Long-term population declines in Afro-Palearctic migrant birds

We present the first continent-wide analysis of the population trends of European breeding birds to show that populations of Afro-Palearctic migrant birds have shown a pattern of sustained, often severe, decline. The mean trend of inter-continental migrants was significantly negative between 1970 and 1990 and non-significantly so between 1990 and 2000. Mean population trends were positively correlated between periods, suggesting little change in the trajectory of most migrant species’ populations over this 30-year period. In both periods, trends of inter-continental migrants were significantly more negative than those of short-distance migrants or residents. This negative trend appeared to be largely, although not entirely, due to declines in species wintering in dry, open habitats in Africa. Analyses of trends of 30 closely related pairs of species, one a long-distance migrant and the other not, indicated significantly more negative trends in the former, irrespective of breeding habitat. Conservation action to address these declines is required under the Convention on Migratory Species and the Pan-European Biological and Landscape Diversity Strategy, to which most European countries are signatories and which aim, respectively, to conserve migratory species and to halt the loss of biodiversity by 2010. Our results indicate that more conservation action may be required outside Europe to achieve these targets. Further research is needed to assess whether the declines are caused by factors operating on the birds’ wintering grounds, breeding grounds or on migration routes, and to identify ways to reverse them.     

广西沿海红树林区的水鸟

广西沿海地区位于一条重要的候鸟迁徙通道上，那里的红树林区给为数众多的水鸟提供了繁殖、越冬和迁徙中途歇息的场所。在红树林区记录到115种水鸟。这些鸟类中，102种是候鸟，包括13种夏候鸟、64种冬候鸟、25种旅鸟，因此红树林区水鸟类的多样性表现出明显的季节性。迁徙季节水鸟的种类和数量都最多，繁殖季节则最少。黑脸瑟鹭（Platalea minor)是世界上最濒危的鸟类之一，一个越冬种群在该地区红树林中被发现。     

Population trends in a community of large Procellariiforms of Indian Ocean: Potential effects of environment and fisheries interactions

Despite the worrying conservation status of several albatross and petrel population, the long-term trends of many populations remain largely unknown and the causes of decline in many cases are known or very strongly suspected to be incidental mortality in fisheries. Here we combine long-term monitoring of population trends, breeding success and band recoveries to examine the past and current status of five species of albatrosses and giant petrels breeding at the same site: sooty albatross (Phoebetria fusca), light-mantled albatross (Phoebetria palpebrata), wandering albatross (Diomedea exulans), northern giant (Macronectes halli) and southern giant petrels (Macronectes giganteus) on Possession Island, Crozet archipelago. We identified three groups of trends over a 25-years period (1980-2005) suggesting common underlying causes for these species in relation to their bioclimatic foraging ranges. The Antarctic species - light-mantled albatross and southern giant petrel - appeared stable and increased recently, the Sub-Antarctic species - wandering albatross and northern giant petrel - declined with intermediate periods of increase, and finally the subtropical species - sooty albatross - declined all over the period. Breeding success, indicative of environmental conditions, showed two kinds of pattern (low and fluctuating versus high and/or increasing) which were consistent with oceanographic variations as found in a previous study. We present the analysis of fisheries-related recoveries, indicative of fisheries bycatch risks showing specific catch rates. No direct relationship between population trends and longline fishing effort was detected, probably because census data alone are not sufficient to capture the potentially complex response of demographic parameters of different life stages to environmental variation. This study highlights the contrasted changes of procellariiform species and the particularly worrying status of the subtropical sooty albatrosses, and in a lesser extent of Sub-Antarctic species.     

Wildfowl population trends in Mexico, 1961-2000: a basis for conservation planning

We analysed population trends of 24 wildfowl species in Mexico. Wildfowl numbers peaked during the early 1980s; lowest counts were recorded in 1997. Total wildfowl numbers (all species combined) and duck numbers (duck species combined) showed significant short-term (1981-2000) declines, while geese (goose species combined) showed a significant long-term (1961-2000) increase. Six wildfowl species suffered significant long-term declines, while four showed increases. During 1981-2000, 11 species declined, but none had significant increases. Redhead (Aythya americana), Mexican duck (Anas diazi), northern pintail (A. acuta) and black brant (Branta bernicla nigricans) should be given high conservation priority because of the high proportions of their North American populations in Mexico. Declining numbers of the later two species should trigger further investigation into the possibility of assigning them legal protection status. Other species with apparent declines in numbers should also be more closely monitored. For setting hunting limits in the country, the population status of each species should be accounted for, as well as the condition of breeding populations the previous spring. Other species with poor data or combined counts should be targeted for basic population studies. We suggest that the mid-winter counts be expanded to cover non-surveyed areas and conducted every year to more precisely detect wildfowl population change. Integrated to a site-selection analysis, the information presented here can provide the basis for a wildfowl conservation strategy in Mexico.     

Status, distribution and long-term changes in the waterbird community wintering in Doñana, south-west Spain

The Guadalquivir Marshes or Doñana wetland complex is the most important wintering site for migratory waterbirds in the Mediterranean region. However, there is a lack of previous information on the status of different species in this area. Using monthly aerial counts conducted from 1978 to 2005, we analysed the size of wintering populations of 21 waterbird species, their distribution within the Guadalquivir Marshes, and their long-term population trends. We used Underhill indices to replace missing values and to correct for flocks of unidentified ducks. Based on long-term means, we identified 16 species whose populations at Doñana exceed 1% of the biogeographical flyway population. For at least 1 month of the year, mean counts were around 10% of the flyway population for six species. The natural, temporary marshes of Doñana National Park were particularly important for Anatidae, ricefields for gulls, white storks and grey herons, fish ponds for flamingos, cormorants and avocets, and salt pans for shelduck. Four Anatidae species have undergone long-term declines and eight non-Anatidae have undergone long-term increases. Population trends were related with trophic guild, migratory status and habitat use. Winter visitors and herbivorous species showed more negative trends than resident, omnivorous-carnivorous species. Those species concentrated in strictly-protected natural marshes have tended to decline. The surface area of ricefields and fish ponds has increased over the study period, and bird species concentrated in these artificial wetlands have tended to increase. This raises questions about the value of waterbirds as flagship or umbrella species for wetland conservation.     

The proportion of immature breeders as a reliable early warning signal of population decline: evidence from the Spanish imperial eagle in Doñana

Methods to evaluate population trends have recently received particular attention because of perceived declines in several species during the 20th century. We investigated whether age at first breeding could be used as an “early warning signal” to detect possible changes in population trends in long-lived species with deferred maturity using data from the Spanish imperial eagle (Aquila adalberti) population in Doñana National Park (Spain). This bird of prey is an endangered species that has suffered a rapid decline in this population during the last 10 years. As a result of our 27-year monitoring (1976-2002) study, we detected that an increase in immature breeding birds occurred before population decline became evident. The proportion of immature-plumaged breeders in the population was significantly higher during the period of decline than during the period of stability. In our case, more than 10% of immature breeders can be considered as an “early warning signal” that anticipates population decline. Owing to the ignorance of this warning signal, urgent actions for the recovery of this eagle population started 10 years later than necessary, and when population size had been reduced.     

Rapid declines of common, widespread British moths provide evidence of an insect biodiversity crisis

A fundamental problem in estimating biodiversity loss is that very little quantitative data are available for insects, which comprise more than two-thirds of terrestrial species. We present national population trends for a species-rich and ecologically diverse insect group: widespread and common macro-moths in Britain. Two-thirds of the 337 species studied have declined over the 35 yr study and 21% (71) of the species declined >30% 10 yr⁻¹. If IUCN (World Conservation Union) criteria are applied at the national scale, these 71 species would be regarded as threatened. The declines are at least as great as those recently reported for British butterflies and exceed those of British birds and vascular plants. These results have important and worrying implications for species such as insectivorous birds and bats, and suggests as-yet undetected declines may be widespread among temperate-zone insects.     

The potential importance of migratory stopover sites as flight feather molt staging areas: a review for neotropical migrants

The decline of many species of Neotropical migrants has prompted increased research on their ecology on their breeding and wintering grounds. However, studies of their ecology during migration are relatively few. Despite documentation of molt-migration in at least six Neotropical passerine species, this phenomenon has been ignored in current conservation strategies for Neotropical migrants. In this review paper, we suggest that molt studies need to be done as a way to refine and improve conservation plans for Neotropical migrants. We identify three important questions that merit further study: (1) which Neotropical migrant species undergo flight feather molt at migratory-stopover sites; (2) where are molt-migration stopover sites geographically located; and (3) why are these sites preferred as stopover sites during molt? Finding answers to these questions will allow us to protect molt staging areas occupied by Neotropical migrants during migration as many wetland and nearshore oceanic habitats have been protected for molting waterfowl, shorebirds, and seabirds.     

Numbers of wintering waterbirds in Great Britain and the Isle of Man (1994/1995-1998/1999): II. Coastal waders (Charadrii)

Great Britain's wintering coastal wader populations have been estimated for the period 1994/1995-1998/1999 from data provided from two sources: the Wetland Bird Survey (WeBS) and the Non-estuarine Coastal Waterfowl Survey (UK-NEWS). New methodology for estimating the number of wintering waders is applied. It imputes (fills in) the value of missing counts before estimating the population size of each species as being the mean of the largest annual count made between November and March over the relevant 5-year period. This methodology has led to an 11% larger estimate of the number of waders present on Great Britain's coasts than the traditional approach based on averaging just January counts over a 5-year period, and it suggests that Great Britain's coastline supports ca. 2.1 million waders. Updated values are presented from which site evaluations based on 1% of the national population can be derived. Great Britain is of considerable international importance for waders. It holds >25 and >50% of the flyway populations of nine and four species of wader, respectively, but for the first time since the start of monitoring in the early 1970s, the historical increase in the number of predominantly coastal waders wintering in Great Britain is coming to an end. Seven of the 14 species that have shown population changes of >5% since the last set of 1987/1988-1991/1992 population estimates have declined in numbers. The possible causes of the fluctuations in wader populations, such as climate change and changing nutrient inputs to coastal waters are discussed. There is an urgent need to identify the causative factors leading to these declines, and to use the new population estimates to identify new sites that should be afforded legal protection, an action that should help Great Britain maintain its internationally important wader populations. The decrease in the updated population estimate of Eurasian oystercatcher, for example, has made it possible to determine that 19 rather than 17 sites in Great Britain are worthy of statutory protection on the basis of holding 1% or more of its national population.     

The use of historical collections to estimate population trends: A case study using Swedish longhorn beetles (Coleoptera: Cerambycidae)

Long term data to estimate population trends among species are generally lacking. However, Natural History Collections (NHCs) can provide such information, but may suffer from biases due to varying sampling effort. To analyze population trends and range-abundance dynamics of Swedish longhorn beetles (Coleoptera: Cerambycidae), we used collections of 108 species stretching over 100 years. We controlled for varying sampling effort by using the total number of database records as a reference for non-red-listed species. Because the general frequency of red-listed species increased over time, a separate estimate of sampling effort was used for that group. We observed large interspecific variation in population changes, from declines of 60% to several hundred percent increases. Most species showed stable or increasing ranges, whereas few seemed to decline in range. Among increasing species, rare species seemed to expand their range more than common species did, but this pattern was not observed in declining species. Historically, rare species did not seem to be at larger risk of local extinction, and population declines were mostly due to lower population density and not loss of sub-populations. We also evaluated the species’ declines under IUCN red-list criterion A, and four currently not red-listed species meet the suggested threshold for Near Threatened (NT). The results also suggested that species’ declines may be overlooked if estimated only from changes in species range.     

Declines in abundance and distribution of the ivory gull (Pagophila eburnea) in Arctic Canada

The ivory gull (Pagophila eburnea) is a seabird that inhabits Arctic oceans throughout the year, often in association with polar pack ice. It is rare (<14,000 breeding pairs globally) and remains one of the most poorly known seabird species in the world. Canada supports breeding populations of international significance, and residents of communities in the Canadian High Arctic currently observe fewer ivory gulls than they did in the 1980s. However, no population trend data existed for this species in Canada prior to this study. We initiated aerial surveys in July 2002 and 2003 of most known ivory gull colonies in Canada to assess current population levels. Forty two colonies were visited, 14 of which were new discoveries. We recorded an 80% decline in numbers of nesting ivory gulls. Several of the largest known colonies were completely extirpated and those that remained supported significantly fewer nesting birds than previously observed. Results were similar in both years despite some differences in local sea ice conditions, suggesting a numerical decline in the population and not simply annual fluctuations in colony occupation. Declines have occurred in all habitat types and across the known Canadian breeding range, suggesting that causes of the decline may be related to factors occurring during migration or on wintering grounds. We recommend that international efforts now be directed at assessing population status and trends of this species in other circumpolar countries.     

Losing a staging area: Eastward redistribution of Afro-Eurasian ruffs is associated with deteriorating fuelling conditions along the western flyway

The fuelling performance of long-distance migrants at staging areas indicates local conditions and determines the viability of migration routes. Here we present a first case study where long-term fuelling performance was documented along two migration routes with differential population trends. Ruffs (Philomachus pugnax) are shorebirds of inland freshwater wetlands that migrate from the sub-Saharan wintering grounds, via Europe, to the northern Eurasian breeding grounds. Assessments from 2001 to 2008 of fuelling during northward migration at the major western and eastern staging site revealed that daily mass gain rates steeply declined across years in the grasslands for dairy production in Friesland, The Netherlands, and remained constant in the Pripyat floodplains in Belarus, 1500 km further east. Migrants in Friesland decreased from 2001 to 2010 by 66%, amounting to a loss of 21,000 individuals when counts were adjusted for length of stay as determined by resightings. In the same period numbers in Pripyat increased by 12,000. Ruffs individually ringed in Friesland were resighted in subsequent springs at increasingly eastern sites including Pripyat. Our results corroborate published evidence for an eastward redistribution of Arctic breeding ruffs and suggest that the decreasing fuelling rates in the westernmost staging area contribute to this redistribution. The shift implies that responses occur within a single generation. The hypothesis that the choice of route during northward migration may be driven by food availability can now be tested by creating greater areas of wet grasslands in Friesland. When local staging conditions improve we predict that ruffs will make the reverse shift.     

Trends associated with residential development in riparian breeding bird habitat along the Snake River in Jackson Hole, WY, USA: Implications for conservation planning

Throughout North America, bird population declines may be attributable to loss of habitat on the breeding grounds. Human land uses such as residential development, greatly impact landscapes and biota, particularly breeding birds. Riparian areas, which are essential to breeding birds, are particularly vulnerable to development pressures. In North America, most studies have focused on eastern birds and it is unclear how western bird assemblages respond to the effects of residential development. We sampled bird community parameters and habitat variables at three spatial scales (microhabitat, macrohabitat, and landscape) along a residential development gradient within the Snake River riparian corridor in Jackson Hole, WY, USA. Principal component analysis and multiple linear regression statistical tests were used to determine the effects of housing densities on avian community parameters, guilds, individual species distributions, and environmental variables. Landscape-level features were most affected by residential development and trends associated with increasing housing densities, such as anthropogenic habitat fragmentation primarily structured local bird communities. Overall species richness and diversity declined with increasing residential development. Neotropical migrant species were most negatively impacted and consistently declined in proportional representation on forested plots as residential development densities increased. Food generalists, ground gleaners, and avian nest predators all increased with increasing residential development. Brood parasites, on the other hand, did not increase with increasing housing densities and their distribution may reflect the availability of nest host species. These results suggest that residential development within riparian habitats may be exerting a strong negative influence on western bird communities and at high densities may lead to a depauperate avian biota. The results of our study indicate that preserving forest structure may benefit certain species but will not likely conserve as diverse and rich an avian assemblage as minimizing fragmentation associated with residential development.     

The amphibian chytrid fungus along an altitudinal transect before the first reported declines in Costa Rica

Amphibian populations have declined and disappeared in protected and apparently undisturbed areas around the world, especially in montane areas of the tropics. The amphibian chytrid fungus, Batrachochytrium dendrobatidis has been implicated in many of these declines. In Costa Rica most declines occurred in the highlands. We examined an amphibian collection made in Braulio Carrillo National Park in 1986 for the amphibian chytrid fungus B. dendrobatidis, prior to the well documented amphibian declines in Monteverde, along an altitudinal transect from 100 to 2600 m elev. Skin from the pelvic patch of 202 specimens corresponding to 30 species was examined histologically to determine whether the disease was present in the highlands of the park before amphibian populations declined. For comparison, in 2002 we collected and examined 18 specimens of seven species of Eleutherodactylus and Craugastor from two other lowland Caribbean sites. The chytrid fungus was present in almost all altitudes in 1986, including lower areas. The pathogen was also found in both species that later declined and in species that did not do so. We detected chytrid fungus on amphibians collected at almost all altitudes in 1986, including those sampled at 280 m. B. dendrobatidis was abundant in frogs collected in the 2002 survey, and seems to be endemic in most of Costa Rica. More retrospective museum surveys are needed in order to determine whether it can be found in the area before 1986.     

Agri-environment schemes as a tool for reversing declining populations of grassland waders: Mixed benefits from Environmentally Sensitive Areas in England

Agri-environment schemes (AES) are a key tool in attempts to reverse long-term declines in farmland biodiversity within the European Union (EU). Approximately 20% of EU farmland is under AES agreement, at a cost of over €24 billion between 1994 and 2003. Despite this huge investment, few studies have investigated the effectiveness of schemes and those studies that do exist have often been inadequately designed or analysed. In southern England, repeat censuses of lowland breeding waders provide a rare opportunity to evaluate effectiveness of the Environmentally Sensitive Areas scheme (ESA), an AES designed with broad environmental objectives, including the maintenance or enhancement of the populations of these birds. The censuses provide a quasi-experimental approach, allowing a comparison to be made of breeding population trends of three species, Lapwing, Redshank and Snipe, on scheme and non-scheme land. The results show mixed success. For all three species, population trends were most favourable (increasing or declining less rapidly) in the more expensive ESA options aimed at enhancing habitat; the less expensive, habitat maintenance options, appear to have little benefit for Lapwing and Snipe, although Redshank has benefited. The results also show the increasing importance of nature reserves for these species in southern England. We suggest that although AES can result in significant benefits, especially when monetary investment is high, delivery of biodiversity targets are by no means guaranteed.     

Alarming houbara bustard population trends in Asia

Relative abundance and density estimates of Asian houbara were assessed during the breeding season in two breeding grounds of migrant populations (China and south Kazakhstan) and in one breeding ground of a resident population (Oman), between 1998 and 2002. For the study period, the relative abundance was from 0.004 to 0.06 individual per km driven and density estimates varied from 0.01 to 0.2 houbara per km². Relative abundance and density of houbara declined by 63% and 69%, respectively in China, by 60% and 49%, respectively in Kazakhstan and by 50% and 75%, respectively in Oman. Overall, an average of 27-30% annual decline in both relative abundance and density was observed for the three regions. Despite being legally a strictly protected species in China, Kazakhstan and Oman, houbara are heavily hunted and poached on all their migration routes and wintering grounds. The current levels of hunting and poaching are not sustainable and without the immediate agreement and implementation of international conservation measures, the Asian houbara may face extinction in the wild in the foreseeable future.     

Life-history and ecological correlates of population change in Dutch breeding birds

Predicting relative extinction risks of animals has become a major challenge in conservation biology. Identifying life-history and ecological traits related to the decline of species helps understand what causes population decreases and sets priorities for conservation action. Here, we use Dutch breeding bird data to correlate species characteristics with national population changes. We modelled population changes between 1990 and 2005 of all 170 breeding bird species using 25 life-history, ecological and behavioural traits as explanatory variables. We used multiple regression and multi-model inference to account for intercorrelated variables, to assess the relative importance of traits that best explain interspecific differences in population trend, and to identify the environmental changes most likely responsible. We found that more breeding birds have increased than decreased in number. The most parsimonious models suggest that ground-nesting and late arrival at the breeding grounds in migratory birds are most strongly correlated with decline. Increasing populations are mainly found among herbivores, sedentary and short-distance migrants, herb- and shrub-nesting birds and large species with a small European range. Declines in ground-nesting and late arriving migrant birds suggest that agricultural intensification, eutrophication and climate change are most likely responsible for changes in Dutch breeding bird diversity. We illustrate that management strategies should primarily focus on the traits and causes responsible for the population changes, in order to be effective and sustainable.     

Rarity and decline in bumblebees - A test of causes and correlates in the Irish fauna

Bees are believed to be in decline across many of the world’s ecosystems. Recent studies on British bumblebees proposed alternative theories to explain declines. One study suggested that greater dietary specialization among the rarer bumblebee species makes them more susceptible to decline. A second study disputed this theory and found that declines in British bumblebees were correlated with the size of species’ European ranges, leading to the suggestion that climate and habitat specialization may be better indicators of the risk of decline. Here we use a new and independent dataset based on Irish bumblebees to test the generality of these theories. We found that most of the same bumblebee species are declining across the British Isles, but that, within Ireland, a simple food-plant specialization model is inadequate to explain these declines. Furthermore, we found no evidence of a relationship between declines in Irish bumblebees and the size of species’ European ranges. However, we demonstrate that the late emerging species have declined in Ireland (and in Britain), and that these species show a statistically significant westward shift to the extremity of their range, probably as a result of changing land use. Irish data support the finding that rare and declining bumblebees are later nesting species, associated with open grassy habitats. We suggest that the widespread replacement of hay with silage in the agricultural landscape, which results in earlier and more frequent mowing and a reduction in late summer wildflowers, has played a major role in bumblebee declines.     

Recent, substantial, and unexplained declines of the common toad Bufo bufo in lowland England

A decline in numbers of a large common toad (Bufo bufo) population in south-east England during the 1990s, together with anecdotal reports of similar trends in other toad populations, prompted a nation-wide survey of this species. The survey also included the common frog (Rana temporaria) as a control for which there was no comparable evidence of recent decline. A questionnaire requesting information on the fate of toad and frog populations in the last 15 years of the 20th century was distributed to professional and amateur herpetologists during autumn 2001. Ninety-five respondents provided data on a total of 277 sites, including 232 frog and 202 toad populations in England, Scotland and Wales. More than 80% of the reported sites were rural for both species. Rural frog populations were generally doing well in most parts of Britain, with almost as many increasing as decreasing populations and a high proportion of stable populations. Rural toads also showed no overall trend across the country as a whole. However, regional analysis indicated that although toads were faring at least as well as frogs in the north and west of Britain, they were declining seriously in central and eastern/south-eastern areas. In these regions 50% or more of toad populations have experienced recent declines, whereas frogs have fared as well as they have elsewhere. Toads breeding alone have fared significantly worse than toads breeding at sites where frogs were also present. Reasons for apparently toad-specific declines in lowland England remain unknown.