Diet and Geophagy Across a Western Amazonian Parrot Assemblage

We identified species‐ and community‐level dietary characteristics for a species‐rich Amazonian parrot assemblage to determine relationships among dietary metrics and use of geophagy sites. Previous studies suggest that soil is consumed at geophagy sites in this region mainly to supplement dietary sodium. We accumulated 1400 feeding records for 16 parrot species over 2 yr and found that seeds, flowers, and fruit pulp featured prominently in diets, while bark, insects, and lichen were consumed in small quantities. Food availability across 1819 trees was measured, and we found that flower availability was highest in the dry season and fruit production peaked in the wet season, but that phenology patterns of the 20 most commonly foraged plant species suggest no serious food bottlenecks. Partitioning of available food resources among the 13 most commonly encountered parrots is suggested by an ordination analysis (DCA), which placed the large macaws (Ara) with the Amazona parrots at the ‘primary forest’ end of a dietary resource axis and four smaller species at the ‘successional forest’ end of the axis. Parrot species associated with successional forest also consumed less plant species overall. Furthermore, these parrot species consuming successional forest resources had higher claylick visitation rates than those consuming primary forest resources suggesting they derive the greatest benefits from soil consumption.     

Seasonality of reproduction of wild black-and-white snub-nosed monkeys (Rhinopithecus bieti) at Mt. Lasha, Yunnan, China

Black-and-white snub-nosed monkeys (Rhinopithecus bieti) inhabit one of the harshest habitats by any nonhuman primate. Reliable predictive cues to initiate reproduction may be particularly critical for R. bieti because they inhabit such seasonally energetically challenging environments. To better understand the seasonal distribution of and predictive cues to reproduction, we collected breeding and birth data in a population of R. bieti at Mt. Lasha in Yunling Nature Reserve, Yunnan, China, from January 2008 to May 2010, using a combination of 10-min instantaneous scans and ad libitum observations. We examined variations in temperature, rainfall, and food availability, as well as photoperiod differences between Mt. Lasha and the more northerly Xiaochangdu to identify environmental influences on the timing of reproductive events. Our data show the area exhibited distinct seasonal fluctuations in rainfall, temperature, and food availability. Mating occurred year-round, but peaked in August, coinciding with the end of the period of highest temperatures and food availability, and during the peak rainfall. Copulation frequency peaked 1 month after corresponding peaks in staple foods, rainfall, and minimum temperatures, and 3-4 months after peaks in high-quality foods. Births were significantly seasonal, with a birth peak from mid-February to early April, and a mean birth date of 14 March. Eleven births occurred in 41 days in 2009, and 16 births occurred in 52 days in 2010. Births occurred during periods of increasing temperatures and food availability. Our findings are suggestive of at least one environmental control of conception timing, and support the notion that food availability during key reproductive stages is an ultimate factor for birth seasonality, but provide no supporting evidence for photoperiod during the conception season as a proximate cue to reproduction in R. bieti.     

Benefits of extra food to reproduction depend on maternal condition

The amount of food resources available to upper‐level consumers can show marked variations in time and space, potentially resulting in food limitation. The availability of food resources during reproduction is a key factor modulating variation in reproductive success and life‐history tradeoffs, including patterns of resource allocation to reproduction versus self‐maintenance, ultimately impacting on population dynamics. Food provisioning experiments constitute a popular approach to assess the importance of food limitation for vertebrate reproduction. In this study of a mesopredatory avian species, the lesser kestrel Falco naumanni, we provided extra food to breeding individuals from egg laying to early nestling rearing. Extra food did not significantly affect adult body condition or oxidative status. However, it increased the allocation of resources to flight feathers moult and induced females to lay heavier eggs. Concomitantly, it alleviated the costs of laying heavier eggs for females in poor body condition, and reduced their chances of nest desertion (implying complete reproductive failure). Extra food provisioning improved early nestling growth (body mass and feather development). Moreover, extra food significantly reduced the negative effects of ectoparasites on nestling body mass, while fostering forearm (a flight apparatus trait) growth among highly parasitized nestlings. Our results indicate that lesser kestrels invested the extra food mainly to improve current reproduction, suggesting that population growth in this species can be limited by food availability during the breeding season. In addition, extra food provisioning reduced the costs of the moult–breeding overlap and affected early growth tradeoffs by mitigating detrimental ectoparasite effects on growth and enhancing development of the flight apparatus with high levels of parasitism. Importantly, our findings suggest that maternal condition is a major trait modulating the benefits of extra food to reproduction, whereby such benefits mostly accrue to low‐quality females with poor body condition.     

At the crossroads of physiology and ecology: Food supply and the timing of avian reproduction

The decision of when to breed is crucial to the reproductive success and fitness of seasonally breeding birds. The availability of food for adults prior to breeding has long been thought to play a critical role in timing the initiation of seasonal reproductive events, in particular laying. However, unequivocal evidence for such a role remains limited and the physiological mechanisms by which an increase in food availability results in seasonal activation of the reproductive system are largely speculative. This lack of mechanistic information partly reflects a lack of integration of ecological and physiological approaches to study seasonal reproduction. Indeed, most work pertaining to the role of food availability for adults on the timing of avian reproduction has been ecological and has focused almost exclusively on female traits associated with reproductive timing (e.g., lay date and clutch size). By contrast, most work on the physiological bases of the relationship between food availability and the timing of reproduction has investigated male traits associated with reproductive development (e.g., reproductive hormones and gonadal development). To advance our understanding of these topics, we review the role of proximate factors including food availability, social factors, and ambient temperature in the control of breeding decisions, and discuss the role of three potential candidates (leptin, glucocorticoids, and GnIH–neuropeptide Y) that may mediate the effects of food availability on these decisions. We emphasize that future progress in this area is heavily contingent upon the use of physiology-based approaches and their integration into current ecological frameworks.     

Fruit availability, chimpanzee diet, and grouping patterns on Rubondo Island, Tanzania

We examined seasonal patterns of fruit availability, dietary quality, and group size in the descendants of an introduced chimpanzee population on Rubondo Island, Tanzania. The site has supported a free-ranging population without provisioning for 40 years. Our goals were to determine whether Rubondo chimpanzees experience periods of fruit shortage, and whether they respond to changes in fruit availability similarly to chimpanzees at endemic sites. We indexed the fruit availability of tree and liana species on transects stratified across three chimpanzee ranging areas. We used fecal analyses to evaluate seasonal changes in diet, and used data on party size and nesting group size to examine seasonal patterns of grouping. Tree fruit availability was positively correlated with rainfall, with a period of relative tree fruit scarcity corresponding with the long dry season. Liana fruit availability was not related to rainfall, and lianas exhibited less variable fruiting patterns across seasons. Fruits made up the majority of the chimpanzee diet, with lianas accounting for 35% of dietary fruit species. Fruits of the liana Saba comorensis were available during all months of phenological monitoring, but they were consumed more when tree fruit was scarce, suggesting that Saba comorensis fruits may be a fallback food for Rubondo chimpanzees. There were no increases in consumption of lower-quality plant parts between seasons, and there were no changes in group size between seasons. These results contrast with evidence from several endemic chimpanzee study sites, and indicate that Rubondo chimpanzees may have access to abundant and high-quality foods year round.     

Influence of environmental variability on the growth of Lilac-crowned Parrot nestlings

Growth rate parameters were analysed for Lilac-crowned Parrot Amazona finschi nestlings in the tropical dry forest of the Reserva de la Biosfera Chamela-Cuixmala, Mexico. Growth rates for psittacine species follow the inverse relation with body mass observed for neotropical landbirds, with larger parrot species exhibiting slower growth rates. There was significant variation between years in size and growth rates of Lilac-crowned Parrot nestlings with nestlings exhibiting slower growth rates in 1996 than in 1997. Food abundance for parrots also varied significantly between years, with greater food availability during the 1997 breeding season than that of 1996. The increased size and growth rates of nestlings in 1997 may have reflected this, and suggests the potential influence of environmental variability on parrot reproduction, particularly in such a markedly seasonal habitat.     

SOME ASPECTS OF THE BEHAVIOUR OF THE WATTLED PLOVER AFRIBYX SENEGALLUS (LINNAEUS)

The question of how aridity might influence avian clutch size, through the influences of rainfall seasonality and environmental stochasticity (unpredictability), has received little attention. A marked east-west gradient in aridity across South Africa provides a unique opportunity to test for such influences. Using an extensive collection of nest records for 106 terrestrial bird species from the South African Nest Record Card Scheme, we tested three predictions related to rainfall seasonality and stochasticity. Analyses were conducted at two levels, the first examining each species independently, and the second grouping species into five dietary guilds. The first prediction, that clutch size should generally increase with higher rainfall seasonality (i.e. higher seasonal fluctuation of food availability), was supported, particularly in the most arid environments where food abundance is more closely linked to rainfall. Controlling for rainfall seasonality, the second prediction, that clutch size should generally decrease as a bet-hedging strategy in arid, stochastic environments, was also supported. Although the timing of the rainy season differs among regions in South Africa (winter, early summer, later summer, year-round), birds primarily nest during spring. The relative timing of rainfall and breeding is expected to have different consequences for seasonal variation in clutch size among rainfall regions. The third prediction, of different patterns of seasonal variation in clutch size between rainfall regions, was also supported. In the winter and early-summer rainfall regions, early-nesting birds (breeding with or soon after the rains) generally had a larger clutch size than late-nesting birds. In the late-summer rainfall region, early-nesting birds (breeding well before the rains) had a smaller clutch size than late-nesting birds.     

Responses of Javan Gibbon (Hylobates moloch) Groups in Submontane Forest to Monthly Variation in Food Availability: Evidence for Variation on a Fine Spatial Scale

Primates tend to prefer specific plant foods, and primate home ranges may contain only a subset of food species present in an area. Thus, primate feeding strategies should be sensitive to the phenology of specific species encountered within the home range in addition to responding to larger scale phenomena such as seasonal changes in rainfall or temperature. We studied three groups of Javan gibbons (Hylobates moloch) in the Gunung Halimun‐Salak National Park, Indonesia from April 2008 to March 2009 and used general linear mixed models (GLMM) and a model selection procedure to investigate the effects of variation in fruit and flower availability on gibbon behavior. Preferred foods were defined as foods that are overselected relative to their abundance, while important food species were those that comprised >5% of feeding time. All important species were also preferred. Season and measurements of flower and fruit availability affected fruit‐feeding time, daily path lengths (DPL), and dietary breadth. Models that included the availability of preferred foods as independent variables generally showed better explanatory power than models that used overall fruit or flower availability. For one group, fruit and preferred fruit abundance had the strongest effects on diets and DPL in the models selected, while another group was more responsive to changes in flower availability. Temporal variation in plant part consumption was not correlated in neighboring groups. Our results suggest that fine‐scale local factors are important determinants of gibbon foraging strategies. Am. J. Primatol. 74:1154‐1167, 2012. © 2012 Wiley Periodicals, Inc.     

The effects of tourist and boat traffic on parrot geophagy in lowland Peru

Ecotourism generates important revenue in many developing economies, but poorly regulated ecotourism can threaten the long‐term viability of key biological resources. We determined the effects of tourism, boat traffic, and natural disturbances on parrot geophagy (soil consumption) across seven riverine claylicks in the lowlands of Madre de Dios, Peru. Claylick use significantly decreased when visitors did not follow good practice guidelines and tourist numbers exceeded the capacity of the observation blinds. Otherwise, tourist presence and natural disturbance did not have a significant effect. However, large macaws, particularly Red‐and‐green Macaws (Ara chloropterus), avoided visiting claylicks during periods of peak tourist numbers. Where parrots had multiple geophagy sites to choose from, they preferred sites further from tourist groups. The effect of boat disturbance was greatest on a narrow river with infrequent boat events. On a wider river with heavier traffic, boat disturbance had less of an effect and this effect was inversely proportional to the distance of boats from the claylick. Where visitors followed good‐practice tourism guidelines, they had a low overall negative effect on parrot geophagy. We recommend that visitors respect the claylick observation guidelines to minimize anthropogenic disturbance on parrots and maintain these sites for the benefit of wildlife and humans alike.     

Breeding Phenology of Birds: Mechanisms Underlying Seasonal Declines in the Risk of Nest Predation

Seasonal declines in avian clutch size are well documented, but seasonal variation in other reproductive parameters has received less attention. For example, the probability of complete brood mortality typically explains much of the variation in reproductive success and often varies seasonally, but we know little about the underlying cause of that variation. This oversight is surprising given that nest predation influences many other life-history traits and varies throughout the breeding season in many songbirds. To determine the underlying causes of observed seasonal decreases in risk of nest predation, we modeled nest predation of Dusky Flycatchers (Empidonax oberholseri) in northern California as a function of foliage phenology, energetic demand, developmental stage, conspecific nest density, food availability for nest predators, and nest predator abundance. Seasonal variation in the risk of nest predation was not associated with seasonal changes in energetic demand, conspecific nest density, or predator abundance. Instead, seasonal variation in the risk of nest predation was associated with foliage density (early, but not late, in the breeding season) and seasonal changes in food available to nest predators. Supplemental food provided to nest predators resulted in a numerical response by nest predators, increasing the risk of nest predation at nests that were near supplemental feeders. Our results suggest that seasonal changes in foliage density and factors associated with changes in food availability for nest predators are important drivers of temporal patterns in risk of avian nest predation.     

黄山短尾猴食土行为

从行为生态学角度,依据黄山短尾猴食土行为在年龄、性别、社会等级序位、食土量、食土频率、食土持续时间中的分布和变化规律,结合土壤基本理化性质测定和分析,探讨了黄山短尾猴食土行为。黄山短尾猴对土壤的摄取是寻找和有目的的选择,有些场所是其"喜好"或"常去之处",食土场所通常是以多个体多次取食挖掘而形成的洞穴形式存在。取食土壤颜色黄色或黄棕色,酸性土壤,富含铁、钙、镁等矿物元素,粘土比例较高。社群各年龄段及性别个体均参与食土行为。平均食土行为持续时间在年龄和性别之间无显著差异;平均食土频率和食土量在成年雌性或雄性个体的社会等级序位之间无显著性差异;而成年雌性的平均食土频率和食土量,显著高于其它年龄或性别组,与雌性正值怀孕末期及产仔哺乳期,需要补充大量铁等矿物元素,以维持生理所需和体力消耗有关。典型的植食性动物黄山短尾猴有规律地取食粘土的行为,支持了食土行为具有"食物解毒作用"假说。人工投喂和食土行为的相关性表现为提高了食土频率,可能与粘土能够缓解高热量、低纤维人工食物造成的胃肠不适有关。     

Nest predation,food, and female age explain seasonal declines in clutch size

The selection pressures responsible for intra- and interspecific variation in avian clutch size have been debated for over half a century. Seasonal declines in clutch size represent one of the most robust patterns in avian systems, yet despite extensive research on the subject, the mechanisms underlying this pattern remain largely unknown. We tested a combination of experimental and observational predictions to evaluate ten hypotheses, representing both evolutionary and proximate mechanisms proposed to explain seasonal declines in avian clutch size. In line with long held life-history theory, we found strong support for both an evolved and proximate response to food availability for young. We also found evidence consistent with predictions that proximate level experiential nest predation influences seasonal declines in clutch size. Finally, older females appear to invest more in reproduction (initiate nests earlier and lay larger clutches) and choose better territories than younger females. Our results highlight the importance of examining multiple hypotheses in a theoretical context to elucidate the ecological processes underlying commonly observed patterns in life history.     

Seasonal patterns in reproductive success of temperate‐breeding birds: Experimental tests of the date and quality hypotheses

For organisms in seasonal environments, individuals that breed earlier in the season regularly attain higher fitness than their late‐breeding counterparts. Two primary hypotheses have been proposed to explain these patterns: The quality hypothesis contends that early breeders are of better phenotypic quality or breed on higher quality territories, whereas the date hypothesis predicts that seasonally declining reproductive success is a response to a seasonal deterioration in environmental quality. In birds, food availability is thought to drive deteriorating environmental conditions, but few experimental studies have demonstrated its importance while also controlling for parental quality. We tested predictions of the date hypothesis in tree swallows (Tachycineta bicolor) over two breeding seasons and in two locations within their breeding range in Canada. Nests were paired by clutch initiation date to control for parental quality, and we delayed the hatching date of one nest within each pair. Subsequently, brood sizes were manipulated to mimic changes in per capita food abundance, and we examined the effects of manipulations, as well as indices of environmental and parental quality, on nestling quality, fledging success, and return rates. Reduced reproductive success of late‐breeding individuals was causally related to a seasonal decline in environmental quality. Declining insect biomass and enlarged brood sizes resulted in nestlings that were lighter, in poorer body condition, structurally smaller, had shorter and slower growing flight feathers and were less likely to survive to fledge. Our results provide evidence for the importance of food resources in mediating seasonal declines in offspring quality and survival.     

Breeding cues in a wetland‐dependent Australian passerine of the seasonally wet‐dry tropics

The Capricorn yellow chat Epthianura crocea macgregori (Aves: Meliphagidae) occurs in the seasonal wet‐dry tropics. This region, although coastal, is typified by highly variable annual rainfall. The Capricorn yellow chat breeds in wetlands, predominantly in the summer–autumn period, but has the capacity to breed in response to out‐of‐season rainfall events, consistent with an opportunistically breeding species. Most studies of breeding cues in passerines have been on species centred on temperate climates with predictable rainfall season, arid biomes with a highly variable rainfall quantity and season, and the relatively non‐seasonal wet tropics. This study was focused on a species that occurs in an intermediate situation with a highly variable but summer dominant rainfall season. It aimed to identify which proximal cues are used by birds in such environments to prepare for breeding. Monthly observations at a breeding ground over a 45‐month period were regressed against environmental and climatic variables. There was a significant positive relationship of chat abundance with average minimum monthly air temperature and the extent of inundation. Invertebrate food availability was also sampled. Cross‐correlation with prior monthly rainfall showed that abundance of insects (Diptera, Hemiptera and Lepidoptera) and semi‐aquatic invertebrates peaked 1–2 months following large rainfall events, coinciding with peaks in presence of dependent young of Capricorn yellow chats. Thus, the Capricorn yellow chat matches the model for arid‐adapted birds in which seasonal cues (e.g. increasing day‐length or temperature) in spring lead to breeding preparedness, but breeding only occurs in response to proximal factors such as rainfall. However, the Capricorn yellow chat differs in that breeding is delayed until rainfall is sufficient to inundate its wetland habitat and stimulate the production of food resources associated with the low vegetation and muddy margins of the temporarily flooded pools and channels; suggesting that inundation may be the most important breeding cue.     

Late‐season snowfall is associated with decreased offspring survival in two migratory arctic‐breeding songbird species

While the effect of weather on reproduction has been studied for many years in avian taxa, the rapid pace of climate change in arctic regions has added urgency to this question by changing the weather conditions species experience during breeding. Given this, it is important to understand how factors such as temperature, rain, snowfall, and wind affect reproduction both directly and indirectly (e.g. through their effects on food availability). In this study, we ask how weather factors and food availability influence daily survival rates of clutches in two arctic‐breeding migratory songbirds: the Lapland longspur Calcarius lapponicus, a circumpolar breeder, and Gambel's white‐crowned sparrow Zonotrichia leucophrys gambelii, which breeds in shrubby habitats across tundra, boreal and continental climates. To do this, we monitored clutch survival in these two species from egg‐lay through fledge at field sites located near Toolik Field Station (North Slope, Alaska) across 5 yr (2012–2016). Our results indicate that snowfall and cold temperatures decreased offspring survival rates in both species; although Lapland longspurs were more susceptible to snowfall. Food availability, quantified by pitfall sampling and sweep‐net sampling methods, had minimal effects on offspring survival. Some climate models predict increased precipitation for the Arctic with global warming, and in the Toolik region, total snow accumulation may be increasing. Placed in this context, our results suggest that changes in snow storms with climate change could have substantial consequences for reproduction in migratory songbirds breeding in the North American Arctic.     

Food availability as a major driver in the evolution of life‐history strategies of sibling species

Life‐history theory predicts trade‐offs between reproductive and survival traits such that different strategies or environmental constraints may yield comparable lifetime reproductive success among conspecifics. Food availability is one of the most important environmental factors shaping developmental processes. It notably affects key life‐history components such as reproduction and survival prospect. We investigated whether food resource availability could also operate as an ultimate driver of life‐history strategy variation between species. During 13 years, we marked and recaptured young and adult sibling mouse‐eared bats (Myotis myotis and Myotis blythii) at sympatric colonial sites. We tested whether distinct, species‐specific trophic niches and food availability patterns may drive interspecific differences in key life‐history components such as age at first reproduction and survival. We took advantage of a quasi‐experimental setting in which prey availability for the two species varies between years (pulse vs. nonpulse resource years), modeling mark‐recapture data for demographic comparisons. Prey availability dictated both adult survival and age at first reproduction. The bat species facing a more abundant and predictable food supply early in the season started its reproductive life earlier and showed a lower adult survival probability than the species subjected to more limited and less predictable food supply, while lifetime reproductive success was comparable in both species. The observed life‐history trade‐off indicates that temporal patterns in food availability can drive evolutionary divergence in life‐history strategies among sympatric sibling species.     

Geophagy in chacma baboons: patterns of soil consumption by age class, sex, and reproductive state

Despite baboons' widespread distribution across Africa, geophagy among all subspecies has been poorly documented. We used video camera traps and soil analyses to investigate geophagy in chacma baboons (Papio cynocephalus ursinus) inhabiting the Western Cape of South Africa. During an 18‐month study, from August 2009 to January 2011, we continually monitored the largest and most frequently visited geophagy sites with camera traps for 545 days and captured soil consumption at one or more sites on 266 of those days (49%). In 3,500 baboon visits to geophagy sites, video camera traps captured 58.6 hr of geophagy. From these data, we evaluated site preference based on time spent consuming soil among these four geophagy sites. One hundred and seventy days of soil consumption data from the most frequently visited geophagy site allowed us to look for demographic trends in geophagy. Selected consumed soils from geophagy sites were analyzed for mineral, physical, and chemical properties. The baboons spent more time consuming white alkaline soils with high percentages of clay and fine silt, which contained higher concentrations of sodium than non‐white acidic soils that contained higher concentrations of iron. Our data indicate that pregnant chacma baboons spent more time consuming soil at monitored geophagy sites than baboons of any other age class, sex, or reproductive state. Based on analytical results, the soils consumed would be effective at alleviating gastrointestinal distress and possibly supplementing minerals for all age/sex classes, but potentially for different age/sex requirements. Am. J. Primatol. 74:48–57, 2012. © 2011 Wiley‐Liss, Inc.     

Annual Variation in Ecology and Reproduction of Wild Simakobu (Simias concolor)

Seasonal breeding in primates is related to the degree of environmental seasonality, particularly the availability and predictability of food. Southeast Asian species in general show moderate birth seasonality due to either low environmental seasonality or unpredictable fluctuations of mast-fruiting food resources. One Southeast Asian primate, the simakobu (Simias concolor), however, has been reported to be a strict seasonal breeder with births occurring in June and July only. It is unclear whether these observations are characteristic of the species or result from a sampling bias. To address this question, we documented the annual distribution of 11 births in eight groups of simakobu over two consecutive years at Pungut, an undisturbed site on Siberut Island, Indonesia. We assessed annual variation in ecology and reproduction via rainfall, temperature, food availability, feeding time, physical condition, conceptions, and births. Mean monthly temperature was nearly constant (26.3–27.1?°C), and monthly precipitation always high (219–432?mm). Although simakobu foods were abundant year-round, there were two fruit-feeding peaks in June and September. In contrast to previous reports, we documented births in 7?mo. Most births occurred in October (45?%), the wettest month of the year, and most conceptions in March and April, following a peak in unripe fruit availability. Although sample sizes are very small, females seemed to conceive when their physical condition was best, suggesting that simakobu time conceptions flexibly to the recovery of energy reserves. Across study sites, births occurred in 10 calendar months, indicating that simakobu reproduction is not strictly seasonal.     

New insights into the patterns and drivers of avian altitudinal migration from a growing crowdsourcing data source

Altitudinal migration is a common and important but understudied behavior in birds. Difficulty in characterizing avian altitudinal migration has prevented a comprehensive understanding of this behavior. To address this, we investigated the altitudinal migration patterns and explored potential drivers for a major proportion (~70%) of the entire resident bird community along an almost 4000 m elevational gradient on the main island of Taiwan. Based on the occurrence records collected by citizen scientists, we examined the seasonal shifts in the center and the upper and lower boundaries of elevational distributions for 104 individual species. We then built phylogeny‐controlled regression models to investigate the associations between the birds’ seasonal distribution shifts and seven of their traits, and examined whether the observed shifts can be explained by three main hypotheses on potential drivers. Results showed that at least 60 species (58%) seasonally changed their distributions along elevations. While most of them (42 species) tended to move downhill in winter, a considerable number of species (14) tended to move uphill. While the species breeding at high or low elevations tended to move downhill in winter, those breeding at medium‐low elevations tended to move or extend their distributions to higher elevations. Our regression models suggested that seasonal variations in climates and food availability could be major drivers of the behavior. However, the three hypotheses can only partially explain the observed downhill migration patterns and none of them can well explain the uphill patterns, indicating an important knowledge gap. This study investigated avian altitudinal migration from a new perspective with a novel and generalizable approach, and revealed interesting patterns that could be difficult to identify with conventional approaches. It demonstrated the power of citizen science data to provide new insights into this behavior by characterizing the general patterns and mechanisms across a large number of species.     

The impacts of climate change on the annual cycles of birds

Organisms living today are descended from ancestors that experienced considerable climate change in the past. However, they are currently presented with many new, man-made challenges, including rapid climate change. Migration and reproduction of many avian species are controlled by endogenous mechanisms that have been under intense selection over time to ensure that arrival to and departure from breeding grounds is synchronized with moderate temperatures, peak food availability and availability of nesting sites. The timing of egg laying is determined, usually by both endogenous clocks and local factors, so that food availability is near optimal for raising young. Climate change is causing mismatches in food supplies, snow cover and other factors that could severely impact successful migration and reproduction of avian populations unless they are able to adjust to new conditions. Resident (non-migratory) birds also face challenges if precipitation and/or temperature patterns vary in ways that result in mismatches of food and breeding. Predictions that many existing climates will disappear and novel climates will appear in the future suggest that communities will be dramatically restructured by extinctions and changes in range distributions. Species that persist into future climates may be able to do so in part owing to the genetic heritage passed down from ancestors who survived climate changes in the past.