Does intraspecific competition facilitate age separation in timing of southward migration in waders?

In many Palaearctic wader species there is a clear separation in the timing of adult and juvenile southward migration. This phenomenon is traditionally explained by the selection on adults to depart early from breeding grounds and necessity of juveniles to prepare longer for migration. In this study we hypothesize that late departure from natal grounds may also be adaptive for juveniles, as it allows them to avoid intensified interference competition at stopover sites with adult, usually more dominant conspecifics. To test this hypothesis we analysed long-term data on stopover behaviour of juvenile wood sandpipers (Tringa glareola) staying at a central Polish stopover site under varying levels of competition from adult birds. The results clearly indicated that juveniles were highly disadvantaged by the simultaneous presence of adults at the same staging site, as under intense competition from older conspecifics they refuelled more slowly and attained lower fat reserves. It was also found that juveniles which were forced to compete with adults left the site quickly and possibly searched for more favourable staging places. All these imply that delayed departure from natal grounds may be adaptive for juvenile waders, allowing them to mismatch the timing of their first migration with the peak of adult passage and, thus, reduce the negative consequences of intraspecific competition during migration.     

Assessing alternative anthropogenic habitats for conserving waterbirds: salinas as buffer areas against the impact of natural habitat loss for shorebirds

Because many natural waterbird habitats are threatened by human disturbance and sea level rise, it is vitally important to identify alternative wetlands that may supplement declining natural habitats. Coastal salinas are anthropogenic habitats used for obtaining salt by evaporation of sea water. These habitats support important numbers of waterbirds around the world, but their importance as feeding habitats is poorly understood. I evaluated salinas as feeding habitats relative to natural intertidal habitats by comparing time spent foraging, prey-size selection, and net energy intake rate of four overwintering small-sized shorebird species on intertidal mudflats and on adjacent salinas. In winter, Dunlin Calidris alpina, Curlew Sandpiper C. ferruginea and Sanderling C. alba predominantly used the mudflats, whereas Little Stint C. minuta fed mainly on the salina. In the pre-migration fattening period, all species preferred to feed on the salina, significantly increasing the time they spent feeding in the supratidal pans. Net energy intake rates (kJ min^–1) were significantly higher on the salina than on the intertidal mudflats in 60% of all comparisons. On average, salina contributed 25.2 ± 24.2% (range: 4–54%) of the daily consumption in winter and 78.7 ± 16.4% (range: 63–100%) of the daily consumption in the pre-migration period. I recommend that modern active salinas maintain flooding conditions in the evaporation pans throughout winter, thus increasing the available surface for foraging waterbirds. I conclude that the conservation of salinas at coastal wetlands is a viable approach for shorebird conservation.     

Warmer springs advance the breeding phenology of golden plovers Pluvialis apricaria and their prey (Tipulidae)

Most studies of climate-driven changes in avian breeding phenology have focused on temperate passerines, yet the consequences of such environmental change may be more deleterious for other avian taxa, such as arctic and sub-arctic waders (Charadrii). We therefore examine large-scale climatic correlates of the breeding phenology of one such species (golden plover Pluvialis apricaria), and the timing of emergence of their adult tipulid prey, to assess the potential for climate change to disrupt breeding performance. Golden plover first-laying dates were negatively correlated with both March and April temperature, the mean laying date of first clutches was additionally negatively correlated with March rainfall. The timing of final laying dates were negatively correlated with April temperature only. The timing of tipulid emergence was negatively correlated with May temperature. In combination with historical climatic data, these models suggest a 9-day advancement of golden plover first-laying dates occurred during the 1990s, although this remains within the range of natural variation for the twentieth century. The magnitudes of predicted changes in mean and final laying dates, and the timing of tipulid emergence, were smaller. Climate predictions for 2070-2099 suggest potential advances in first-laying dates by 25 days, whilst the timings of mean and final laying dates are predicted to change by 18 days and 13 days, and tipulid emergence by 12 days. Given the importance of adult tipulids to young golden plover chicks, these changes may result in a mismatch between the timing of first-laying dates and tipulid emergence, so reducing the success of early breeding attempts. Modelling suggests that these changes could reduce breeding success in a South Pennines population by about 11%.     

The macrobenthos fraction accessible to waders may represent marginal prey

Summary The relationship between relative body condition (deviation from expected mean body weight) and burying depth was investigated in five macro-zoo benthic species living in a marine intertidal habitat. Body weight increased with depth when animals of the same size were compared. The increase amounted to 50% in the clamScrobicularia plana, ca. 40% in the wormNereis diversicolor, 25% in the clamMacoma balthica and 20% in the cockleCerastoderma edule and the clamMya arenaria. Only a part of the prey was within reach of some feeding wader species. Therefore prey value may be overestimated if one does not take into account the fact that shallow and accessible prey often have a relatively poor body condition.     

Thermal emissivity of avian eggshells

The hypothesis has been tested that evolution has resulted in lower thermal emissivity of eggs of birds breeding openly in cold climates than of eggs of birds that nest under protective covering or in warmer climates. Directional thermal emissivity has been estimated from directional–hemispherical reflectance spectra. Due to several methodological difficulties the absolute emissivity is not accurately determined, but differences between species are obvious. Most notably, small waders of the genus Calidris, breeding in cold climates on the tundra, and in most cases with uniparental nest attendance, have low directional emissivity of their eggshells, about 0.92 when integration is carried out for wavelengths up to 16 μm. Species belonging to Galloanserinae have the highest directional emissivity, about 0.96, of their eggs. No differences due to climate or breeding conditions were found within this group. Eggs of most other birds tested possess intermediate emissivity, but the values for Pica pica and Corvus corone cornix are as low as for Calidris. Large species-dependent differences in spectral reflectance were found at specific wavelengths. For instance, at 4.259 μm the directional–hemispherical reflectance for galliforms range from 0.05 to 0.09, while for Fratercula arctica and Fulmarus glacialis it is about 0.3. The reflection peaks at 6.5 and 11.3 μm due to calcite are differentially attenuated in different species.In conclusion, the hypothesis that evolution has resulted in lower thermal emissivity of bird eggs being exposed in cold climates is not supported by our results. The emissivity is not clearly related to nesting habits or climate, and it is unlikely that the small differences observed are ecologically important. The spectral differences between eggs that nevertheless exist should be taken into account when using infrared thermometers for estimating the surface temperature of avian eggs.     

Evaluating impacts of shellfish and baitworm digging on bird populations: short-term negative effects on the availability of the mudsnail Hydrobia ulvae to shorebirds

Many shorebird populations show evidence of declines. To identify the causes is a key issue in developing comprehensive shorebird conservation plans. In coastal areas, shorebirds are vulnerable to effects of shellfish and baitworm digging, including reduction of the food supply. The mudsnail Hydrobia ulvae is often reported to be the dominant inhabitant of intertidal mudflats, and is common in the diet of migrating and wintering shorebirds. This prosobranch mollusc lives at or just below the surface of intertidal mudflats, so it might be directly damaged and killed or buried within the mud by hand diggers. We studied the short-term effects of digging by hand on the availability of mudsnail to shorebirds. Twenty centimetres deep core samples were collected from undisturbed and recently disturbed intertidal mud. The total mudsnail density and biomass per core sample was similar in disturbed and undisturbed mud. However, mudsnail density and biomass were significantly lower in disturbed mud than in undisturbed mud when only the upper five centimetres of the mud were compared. If only the mudsnails found in this surface layer are potentially available for shorebirds, the available mudsnail density and biomass fraction for shorebirds had decreased by 62.6? ?±? 11.4% and 75.7? ?±? 7.2% in disturbed mud, respectively. The potential impact of this decreasing mudsnail fraction on shorebirds is addressed.     

青海湖鸻鹬类群落特征和时空分布

于2006年至2009年间对环青海湖鸻鹬类的群落特征和时空分布进行了资源调查,以期对青海湖保护管理提供科学依据。根据青海湖的地形、植被和水系分布以及水鸟聚集特点,环青海湖选择了15个调查地点,采用直接计数法进行了14次调查,并应用Shannon-wiener指数进行了多样性分析。共记录到鸻鹬类4科28种。数量上红脚鹬(Tringa totanus)、环颈鸻(Charadrius alexandrinus)和黑尾塍鹬(Limosa limosa)是当地的主要物种,分别占鸻鹬类调查总数的33.3%、22.0%和16.2%。分布上环颈鸻最为广泛,在各调查地点均有发现,其次为红脚鹬、黑尾塍鹬和青脚滨鹬(Calidris temminckii),分布地点达10处以上。黑马河和布哈河口多样性较高,这与其适宜的河漫滩和沼泽等栖息环境以及丰富的食物有关。季节上8~10月多样性较高,其次是4~5月。青海湖鸻鹬类的数量高峰依次为10月、8月和5月,物种数高峰为8月和4月,并且秋季物种数高于春季。主要物种红脚鹬和环颈鸻的迁徙动态较为一致,均是8月份达到全年数量最高值,次高峰为5月和10月;黑尾塍鹬的数量在10月份达到全年最高峰。青海湖鸻鹬类迁徙时间与渤海湾较为一致,这可能与历史上长期形成的迁徙模式有关。鄱阳湖和洞庭湖的鸻鹬类主要物种与青海湖比较接近,但数量远远多于青海湖。近年来,游客和游船等人为活动的增加导致青海湖产生局部污染,因此应重视环青海湖生态环境的保护管理,减少对鸻鹬类等水鸟栖息地的人为干扰。     

Evolutionary trends in wading birds

For the most part populations ot wading birds have expanded and contracted with the variations in the extent of their habitats during the Pleistocene. It is suggested that as a result of geographical isolation, populations of the same species have evolved to a level at which secondary hybridization has resulted on their again coming together. 'Southern' forms of some wading birds have resulted from this secondary hybridization and in some cases the increased heterogeneity has given rise to new evolutionary potential. It is suggested that this may have occurred many times during the Pleistocene and that microevolution has played a significant part in the evolution of wading birds.     

Does vigilance always covary negatively with group size? Effects of foraging strategy

The possible effects of foraging strategy on the relationship between vigilance and group size were studied in three species of waders with different foraging strategies. I predict that (1) pause–travel species should show no relationship between scanning and group size, because these species scan for prey as well as for predators; (2) continuous-tactile foraging species should show a positive relationship between flock size and vigilance level, because in their large groups vigilance towards other birds could be used to avoid interference and aggression; and (3) continuous-visual searching species should show the general pattern of decreasing vigilance when group size increases as predicted by both the 'many eyes' and the 'predatory risk' hypotheses. Results support the predictions for the influence of foraging strategy on the relationship between vigilance level and group size. The mutual exclusion of foraging and scanning can determine the importance of the 'many eyes' hypothesis. Such exclusion seems to be determined by foraging strategy. The influence of foraging on scanning must be taken into account in future studies on the group-size effect. Electronic Publication     

福建沿海湿地鸻鹬类资源调查

1997年1月～2003年4月,采用直接计数法与航线调查法相结合的方法对福建省海岸湿地的涉禽进行了调查,共发现鸻鹬类43种及亚种计56386只。结合以往的调查记录,得知福建沿海鸻鹬类共53种及亚种,占全国该类群总种数的62％。冬候鸟和旅鸟是本地鸻鹬类中占优势的生态类群。目前沿海滩涂的围垦和鸟类食物的减少,是鸻鹬类所面临的主要威胁。尽快制定湿地保护与合理利用的规划,对福建沿海湿地鸟类的保护至关重要。闽江口湿地不仅是鸻鹬类集中分布的区域,同时也是世界珍禽黑脸琵鹭(Platalea minor)重要的停歇地,应尽快建立闽江口湿地自然保护区。