Altitudinal migration by birds: a review of the literature and a comprehensive list of species

Altitudinal migration is the seasonal altitudinal movement of birds from breeding areas to non‐breeding or wintering areas at different elevations. Although this type of migration is widely reported, questions remain concerning the number of species that perform altitudinal migration, possible variation among different taxa and geographic locations in the extent of altitudinal migration, and the foraging guilds of altitudinal migrants. We conducted an extensive bibliographic survey and compiled a list of altitudinal migrant birds worldwide. We characterized species in terms of their foraging guilds because the spatial distribution of food resources along altitudinal gradients is often evoked as a driver of bird altitudinal migration. We identified 1238 species of altitudinal migrants, ~10% of the ~10,000 extant species of birds. We found a strong geographic bias in publications focusing on avian altitudinal migration toward the United States and Costa Rica, and a paucity of studies in megadiverse regions such as the Afrotropical and Indomalayan realms, and areas in the Neotropics other than Costa Rica. We also found that most species of altitudinal migrants were invertivores rather than frugivores or nectarivores. This general pattern held true for all zoogeographic realms except the Neotropics, where nectarivores and frugivores predominated among altitudinal migrants. The prevalence of invertivore birds among altitudinal migrants is not unexpected because this is the most common foraging guild among birds worldwide. Overall, we found no prevalence of any specific foraging guild among altitudinal migrants across zoogeographic regions. The results of studies to date suggest that altitudinal migration by birds may be driven by a number of factors, including access to increased food resources for breeding or molting, weather conditions, and mating and nesting opportunities. However, to better understand the mechanisms underlying altitudinal migration, broadening the geographic scope of studies is paramount, with additional study of altitudinal migration especially needed in the megadiverse tropical regions of sub‐Saharan Africa, Southeast Asia, and South America.     

Why migrate? A test of the evolutionary precursor hypothesis

The question of why birds migrate is still poorly understood despite decades of debate. Previous studies have suggested that use of edge habitats and a frugivorous diet are precursors to the evolution of migration in Neotropical birds. However, these studies did not explore other ecological correlates of migration and did not control for phylogeny at the species level. We tested the evolutionary precursor hypothesis by examining the extent to which habitat and diet are associated with migratory behavior, using a species-level comparative analysis of the Tyranni. We used both migratory distance and sedentary versus migratory behavior as response variables. We also examined the influences of foraging group size, membership in mixed-species flocks, elevational range, and body mass on migratory behavior. Raw species analyses corroborated some results from studies that put forth the evolutionary precursor hypothesis, but phylogenetically independent contrast analyses highlighted an important interaction between habitat and diet and their roles as precursors to migration. Foraging group size was consistently associated with migratory behavior in both raw species and independent contrast analyses. Our results lead to a resource variability hypothesis that refines the evolutionary precursor hypothesis and reconciles the results of several studies examining precursors to migration in birds.     

Evaluating the contribution of dispersal to community structure in Neotropical passerine birds

For two centuries evolutionary biologists have sought to explain elevated biodiversity in the Neotropics. Although different process are known to be important, it is still not uncommon for researchers to emphasize a single mechanism. Recently, arguments have highlighted the importance of dispersal shaping community structure and evolution across the region. We examine this hypothesis by visualizing spatial variation in community structure for the majority of South American passerines (Aves) across the northern half of South America. By sampling over a contiguous area we show how community structure varies widely across Amazonia and surrounding regions. Our results support a combination of processes including: the inability of species to disperse across geographic barriers, Andean uplift, and variation in habitat type. Although dispersal is a factor, our results emphasize a lack of dispersal, driven primarily by features of the landscape, coupled with historical changes in climate to be important drivers of Neotropical diversity.     

A comparative study of gut microbiomes in captive nocturnal strepsirrhines

Feeding strategy and diet are increasingly recognized for their roles in governing primate gut microbiome (GMB) composition. Whereas feeding strategy reflects evolutionary adaptations to a host's environment, diet is a more proximate measure of food intake. Host phylogeny, which is intertwined with feeding strategy, is an additional, and often confounding factor that shapes GMBs across host lineages. Nocturnal strepsirrhines are an intriguing and underutilized group in which to examine the links between these three factors and GMB composition. Here, we compare GMB composition in four species of captive, nocturnal strepsirrhines with varying feeding strategies and phylogenetic relationships, but nearly identical diets. We use 16S rRNA sequences to determine gut bacterial composition. Despite similar husbandry conditions, including diet, we find that GMB composition varies significantly across host species and is linked to host feeding strategy and phylogeny. The GMBs of the omnivorous and the frugivorous species were significantly more diverse than were those of the insectivorous and exudativorous species. Across all hosts, GMBs were enriched for bacterial taxa associated with the macronutrient resources linked to the host's respective feeding strategy. Ultimately, the reported variation in microbiome composition suggests that the impacts of captivity and concurrent diet do not overshadow patterns of feeding strategy and phylogeny. As our understanding of primate GMBs progresses, populations of captive primates can provide insight into the evolution of host‐microbe relationships, as well as inform future captive management protocols that enhance primate health and conservation.     

Evolutionary Divergence in Brain Size between Migratory and Resident Birds

Despite important recent progress in our understanding of brain evolution, controversy remains regarding the evolutionary forces that have driven its enormous diversification in size. Here, we report that in passerine birds, migratory species tend to have brains that are substantially smaller (relative to body size) than those of resident species, confirming and generalizing previous studies. Phylogenetic reconstructions based on Bayesian Markov chain methods suggest an evolutionary scenario in which some large brained tropical passerines that invaded more seasonal regions evolved migratory behavior and migration itself selected for smaller brain size. Selection for smaller brains in migratory birds may arise from the energetic and developmental costs associated with a highly mobile life cycle, a possibility that is supported by a path analysis. Nevertheless, an important fraction (over 68%) of the correlation between brain mass and migratory distance comes from a direct effect of migration on brain size, perhaps reflecting costs associated with cognitive functions that have become less necessary in migratory species. Overall, our results highlight the importance of retrospective analyses in identifying selective pressures that have shaped brain evolution, and indicate that when it comes to the brain, larger is not always better.     

Sociality,ecology and developmental constraints predict variation in brain size across birds

Conflicting theories have been proposed to explain variation in relative brain size across the animal kingdom. Ecological theories argue that the cognitive demands of seasonal or unpredictable environments have selected for increases in relative brain size, whereas the ‘social brain hypothesis’ argues that social complexity is the primary driver of brain size evolution. Here, we use a comparative approach to test the relative importance of ecology (diet, foraging niche and migration), sociality (social bond, cooperative breeding and territoriality) and developmental mode in shaping brain size across 1886 bird species. Across all birds, we find a highly significant effect of developmental mode and foraging niche on brain size, suggesting that developmental constraints and selection for complex motor skills whilst foraging generally imposes important selection on brain size in birds. We also find effects of social bonding and territoriality on brain size, but the direction of these effects do not support the social brain hypothesis. At the same time, we find extensive heterogeneity among major avian clades in the relative importance of different variables, implying that the significance of particular ecological and social factors for driving brain size evolution is often clade- and context-specific. Overall, our results reveal the important and complex ways in which ecological and social selection pressures and developmental constraints shape brain size evolution across birds.     

Dietary specialization and fruit availability among frugivorous birds on Sulawesi

Over 20 months I collected data on the diet composition and fruit availability for 23 frugivorous bird species (pigeons, parrots, hornbills and passerines) in two lowland rain forests on Sulawesi, Indonesia. Using these data I determined species dependency on fruit, diet composition, diet breadth and the availability of their fruit resources. Fruit dependency ranged from 44 to 100% of diets across the assemblage, with significant inter-order differences reflecting shared evolutionary history within orders. By contrast, diet breadths did not differ between bird orders owing to high within-order variability, possibly as a result of species-specific foraging strategies. Overall, no significant relationship existed between fruit dependency and diet breadth, which indicated that they are not interchangeable measures of dietary specialization, but that each provided important information on dietary specialization, and enabled assessment of resource requirements and availability. The assemblage consumed the fruits of 120 species representing 40 plant families. Figs ( Ficus spp.) were of great importance across the assemblage and comprised 57% of all fruit-eating records. For hornbills, passerines and pigeons, figs accounted for substantial proportions of monthly feeding records (= 58%) and were consumed whatever the availability of other fruits. Figs were therefore a fundamental part of species' diets, possibly every month, and not merely important during times of relative scarcity of other fruit. Conservation of fig trees both inside and outside protected areas is likely to be important in maintaining healthy populations of figs and the frugivorous birds that depend on them.     

Geographic locale and relative dominance patterns among North American passerine communities

Numerous studies have addressed variation in the local occurrence and abundance of species, but only recently have investigators begun considering the influence of spatial context on community structure. We examined the influence of geographic position within a species’ range on its dominance (relative abundance) within the community. Our three primary questions were: 1) Does dominance within a community vary across a species’ range? 2) Do dominance‐location trends differ between widely and narrowly distributed species? and 3) Does dominance within a guild vary across a species range? We examined 40 passerine species (20 widely distributed, 20 narrowly distributed) and their communities using North American Breeding Bird Survey data, of which, a subset of 11 species belonging to a single foraging guild were used for addressing guild effects. Data were gathered from communities at the center (10 locations) and periphery (10 locations) of each species’ range. Focal species were significantly less dominant at locations on the periphery of their ranges compared to central locations, and did not differ between widely and narrowly distributed species. In examining factors influencing these patterns, it was found that narrowly distributed species occur in communities of fewer individuals and fewer species compared to widely distributed species irrespective of locale. Within the foraging guild, dominance was also lower at the periphery than at the center of focal species’ ranges. However, guild abundance was also lower at the periphery of ranges while guild richness did not vary with locale. Specifically, focal species abundance decreased at a greater rate than abundance of other members of the foraging guild. Contrary to overall community data, widely distributed species were more dominant members of their guild at the center of their ranges. No significant patterns were found between distribution and guild dominance at the periphery of ranges.     

Responses to chemical cues from animal and plant foods by actively foraging insectivorous and omnivorous scincine lizards

If tongue-flicking is important to lizards to sample chemical cues permitting identification of foods, tongue-flicking and subsequent feeding responses should be adjusted to match diet. This hypothesis can be examined for plant foods because most lizards are insectivores, but herbivory/omnivory has evolved independently in many lizard taxa. Here we present experimental data on chemosensory responses to chemical cues from animal prey and palatable plants by three species of the scincine lizards. When tested with chemical stimuli presented on cotton swabs, the insectivorous Eumeces fasciatus responded strongly to prey chemicals but not to chemicals from plants palatable to omnivorous lizards or to pungent or odorless control stimuli. Two omnivorous species, E. schneideri and Scincus mitranus, responded more strongly to chemical cues from both prey and food plants than to the control chemicals. All available data for actively foraging lizards, including these skinks, show that they are capable of prey chemical discrimination, and insectivores do not exhibit elevated tongue-flicking or biting responses to chemical cues from palatable plants. In all of the several species of herbivores/omnivores tested, the lizards show elevated responses to both animal and plant chemicals. We suggest two independent origins of both omnivory and plant chemical discrimination that may account for the evolution of diet and food chemical discriminations in the eight species of skinks studied, five of which are omnivores. All data are consistent with the hypothesis that acquisition of omnivory is accompanied by acquisition of plant chemical discrimination, but data on a broad diversity of taxa are needed for a definitive comparative test of the evolutionary hypothesis. J. Exp. Zool. 287:327-339, 2000.     

Long-distance migrating species of birds travel in larger groups

How individuals migrate over long distances is an enduring mystery of animal migration. Strong selection pressure for travelling in groups has been suggested in long-distance migrating species. Travelling in groups can reduce the energetic demands of long migration, increase navigational accuracy and favour group foraging at migratory halts. Nevertheless, this hypothesis has received scant attention. I examined evolutionary transitions in migration distance in all North American breeding species of birds. I documented 72 evolutionary shifts in migration distance in the pool of 409 species. In contrasting clades, long-distance migration, as opposed to short-distance migration, was associated with a larger travelling group size. No other transitions occurred alongside in other traits such as group size in the non-breeding season or body mass. The results suggest that larger group sizes have been beneficial in the evolution of long-distance migration in a large clade of birds.     

Behavioural environments and niche construction: the evolution of dim-light foraging in bees

Most bees forage for floral resources during the day, but temporal patterns of foraging activity vary extensively, and foraging in dim-light environments has evolved repeatedly. Facultative dim-light foraging behaviour is known in five of nine families of bees, while obligate behaviour is known in four families and evolved independently at least 19 times. The light intensity under which bees forage varies by a factor of 10⁸, and therefore the evolution of dim-light foraging represents the invasion of a new, extreme niche. The repeated evolution of dim-light foraging behaviour in bees allows tests of the hypothesis that behaviour acts as an evolutionary pacemaker. With the exception of one species of Apis , facultative dim-light foragers show no external structural traits that are thought to enable visually mediated flight behaviour in low-light environments. By contrast, most obligate dim-light foragers show a suite of convergent optical traits such as enlarged ocelli and compound eyes. In one intensively studied species ( Megalopta genalis ) these optical changes are associated with neurobiological changes to enhance photon capture. The available ecological evidence suggests that an escape from competition for pollen and nectar resources and avoidance of natural enemies are driving factors in the evolution of obligate dim-light foraging.     

Brain size, innovative propensity and migratory behaviour in temperate Palaearctic birds

The evolution of migration in birds remains an outstanding, unresolved question in evolutionary ecology. A particularly intriguing question is why individuals in some species have been selected to migrate, whereas in other species they have been selected to be sedentary. In this paper, we suggest that this diverging selection might partially result from differences among species in the behavioural flexibility of their responses to seasonal changes in the environment. This hypothesis is supported in a comparative analysis of Palaearctic passerines. First, resident species tend to rely more on innovative feeding behaviours in winter, when food is harder to find, than in other seasons. Second, species with larger brains, relative to their body size, and a higher propensity for innovative behaviours tend to be resident, while less flexible species tend to be migratory. Residence also appears to be less likely in species that occur in more northerly regions, exploit temporally available food sources, inhabit non-buffered habitats and have smaller bodies. Yet, the role of behavioural flexibility as a response to seasonal environments is largely independent of these other factors. Therefore, species with greater foraging flexibility seem to be able to cope with seasonal environments better, while less flexible species are forced to become migratory.     

城市公园植被特征对陆生鸟类集团的影响

城市公共绿地是城市生态系统中重要的鸟类栖息地,其植被特征对鸟类集团存在显著影响。在通过分析植被特征对陆生鸟类集团的作用,从而为公园合理配置植被来提高其作为野生动物栖息地的生态服务功能提供理论基础。2009年10月至2011年10月,采用样线法对上海滨江森林公园进行鸟类调查,利用主成分分析划分鸟类集团,用高度定义植被层次,用卡方检验分析鸟类行为在植被层次上的差异。结果表明,滨江森林公园陆生鸟类群落在乔木层的栖息行为和运动行为频次显著多于其在灌木层和地被层的行为频次,在地被层的取食行为频次显著多于其在乔木层和灌木层的行为频次。陆生鸟类可划分为8个鸟类集团,鸟类集团之间存在栖息、运动和取食空间生态位的重叠。食虫拾取集团、杂食拾取集团、食肉飞取集团和植食拾取集团在栖息、运动和取食空间生态位上均存在较高的重叠度,其通过食性分离各自空间生态位。食虫探取集团和食虫飞取集团互为栖息空间生态位重叠度最高集团,其通过取食方式的不同来实现生态位的分离。根据公园植被特征对鸟类集团的影响结果对上海市公园绿地植被配置提出了建议。     

Sexual selection accelerates signal evolution during speciation in birds

Sexual selection is proposed to be an important driver of diversification in animal systems, yet previous tests of this hypothesis have produced mixed results and the mechanisms involved remain unclear. Here, we use a novel phylogenetic approach to assess the influence of sexual selection on patterns of evolutionary change during 84 recent speciation events across 23 passerine bird families. We show that elevated levels of sexual selection are associated with more rapid phenotypic divergence between related lineages, and that this effect is restricted to male plumage traits proposed to function in mate choice and species recognition. Conversely, we found no evidence that sexual selection promoted divergence in female plumage traits, or in male traits related to foraging and locomotion. These results provide strong evidence that female choice and male–male competition are dominant mechanisms driving divergence during speciation in birds, potentially linking sexual selection to the accelerated evolution of pre-mating reproductive isolation.     

Global gradients of avian longevity support the classic evolutionary theory of ageing

Senescence, the process of physiological deterioration associated with growing old, is a shared characteristic of a wide range of animals. Yet, lifespan varies dramatically among species. To explain this variation, the evolutionary theory of ageing has been proposed more than 50 yr ago. Although the theory has been tested experimentally and through comparative analyses, there remains debate whether its fundamental prediction is empirically supported. Here, we use a comprehensive database on avian life history traits to test the evolutionary theory of ageing at a global scale. We show that pronounced geographical gradients of maximum longevity exist, that they are predicted by measures of predator diversity and only partly depend on correlated life‐history traits. The results are consistent with species‐level analyses and can be replicated across bio‐geographical regions. Our analyses suggest that stochastic predation is an important driver of the evolution of lifespan, at least in birds.     

Assessing species traits and landscape relationships of the mammalian carnivore community in a neotropical biological corridor

Mammalian carnivores play an important role in regulating food webs and ecosystems. While many carnivore populations are facing various threats such as habitat loss and fragmentation, poaching, and illegal trade, others have adapted to human-dominated landscapes. Information about Neotropical carnivore communities in particular is limited, especially in disturbed landscapes. We conducted a camera trap survey at 38 sites across the San Juan–La Selva Biological Corridor in Costa Rica to assess occupancy and detection probabilities of the carnivore community. We developed hypotheses within a likelihood-based framework in order to determine the landscape features and species traits (diet and size) that influenced their occupancy. We detected nine of the 13 native carnivores predicted to occur in the corridor. When modeled separately, each species responded to land cover changes differently, suggesting no strong community-wide predictors of occupancy. We then modeled three separate guilds within the carnivore community: omnivorous mesopredators, obligate carnivorous mesopredators, and apex predators. These community guild models revealed a negative relationship between omnivorous mesopredators and increasing forest and tree plantation cover, suggesting omnivores utilize forest fragments and edge habitats in agricultural landscapes. Obligate carnivorous mesopredator models did not reveal any strong habitat relationships, but landscape effects tended to contradict our a priori predictions. Apex predators were positively associated with increasing forest and tree plantation cover, protected areas, and increasing distances to villages. Alarmingly, apex predators and obligate carnivorous mesopredators were generally rare within the biological corridor. A lack of top-down control alone might result in heightened occupancy for all mesopredators, but because the community is dominated by omnivorous species, bottom-up release from human-induced land cover changes and resource provision may better explain their high occupancy.     

Dispersal limitation: Evolutionary origins and consequences in arthropods

Niche and dispersal ability are key traits for explaining the geographical structuring of species into discrete populations, and its evolutionary significance. Beyond their individual effects, the interplay between species niche and its geographic limits, together with the evolutionary lability of dispersal ability, can underpin trait diversification and speciation when exposed to gradients of selection. In this issue of Molecular Ecology, two complementary papers demonstrate how evolutionary lability for dispersal ability linked to niche shift can drive such a model in a context that includes selection. Both papers investigate the evolution of dispersal limitation in arthropods across altitudinal gradients, but using taxa with contrasting ecologies. McCulloch et al. (2019) investigate the evolution of wing loss at higher altitudes in stoneflies, a taxon inhabiting freshwater systems. Suzuki et al. (2019) report a similar phenomenon, but involving wing reduction at higher altitudes in scorpionflies, a taxon associated with moist terrestrial habitats. Here, we compare and contrast the results of both studies to explore their broader implications for understanding diversification and speciation within arthropods.     

Seasonal dynamics of guild structure in a bird assemblage of the central Monte desert

Most studies of ecological guilds consider guild membership as a fixed attribute of species, and the guild structure as a fixed attribute of a community. Consequently, almost no study tackled the examination of temporal changes in the guild structure of a particular assemblage. We used data on foraging patterns of central Monte desert birds to assess seasonal differences in resource use by resident species, and to examine seasonal changes in the guild structure of the assemblage. From 1993 until 1999, we quantified the use of foraging substrates, manoeuvres, and height strata, and the utilisation of plants by 18 bird species. Resident species showed different kinds of seasonal dynamics, from no noticeable to drastic changes in their foraging patterns. Seasonal changes in guild structure were remarkable. Only two guilds were present all year round (ground foragers and foliage foragers), although they suffered important species turnover. Three other guilds had a seasonal occurrence: graminivores (during the non-breeding season), arboreal herbivores, and aerial feeders (during the breeding season). Two species changed from one guild to another between seasons. Both presence–absence of migrant species, and changes in the feeding ecology of resident species had an influence on the temporal dynamics of guild structure. These factors appeared to be related with changing resource availability, especially with the birds’ ability for facing lean conditions through migration and with the opportunistic use of seasonally superabundant resources. Our results undermine the trust in studies in which guild structure was assessed irrespective of temporal variations. We show also that guild membership is not a fixed attribute of a species: we should rather evaluate the individuals’ resource use in a given moment to assign them to a guild, instead of obtaining a single measure purporting to represent a species’ fixed attribute.     

云南哀牢山徐家坝常绿阔叶林的鸟类取食集团

2006年3-4月,采用无距离估计样线法对云南哀牢山徐家坝中山湿性常绿阔叶林中的鸟类群落做了直接观察,观察到鸟类取食行为14 345次只.运片j聚类分析,依据鸟类的栖息取食行为格局将62种鸟划分为11个取食集团:(G1)地面拾取集团、(G2)地面扒取集团、(G3)树冠层飞取/拾取集团、(G4)树冠层飞取集团、(G5)树干层探取集团、(G6)灌层竹秆探取集团、(G7)树干粗枝搜寻集团、(G8)树冠层粗枝搜寻集团、(G9)树冠层拾取集团、(G10)灌丛下层叶层/树干/地面拾取集团、(G11)灌层拾取集团.结果表明,由于各个集团在栖息基层、取食基层及取食方式上的分离,使各集团分割了该地区的取食空间和食物资源;而集团内部的各个种间主要通过对取食高度的划分,使得集团内部的取食空『白j和食物资源得到了更深层次的利用,使种间竞争减至最小.其结果还表明,鸟类取食集团的数量和结构因不同的植被类型而异,顶级群落中包含的鸟类种类更多,各个种间的生态位分化也更为细致.     

The Evolution of Olfactory Capabilities in Wild Birds: A Comparative Study

Modern birds possess an olfactory apparatus similar to that of other vertebrates, yet the major evolutionary forces that drove the evolution of diversity in olfactory capabilities in birds remain elusive. Several non-mutually exclusive evolutionary scenarios for the evolution of olfactory capability in birds have been proposed. Olfactory capability may have evolved due to its role in recognition in social contexts. In addition, olfactory capability may have evolved because it provides a selective advantage in foraging or navigation. Finally, olfactory capability could be favored whenever the ecological conditions of species hindered the use of other senses and/or favored olfaction. Here we evaluate predictions from these hypotheses in a comparative study using a species-level phylogeny of 142 bird species and considering the indirect effects of some predictors on others. We find an interactive effect of aquatic dependence and diet on the size of the olfactory bulb: vegetarian and omnivore birds living in aquatic environments have larger olfactory bulbs than terrestrial birds, whereas species with an animal diet, aquatic and terrestrial species have similar-sized olfactory bulbs. In addition, the size of the olfactory bulb was weakly related with social complexity, with colonial species having relatively larger olfactory bulb than solitary breeders or those forming small aggregations. Our results suggest that the role of foraging in driving enhancements in the avian olfactory apparatus is contingent on ecological conditions that may affect the transmission of odor-based signals. This provides evidence for the largely neglected possibility that the evolution of the olfactory apparatus of birds has been driven by the interaction between ecological and behavioral traits, rather than being solely due to main effects of these traits.