tolerance, (2) food limitation, (3) predation avoidance and (4) sexual selection. The predation avoidance and sexual selection hypotheses received the most support, although we also found some support for the thermal tolerance and food limitation hypotheses. Heavy squirrels increased hibernation duration regardless of environmental conditions, as predicted solely by the predation avoidance hypothesis. Reproductive males emerged from hibernation earlier in spring than other sex–age classes, a pattern predicted by the sexual selection hypothesis. Temperature and food availability explained a much smaller amount of the variation in hibernation behaviour, only partially supporting predictions of the thermal tolerance and food limitation hypotheses. Our results indicate that animals navigate life‐history trade‐offs between energetic allocation to survival and reproduction via state‐dependent optimization of hibernation phenology. Consequently, any future environmental changes that influence body condition will have implications for population ecology and life‐history evolution of hibernating animals due to stark differences in daily survival probability between hibernation and the active season. Read the free Plain Language Summary for this article on the Journal blog.

Time Shift in the Exploitation of Fish Stocks by Great Cormorants Phalacrocorax carbo at Lake IJsselmeer: How Wintering Birds began Competing for Fish with Breeding Conspecifics

Article

Full-text available

Jul 2022

Monthly aerial bird counts showed a strong increase in the number of wintering Great Cormorants Phalacrocorax carbo sinensis since the late 1990s at Lake IJsselmeer but not at Lake Markermeer-IJmeer. Compared to the 19801990s, breeding numbers also increased in this part of the system. The resulting increased exploitation of fish stocks was thought to have been possible because of a long-term increase in the stock of Ruffe Gymnocephalus cernuus, despite a clear overall decline of total estimated fish biomass in the lake during the same period. The most likely cause of these shifts was thought to be the intensive commercial fishing regime, removing the large predatory fish first, followed by a strong reduction of stocks of large Bream Abramis brama, in turn paving the way for increases in the stocks of Ruffe. Increased predation by Cormorants on the enhanced stocks of small fishes was possible because of ameliorated underwater visibility in Lake IJsselmeer. Starting in 2000, there was a strong shift in both temporal habitat use and associated fish consumption by Cormorants towards the winter period. The local breeding birds, exploiting the same age- and size-structured community of fishes in the spring, thus face an already-depleted food resource. Compared to the 19801990s, fish consumption by Cormorants in winter increased by a factor of ten, whereas that by breeders did so by a factor of 1.6. Our calculations showed that the actual harvest of available fish stock by wintering and breeding Cormorants together was c. 5% in 19852000 and c. 15% in 20012015. The disproportionate division of the overall consumption (harvest) of the fish stock towards the wintering birds is a strong argument for direct competition with their conspecifics breeding locally. In conclusion, we calculate that because of the increased winter exploitation initiated by the activities of an intensive commercial fishery, the fish consumption in summer and early autumn by breeding Cormorants and their offspring was suppressed by a factor of six.

Differences in stopover duration and body mass change among Emberiza buntings during autumn migration in the Russian Far East

Article

Full-text available

Mar 2022

Stopover periods between flights are essential for migrating birds, and the time birds spend at stopover sites as well as the refuelling rate is determined by intrinsic and extrinsic factors, such as competition and environmental conditions. While most studies on stopover ecology have been conducted along the Nearctic-Neotropical and the Palaearctic-African flyways, little is known about species migrating along the East Asian flyway. To address this, we compared stopover duration and body mass change of 13 closely related Emberiza bunting species during autumn migration in the Russian Far East. We found significant differences in stopover duration between the species but no differences in body mass change. Overall, stopover duration decreased during the season, suggesting that late-arriving individuals leave earlier due to external factors like unfavourable climatic conditions or food availability or as a result of their endogenous spatiotemporal migration program. We also found that stopover duration correlates with the fat score at arrival and the geographic position of breeding grounds. Juveniles stayed longer at the stopover site than adults, suggesting that the latter might be able to migrate more efficiently. No sex-specific differences in stopover duration were found. We found that body mass change was positively correlated with stopover duration and arrival date. We argue that buntings modulate their stopover duration depending on the energy required to continue migration. Our results suggest the applicability of optimal migration theory for the East Asian flyway.

Two-Sex Demography, Sexual Niche Differentiation, and the Geographic Range Limits of Texas Bluegrass (Poa arachnifera)

Article

Mar 2022

Understanding the mechanisms that generate biogeographic range limits is a long-standing goal of ecology. It is widely hypothesized that distributional limits reflect the environmental niche, but this hypothesis is complicated by the potential for intraspecific niche heterogeneity. In dioecious species, sexual niche differentiation may cause divergence between the sexes in their limits of environmental suitability. We studied range boundary formation in Texas bluegrass (Poa arachnifera), a perennial dioecious plant, testing the alternative hypotheses that range limits reflect the niche limits of females only versus the combined contributions of females and males, including their interdependence via mating. Common garden experiments across a longitudinal aridity gradient revealed female-biased flowering approaching eastern range limits, suggesting that mate limitation may constrain the species' distribution. However, a demographic model showed that declines in λ approaching range limits were driven almost entirely by female vital rates. The dominant role of females was attributable to seed viability being robust to sex ratio variation and to low sensitivity of λ to reproductive transitions. We suggest that female-dominant range limits may be common to long-lived species with polygamous mating systems and that female responses to environmental drivers may often be sufficient for predicting range shifts in response to environmental change.

Geographic Variation and Its Climatic Correlates in the Sex Ratio of Eastern-Wintering Dark-Eyed Juncos (Junco Hyemalis Hyemalis)

Abstract

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