Altitudinal Migration Research Articles

Climate factors and food availability shape the altitudinal migration of birds in the Xiling Snow Mountains, China.

Many bird species in montane regions display altitudinal migration, but so far, the underlying ecological driving mechanisms are not clear. We studied the altitudinal migration behavior patterns and factors influencing altitudinal migration in the Xiling Snow Mountains, which are part of the Hengduan mountain range in southwest China. We recorded the local bird diversity, the seasonal change of: the average temperature (AT), the average humidity (AH), the average invertebrate biomass (AIB), and the amount of plant food sources (PFS) at two study sites (∼1300 and ∼2100 m a.s.l.) during two migration seasons from September 2022 to May 2023. During our surveys, we recorded 96 bird species in total. Among these, 15 altitudinal migrants were identified. The most common family among altitudinal migrants was Leiothrichidae. AT, AIB, and PFS had a significant positive correlation with the monthly number of individuals (MNI) several bird species, implying that increasing temperatures and an increasing abundance of invertebrates and PFS possibly induced upward migration of altitudinal migrants and vice versa. AH possibly only played a minor role in influencing altitudinal migration, since it exhibited no significant correlation with the MNI. Furthermore, we found that the upward migration temperature range of altitudinal migrants ranged between 9.8°C and 13.9°C during spring and the downward migration temperature range ranged between 12.2°C and 7.9°C during autumn. In conclusion, our study and several other studies revealed that the same environmental factors influenced the altitudinal migration patterns of birds in the Hengduan Mountains.

Toward a comparative framework for studies of altitudinal migration.

The study and importance of altitudinal migration has attracted increasing interest among zoologists. Altitudinal migrants are taxonomically widespread and move across altitudinal gradients as partial or complete migrants, subjecting them to a wide array of environments and ecological interactions. Here, we present a brief synthesis of recent developments in the field and suggest future directions toward a more taxonomically inclusive comparative framework for the study of altitudinal migration. Our framework centers on a working definition of altitudinal migration that hinges on its biological relevance, which is scale-dependent and related to fitness outcomes. We discuss linguistic nuances of altitudinal movements and provide concrete steps to compare altitudinal migration phenomena across traditionally disparate study systems. Together, our comparative framework outlines a "phenotypic space" that contextualizes the biotic and abiotic interactions encountered by altitudinal migrants from divergent lineages and biomes. We also summarize new opportunities, methods, and challenges for the ongoing study of altitudinal migration. A persistent, primary challenge is characterizing the taxonomic extent of altitudinal migration within and among species. Fortunately, a host of new methods have been developed to help researchers assess the taxonomic prevalence of altitudinal migration-each with their own advantages and disadvantages. An improved comparative framework will allow researchers that study disparate disciplines and taxonomic groups to better communicate and to test hypotheses regarding the evolutionary and ecological drivers underlying variation in altitudinal migration among populations and species.

On the physiology of high-altitude flight and altitudinal migration in birds.

Many bird species fly at high altitudes for short periods and/or shift seasonally in altitude during migration, but little is known about the physiology of these behaviors. Transient high-altitude flight, or short-term flight at extreme altitudes, is a strategy used by lowland-native birds, often in the absence of topographic barriers. Altitudinal migration, or seasonal roundtrip movement in altitude between the breeding and non-breeding seasons, is a form of migration that occurs as a regular part of the annual cycle and results in periods of seasonal residency at high altitudes. Despite their nuanced differences, these two behaviors share a common challenge: Exposure to reduced oxygen environments during at least part of the migratory journey. In this perspective piece, we compare what is known about the physiology of oxygen transport during transient high-altitude flight and altitudinal migration by highlighting case studies and recent conceptual advances from work on captive and wild birds. We aim to open avenues for integrative research on the ecology, evolution, and physiology of high-flying and mountain-climbing birds.

Barometric geolocators can reveal unprecedented details about the migratory ecology of small birds

Abstract Knowing the location of migratory birds throughout their annual cycle is fundamental for many questions in ornithology. Technological advances have provided several approaches, with increasing miniaturization allowing deployment on smaller and smaller birds. Here, we examine the strengths and limitations of barometric pressure geolocators (pressure tags), which have recently been shown to be extremely effective in tracking small birds (<25 g). The newly developed geolocation by pressure workflow (GeoPressureR) uses a global weather analysis dataset and hidden Markov movement model to reveal locations more accurately or continuously than can be achieved by other available light-weight devices (e.g., light-level geolocators, automated radio telemetry, and archival GPS tags). Additionally, pressure data can provide altitude information and document generally intractable flight behavior, as well as exact migratory phenologies. This new technology can be applied to important unresolved problems such as altitudinal migration, stopover site use, molt migration, vertical airspace use, and drivers of migratory flight initiation, duration, and direction. We provide an example of a pressure tag on a Swainson’s Warbler (Limnothlypis swainsonii) deployed on its breeding territory in Virginia, USA, revealing the complete story of its migration to and from Cuba, including its refined wintering site, stopover sites, and migration routes, all with precise timing. Studies relying on pressure tags are still subject to biases related to recovery of the devices for data extraction, and application to birds that exhibit extensive aerial movements (e.g., swallows and swifts) remains challenging. Widespread deployment of pressure tags could show unprecedented details of bird migration and other aspects of aerial behavior, which could benefit conservation and greatly enrich our understanding of avian movement ecology.

Conservation Responsibility for Priority Habitats under Future Climate Conditions: A Case Study on Juniperus drupacea Forests in Greece

Juniperus drupacea is a highly morphologically and genetically differentiated Tertiary relict, displaying a disjunct geographical range in the eastern Mediterranean. Being a thermophilous, light-demanding, and moderately drought-resistant tree, it survived the past climatic oscillations via altitudinal migration. The species has its westernmost range limit, and its only populations in the EU, in Mts Parnon and Taygetos (Greece). These populations are genetically isolated and distinct compared to their Asian counterparts. For Europe, Juniperus drupacea is categorized as an endangered species by the IUCN. Juniperus drupacea forests constitute a priority habitat for conservation in the EU. However, the species’ conservation status has never been assessed in Greece and the same applies to its climate and land-use change assessment. As Greece is already facing the short-term impacts of climate- and human-induced land-use change, studies dealing with the potential long-term climate- and land-use change effects on rare plant species distribution are urgently needed to implement efficient conservation management plans. Our research employs species distribution models, considering multiple climate scenarios and abiotic factors across different timeframes (2020s, 2050s, 2080s), factoring in the potential threat of forest fires. Additionally, we assess the species’ extinction risk at the European level, according to IUCN Criteria A and B. Study findings indicate significant habitat changes and an elevated extinction risk for Juniperus drupacea in Greece. To safeguard this priority habitat, informed conservation strategies, management plans, and policy making are recommended, based on our scientific insights.

To move or not to move—factors influencing small-scale herder and livestock movements in the Dzungarian Gobi, Mongolia

In Mongolia, where nomadic pastoralism is still practiced by around one-third of the population, increasing livestock numbers, socio-economic constraints and climate change raise concerns over rangeland health. Little empirical evidence explains what triggers camp moves of pastoralists in the Dzungarian Gobi in Mongolia, which factors influence grazing mobility around camps, and how altitudinal migration benefits small livestock. We combined GPS tracking data of 19 small livestock herds monitored from September 2018 to April 2020 with remotely sensed climate and environmental data. We used general linear-mixed models to analyse variables influencing camp use duration and daily mobility patterns. To understand the importance of the altitudinal migration, we compared climatic conditions along the elevation gradient and looked at seasonal body weight changes of small livestock. We found that available plant biomass and season best explained camp use duration. Daily walking distance and maximum distance from camp increased with camp use duration. Pasture time increased with increasing biomass and rising temperatures. We conclude that herders in the Dzungarian Gobi have optimized pasture use by reacting to changes in biomass availability at landscape and local scale, and by embracing altitudinal migration. Flexibility in grazing mobility seems to have enabled local herder communities to practise sustainable pasture use. Maintaining this mobility will most likely be the best strategy to deal with environmental change under the current climate change scenarios.

A coupled modelling framework for predicting tree species’ altitudinal migration velocity in montane forest

Climate change is projected to cause rapid elevational migration of mountain plants. However, it is poorly understood the direction and magnitude of elevational range shifts across species because species’ life history traits are highly individualistic. Species with limited dispersal ability, reproductive rate, and ecological generalization may hardly expand into new regions under climate change. Therefore, such species’ shifts may not keep pace with climate change. We used a new framework for coupling a forest ecosystem model (LINKAGES) and a landscape model (LANDIS PRO), that accounted for climate change, population dynamics, and species’ life history traits to predict tree species’ migrations. We quantified the velocity of tree migration under different climate scenarios. We further investigated the effects of climate change and life history traits on tree species’ elevational migration. We found climate change accelerated the upward shifts at the optimum elevation and the leading edge, and limited the downward migration capacity of tree species at optimum elevation and the rear edge. The velocities of tree species’ elevational shifts (usually < 1.5 m/year) lagged behind those of climate change (about 25 m/year) under the climate change scenario. Range shifts at the leading edge, optimum elevation, and rear edge tended to be associated with temperature, precipitation, and thermal tolerance. However, species’ drought tolerance, shade tolerance, and seed dispersal ability had little effect on the velocity of simulated range shifts. Our results suggest that wide variation in tree range shift is likely driven by individual species’ life history traits in response to interacting environmental factors. This study underscores the importance of understanding the role of species’ life history traits when predicting future tree species’ distribution.

Diverse migration patterns and seasonal habitat use of Stone's sheep (Ovis dalli stonei).

We describe temporal and spatial patterns of seasonal space-use and migration by 16 GPS-collared Stone's sheep (Ovis dalli stonei) from nine bands in the Cassiar Mountains of northern British Columbia, Canada. Our objectives were to identify the timing of spring and fall migrations, characterize summer and winter ranges, map and describe migration routes and use of stopover sites, and document altitudinal change across seasons. Our last objective was to assess individual migration strategies based on patterns of geographic migration, altitudinal migration, or residency. Median start and end dates of the spring migration were 12 and 17 Jun (range: 20 May to 05 Aug), and of the fall migration were 30 Aug and 22 Sep (range: 21 Aug to 07 Jan). The median area of winter and summer ranges for geographic migrants were 630.8 ha and 2,829.0 ha, respectively, with a broad range from about 233.6 to 10,196.2 ha. Individuals showed high fidelity to winter ranges over the limited duration of the study. The winter and summer ranges of most individuals (n=15) were at moderate to high elevations with a median summer elevation of 1,709 m (1,563-1,827 m) and 1,673 m (1,478-1,751 m) that varied <150 m between ranges. Almost all collared females (n=14) exhibited changes in elevation use that coincide with abbreviated altitudinal migration. Specifically, these females descended to lower spring elevations from their winter range (Δ>150 m), and then gradually moved up to higher-elevation summer ranges (Δ>150 m). In the fall, they descended to lower elevations (Δ>100 m) before returning to their higher winter ranges. The median distance travelled along geographic migration routes was 16.3 km (range: 7.6-47.4 km). During the spring migration, most geographic migrants (n=8) used at least one stopover site (median = 1.5, range: 0-4), while almost all migrants (n=11) used stopover sites more frequently in the fall (median = 2.5, range: 0-6). Of the 13 migratory individuals that had at least one other collared individual in their band, most migrated at about the same time, occupied the same summer and winter ranges, used similar migration routes and stopover sites, and exhibited the same migration strategy. We found collared females exhibited four different migration strategies which mostly varied across bands. Migration strategies included long-distance geographic migrants (n=5), short-distance geographic migrants (n=5), vacillating migrants (n=2), and abbreviated altitudinal migrants (n=4). Different migratory strategies occurred within one band where one collared individual migrated and two did not. We conclude that female Stone's sheep in the Cassiar Mountains displayed a diverse assemblage of seasonal habitat use and migratory behaviors. By delineating seasonal ranges, migration routes and stopover sites, we identify potential areas of priority that can help inform land-use planning and preserve the native migrations of Stone's sheep in the region.

Role of dispersal in the altitudinal migration of Pinus hartwegii and Abies religiosa in mountain systems

Seed long-distance dispersal (LDD) is essential to explain plant migration. However, few studies have addressed the magnitude and frequency of LDD events given the difficulty of measuring them in situ. Computational simulation offers an alternative to the in situ methods. In this study we proposed a simulation model of seed dispersal for two anemochoric conifers, which includes wind patterns, seed and tree traits. We proposed and measured 18 dispersal traits for Abies religiosa and Pinus hartwegii and analyzed variation between traits and species through a principal component analysis. We used the Weather Research and Forecasting (WRF) atmospheric simulation model to obtain wind speed and direction data at the study zone (Iztaccihuatl volcano, central Mexico). We performed linear regression models to simulated seed dispersal events considering horizontal wind speed, seed traits and seed release height, and using a mechanistic model, we integrated vertical wind speed and wind direction. Seeds of both species presented similar morphology but were sorted into two groups. The relationship between wing size and seed weight may be a key element to dispersal, as it influences the interaction of the seed with the wind. Although we expected that P. hartwegii, seed traits and higher distribution would promote more and longer LDD events, A. religiosa presented more and longer LDD. The maximum dispersal distance was 105 m for A. religiosa and 64 m for P. hartwegii. Both species showed differences in dispersal capacity, which may be related to their seed traits. The frequency of LDD events indicates that a low proportion of seeds would travel more than 20 m away from the parent tree. This suggests that, under migration scenarios, new trees movement up would take place gradually.

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

To cope with life in the mountains, populations of the same species can exhibit substantial 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 information can be useful for conservation efforts in mountain ecosystems. Here, we used δ2H values of feathers and blood to evaluate latitudinal variation in altitudinal migration 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 associated with elevation. Notably, we found that fast-explorer birds inhabiting low elevations 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.

A population in perpetual motion: Highly dynamic roosting behavior of a tropical island endemic bat.

Although island endemic bats are a source of considerable conservation concerns, their biology remains poorly known. Here, we studied the phenology and roosting behavior of a tropical island endemic species: the Reunion free-tailed bat (Mormopterus francoismoutoui). This widespread and abundant species occupies various natural and anthropogenic environments such as caves and buildings. We set up fine-scale monitoring of 19 roosts over 27 months in Reunion Island and analyzed roost size and composition, sexual and age-associated segregation of individuals, as well as the reproductive phenology and body condition of individuals. Based on extensive data collected from 6721 individuals, we revealed a highly dynamic roosting behavior, with marked seasonal sex-ratio variation, linked to distinct patterns of sexual aggregation among roosts. Despite the widespread presence of pregnant females all over the island, parturition was localized in a few roosts, and flying juveniles dispersed rapidly toward all studied roosts. Our data also suggested a 7-month delay between mating and pregnancy, highlighting a likely long interruption of the reproductive cycle in this tropical bat. Altogether, our results suggest a complex social organization in the Reunion free-tailed bat, with important sex-specific seasonal and spatial movements, including the possibility of altitudinal migration. Bat tracking and genetic studies would provide additional insights into the behavioral strategies that shape the biology of this enigmatic bat species. The fine-scale spatiotemporal data revealed by our study will serve to the delineation of effective conservation plans, especially in the context of growing urbanization and agriculture expansion in Reunion Island.

Altitudinal migration behavior patterns of birds on the eastern slope of Mt. Gongga, China

Many bird species in montane regions exhibit altitudinal migration behavior; however, altitudinal migration of birds is still understudied, especially in Asia. Mt. Gongga (7556 ​m) is the highest peak of the Hengduan Mountains in Southwest China. The steep elevation gradient and the high bird diversity make the eastern slope of Mt. Gongga (Hailuo Valley) an ideal place for studying the altitudinal migration behavior patterns of birds. We synchronously recorded the local bird diversity, temperature and humidity at two sites (1800 and 3000 ​m a.s.l.) during three migration seasons from September 2020 to June 2021 to identify birds exhibiting altitudinal migration behavior. During our surveys, we recorded 146 bird species in total and 20 passerine bird species were altitudinal migrants according to our altitudinal migration formula. Among those 20 altitudinal migrant species, eight bird species displayed a typical altitudinal migration pattern (upward migration during the breeding season and downward migration during the non-breeding season). Moreover, temperature was correlated with the daily number of individuals (DNI) at each study site. Therefore, increasing temperatures possibly caused upward migration of birds (DNI decreased at 1800 ​m and increased at 3000 ​m) and vice versa. To further elaborate, the Rufous-gorgeted Flycatcher (Ficedula strophiata), the species with the most prominent altitudinal migration behavior, initiated upward migration at a temperature of 11–12 ​°C at 1800 ​m and initiated downward migration at a temperature of 12–13 ​°C at 3000 ​m. Besides, humidity was positively correlated with the DNI. Therefore, increasing humidity (equals to increasing rainfall or snow) possibly caused downward migration of birds (DNI increased) and vice versa. Furthermore, bird species exhibiting a typical altitudinal migration behavior pattern are feeding on insects. Thus, the spatial and temporal changes of the invertebrate biomass might be an important ecological driver for the altitudinal migration of invertivorous (birds eating invertebrates) birds. This study provides fundamental data for the altitudinal migration of birds in the Hengduan Mountains and shows how altitudinal migration is seasonally dynamic across an elevational gradient in a subtropical mountain region.

Seasonal altitudinal movements of birds in Brazil: a review

Birds’ seasonal altitudinal movements in Brazil are poorly understood. The main source of information and has fostered interest since the 1980s. However, most of the available information is anecdotal, sources are repeatedly cited, and the information provided is quite superficial and speculative. Through bibliographic searches, we found 107 studies, 83 (77%) of which we consider valid, and only 63 (59%) were peer-reviewed. Most studies were carried out in southern and southeastern Brazil. Only 11 studies explicitly addressed seasonal altitudinal movements. Surprisingly, none of the studies simultaneously comprised a full year of study, standardized sampling methods, and encompassed the entire altitudinal range through which the birds might have moved. As a consequence, the quality of the data is questionable, and the expression “altitudinal migration” is unlikely to be accurate and has never been unequivocally demonstrated for birds in Brazil. Mention of “altitudinal migration” was found for 68 bird species, but these must be more clearly defined and appropriately tested.

Altitudinal Migration of Species of Fir (Abies spp.) in Adaptation to Climate Change

Altitudinal Migration of Species of Fir (Abies spp.) in Adaptation to Climate Change

Behavioural thermoregulation by montane ungulates under climate warming

AbstractAimGlobal warming is threatening species survival worldwide. Cold‐adapted montane ungulates may be among the first species to be affected by global warming. Here, we investigate the behavioural thermoregulation hypothesis that montane ungulates buffer the effects of warming climate through behavioural adjustment.LocationFoping National Nature Reserve (FNNR) on the southern slopes of the Qinling Mountains, Shaanxi, China.MethodsWe used infrared camera traps over six consecutive years to monitor behavioural responses of montane ungulates to seasonal and diurnal changes in ambient temperature. We evaluated how seasonal altitudinal migration and changes to their daily activity budget may mitigate the effect of warming on montane ungulates.ResultsAll four montane ungulate species examined here preferred ambient temperatures &lt;22°C in summer. On this basis, we estimate that 27.9% (+2°C) and 46.7% (+3°C) of suitable summer habitats will become unsuitable under climate change. Chinese muntjac and tufted deer displayed behavioural changes to daily activity budgets, which may help them overcome global climate warming to a certain extent. By contrast, golden takin and wild boar did not display similar behavioural changes, and it may be because they are not affected by current shifts in climate due to larger body size and thus lower thermal stress.Main ConclusionsThese analyses demonstrate different species responses to warming are likely and are determined by specific tolerances to ambient temperature thresholds. However, it remains to be seen whether species interactions caused by behavioural shifts may affect species ability to respond to climate.

Partial altitudinal movement of Himalayan Bulbul Pycnonotus leucogenys in Himalayan Siwalik range

Himalayan Bulbul Pycnonotus leucogenys is widely spread in the Himalayan Siwalik range but information is available on its migratory behavioural patterns. Hence, a two-year study was undertaken to investigate its distribution range of the species in the summer and winter seasons in Punjab and Himachal Pradesh. A total of twenty variables including 19 bioclimatic variables and elevation were selected for the development of Species distribution Modelling (SDM). Occurrence records of P. leucogenys in summer and winter were processed at the Maximum entropy model (MaxEnt) using the ENMeval data package. The results suggested a downward movement from the upper Siwalik Himalayan ranges to the lower Siwalik in winter, and with return migration movement in summer. However, a large fraction of the distribution range was found overlapping in both the models, which suggests partial altitudinal migration of P. leucogenys. The data recorded on the ground subordinate the finding of the model. A wide range of tolerance for bioclimatic variables was observed in P. leucogenys, however temperature-related factors played a vital role in the variation in the species distribution range in the annual cycle of partial migration. The finding of this study would be a valuable reference for future studies on ecological and behavioral aspects of partial-migration of bird species in the Himalaya.

Turdus flavipes altitudinal migration in the Atlantic Forest The Yellow-legged Thrush is a partial altitudinal migrant in the Atlantic Forest

Few studies on bird migration address altitudinal migration in South America, a regional-scale movement currently known for only nine species within the threatened Atlantic Forest biome. The Yellow-legged Thrush Turdus flavipes (YLTH) is one of such migrants thus far studied within a narrow altitudinal gradient and for which only fruits are pointed as the likely triggers of its seasonal movements. Here, we expand this knowledge by testing the hypotheses that arthropod and fleshy fruit availabilities, and climatic variables may all play roles in the seasonal abundance of this species along a broader altitudinal gradient (10-1,100 m asl) in the Atlantic Forest. We estimated YLTH density and its food resource availability in sites at three different altitudes. Besides supporting previous findings on the YLTH migratory behaviour, our findings reveal a novel and complex seasonal density variation of the species across altitudes, consistent with a partial altitudinal migration from higher altitudes. Aside from fruit availability, rainfall also partially influenced such behaviour, a new perspective for this species. Besides providing a broader picture for the altitudinal migration of YLTHs, we conclude by stressing the need for further studies on the understudied altitudinal migration system of birds within South America, including the assessment of the general validity of current hypotheses on the mechanisms underlying this interesting behaviour and its evolution.

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

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.

Ecological traits affect the seasonal migration patterns of breeding birds along a subtropical altitudinal gradient

Altitudinal bird migration involves seasonal shifts up and down the altitude gradient annually. Asia as the place with the largest number of altitudinal migrants, has quite few related studies, especially for montane and temperate avifaunas. To explore the potential drivers of seasonal altitudinal migration for birds in the middle of Hengduan Mountains, we conducted a three-year investigation on breeding and non-breeding season bird communities at eight elevational bands (1200–4200 ​m) in the Gongga Mountains. We examined the altitudinal migration patterns and relationships between seasonal distribution shifts and species' traits of 50 species with sufficient data recorded in both seasons. We found that a large proportion of breeding birds underwent altitudinal migration and showed three migration patterns (downslope shift, upslope shift, no shift). Seasonal distribution shifts were mainly correlated with certain ecological traits. Species breeding at high and mid-elevations, nesting in scrub and being omnivorous are more likely to show downslope movements during the non-breeding season. In addition, territorially weaker species exhibited more diverse migration patterns. Notably, we found the hand-wing index (HWI) was actually more convincing than body mass in explaining altitudinal migration. These results consolidate the studies of seasonal altitudinal migration in montane birds. Our study could be used to bridge existing knowledge gaps that currently impeding effective conservation for montane avifaunas in the Hengduan Mountains.

Are recaptures of banded birds efficient at detecting altitudinal migrations in the Atlantic Forest?

Altitudinal migration in birds comprises seasonal movements between breeding and non-breeding areas in mountainous regions, attributed to biotic and abiotic factors. Different authors have suggested the existence of altitudinal migration between high and low areas of the mountains of the Atlantic Forest, with movement from high to low during the winter when birds would be fleeing the cold and in search of food, but there is no documented evidence. Through recaptures of understory birds, we investigated possible altitudinal migration in a region of the Atlantic Forest in Southeast Brazil. Twenty mist-nets were set at four locations between 15 and 729 m a.s.l. during 143 days of field work, distributed over 54 months and covering all seasons of the year. A total of 1946 birds (98 species) were captured/banded with 558 being recaptured (28.6%; 45 species). However, only 42 of the recaptures were at a different elevation. Most of the movements were of short distances and performed only once by birds, showing no seasonal pattern. These movements may be better interpreted as daily movements undertaken by birds of mixed-species flocks looking for food or moving around their respective home-ranges. Our results show that mist-nets may not be an effective tool in detecting altitudinal movements of birds and that other methods should be evaluated for this purpose.