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1.
Although most UK sand dune systems are now fossilized, with little mobility and reducing amounts of bare sand, they support
important populations and assemblages of terrestrial invertebrates. Offering open conditions, warm substrates and a range
of habitats and habitat structures, they have become increasingly significant as other coastal habitats have been lost. In
Wales, 680 Red Data Book and Nationally Scarce species have been recorded from dunes. 109 species in the UK are restricted
to dunes, and in Wales there are an additional 145 species confined to dunes and 208 species strongly associated with dunes.
Of these, 172 species are dependent upon bare and sparsely-vegetated sand, in grey dunes and early-successional dune grassland,
at some stage of their life cycle, rising to 292 species if those associated with the strandline, foredunes, yellow dunes
and pioneer dune slacks are included, equating to 63% of the 462 dune species. Bees and wasps are particularly well represented,
with 278 species (68% of the Welsh fauna) recorded on Welsh dunes, including 17 obligates and 44 species with a strong dependence,
52 of which are associated with bare and sparsely-vegetated sand. Key to maintaining invertebrate populations on UK dunes
is the provision of bare sand but in Wales, bare sand accounts for only 1.7% of the total sand dune resource. As a more appropriate
bare sand threshold is likely to range between 10 and 30%, radical action is required to re-mobilize at least the key sand
dune systems. 相似文献
2.
《Conservation biology》2009,23(2):i-i
Cover: Radar imagery can be used to map the locations from which migratory birds depart and to highlight important stopover sites. Shown are movements of long-distance migrants, such as the Blackburnian Warbler ( Dendroica fusca ), detected during spring migration near Buffalo, New York. Warbler photo by Charles Eiseman. See pages 440–448. 相似文献
3.
Time of departure and landing of nocturnal migrants are of great importance for understanding migratory strategy used by birds.
It allows us to estimate flying time and hence the distance that migrants cover during a single night. In this paper, I studied
the temporal schedule of nocturnal departures of European robins during spring migration. The study was done on the Courish
Spit on the Baltic Sea in 1998–2003 by retrapping 51 ringed birds in high mist nets during nocturnal migratory departure.
Take-offs of individual birds occurred between the first and tenth hour after sunset (median 176 min after sunset). Departure
time was not related to fuel stores at arrival and departure, stopover duration and progress of the season. The results suggest
that one reason for temporal variation in take-off time was differential response of European robins with high and low motivation
to depart to such triggers as air pressure and its trend. If these parameters reach a certain minimum threshold shortly before
sunset, robins with a high migratory motivation take off in the beginning of the night. When air pressure or its trend reaches
a maximum, it may trigger to take off later during the night birds with lower initial motivation for departure, including
those that have low refuelling efficiency. In regulation of timing of take-offs of robins, an important role is also played
by their individual endogenous circadian rhythm of activity which is related to the environment in a complex way. 相似文献
4.
Jann Peyrat Małgorzata Braun Christian Dolnik Maike Isermann Hartmut Roweck 《Journal of Coastal Conservation》2009,13(4):235-246
Coastal dune ecosystems are among the most dynamic habitats with high conservation value in Europe but are also under strong
anthropogenic pressure regarding coastal protection and recreation. Hence, it is of high importance to know about long-term
natural and anthropogenic changes and development of protected dune habitats for nature conservation, as well as for coastal
management. This paper aims to identify the vegetation dynamics on the Łeba Bar/Poland over a period of 74 years by cartometric
comparison using modern Geographical Information System (GIS). To quantify the rate of vegetation dynamics two aerial photographs
dating from 1932 and 2006 were digitalized and analyzed with GIS to produce digital vegetation maps. Information about decrease,
increase and stability of vegetation types of this area are discussed. The results show that there has been a clear reduction
in the total area of bare sand and a considerable increase of woodlands and dense grass communities. Nevertheless, the remaining
extensive drift sand areas and deflation hollows on the Łeba Bar offer one of the most important habitats for pioneer vegetation
on bare sand of migrating dunes and dunes at the Southern Baltic coast. The present work proved the need to observe the future
development of the vegetation communities and to implement management measures to maintain the dynamic of this unique dune
landscape. 相似文献
5.
Robert W. Russell F. Lynn Carpenter Mark A. Hixon David C. Paton 《Conservation biology》1994,8(2):483-490
We examined the impact of variation in habitat quality on migrating Rufous Hummingbirds ( Selasphorus rufus ) in the California Sierra Nevada. As do other migratory species, these birds depend on "stopover" habitats en route for feeding and replenishing depleted energy stores. During seven years of study, the quality of the stopover habitat (assessed in terms of the density of nectar food resources) varied widely due to natural variation in flowering. In years when stopover habitat quality was poor, incoming body masses were low and stopover durations were long. Population densities of migrant hummingbirds at the study site were coupled to habitat quality both within and among years. These observations demonstrate important effects of stopover habitat variation on the physiological, behavioral, and population ecology of migrating hummingbirds. High-quality stopover habitats are critical links between breeding and wintering areas for many species, and their preservation should be considered an essential component of strategies aiming to conserve migratory bird populations. 相似文献
6.
A multi-scale examination of stopover habitat use by birds 总被引:1,自引:0,他引:1
Most of our understanding of habitat use by migrating land birds comes from studies conducted at single, small spatial scales, which may overemphasize the importance of intrinsic habitat factors, such as food availability, in shaping migrant distributions. We believe that a multi-scale approach is essential to assess the influence of factors that control en route habitat use. We determined the relative importance of eight variables, each operating at a habitat-patch, landscape, or regional spatial scale, in explaining the differential use of hardwood forests by Nearctic-Neotropical land birds during migration. We estimated bird densities through transect surveys at sites near the Mississippi coast during spring and autumn migration within landscapes with variable amounts of hardwood forest cover. At a regional scale, migrant density increased with proximity to the coast, which was of moderate importance in explaining bird densities, probably due to constraints imposed on migrants when negotiating the Gulf of Mexico. The amount of hardwood forest cover at a landscape scale was positively correlated with arthropod abundance and had the greatest importance in explaining densities of all migrants, as a group, during spring, and of insectivorous migrants during autumn. Among landscape scales ranging from 500 m to 10 km radius, the densities of migrants were, on average, most strongly and positively related to the amount of hardwood forest cover within a 5 km radius. We suggest that hardwood forest cover at this scale may be an indicator of habitat quality that migrants use as a cue when landing at the end of a migratory flight. At the patch scale, direct measures of arthropod abundance and plant community composition were also important in explaining migrant densities, whereas habitat structure was of little importance. The relative amount of fleshy-fruited trees was positively related and was the most important variable explaining frugivorous migrant density during autumn. Although constraints extrinsic to habitat had a moderate role in explaining migrant distributions, our results are consistent with the view that food availability is the ultimate factor shaping the distributions of birds during stopover. 相似文献
7.
Sand dunes are complex systems that contain several habitats, often as mosaics or transitions between types. Several of these habitats are afforded protection under European Legislation and in the UK nationally within Special Areas of Conservation (SAC) and Sites of Special Scientific Interest (SSSI). Natural England has a statutory duty to report to Europe on the conservation status and condition of sand dunes; and is required to report to the UK Government on designated sites. To achieve this we have sought ways of capturing, analysing and interpreting data on the extent and location of sand dune habitats. This requires an ability to be able to obtain data over large areas of coastline in an efficient way. Natural England and Environment Agency Geomatics have worked collaboratively for over 16 years, sharing data and ecological knowledge. In 2012 work started to evaluate the use of remote sensing to map UK BAP and Annex I sand dune habitats. A methodology has now been developed and tested to map sand dune habitats. The key objective was to provide an operational tool that will help to map these habitats and understand change on sites around England. This has been achieved through analysis of LIDAR and Compact Airborne Spectrographic Imager (CASI) data using Object Orientated Image Analysis. Quality Control (QC) and accuracy assessments have shown this approach to be successful and 11 sites have been mapped to date. These techniques are providing a new approach to monitoring change in coastal vegetation communities and informing management of protected sites. 相似文献
8.
Heiko Schmaljohann Felix Liechti Bruno Bruderer 《Behavioral ecology and sociobiology》2009,63(11):1609-1619
Meteorological conditions influence strongly the energy and water budget of birds. By adjusting their flights spatially and
temporally with respect to these conditions, birds can reduce their energy expenditure and water loss considerably. By radar,
we quantified songbird migration across the western Sahara in spring and autumn. There autumn migrants face the trade-off
between (a) favorable winds combined with hot and dry air at low altitudes and (b) unfavorable winds combined with humid and
cold air higher up. Thus, it can be tested whether birds may chose altitudes to minimize water loss instead of energy expenditure.
We predicted optimal flight altitudes with respect to water loss and energy expenditure based on a physiological flight model
when crossing the western Sahara and compared these model predictions spatially and temporally with measured songbird densities.
The model aiming for minimal water consumption predicted a mean flight altitude of 3,400 m under autumn conditions. However,
64% of the nocturnal songbird migration flew at altitudes below 1,000 m above ground level profiting from tailwind. This preference
for tailwind in autumn, despite the hot and dry air, emphasizes the importance of energy savings and diminishes the significance
of possible water stress for the selection of flight altitude. Nevertheless, during daytime, high energy expenditure due to
air turbulences and water loss due to warmer air and direct solar radiation prevent songbirds from prolonging their nocturnal
flights regularly into the day. Birds crossing the Sahara save water by nocturnal flights and diurnal rests. 相似文献
9.
Jannika E. Boström Thord Fransson Ian Henshaw Sven Jakobsson Cecilia Kullberg Susanne Åkesson 《Behavioral ecology and sociobiology》2010,64(11):1725-1732
Recent experiments exposing migratory birds to altered magnetic fields simulating geographical displacements have shown that
the geomagnetic field acts as an external cue affecting migratory fuelling behaviour. This is the first study investigating
fuel deposition in relation to geomagnetic cues in long-distance migrants using the western passage of the Mediterranean region.
Juvenile wheatears (Oenanthe oenanthe) were exposed to a magnetically simulated autumn migration from southern Sweden to West Africa. Birds displaced parallel
to the west of their natural migration route, simulating an unnatural flight over the Atlantic Ocean, increased their fuel
deposition compared to birds experiencing a simulated migration along the natural route. These birds, on the other hand, showed
relatively low fuel loads in agreement with earlier data on wheatears trapped during stopover. The experimental displacement
to the west, corresponding to novel sites in the Atlantic Ocean, led to a simulated longer distance to the wintering area,
probably explaining the observed larger fuel loads. Our data verify previous results suggesting that migratory birds use geomagnetic
cues for fuelling decisions and, for the first time, show that birds, on their first migration, can use geomagnetic cues to
compensate for a displacement outside their normal migratory route, by adjusting fuel deposition. 相似文献
10.
S. Åkesson Lennart Karlsson Göran Walinder Thomas Alerstam 《Behavioral ecology and sociobiology》1996,38(5):293-302
Extensive ringing data from a coastal site (Falsterbo Bird Observatory) in southwesternmost Sweden were used to investigate
the occurrence of reverse autumn migration among 20 passerine bird species of widely different migration categories. The data
demonstrate that reverse migration is a widespread and regular phenomenon among nocturnal as well as diurnal migrants and
among irruptive migrants, temperate zone migrants, and long-distance migrants destined for tropical winter quarters. The reoriented
movements were directed approximately opposite to the normal migration direction, i.e. between NNW and ENE from the coast
and towards inland. Median distances of reverse movements varied between 9 and 65 km. Some individuals of irruptive and partial
migrants settled to winter in the reverse direction. Bird species with relatively small fat reserves at capture were more
likely to perform reverse migratory movements than species with larger fat deposits. In two species birds performing forward
migration were significantly heavier within 10 days after capture than individuals performing reverse movements. The reoriented
movements probably are of adaptive significance for birds confronted with the sea and pre-disposed to refuelling during migration.
A bimodal orientation mechanism will bring the birds from an area with high competition for food and high predation risk to
more suitable resting and feeding grounds before resuming migration in the forward direction and crossing the barrier.
Received: 11 July 1995/Accepted after revision: 19 November 1995 相似文献
11.
Vestergaard Peter 《Journal of Coastal Conservation》1997,3(1):103-112
According to estimates from the Danish Meteorological Institute global warming until 2080 may cause a relative sea-level rise in Danish waters of 33–46 cm. In the present paper the possible impact of a sea-level rise of this magnitude on coastal habitat types is discussed for three case studies, based on previous investigations of vegetation, topography and soil of localities at the Baltic coast of Denmark. The case studies include the following types of localities and habitats: (1) an off-shore barrier complex: sandy beach, sand dune, geolittoral, brackish, low-tidal meadow, reed bed; (2) a protected bay: geolittoral, brackish meadow, coastal grassland; (3) a dune area: mobile and fixed dune communities, and adjoining sea wall: coastal grassland. In the geolittoral meadow and coastal grassland habitats the sea-level rise is expected to cause a horizontal displacement of vegetation zones and a reduction in area, depending on accretion rate (sedimentation, peat formation), local topography and inland land-use. In the beach and sand dune habitats the sea-level rise is expected to cause a change in groundwater level, influencing slack vegetation, and a change in the erosion/accretion pattern, resulting in landward rebuilding of the mobile dune as well as in a more or less diffuse inland sand drift, causing destabilization of fixed dune vegetation. 相似文献
12.
Toward Conservation of Midcontinental Shorebird Migrations 总被引:1,自引:0,他引:1
Shorebirds represent a highly diverse group of species, many of which experience tremendous energy demands associated with long-distance migratory flights. Transcontinental migrants are dependent upon dynamic freshwater wetlands for stopover resources essential for replenishment of lipid reserves and completion of migration. Patterns of shorebird migration across midcontinental wetlands were detected from migration reports to American Birds and information provided by U.S. Fish and Wildlife Service national wildlife refuges. Patterns in species composition and abundance varied geographically, emphasizing the uniqueness of different regions to migrating shorebirds. Smaller species and neotropical migrants moved primarily across the Great Plains, whereas larger species and North American migrants predominated in assemblages in the intermountain west Shorebirds were broadly dispersed in wetland habitats with dynamic water regimes. Whereas populations of shorebirds in coastal systems appear to concentrate at sites of seasonally predictable and abundant food resources, we propose that transcontinental shorebirds disperse and use wetlands opportunistically. This migration system exemplifies the need for large-scale, coordinated regional management efforts that recognize the dynamic nature of ecosystem processes. 相似文献
13.
Håkan Karlsson Johan Bäckman Cecilia Nilsson Thomas Alerstam 《Behavioral ecology and sociobiology》2010,64(12):2021-2031
Using tracking radars, we investigated the variability of flight directions of long-distance nocturnal passerine migrants
across seasons (spring versus autumn migration) and sites at the southern (56° N) and northern (68° N) ends of the Scandinavian
Peninsula (Lund versus Abisko). Whilst most migrants at Lund are on passage to and from breeding sites in Fennoscandia, the
majority of the migrants at Abisko are close to their breeding sites, and migration at Abisko thus to a large degree reflects
initial departure from breeding sites (autumn) or final approach to breeding destinations (spring). The radar data were used
to test predictions about differences in orientation and wind drift effects between adult and juvenile birds (a large proportion
of autumn migrants consists of juvenile birds on their first journey), between situations far away from or near the goals
and between different phases of migration (initial departure, en route passage, final approach to goal). The concentrations
(both total and within-night concentrations) of flight directions differed significantly between seasons as well as sites,
with the highest concentration at Lund in spring (mean vector length of track directions, r = 0.79) and lowest at Abisko during spring (r = 0.35). Partial wind drift and partial compensation were recorded at Lund, with a similar effect size in spring and autumn,
whilst possible wind drift effects at Abisko were obscured by the large directional scatter at this site. The results from
Lund support the prediction that the high proportion of juveniles in autumn contributes to increase the directional scatter
during this season, whilst there was no support for predictions of differential wind drift effects between seasons and situations
with different goal distances. The most striking and surprising result was the exceedingly large scatter of flight directions
at Abisko, particularly in spring. We suggest that such an exaggerated scatter may be associated with final approach orientation,
where migrants reach their specific goals from all various directions by final navigation within a more wide-ranging goal
region. The larger scatter of autumn flight directions at Abisko compared to Lund may be due to exploratory flights in variable
directions being more common at initial departure from breeding sites than later during migratory passage. These surprising
results highlight the importance of studying and analysing orientation during final approach to (and initial departure from)
migratory goals for understanding the orientation systems of migratory birds. 相似文献
14.
Topography and vegetation of restored dunes on a developed barrier island were examined after a large-scale beach nourishment
project. Restoration began in 1993 using sand-trapping fences andAmmophila breviligulata Fern. plantings. Subsequent growth of dunes was favored by installing new fences and suspending beach raking to accommodate
nesting birds. Plant species richness, percent cover of vegetation, and height ofA. breviligulata were sampled in 1999 on seven shore perpendicular transects in six dune microhabitats (backdune, primary crest, mid-foredune,
swale, seaward-most fenced ridge, incipient dune on the backbeach).
A total of 26 plant taxa were found at all seven sites. Richness and percent cover were greatest in the backdune and crest,
especially in locations that predated the 1992 nourishment. Richness was greater where fences enhanced stabilization. Fences
initially compensate for time and space and allow vegetation to develop rapidly, but maintenance nourishment is required to
protect against wave erosion and ensure long-term viability of habitat. An expanded environmental gradient is an option, where
beach nourishment provides space for a species-rich crest and backdune to develop, while the incipient dune remains dynamic.
Options where space is restricted include a dynamic, full-sized seaward section of a naturally functioning dune (truncated
gradient) or a spatially restricted sampler of a wider natural dune (compressed gradient) maintained using fences. Expanded
and truncated gradients may become self-sustaining and provide examples of natural cycles of change. Compressed gradients
provide greater species richness and flood protection for the available space, but habitats are vulnerable to erosion, and
resident views may be impaired. 相似文献
15.
Characteristics of Important Stopover Locations for Migrating Birds: Remote Sensing with Radar in the Great Lakes Basin 总被引:1,自引:0,他引:1
DAVID N. BONTER†‡ SIDNEY A. GAUTHREAUX JR§ . THERESE M. DONOVAN‡ 《Conservation biology》2009,23(2):440-448
Abstract: A preliminary stage in developing comprehensive conservation plans involves identifying areas used by the organisms of interest. The areas used by migratory land birds during temporal breaks in migration (stopover periods) have received relatively little research and conservation attention. Methodologies for identifying stopover sites across large geographic areas have been, until recently, unavailable. Advances in weather-radar technology now allow for evaluation of bird migration patterns at large spatial scales. We analyzed radar data (WSR-88D) recorded during spring migration in 2000 and 2001 at 6 sites in the Great Lakes basin (U.S.A.). Our goal was to link areas of high migrant activity with the land-cover types and landscape contexts corresponding to those areas. To characterize the landscapes surrounding stopover locations, we integrated radar and land-cover data within a geographic information system. We compared landscape metrics within 5 km of areas that consistently hosted large numbers of migrants with landscapes surrounding randomly selected areas that were used by relatively few birds during migration. Concentration areas were characterized by 1.2 times more forest cover and 9.3 times more water cover than areas with little migrant activity. We detected a strong negative relationship between activity of migratory birds and agricultural land uses. Examination of individual migration events confirmed the importance of fragments of forested habitat in highly altered landscapes and highlighted large concentrations of birds departing from near-shore terrestrial areas in the Great Lakes basin. We conclude that conservation efforts can be more effectively targeted through intensive analysis of radar imagery. 相似文献
16.
Habitat use pattern and status of shorebirds in southern India were investigated in six tidal flats comprising three mudflats and three sand flats on the east coast of southern India. Totally, 7757 shorebirds belonging to 21 species were recorded during September 2000–March 2002. The birds preferred mudflats over sand flats. Density, diversity and richness of shorebirds were relatively higher in tidal flats, especially in mudflats. The shorebirds preferred mudflats over sand flats as stopover sites and sites for refueling the required energy during migration. Rhythmic changes in tidal pattern also influenced the allochthonous nutrients and prey species, which also attracted the migratory shorebirds. However, the abundance of shorebirds with reference to tidal flats *season*tide and habitats*seasons * tide had strong variations (P < 0.001). During migratory season, bird density, diversity and species richness were observed higher than in other seasons. 相似文献
17.
Teja Tscharntke 《Conservation biology》1992,6(4):530-536
Results from populations of insects and birds inhabiting Phragmites habitats were used to analyze effects of fragmentation. Flush-crash cycles of the stem-boring moth Archanara geminipuncta (Lepidoptera, Noctuidae) showed regionally concurrent, local extinctions despite an originally enormous population size (more than 180,000 adults), emphasizing the importance of metapopulation dynamics. Further, A. geminipuncta could be considered a keystone species, since shoot damage facilitated more than twenty species of herbivores, saprovores (of the caterpillars' feces), and their parasitoids. The gall midge Lasioptera arundinis could survive only in side shoots induced by shoot damage of A. geminipuncta .
Small Phragmites stands had thinner shoots (due to a water or nutrient deficiency) and shoots with more leaves (due to a better light supply) than large stands, thereby influencing species-specific demands for habitat suitability and nutritiousness of reed tissue. In other words significance of habitat fragmentation could not be assessed by area alone. For example, two chloropid flies depending on thin, yellowish shoots survived only in small habitats or in the unmown edges of large habitats.
Local persistence of Phragmites herbivores depended on much larger population sizes than could be expected from a population size sufficient to maintain genetic variation. At least 11,000 adults of the gall midge Giraudiella inclusa (or more than 84,000 galls) were necessary to avoid local extinction.
With regard to conservation management of reed habitats, nature reserves should consist of old and unmown reeds, have fewer disturbed (particularly, fewer mown) habitat edges, measure more than two hectares (priority should go to the largest remaining fragments), and be surrounded by nearby reed habitats providing reservoir populations and diverse shoot types. 相似文献
Small Phragmites stands had thinner shoots (due to a water or nutrient deficiency) and shoots with more leaves (due to a better light supply) than large stands, thereby influencing species-specific demands for habitat suitability and nutritiousness of reed tissue. In other words significance of habitat fragmentation could not be assessed by area alone. For example, two chloropid flies depending on thin, yellowish shoots survived only in small habitats or in the unmown edges of large habitats.
Local persistence of Phragmites herbivores depended on much larger population sizes than could be expected from a population size sufficient to maintain genetic variation. At least 11,000 adults of the gall midge Giraudiella inclusa (or more than 84,000 galls) were necessary to avoid local extinction.
With regard to conservation management of reed habitats, nature reserves should consist of old and unmown reeds, have fewer disturbed (particularly, fewer mown) habitat edges, measure more than two hectares (priority should go to the largest remaining fragments), and be surrounded by nearby reed habitats providing reservoir populations and diverse shoot types. 相似文献
18.
On the German island Norderney rabbit grazing effects on vegetation, soil and microclimate were investigated with exclosures
in different dune vegetation. Differences in species composition between grazed and ungrazed plots increased with grazing
activity. A decline in growth height resulted in higher light availability and temperature on the grazed sites. One of the
most visible effects was the decline in flowering plants. Most grazing effects varied between habitat types. Grey dunes were
distinctly affected by rabbit grazing. In relation to the habitat type, life forms were differently affected: in closed vegetation,
rabbit activities further open patches, resulting in more therophytes. In contrast, in open vegetation rabbit activities were
too strong and following sand dynamics too high for many therophytes. In general, grazing diversified habitats, slightly supported
the total species-richness, and enhanced the heterogeneity of species composition. Highest species-richness in total and of
herbs was reached at intermediate levels of grazing pressure. The study is in line that highest species-diversity will be
found at intermediate levels of disturbance and environmental stress and that grazing effects vary with the habitat type. 相似文献
19.
Welsh coastal dune systems have become increasingly vegetated in recent decades. Several rare species of plants and invertebrates have declined dramatically in abundance, and in some areas lost entirely. Of the ten dune habitats and species recognized as being features of European importance within the Welsh Natura 2000 sites, nine are currently in Unfavourable condition on at least one site. The decline in active aeolian processes has also reduced the geomorphological interest of the sites, several of which were designated as Geological Conservation Review sites principally on the basis of their physical processes and landforms. The decline in bare sand area between the 1940-50s and 2009 has been quantified at twelve Welsh dune sites using aerial photography and GIS. The decline ranged from 41 % at Gronant Dunes and Talacre Warren to 97 % at Kenfig Burrows, with an average of 81 %. Morfa Dyffryn had the highest remaining percentage of bare sand in 2009 (20 %), with 30–40 % coverage of mobile dune and pioneer communities, while seven sites had < 5 % bare sand. Dune stabilization over the past 60 years has been favoured by a number of factors, including less windy conditions, higher temperatures and longer growing season, increased atmospheric nitrogen deposition, a reduction in grazing intensity, and dune management policies aimed at controlling mobile sand. Climate change projections suggest that, in the next 50 to 100 years, Wales and adjoining areas are likely to experience higher temperatures and higher rainfall, especially in winter, and a further slight reduction in wind speeds. Without intervention, dune and dune slack habitats are likely to be increasingly replaced by fixed dune grassland and scrub, resulting in the extinction of rare plants, invertebrates and other species which require open, mobile conditions. Several intervention options exist, ranging in scale and potential impact. Increased livestock grazing, re-introduction of rabbits, scrub clearance, turf stripping and the creation of shallow ‘scrapes’ can be beneficial but will not by themselves create self-sustaining mobile dunes. In order to have any chance of achieving any significant impact, larger-scale intervention measures, involving large-scale vegetation removal and sand-re-profiling, will be required. At least in the short-term, maintenance measures will be required to prevent vegetation re-growth, and the challenge will be to encourage the development of mobile dune features which will be naturally mobile in the medium to longer term. 相似文献
20.
Arseny Tsvey Victor N. Bulyuk Vlad Kosarev 《Behavioral ecology and sociobiology》2007,61(11):1665-1674
How migratory birds decide when to leave a stopover site is important to the understanding of bird migration strategies. Our
study looks at how body condition and the weather affect the decision to depart on nocturnal migratory flight. During two
autumn migration seasons (2002–2003), we radio tracked 51 first-year European robins, Erithacus rubecula, at a stopover site on the Courish Spit (Eastern Baltic) from the first day after landing until their migratory departure.
The tagged robins stopped over for 1–14 days. There was no clear relationship between stopover duration and energetic condition
on arrival. Weather conditions (wind, precipitation, and cloud cover) on departure differed measurably between years. In 2002,
robins took off mainly under following winds and clear skies. In 2003, there were mainly light head winds and partially cloudy
or overcast skies. This could be explained by the year-specific role of weather factors in making the decision to depart.
In both years, robins making short (1–2 days) stopovers took off in more varied weather situations than those individuals
with long stopovers. This suggests that robins from the former group were more inclined to continue with migration than longer-stay
birds that, apart from re-fuelling, could be waiting for favourable weather. The lack of a relationship between stopover duration
and body condition and some departures under unfavourable weather conditions suggest that endogenous spatiotemporal programmes
may play an important role in controlling stopover duration in robins. 相似文献