迁徙鸟类对中途停歇地的利用及迁徙对策

中途停歇地是迁徙鸟类在繁殖地和非繁殖地之间的联系枢纽,对于迁徙鸟类完成其完整的生活史过程具有重要作用。从鸟类的迁徙对策、中途停歇地的选择、鸟类在中途停歇地的停留时间、体重变化和种群特征以及中途停歇地的环境状况等方面,回顾了中途停歇生态学在近年来的研究进展,并提出了在迁徙对策理论的实验研究,小型鸟类在中途停歇地的停歇时间及体重变化的准确确定等目前有待解决的问题。     

迁徙鸟类中途停歇期的生理生态学研究

大多数候鸟的迁徙活动由迁徙飞行和中途停歇两个部分组成。在迁徙过程中,鸟类要多次交替经历消耗能量的飞行阶段和积累能量的中途停歇阶段。从鸟类在中途停歇时期的能量积累速度、体重变化模式以及迁徙飞行中的禁食或食物限制、食物种类的改变、中途停歇的能量快速积累过程对消化器官的影响等方面,对目前迁徙鸟类的生理生态学研究成果进行回顾,并提出有待解决的问题及今后的研究方向。     

Artificial light at night confounds broad‐scale habitat use by migrating birds

With many of the world's migratory bird populations in alarming decline, broad‐scale assessments of responses to migratory hazards may prove crucial to successful conservation efforts. Most birds migrate at night through increasingly light‐polluted skies. Bright light sources can attract airborne migrants and lead to collisions with structures, but might also influence selection of migratory stopover habitat and thereby acquisition of food resources. We demonstrate, using multi‐year weather radar measurements of nocturnal migrants across the northeastern U.S., that autumnal migrant stopover density increased at regional scales with proximity to the brightest areas, but decreased within a few kilometers of brightly‐lit sources. This finding implies broad‐scale attraction to artificial light while airborne, impeding selection for extensive forest habitat. Given that high‐quality stopover habitat is critical to successful migration, and hindrances during migration can decrease fitness, artificial lights present a potentially heightened conservation concern for migratory bird populations.     

Geographical and temporal flexibility in the response to crosswinds by migrating raptors

Wind and ocean currents may potentially have important effects on travelling animals, as an animal which does not respond to lateral flow will be drifted from its intended direction of movement. By analysing daily movements of migrating ospreys Pandion haliaetus and marsh harriers Circus aeruginosus, as recorded by satellite telemetry, in relation to global wind data, we showed that these raptors allow on average 47 per cent drift. Furthermore, our analyses revealed significant geographical and temporal variation in the response to crosswinds. During some parts of the migration, the birds drifted and in other parts they compensated or even overcompensated. In some regions, the response of marsh harriers depended on the wind direction. They drifted when the wind came from one side and (over)compensated when the wind came from the opposite side, and this flexible response was different in different geographical regions. These results suggest that migrating raptors modulate their response to crosswinds at different places and times during their travels and show that individual birds use a much more varied repertoire of behavioural responses to wind than hitherto assumed. Our results may also explain why contrasting and variable results have been obtained in previous studies of the effect of wind on bird migration.     

Migration timing influences the responses of birds to food shortage at their refuelling site

Because migration is highly time‐constrained and migration timing varies among individuals, the responses of migrants to food shortage at a refuelling site could differ between individuals that arrive early and late at the site. To test this hypothesis, we compared the stopover decision, in terms of occurrence and length of stay (LOS), of radiotagged Great Knots Calidris tenuirostris before (2012) and after (2015) a dramatic decline in food supply at a critical spring final pre‐breeding refuelling site in the northern Yellow Sea. The probability of occurrence at the refuelling site was consistent between the two years, whereas the average LOS significantly shortened in the year of food shortage in late‐arriving individuals. This suggests migration timing intensifies the influence of food shortage in late‐arriving individuals, which might be more sensitive and vulnerable to food shortage at refuelling sites compared with early‐arriving individuals.     

Mesozooplankton and microzooplankton grazing during cyanobacterial blooms in the western basin of Lake Erie

Lake Erie is the most socioeconomically important and productive of the Laurentian (North American) Great Lakes. Since the mid-1990s cyanobacterial blooms dominated primarily by Microcystis have emerged to become annual, late summer events in the western basin of Lake Erie yet the effects of these blooms on food web dynamics and zooplankton grazing are unclear. From 2005 to 2007, grazing rates of cultured (Daphnia pulex) and natural assemblages of mesozooplankton and microzooplankton on five autotrophic populations were quantified during cyanobacterial blooms in western Lake Erie. While all groups of zooplankton grazed on all prey groups investigated, the grazing rates of natural and cultured mesozooplankton were inversely correlated with abundances of potentially toxic cyanobacteria (Microcystis, Anabaena, and Cylindrospermopsis; p < 0.05) while those of the in situ microzooplankton community were not. Microzooplankton grazed more rapidly and consistently on all groups of phytoplankton, including cyanobacteria, compared to both groups of mesozooplankton. Cyanobacteria displayed more rapid intrinsic cellular growth rates than other phytoplankton groups under enhanced nutrient concentrations suggesting that future nutrient loading to Lake Erie could exacerbate cyanobacterial blooms. In sum, while grazing rates of mesozooplankton are slowed by cyanobacterial blooms in the western basin of Lake Erie, microzooplankton are likely to play an important role in the top-down control of these blooms; this control could be weakened by any future increases in nutrient loads to Lake Erie.     

Male post-breeding movements and stopover habitat selection of an endangered short-distance migrant,the Little Bustard Tetrax tetrax

Migratory decisions, such as the selection of stopover sites, are critical for the success of post-breeding migratory movements and subsequent survival. Recent advances in bio-logging have revealed the stopover strategies of many long-distance migrants, but far less attention has been given to short-distance migrants. We investigated the stopover ecology of an endangered grassland bird, the Little Bustard Tetrax tetrax, a short-distance migrant in Iberia. Using high-resolution spatial GPS/GSM data, 27 male Little Bustards breeding in southern Portugal were tracked between 2009 and 2011. We studied post-breeding movements using Dynamic Brownian Bridge models to identify the main stopover sites, and generalized linear mixed models to examine habitat selection in stopovers. During their post-breeding movements, males were essentially nocturnal migrants, making frequent stopovers while maintaining a relatively fast pace to reach more productive agricultural post-breeding areas. Stopovers occurred in most post-breeding movements (83%) regardless of the total distance covered (average 64.3 km), and most stopovers (84%) lasted less than 24 h. Birds used mostly agricultural non-irrigated and irrigated croplands as stopover sites and avoided other land uses and rugged terrain. There was a negative relationship between stopovers and the proximity to roads, but not to power lines. The high frequency of stopovers during post-breeding movements, despite the short distances travelled, together with the nocturnal migratory behaviour of bustards, may impose additional risks to a bird mainly threatened by collision with power lines in non-breeding areas. We also conclude that even for short-distance migrants, habitat connectivity between breeding and post-breeding areas is likely to be a key conservation concern.     

An inventory of the possible effects of climatic change on western palearctic migratory birds

This paper presents an assessment of the possible effects of future climatic change on migratory birds. The assessment is based on two approaches: firstly an inventory is made of the environmental factors that may change which directly affect migratory birds. These factors include physical (temperature, hydrology, ocean and air streaming patterns) as well as biological (floral and faunal composition of ecosystems) and landuse aspects of the environment.Secondly, these possible changes were related to the annual cycles of migratory birds in order to estimate the problems that different groups of migratory birds have to cope with at various stages in their annual cycle. It is concluded that many migratory bird species will be influenced by climatic change, leading to adaptations in the birds annual cycle. The biggest problems may arise for those birds which depend on wetlands, because many of these wetlands may dessicate.     

Age and growth of round goby Neogobius melanostomus associated with depth and habitat in the western basin of Lake Erie

Round goby Neogobius melanostomus were examined from the Bass Islands area in the western basin of Lake Erie, U.S.A., to determine age and growth correlations. A total of 188 specimens were collected and examined during summer 2011 with 90 aged using scale analysis. Fish were grouped by sex, depth of habitat and habitat type (anthropogenically modified shallows, natural shallows and open lake deep water). Fish ranged from 17 to 117 mm total length (L_T) and 0+ to 3+ years. Males dominated the population (1·94:1) and backcalculated age showed that both sexes grew exponentially, with male growth rate increasing faster than female. Males were significantly larger than females in L_T and mass (both P < 0·001). The relative mass index (W_r) was low for the sampled population (mean ± s.d . = 32·00 ± 26·87 g), implying that the health of the Bass Island area population is very poor when compared with the species throughout its range. This could be due to a lack of food resources related to population size or that the fish is not optimally utilizing the available food resources. In contradiction to these findings, regression slope coefficient (b), calculated using Fulton's condition factor (K) (mean ± s.d . =1·50 ± 0·20), was very low for each habitat, implying a healthy population throughout. This seemingly opposite effect may be due to more individuals per unit area in shallow waters, which would cause increased competition for resources. Poor condition may indicate that the Lake Erie population has reached saturation or may reflect indirect fitness costs associated with increasing anoxic or hypoxic hypolimnion conditions.     

Wind conditions affect stopover decisions and fuel stores of shorebirds migrating through the south Yellow Sea

We assessed the effects of wind conditions on stopover decisions and fuel stores of migratory shorebirds at Chongming Dongtan in the south Yellow Sea along the East Asian–Australasian Flyway. In spring and autumn, wind directions differed among altitudes and wind speed generally increased with altitude. Numbers of shorebirds were related to wind effects at low altitudes (on the ground and at 300 and 800 m above the ground), wind effects at 300 m being the best predictor of shorebird numbers. In spring, total number of shorebirds and numbers of the four most abundant shorebird species were negatively related to wind assistance at low altitudes, more birds departing when tailwinds prevailed and more arriving when headwinds prevailed. In autumn, however, total number of shorebirds and numbers of the four most abundant species were positively related to wind assistance at low altitudes, more birds departing and more arriving with tailwinds than with headwinds. When tailwinds prevailed, the number of arriving birds was higher than the number of departing birds. The fuel stores of captured shorebirds, represented by their body mass, was related to wind effects and change in wind conditions between two consecutive days in both spring and autumn, captured birds being heavier when headwinds prevailed than in tailwind conditions, and when the wind conditions became less favourable for flight between two consecutive days. Our results suggest that wind conditions affect stopover decisions and fuel stores, and thus the optimal migration and fuel deposition strategies of migratory shorebirds.     

An experimental investigation into the effects of traffic noise on distributions of birds: avoiding the phantom road

Many authors have suggested that the negative effects of roads on animals are largely owing to traffic noise. Although suggestive, most past studies of the effects of road noise on wildlife were conducted in the presence of the other confounding effects of roads, such as visual disturbance, collisions and chemical pollution among others. We present, to our knowledge, the first study to experimentally apply traffic noise to a roadless area at a landscape scale—thus avoiding the other confounding aspects of roads present in past studies. We replicated the sound of a roadway at intervals—alternating 4 days of noise on with 4 days off—during the autumn migratory period using a 0.5 km array of speakers within an established stopover site in southern Idaho. We conducted daily bird surveys along our ‘Phantom Road’ and in a nearby control site. We document over a one-quarter decline in bird abundance and almost complete avoidance by some species between noise-on and noise-off periods along the phantom road and no such effects at control sites—suggesting that traffic noise is a major driver of effects of roads on populations of animals.     

Changing social awareness of the illegal killing of migratory birds in the Ionian Islands,western Greece

ABSTRACT

The current study aims at monitoring, measuring and evaluating the ‘Safe havens for wild birds’ campaign, implemented within the framework of the LIFE programme, in Greece and more specifically in the Ionian Islands. The study detects attitude changes that occurred in three target groups (pupils, local hunters and residents) on three islands where the phenomenon of illegal spring killing is more intense. A questionnaire-based survey was conducted in two phases, just before the launch (2013) and after the completion of the campaign (2015), to enable a comparison of answers and data. The results show that pupils and to a lesser extent residents, enhanced their knowledge and awareness of poaching, the migration of avifauna and the consequences of illegal killing on migratory birds, while this aspect of attitude change was not observed in the hunting community which still believes that spring poaching should be treated as a legal activity and part of local culture.     

Limitations and mechanisms influencing the migratory performance of soaring birds

Migration is costly in terms of time, energy and safety. Optimal migration theory suggests that individual migratory birds will choose between these three costs depending on their motivation and available resources. To test hypotheses about use of migratory strategies by large soaring birds, we used GPS telemetry to track 18 adult, 13 sub‐adult and 15 juvenile Golden Eagles Aquila chrysaetos in eastern North America. Each age‐class had potentially different motivations during migration. During spring, the migratory performance (defined here as the directness of migratory flight) of adults was higher than that of any other age‐classes. Adults also departed earlier and spent less time migrating. Together, these patterns suggest that adults were primarily time‐limited and the other two age‐classes were energy‐limited. However, adults that migrated the longest distances during spring also appeared to take advantage of energy‐conservation strategies such as decreasing their compensation for wind drift. During autumn, birds of all age‐classes were primarily energy‐minimizers; they increased the length of stopovers, flew less direct routes and migrated at a slower pace than during spring. Nonetheless, birds that departed later in autumn flew more directly, indicating that time limitations may have affected their decision‐making. During both seasons, juveniles had the lowest performance, sub‐adults intermediate performance and adults the highest performance. Our results show age‐ and seasonal variation in time and energy‐minimization strategies that are not necessarily exclusive of one another. Beyond time and energy, a complex suite of factors, including weather, experience and navigation ability, influences migratory performance and decision‐making.     

Monitoring flight calls of migrating birds from an oil platform in the northern Gulf of Mexico

ABSTRACT.   Millions of birds migrate across the Gulf of Mexico each year. However, most studies of migration in this region involve sampling onshore locations during the day, potentially underrepresenting the diversity and abundance of migrants passing the region. We evaluated a potential solution to this problem by recording the flight calls of passing migrants from an oil platform located southeast of the Alabama coast in the Gulf of Mexico. We detected 2762 calls during 30 nights from 9 September to 2 November 1999, and were able to identify 2329 calls to species. Flight calls by nine species of birds represented 23% of all identified calls. The greatest number of calls during one night (1017 calls) and during a 1-h period (257 calls) were recorded on 10 September. The greatest number of calls was recorded 8 h after sunset, with a secondary peak 2 h after sunset. The peak prior to sunrise may indicate the formation of flocks at dawn, and the peak after sunset may have been caused by the first wave of migrants reaching the platform. However, call counts varied extensively, with 98% of all calls recorded during 13 nights and 40% on a single night, possibly resulting from hourly and nightly differences in bird numbers aloft, atmospheric conditions, and artificial lighting conditions. Although recording on oil platforms can be difficult because of mechanical, wind, and wave noise, our results suggest great potential for describing the species composition of passing vocal migrants and the temporal patterns of flight-calling behavior if quiet recording locations can be found. Moreover, flight call monitoring could be a critically important tool for bird conservation in this region, given recent proposals to develop wind power and the potential bird mortality associated with such developments.     

滦河上游——白枕鹤西部种群的重要停歇地

白枕鹤(Grus vipio)为国家II级重点保护野生动物, 被IUCN列为易危(VU)物种。白枕鹤西部种群繁殖于中蒙俄交界处的达乌尔地区, 数量呈下降趋势。我们于2017-2018年在蒙古国东部给白枕鹤西部种群的50只个体佩戴了GPS-GSM跟踪设备。截至2019年5月, 获得春季和秋季迁徙路径各48条。分析结果显示: 春季91.67%和秋季72.91%的跟踪个体在滦河上游(河北省沽源-内蒙古正蓝旗-多伦区域)停歇, 春季停留时间36.16 ± 15.00天、秋季20.26 ± 11.08天, 分别占春季和秋季迁徙时间的75%和67%, 确定了这一区域是西部种群迁徙途中最重要的停歇地。迁徙路线栖息地选择模型结果显示, 白枕鹤常在距离湖泊较近(< 210 km)、海拔1,200-1,500 m, 且坡度小(< 1°)的区域停歇。而滦河上游和整条迁徙路线停歇位点比较的模型结果显示, 滦河上游停歇地的海拔1,200-1,500 m与整条迁徙路线栖息地选择模型的结果一致; 此外这个区域离河流更近(< 70 km), 不仅有湿地和水体的栖息环境, 还有草地和农田可供觅食和栖息。保护空缺分析发现滦河上游现有四处保护地, 但在保护地内的迁徙停歇点不超过总位点的1.63%。综上, 我们建议将滦河上游整体纳入保护地体系进行管理, 为这一受胁物种及其栖息地管理和保护提供可靠保障。     

Fifty years later: trophic ecology and niche overlap of a native and non-indigenous fish species in the western basin of Lake Erie

Since the introduction of white perch (Morone americana) into Lake Erie over 50 years ago, the population size of native yellow perch (Perca flavescens) has decreased up to 79 % and significant changes to the ecosystem have occurred. We examined long-term population estimates and used stable isotopes of carbon (δ ¹³C) and nitrogen (δ ¹⁵N) paired with stomach content analysis to quantify the trophic ecology and niche overlap of adult yellow perch and white perch in the western basin of Lake Erie. We found that changes in yellow perch abundance since 1979 appeared to be better correlated with changes in fishery exploitation rates than with food competition effects from white perch. At the time of this study, yellow perch were found to have higher δ ¹³C values, indicating greater utilization of benthic food resources than white perch, and white perch occupied higher trophic positions based on δ ¹⁵N. The diets of both species varied spatially and seasonally based on stable isotopes and stomach contents, likely driven by changes in prey abundance. Comparison of niche widths using stable isotope population metrics and Schoener diet similarity index suggested a low to moderate degree of niche overlap between species. Isotopic niches of white perch were generally larger than those of yellow perch demonstrating broader resource utilization by this non-indigenous species. We submit that isotopic niche overlap comparisons are more appropriate for studies seeking to understand interactions among populations over course temporal scales, while diet overlap indices, such as the Schoener index provide a means to study fine-scale interactions such as ontogenetic and seasonal diet shifts.     

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

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

Aspects of seagrass ecology along the western Arabian Gulf coast

Results of semi-quantitative observations and quantitative sampling of seagrasses at coastal and offshore sites along the western Arabian Gulf are presented. Overall seagrass cover (all species together) shows significant positive correlation with latitude, but not with salinity, temperature or depth. The same pattern is shown by Halodule uninervis (Forsk.) Aschers., the dominant species. Mean seagrass biomass ranged from 53–235 g m^-2 (dry weight). These values are comparable with biomass estimates from regions in which environmental conditions are generally less extreme than in the Gulf. Seagrass biomass is significantly negatively correlated with depth and sediment grain size. No significant correlation is apparent between seagrass biomass and factors such as season, salinity, or concentrations of nutrients and heavy metals measured. It is pointed out that any correlations observed are not necessarily taken to imply causality.