Spring migration dynamics and sex-specific patterns in stopover strategy in the Wood Sandpiper Tringa glareola

Due to being a virtually monomorphic wader species, migration dynamics and sex-related migration patterns in the Wood Sandpiper (Tringa glareola) have rarely been investigated. We captured spring migrants at an important stopover site in northeastern Austria. Birds were individually color-marked, and sex was determined by an analysis of DNA from tail feather material. Among temporary residents (birds seen again after day of capture), males migrated on average 3 days earlier than females. However, since sexes did not differ in fat score, the length of stay and the proportion of transients (birds not seen again after day of capture) and temporary residents, we suggest that males and females adopt similar migration strategies in the spring. The large number of transients captured as well as shorter stopover durations in later temporary residents indicate that Wood Sandpipers minimize time at this stage of their northbound migration. Temporary residents earlier in the season exhibited lower fat stores than later ones. Nevertheless, since the fat stores of transients and temporary residents were similar even after the progress of the season had been accounted for, we assume that Wood Sandpipers may afford to exhibit individual flexibility in migration strategy and the use of stopover sites, especially early in the season. This variability may be a necessary adaptation to cope with possible varying environmental conditions at dynamic and unpredictable inland stopover sites. After having reached North Mediterranean regions, mean body mass of spring migrants gradually increases during successive stopovers, indicating that Wood Sandpipers follow a ‘hopping’ migration strategy. This emphasizes the high conservation value of even small artificial mudflat pools as important stepping stones in order to maintain a continuous network of wetland habitats for this continental migrant.     

东亚-澳大利西亚候鸟迁飞区中杓鹬 的迁徙追踪

追踪候鸟的迁徙活动是全面认识其生活史年周期的重要途径。中杓鹬(Numeniusphaeopus)在全球广泛分布,但在东亚-澳大利西亚候鸟迁飞区的迁徙活动一直缺乏追踪研究。2018年2月,在澳大利亚西北部的布鲁姆为捕捉到的中杓鹬成鸟佩戴平台发射终端或全球定位系统-全球移动通讯系统追踪器,以确定其迁徙日程、迁徙路线以及迁徙停歇地和繁殖地的地理位置。我们从成功追踪的7只个体获取了6 378条精度高于1 km的位点数据。分析结果表明,在春季,中杓鹬的迁徙时长为(36±4)d,其间在1～3个迁徙停歇地的停留日期为(23±2)d,从越冬地到繁殖地的迁徙距离为(9 795±346)km(n=7)。追踪的中杓鹬在俄罗斯东部和中部区域繁殖,不同个体的繁殖地纬度相近而经度范围较广。在秋季,中杓鹬的迁徙时长为(90±27)d,相比春季迁徙时长更长;其间,在2～4个迁徙停歇地停留(79±29)d,从繁殖地到越冬地的迁徙距离为(10 101±520)km(n=5)。无论在春季还是秋季迁徙,迁徙停歇地广泛分布于东亚、东南亚沿海及内陆区域。大部分个体春季和秋季的迁徙路线相近,成功追踪的个体均在秋季返回了上一年的越冬地,这表明中杓鹬对越冬地具有很高的忠诚度。     

扎龙湿地白鹤春季停歇地昼间行为时间分配及活动规律

在2004年4～5月,采用瞬时扫描取样法对扎龙国家级自然保护区林甸芦苇沼泽区的野生白鹤(Grusleucogeranus)在春季迁徙停歇地的昼间各种行为进行了研究。结果表明,在整个观察时期内白鹤各种行为具有较强的规律性,活动时间分配比例为:觅食31%、游走27%、静栖19%、警戒17%、修饰6%。白鹤觅食行为在一天中有两个高峰,分别为早晨和黄昏;游走行为基本上与觅食行为呈正相变化,并且几乎每个游走高峰及低潮相应地伴随着觅食的高峰和低潮;由于渔民清晨下苇塘收鱼和放牧,在5:30～6:30和6:30～7:30两个时间段警戒行为比例最高;静栖行为基本与游走及觅食行为呈负相关,对比发现,静栖行为比例低于觅食行为,与笼养鹤类的情况存在一定的差异,原因可能是食物丰富度影响了野生状态下行为的时间分配;修饰行为所占比例较小,是由于修饰行为是非主要行为,其发生是随机的。天气状况对白鹤数量变化有一定影响,阴雨和大风天气,白鹤数量明显减少,鹤群转移。与正常天气情况相比,阴雨和大风对白鹤觅食、静栖和游走行为时间分配影响显著(P阴雨=0·000<0·05,P大风=0·000<0·05),觅食时间缩短,游走行为减少,静栖时间变长。     

渤海湾地区红腹滨鹬迁徙动态的初步研究

红腹滨鹬(Calidris canutus)繁殖于环北极地区,属长距离迁徙鸟类,我国黄渤海地区是其在东亚-澳大利西亚迁徙路线上重要的停歇地。2003~2004年,通过对渤海湾北部双龙河口(东经118°21′,北纬37°2′)及其附近地区红腹滨鹬的种群调查,发现其迁徙高峰期出现在4月底到6月初,峰值为2004年5月15日的3 814只;2004年北迁时期,记录到佩戴有澳大利亚和新西兰脚旗的红腹滨鹬17只次,证实在澳大利亚西北部、东南部以及新西兰等3个地区越冬的2个红腹滨鹬亚种都在北迁时使用渤海湾作为其停歇地。     

Food availability but not melatonin affects nocturnal restlessness in a wild migrating passerine

A large number of passerine species migrate at night, although most of them are diurnal outside the migratory seasons. This diurnal-to-nocturnal transition is a major life-history event, yet little is known about its physiological control. Previous work showed that during the migratory periods captive birds showing nocturnal migratory restlessness (Zugunruhe) have reduced concentrations of circulating melatonin at night compared to non-migratory periods. This suggested that the hormone melatonin, a main component of the avian circadian system, is involved in the expression of Zugunruhe. Other studies demonstrated that the relationship between low melatonin levels and Zugunruhe is not a seasonal correlation. When Zugunruhe was interrupted by exposing birds to a fasting-and-refeeding protocol, melatonin levels increased. Here we studied whether melatonin and food availability influence the intensity of Zugunruhe in wild migrating garden warblers (Sylvia borin) at a stopover site. Birds were held in recording cages overnight, with or without food available, and either bled to determine melatonin concentrations or treated transdermally with melatonin. We found that melatonin levels at night were correlated with the intensity of diurnal locomotor activity and with condition, but were not correlated with Zugunruhe. Similarly, the melatonin treatment did not have effects on Zugunruhe, whereas food availability increased it. Our study shows that the nocturnal melatonin levels in migrating warblers depend on food availability and are correlated with condition. In addition, it suggests that melatonin does not control Zugunruhe and might rather be involved in energy conservation and/or clock synchronization during migration.     

Fuel deposition of three passerine bird species along the migration route

The rate at which migrant birds replenish their energy stores at intermittent stopovers largely determines overall migration speed, the manner in which migration proceeds and success of migration. In this study, data on the fuel deposition rate (FDR) of three long-distance migrants from 17 ringing sites along their autumn migration route were used to examine: (1) effects of endogenous factors on FDR, and (2) how relationships between exogenous factors and FDR affect the organisation of migration. We developed a model to estimate FDR from retrapped birds which takes into account time of day and various other factors which might influence FDR. The two endogenous factors, moult and current energy stores, generally reduced FDR. This may result in lower departure energy loads and more stopovers than expected from optimal migration theory. Differences between species with respect to seasonal, year-to-year and geographical patterns of FDR could be related to differences in availability and predictability of food resources, and help to explain differences in the organisation of migration. A low FDR in northern and central Europe could be related to low, but predictable, food resources and an early departure during moult of the reed warbler (Acrocephalus scirpaceus); FDRs varying between years were related to large spatial and year-to-year variation in the density of the main prey of the sedge warbler (Acrocephalus schoenobaenus); and a high FDR in the garden warbler (Sylvia borin) was related to abundant food resources, due to a switch from a purely invertebrate diet to a mixed diet including fruits which are abundant over large areas of Europe and north Africa. This study demonstrated that the organisation of migration is the outcome of a complex interplay of the seasonal timing of moult, food availability and predictability and a seasonal switch in diet, and can be modified by individual birds in response to a limited amount of time in which to migrate. Received: 26 April 1999 / Accepted: 24 September 1999     

Stable isotopes in breath,blood, feces and feathers can indicate intra-individual changes in the diet of migratory songbirds

We used stable isotopes of C in breath, blood, feces and feathers to identify intra-individual changes in diet and the timescale of diet changes in free-living songbirds at a stopover site. Because accurate interpretation of differences between the ¹³C of breath, plasma, and red blood cells (RBCs) relative to diet requires knowing the turnover rate of C within them, we determined the rate of change of C in breath, plasma and RBCs for yellow-rumped warblers (Dendroica coronata). Half-lives of C in breath, plasma, and RBCs were 4.4±2.1 h, 24.8±12.3 h and 10.9±3.2 days, respectively, for yellow-rumped warblers. ¹³C of breath, plasma, RBCs and feces from wild-caught golden-crowned kinglets (Regulus satrapa), ruby-crowned kinglets (R. calendula) and gray catbirds (Dumetella carolinensis) indicated that they had maintained an isotopically consistent diet for an extended period of time. However, ¹³C of breath and plasma indicated that white-throated sparrows (Zonotrichia albicollis) had recently expanded their diet to include a C₄ dietary component. Likewise, ¹³C of breath, plasma, RBCs and feces indicated that some wild-caught yellow-rumped warblers had consumed foods with a more enriched protein signature prior to their arrival on Block Island, and since arrival, they had consumed mostly northern bayberry (Myrica pensylvanica). Therefore, comparisons of the ¹³C of breath, plasma, RBCs, feces and feathers from individual songbirds can indicate changes in diet and provide an estimate of the timescale of the diet change.     

Foraging strategies involved in habitat use of shorebirds at the intertidal area of Chongming Dongtan, China

Dense flocks of migratory shorebirds from diverse species often concentrate in the intertidal areas for stopover. Trophic structure, food partition, prey availability and selectivity, predation risk, and abiotic factors are often used to explain the differences in habitat use of coexisting shorebirds. We sampled the macrobenthos and surveyed the distribution of shorebird populations to study the effects of foraging strategies on the habitat use of shorebirds at Chongming Dongtan, an important stopover site for shorebirds on the East Asian–Australasian Flyway. Results show that the relative abundance of epifaunal macrobenthos in salt marshes was much higher than that in the bare flats, whereas the relative abundance of infaunal macrobenthos in salt marshes was much lower than that in bare flats. The relative abundance of two life forms of macrobenthos was similar in the transitional zones between the salt marshes and the bare flats. Shorebirds with different foraging strategies exhibited different habitat uses. Pause-travel shorebirds mainly utilized the salt-marsh fringes, while tactile continuous shorebirds relied heavily on the bare flats. There was no significant difference in habitat use for visual continuous shorebirds. The density of tactile continuous shorebirds was positively correlated with bivalve density, and that of visual continuous shorebirds positively with crustacean density. Meanwhile, the relative abundance of pause-travel foraging shorebirds was positively correlated with the relative abundance of epifaunal, but negatively with infaunal macrobenthos. In contrast, the relative abundance of tactile foraging shorebirds had a positive correlation with infaunal but a negative one with epifaunal life form. Therefore, foraging strategies may play important roles in shorebirds’ habitat use in intertidal areas.     

Heat loss in sleeping garden warblers (Sylvia borin) during migration

For small songbirds, energy is often a limiting factor during migration and, for this reason, they are forced to alternate nocturnal flights with stopovers to rest and replenish energy stores. Stopover duration has a key role for a successful migration and may have an important impact on fitness. Thus, migrants need to optimize their energy consumption at this stage to reduce their permanence at the site. A recent study has shown that lean individuals reduce their metabolic rate when tucking the head in the feathers during sleep. The underlying mechanism is very likely a reduction in conductance, but the thermoregulatory benefit of the increased insulation has never been quantified yet. Here, we compared heat loss in individual migratory birds while sleeping in different postures. Using a thermal camera and a within-individual approach, we estimated that Garden Warblers can reduce their rate of heat loss by 54% by sleeping with the head tucked in the feathers. This energy saving has a relevant impact on the individual’s energy balance because it can account for up to 8.69% of daily energy expenditure during stopover. Our study provides novel and important information to understand the fundamental role of thermoregulatory strategies on bird’s energy management.