Migratory and resident Blackcaps Sylvia atricapilla wintering in southern Spain show no resource partitioning

When different populations of the same bird species share non‐breeding habitats, competition for food may promote resource partitioning. We studied food choice by resident and migratory Blackcaps Sylvia atricapilla in sympatric wintering grounds in southern Spain. Resident Blackcaps have a larger bill, which may allow them to feed on a broader range of fruit sizes, and they may know the distribution of food better than do migrants. Based on fruit and bird counts, we transformed both fruit crop and bird abundance to a common energy currency. During two winters with low and high fruit production, available energy from fruit in mid‐January was estimated to be 80 and 1300 times, respectively, the daily requirements of Blackcaps. Furthermore, Blackcap numbers did not track between‐winter changes in fruit abundance during 10 consecutive years of monitoring, further suggesting that fruit food is not limiting. Analysis of food items from 760 samples of 717 individuals showed that migrants and residents fed primarily on fruits of Wild Olive Olea europaea sylvestris, the most energetic fruit resource. There was no evidence that the larger bills of resident Blackcaps provided any foraging benefit. Migratory Blackcaps fed on Wild Olives and invertebrates, two resources with high energetic and structural value, more frequently than did residents. This food choice could be more important for migratory Blackcaps because they have lower body mass to reduce wing load. Our results suggest that the wintering grounds of Blackcaps in Iberia provide abundant food that is used by sympatric migrants and residents without resource partitioning. Slight differences in food choice suggest that migrants might benefit from feeding on more nutritive food than residents to counteract the energetic constraints associated with a smaller body size.     

STOPOVER AND FAT DEPOSITION BY BLACKCAPS SYLVIA ATRICAPILLA FOLLOWING SPRING MIGRATION OVER THE SAHARA

Maitav, A. & Izhaki, I. 1994. Stopover and fat deposition by Blackcaps Sylvia atricapilla following spring migration over the Sahara. Ostrich 65:160-166.

Length of stopover and rate of weight change were studied in Blackcaps that stopover in Eilat (southern Israel) in spring after a trans-Saharan flight. The birds studied had already completed 2000 km of desert crossing and faced just 200 km more. The potential predicted flight range for these transients suggests that the fat depleted Blackcaps (fat class=0) could not reach the east Mediterranean scrublands, which offer more extensive foraging opportunities than the desert area around Eilat, without refueling. However, 46% of the Blackcaps had sufficient fat (fat class > 0) to reach central or northern Israel in a single flight in still air. Recaptured birds stayed in Eilat for 2,4±1,9 days. Although the body mass of an average recaptured bird increased by 0,27±1,44 g/day, which was an increase of 0,8%±7,0% of its body mass per day during stopover, these results were not significantly different from zero. Stopover length, mass change during stopover, and the rate of change in mass did not differ between males and females and between those who stopped over for only one day to those which stayed > 1 day. However, there was a tendency of these lean birds to stay for a shorter period in Eilat than relatively fat birds. There was also some tendency for lean birds to gain more mass during their stopover than fat birds. It seems that in spring, when less time is allotted for the whole migration program, the migrants resume their journey before fat reserves have been replenished.     

Are Blackcaps (Sylvia atricapilla) defending their nests also calling for help from their neighbours?

One hypothesized function of conspicuous mobbing of intruders by bird nest owners is to attract neighbouring birds (“calling for help” hypothesis) or third-party predators (“attract the mightier” hypothesis). These may help the nest owners by distracting and/or attacking the mobbed intruder. To date, these hypotheses have been studied solely during the mobbing of predators. Here, for the first time, I have studied mobbing attraction in the context of brood parasitism. I experimentally tested the Blackcap (Sylvia atricapilla), a small passerine with a highly aggressive and conspicuous nest defence behaviour. I elicited the aggressive responses of Blackcaps by presenting stuffed dummies of the brood parasitic Common Cuckoo (Cuculus canorus) and controls near their nests. At 32% of the nests (n = 75), the responses of the Blackcaps to dummies attracted up to 15 birds per trial from 21 passerine species. Most of the attracted birds were heterospecifics and rarely participated in mobbing; thus the “calling for help” hypothesis was not supported. No potential predators of the Cuckoo were attracted despite them living in the study area and despite prolonged mobbing by Blackcaps; thus rejecting the “attract the mightier” hypothesis. I argue that this hypothesis is unlikely to apply to typical avian predators during nest predation acts because these only last for several seconds. The number of attracted birds was a positive function of the owner’s intensity of nest defence as measured by the rates of alarm calling but not visual cues (rates of attacks). Suitable and unsuitable Cuckoo hosts did not differ in their behaviour in the vicinity of defended nests. The observed pattern of the positive correlation between the intensity of nest defence and the number of attracted birds is most likely a proximate by-product of the conspicuous nest defence by Blackcaps (but may well be adaptive for recruiting neighbours themselves). Thus, the mobbing behaviour of the Blackcap is directed towards the brood parasite and not towards other audience predators or potential recruits to the mob.     

Compensatory frugivory in migratory Sylvia warblers: geographical responses to season length

Seasonal shifts in the diets of Garden Warblers Sylvia borin , Blackcaps S. atricapilla and Lesser Whitethroats S. curruca at a North German site were studied from samples obtained by flushing the digestive tract of the birds. The significance of seven species of berries and pulpy fruits in the diet of these species while feeding in riparian vegetation during the premigratory and migratory seasons was assessed and compared with the pattern of frugivory shown by the same species in southern Germany. Because of the short time span between hatching and onset of migration, first-year long- and medium-distance migratory Sylvia warblers from northern Europe are forced to accelerate their juvenile development. Presumably to meet the higher nutritional demands of an accelerated development, juvenile Garden Warblers and Blackcaps in northern Germany ate relatively more fruit during premigration than Blackcaps in southern Germany. Fruit occurred in about 90% of their diet samples during both premigration and migration. However, this might not hold true for experienced adult birds. Garden Warblers accelerated the rate of fattening and reduced the time needed to prepare for migration when feeding on a mixed fruit diet. There were indications that Blackcaps directly influenced the fruit choice of Garden Warblers when fruits preferred by both species were scarce. Blackcaps and Garden Warblers showed subtle differences in their seasonal preferences for black elder Sambucus nigra and woody nightshade Solanum dulcamara .     

A method for differentiating between sedentary and migratory Blackcaps Sylvia atricapilla in wintering areas of southern Iberia

We used the morphological differentiation of southern, sedentary Iberian Blackcaps Sylvia atricapilla to distinguish them from migratory Blackcaps during the winter. To do so, we studied three morphometric traits (wing length, wing shape and tail length) of three migratory Iberian populations and two sedentary ones during the breeding season. We obtained a discriminant function which allowed us to differentiate the two population types (>90% correct classifications). We discuss the utility of the method for differentiating between sedentary and migratory Blackcaps in their sympatric wintering areas, as well as the implications of our results for the study and conservation of sedentary, perhaps differentiated Blackcaps in southern Iberia.     

Do all Blackcaps Sylvia atricapilla show winter site fidelity?

Fidelity to previous wintering areas (i.e. site fidelity) has important ecological and evolutionary implications. However, since the percentage of recaptures of ringed birds at the same wintering area in subsequent years does not allow the estimation of the proportion of birds alive that exhibit site fidelity, previous studies on different passerine species have failed to show the true extent of this site fidelity. Here we use a recent approach, based on the comparison of survival rate estimates from capture-recapture data at single field stations with recovery data from a much larger area. The idea is to determine the proportion of birds still alive that return to the area. The study was carried out on the Blackcap Sylvia atricapilla , comparing the capture-recapture data of two field stations (Pilas [SW] and Tiana [NE]) situated 1000 km apart in Spain with the complete winter recovery data of the Spanish Ringing Office. Totals of 1936 and 3976 Blackcaps were ringed at Pilas (1981–1986) and Tiana (1975–1986), respectively, and the numbers of recaptures in subsequent winters were 94 and 34. The pooled annual survival rate estimation based on the two sites is 0.40 (s.e. = 0.05). The annual survival rate estimated from the Spanish ringing recovery data was 0.48 (s.e. = 0.08), which is not significantly different. We can conclude, therefore, that migrant Blackcaps in Spain, if alive, tend to return year after year to the previous wintering site.     

Consistency in Egg Rejection Behaviour: Responses to Repeated Brood Parasitism in the Blackcap (Sylvia atricapilla)

To evaluate host responses towards repeated brood parasitism we experimentally parasitized and continuously videotaped blackcap nests in two consecutive trials. The ejection of a foreign egg was the most common response (94.5%) in both trials, but desertion (4.1%) and acceptance (1.4%) also occurred. The general method of ejection was puncturing. In 9.8% of identified ejections, already punctured eggs stuck to the abdominal feathers of the incubating bird and were carried out of the nest. Females were responsible for the majority of ejections in both trials and their response time was significantly shorter than that of males. Blackcaps exhibited consistency in the sex responsible for egg ejection over the two trials; but in five (20.8%) experiments individuals changed their behaviour. Repeatability for host responses within the nest was very high. In ejections accomplished by the same bird, the response was significantly quicker in the second trial, indicating the presence of certain learning abilities. Our results suggest that cuckoo hosts are quite consistent in their responses towards parasitic eggs when parasitized repeatedly within one breeding attempt.     

Habitat effects on resource tracking ability: do wintering Blackcaps Sylvia atricapilla track fruit availability?

If resource availability shapes population distribution, changes in resource abundance should cause parallel changes in population numbers. However, tracking ability may be disrupted by different environmental and behavioural factors that act at different spatial and temporal scales. Here we analyse the ability of wintering Blackcap Sylvia atricapilla populations to track spatio-temporal variation in fruit availability in southern Spain in two habitats (forests and shrublands) with different population structure. Former studies had shown that forests are equally used by both adult migrant and local Blackcaps, whereas shrublands are nearly monopolized by juvenile migrants. These differences might affect resource tracking: it should be disrupted in forests, as local birds remain over winter in their breeding territories, but not in shrublands where similarly competitive juvenile migrants can freely track the spatial distribution of fruits. We analysed the fruit-tracking ability of Blackcap populations among sites and years in both habitat types using a habitat-matching model, which predicts spatio-temporal changes in population abundance proportional to changes in resource availability. We counted Blackcaps and fruiting shrubs (dominated by Lentiscs Pistacia lentiscus and Wild Olives Olea europaea sylvestris ) during four winters in forest and shrubland patches. The abundance of fruits was always higher in shrublands than in forests. In shrublands, Blackcaps seemed to move freely across fruit-rich habitat patches, tracking changes in fruiting-shrub abundance among sites and years. However, such tracking was not observed in forests. This supports the view that fruit-tracking ability may be constrained by local factors, such as the social structure of populations occurring in different habitat types, which introduces spatio-temporal variation in the way fruit availability shapes the abundance distribution of these birds in their Mediterranean wintering grounds.     

Blackaps Sylvia atricapilla stopping over at the desert edge; physiological state and flight-range estimates

Migrating Blackcaps Sylvia atricapilla were mist netted at the desert edge in northern Israel and in Elat (southern Israel) during spring and autumn migrations between 1970 and 1991. Birds in spring in northern Israel were representative of birds that had completed the crossing of the Sahara, while those in Elat still had to cross the 150 km of the Negev Desert, which separates Elat and northern Israel. In autumn, birds captured in northern Israel were representative of those about to cross the Sahara Desert, while those in Elat had already started to cross the desert. The data allowed analysis of seasonal and location differences in the physiological state of Blackcaps before and after crossing the Sahara. Data analysed included body mass, visible fat score and calculated fat content. Autumn migrants were in better physiological condition than spring migrants at both locations, probably as a consequence of their migration route through fertile areas in autumn compared with the crossing of the Sahara in spring. Body mass was less variable after the Sahara crossing in spring than before the crossing in autumn. In spring, 71% and 67% of the birds were fat depleted (fat scores 0 and 1) at Elat and in northern Israel, respectively, while in autumn 34% and 42% were fat depleted. Blackcaps at Elat were 1.6 g lighter than those in northern Israel in autumn and 1.9 g lighter in spring. Potential flight ranges were estimated on the basis of meteorological conditions and flight altitude of passerines above the Negev in Israel (northern Sahara edge) during migration and on a simulation model that considered both energy and water as potential limiting factors for flight duration and distance. The simulation model predicted that half of the Blackcaps that stopped over in Elat and the majority of those that stopped over in northern Israel could not make a nonstop flight over the Sahara Desert in autumn without the assistance of at least an 8 m per s tailwind. Such a wind would still not be sufficient for 34% of the birds in Elat and 42% in northern Israel, and clearly they had insufficient fat reserves to cross the Sahara in a single flight. Although the fattest Blackcaps had accumulated sufficient fat to enable them to traverse the Sahara in a single flight, they probably faced dehydration by at least 12% of their initial body mass when they reached the southern Sahara edge. These birds should use intermittent migration with stopovers at sites with drinking and feeding potential. Their decision to stop over during the day in the desert at sites with shade but without food and water would be beneficial if the meteorological conditions during daytime migration imposed greater risks of dehydration than at night. Spring migrants could not reach their breeding areas in Europe without feeding, but those examined in Elat could cross the remainder of the desert in a single flight.     

Age-related variation in wing shape of migratory and sedentary Blackcaps Sylvia atricapilla

In many passerines, juveniles have shorter and more rounded wings than adults. Given that (1) long and pointed wings improve endurance in migratory flights, (2) shorter and rounded wings improve manoeuvrability, and (3) juvenile birds are more vulnerable to predators than adults, it has been hypothesised that ontogenetic variation in wing shape results from a greater importance of predation avoidance relative to migration performance during the first year of life. If so, wing shape should not change with age in the absence of migration-related selection for longer and more pointed wings. We test this by studying the variation with respect to age in wing length and wing pointedness of migratory and sedentary Blackcaps wintering in southern Spain. Migratory Blackcaps had longer and more pointed wings than sedentary Blackcaps. Juveniles had shorter wings than adults in migratory populations, but not in sedentary populations. The variation with age in wing pointedness was less pronounced, and was found in migratory females only. These differences between the two traits could be related to a stronger selection for pointed wings than for longer wings with increasing distance of migration, and to an increased migratoriness of females in partially migratory Blackcap populations. We hypothesise that, in migratory Blackcaps, a shorter and more rounded wing in juveniles could be selected for if the decrease in predation rate compensated for the somewhat greater costs of the first migration attempt. On the other hand, there are no costs of migration in sedentary Blackcaps, which hence maintain a similar wing shape, giving high manoeuvrability, both as juveniles and as adults.     

Is supplementary feeding in gardens a driver of evolutionary change in a migratory bird species?

Human activities are causing rapid environmental change at a global scale. Urbanization is responsible for some of the most extreme human‐altered habitats and is a known driver of evolutionary change, but evidence and understanding of these processes is limited. Here, we investigate the potential underlying mechanisms contributing to the contemporary evolution of migration behaviour in the Eurasian blackcap (Sylvia atricapilla). Blackcaps from central Europe have been wintering in urban areas of Britain with increasing frequency over the past 60 years, rather than migrating south to the Mediterranean. It has been hypothesized that the popularization of providing supplementary foods for wild birds within Britain may have influenced this marked migratory change, but quantifying the selective forces shaping evolutionary changes remains challenging. Using a long‐term national scale data set, we examine both the spatial distribution and interannual variation in blackcap wintering behaviour in Britain in relation to supplementary food availability and local climate. Over a 12‐year period, we show that blackcaps are becoming increasingly associated with the provision of supplementary foods in British gardens, and that the reliability of bird food supplies is influencing their winter distribution at a national scale. In addition, local climatic temperatures and broader scale weather variation are also important determinants of blackcap wintering patterns once they arrive in Britain. Based on our findings, we conclude that a synergistic effect of increased availability of feeding resources, in the form of garden bird food, coupled with climatic amelioration, has enabled a successful new wintering population to become established in Britain. As global biodiversity is threatened by human‐induced environmental change, this study presents new and timely evidence of the role human activities can play in shaping evolutionary trajectories.     

Fruit size in wild olives: implications for avian seed dispersal

1. The response of frugivorous birds to an enlargement of fruit size, and the consequences for both birds and plants, are analysed for the interaction between avian seed dispersers and olives ( Olea europaea) .
2. The enlargement of fruit size promotes a shift in frugivorous birds' feeding behaviour, from swallowing fruits whole to pecking pieces of pulp. The relative frequency of olive consumption using each feeding behaviour was assessed by combining field data on frequency of appearance of olive pulp and seeds with data from laboratory trials.
3. Sardinian Warblers ( Sylvia melanocephala ) and European Robins ( Erithacus rubecula ) were mainly peckers both on cultivated and wild olives. Blackcaps ( Sylvia atricapilla ) consumed wild olives mainly by swallowing but consumed cultivated olives (larger than the wild ones) primarily by pecking. Song Thrushes ( Turdus philomelos ) were primarily swallowers of both types of fruits.
4. Laboratory trials with Song Thrushes, Blackcaps and European Robins showed that: (a) all were able to peck fruits; (b) fruit size determined a shift from swallowing to pecking, as pecking frequency increased with the enlargement of the fruit size; (c) all the species had an increased fruit handling failure rate when trying to swallow increasingly large fruits; and (d) from the birds' perspective, small shifts in fruit size may have important consequences on fruit profitability.
5. Pecking on olives turns the mutualistic fruit–frugivore interaction into a fruit-pulp predator interaction, thus arising a conflict between the plant and frugivorous birds.
6. This study shows that heavy dependence on fruit is not always simply related to seed dispersal. The same frugivorous bird species can act as a seed disperser or a pulp predator for the same plant species. The threshold between these roles is highly influenced by the ratio gape size/fruit size.     

Predation of codling moth Cydia pomonella L. by the Silvereye Zosterops lateralis (Latham)

Predation of cocooned larvae of codling moth Cydia pomonella by silvereyes Zosterops lateralis was studied in an apple orchard in Nelson, New Zealand. Apple logs with known larval densities were made available to the birds for known periods of time, either in cages or exposed in the apple orchard. The numbers of silvereyes and the natural predation of codling moth were recorded in the same orchard. Predation was density dependent. On caged logs with an initial high density of 32 larvae, 1.1 larvae were consumed per bird‐hour; in contrast, one larva was consumed per 34.5 bird‐hours at three larvae per log. A curvilinear relationship was demonstrated between larval density and the bird‐hours required for predation; this relationship was consistent with the known density dependence of silvereye predation of codling moth. A regression of the total annual winter bird predation of larvae in the orchard on bird numbers was significant. However, the density dependence of predation resulted in declining rates of predation over the winter as larval density declined; the first birds to arrive in the orchard benefitted from particularly high predation rates. As a consequence, fluctuations in bird numbers during the winter had only a secondary influence on predation rates. The numbers of silvereyes in the orchard showed no relationship to the density of the codling moth population present. This study confirmed the importance of silvereyes in the predation of codling moth and a functional, not numerical, rseponse of these birds to codling moth density.     

Resident and transient dynamics, site fidelity and survival in wintering Blackcaps Sylvia atricapilla: evidence from capture–recapture analyses

In their winter quarters, migrant birds may either remain within a small area (resident strategy) or move frequently over a large area looking for locally abundant food (transient strategy). It has been suggested that both strategies could simultaneously occur in the same population. We used time-since-marking capture–recapture models to infer the coexistence of these two behavioural strategies (transient and resident) among wintering Blackcaps Sylvia atricapilla using weekly recapture data over a 7-year period. A related question is whether Blackcaps, if surviving to the next winter, always return to the same wintering area, so we also used this approach to analyse winter site fidelity and to estimate annual survival probabilities. Model selection supported the existence of heterogeneity in survival estimates for both the within-season and the interannual survival probabilities, i.e. there was evidence for the existence of transients. It was estimated that 26% of the Blackcaps were resident during the winter. Mean apparent annual survival probability was 0.46 (se = ±0.11). However, there was some evidence suggesting that not all individuals showed winter site fidelity. The estimated proportion of individuals that, if alive, returned to the wintering area was 28%. This is the first study to show the existence of these two behavioural strategies (residence and transience) among wintering Blackcaps, and the first confirming this pattern using capture–recapture models. These models considering transient and resident dynamics may become an important tool with which to analyse wintering strategies.     

Relationship between avian range limits and plant transition zones in Maine

Aim To determine if vegetation complexity associated with transition zones may be a contributing factor affecting bird species distributions in Maine, USA, and in increased numbers of bird species at about 45° north latitude in northeastern North America. Location Maine, USA; North America north of Mexico. Methods We delineated the ranges within Maine (86,156 km²) of 186 bird species and 240 woody plants using literature and expert review. Maps showing species richness and numbers of range limits, at 324 km² resolution, were developed for woody plants and groups of breeding birds: forest specialists, forest generalists, and those that used barren and urban habitats, early successional areas, and wetlands or open water. Two plant transition zones for Maine were identified previously, with the north–south transition zone mapped across eastern North America. Patterns in bird distribution maps were compared to woody plant maps and to transition zones. Results When the distributions of forest specialists were compared to the north–south vegetation transition zone in Maine, they were spatially coincident, but were not for other groups. Forest specialists had more species with range limits in the state (61%) than generalists (13%) or any other group. At a continental‐scale, the vegetation transition zone within eastern North America agreed fairly well with the areas of highest bird richness. Main conclusions A bird transition zone occurs in Maine and across eastern North America, akin to and overlapping the vegetation transition zone. Seasonality is likely the primary source of the inverse gradient in bird richness in the eastern USA, as reported by others. However, vegetation structure and habitat selection at very broad spatial scales appear to contribute to the reversed gradient. North of the vegetation transition zone, forest structure is simpler and coniferous forests more dominant, and this may contribute to reduced bird species richness. However, the northern (> 49°) typical gradient in bird species richness has been related to many hypotheses, and several are likely involved in the genesis of the gradient.     

Saisonale und tidale Variation in der Nutzung von Wattfl?chen durch nahrungssuchende V?gel

Densities of feeding birds were estimated on tidal mud flats in relation to season and tide. Dunlin, Knot, Bar-tailed Godwit, Oystercatcher, Golden Plover, Common Gull, and Black-headed Gull were most abundant. Seasonal variation was significant in all species. In general, there was a correlation between bird numbers on study plots and total bird numbers in the area. Preferences for a particular sediment type and prominent occurrence at tideline in some species was explained as an adaption to differential food availability.     

Adjustment of incubation according to the threat posed: a further signal of enemy recognition in the Blackcap Sylvia atricapilla?

Nest predation and brood parasitism are costly for nest owners, and natural selection should therefore favour the evolution of parental counterdefences. We addressed the question of whether Blackcaps Sylvia atricapilla change their incubation behaviour in response to various nest intruders and whether this adjustment matches the intensity of mobbing exhibited towards these intruders. Near focal nests, we successively exposed a dummy of a brood parasite, nest predator and an innocuous species. After the parents had responded, we removed the dummy and filmed their incubation. The most aggressive response towards the Common Cuckoo Cuculus canorus and high nest attendance after its disappearance indicated recognition of the brood parasite. Low-intensity response to the Jay Garrulus glandarius, together with reduced subsequent parental care, suggested that Blackcaps perceived it either as less deleterious at the egg stage than the Cuckoo or as a danger to themselves. Almost no aggression towards the Turtle Dove Streptopelia turtur, along with the resumption of incubation after its removal, implied that Blackcaps recognised it as harmless. In addition, we found that the level of aggression positively correlated with nest attendance, suggesting a link between the intensity of mobbing and subsequent parental care. Altogether, our results demonstrate that the issue of enemy recognition may be viewed as a complex of both aggressive and post-presentation behaviours.     

长江师范学院校园夏季鸟类群落与多样性分析

2008年3～7月采用样线法对长江师范学院李渡校园鸟类组成和种群数量进行了调查,共记录鸟类6目21科28种,数量1633只,物种多样性指数为3．9204,均匀性指数为1．1765,其中国家“三有”名录鸟类25种,CITES名录鸟类1种。鸟类区系以东洋界成分为主。对不同生境鸟类多样性的分析结果表明：（1）乔灌林鸟类多样性指数和均匀性指数最高,水域鸟类多样性指数最低,建筑区均匀性指数最低;（2）乔灌林与竹林的相似性指数最高,竹林与水域的相似性最低。     

广州新垦红树林湿地鸟类多样性与生境分析

2005-2006年的1月、4月、7月和10月,利用样带法对广州市新垦红树林湿地和周边农田进行鸟类物种多样性研究。利用Shannon-Wiener指数分析了生境类型的鸟类群落种数、数量、物种多样性、均匀性指数等特征。结果表明,新垦红树林湿地1月鸟类种数高于周边农田湿地2倍,鸟类群落个体数量高于农田湿地9倍;红树林湿地4月和7月鸟类种数高于周边农田湿地1．5倍,鸟类群落个体数量高于农田湿地4倍;红树林湿地10月鸟类种数高于周边农田湿地1．5倍,鸟类群落个体数量高于农田湿地6．8倍;新垦红树林湿地和周边农田湿地鸟类物种多样性表现出明显的季节性变化。     

Experimental refuges for migratory waterfowl in Danish wetlands. I. Baseline assessment of the disturbance effects of recreational activities

1. Potential human sources of disturbance, including fishing, sailing, windsurfing and different types of waterfowl hunting, are described and their effects on autumn-staging waterbirds, including mute swan, wigeon and coot, were examined at a coastal wetland in Denmark from 1985 to 1988.
2. Bird and human distributions were superimposed on the distribution of submerged vegetation and water depths to identify the extent of spatial overlap; likewise, seasonal and diurnal temporal overlap in bird abundance, and human activities were defined. Behavioural and distributional reactions of waterbirds to different human activities, in terms of escape distances, disruption of activity patterns and redistribution, were assessed to establish their relative effects.
3. Sailing and windsurfing showed little spatial overlap, and fishing partial spatial overlap with bird distributions; these activities almost ceased before the peak in autumn bird numbers. Hunting showed a high degree of spatial and temporal overlap with bird presence.
4. Birds responded to windsurfing at greatest distances, whereas hunting (especially from mobile punts) caused the longest disruptions to activities of waterfowl. In terms of behaviour and redistribution, wigeon was more affected by shooting than was mute swan or coot. One or two mobile shooting punts reduced wigeon numbers, whereas numbers were unaffected by the presence of up to 4–6 stationary punts; fishing boats had no effect on wigeon abundance.
5. Hunting, especially shooting from mobile punts, was identified as the most disturbing human activity in relation to staging waterfowl in this area. Similar results and conclusions were reached in another comparable study area. The results have implications for refuge designs and zoning of disturbing recreational activities.