共查询到20条相似文献，搜索用时 31 毫秒
1.
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. 相似文献
2.
Long-term population declines in Afro-Palearctic migrant birds 总被引：1，自引：0，他引：1
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. 相似文献
3.
We used observations of the age structure and breeding productivity of the Scottish population of golden eagles Aquila chrysaetos together with the classic theory of population dynamics to derive current `unmanipulated' estimates of life history parameters. We then used regional differences in age structure associated with differences in persecution intensity to derive estimates of prospective `persecution-free' life history parameters. The different parameter combinations were entered into a population model to simulate their effects on the number of occupied territories over time. Most simulations suggested that with unmanipulated demographic parameters the population should decline. The disparity between these predictions and the observed apparent stability in occupied territories was ascribed to the buffering effect of a lowering in age of breeding in areas where persecution is most intense and that more favourable parameter estimates within the estimated limits may be more realistic. The results indicated, nevertheless, that currently the population is vulnerable to decline as also suggested by the apparent lack of adults to occupy vacant territories. In the absence of the estimated 3-5% annual adult mortality through persecution, modelling suggested the population would increase. Removing estimated effects of persecution on reproductive rate and preadult survival were on their own insufficient to reverse the declines predicted from unmanipulated parameters, although the effect of persecution on preadult survival may be more severe than we estimated. In the absence of persecution we conclude that the population could expand to fill currently vacant but apparently suitable habitat and have a more secure long-term status. 相似文献
4.
Chris A.M. Van Turnhout Ruud P.B. Foppen Rob S.E.W. Leuven 《Biological conservation》2010,143(1):173-71
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. 相似文献
5.
Wind-farms receive public and governmental support as an alternative energy source mitigating air pollution. However, they can have adverse effects on wildlife, particularly through collision with turbines. Research on wind-farm effects has focused on estimating mortality rates, behavioural changes or interspecific differences in vulnerability. Studies dealing with their effects on endangered or rare species populations are notably scarce. We tested the hypothesis that wind-farms increase extinction probability of long-lived species through increments in mortality rates. For this purpose, we evaluate potential consequences of wind-farms on the population dynamics of a globally endangered long-lived raptor in an area where the species maintains its greatest stronghold and wind-farms are rapidly increasing. Nearly one-third of all breeding territories of our model species are in wind-farm risk zones. Our intensive survey shows that wind-farms decrease survival rates of this species differently depending on individual breeding status. Consistent with population monitoring, population projections showed that all subpopulations and the meta-population are decreasing. However, population sizes and, therefore, time to extinction significantly decreased when wind-farm mortality was included in models. Our results represent a qualitative warning exercise showing how very low reductions in survival of territorial and non-territorial birds associated with wind-farms can strongly impact population viability of long-lived species. This highlights the need for examining long-term impacts of wind-farms rather than focusing on short-term mortality, as is often promoted by power companies and some wildlife agencies. Unlike other non-natural causes of mortality difficult to eradicate or control, wind-farm fatalities can be lowered by powering down or removing risky turbines and/or farms, and by placing them outside areas critical for endangered birds. 相似文献
6.
John M. Tirpak William M. Giuliano John W. Edwards M. Seamster 《Biological conservation》2006,133(3):364-378
Ruffed grouse (Bonasa umbellus; hereafter grouse) populations in the central and southern Appalachians are in decline. However, limited information on the dynamics of these populations prevents the development of effective management strategies to reverse these trends. We used radiotelemetry data collected on grouse to parameterize 6 models of population growth to: (1) determine the pattern of growth in these populations, and (2) identify the demographic rates most important to growth. Trend estimates from population models were most similar to trend estimates derived from Breeding Bird Survey and Christmas Bird Count data when models incorporated either a reproductive or survival event. These events randomly increased fecundity or survival, respectively, to their empirical maxima on average once every 5 years. Reproductive events improved estimates on areas dominated by mixed mesophytic forest, while survival events characterized population growth on oak (Quercus spp.)-dominated sites. The finite rate of increase (λ) was most sensitive to brood survival followed by adult and juvenile non-breeding survival on most sites. However, brood survival was low (<0.35 female chicks/hen survived to week 5), and elasticity analyses indicated λ responded more strongly to proportionate change in non-breeding and breeding survival rates of adults and juveniles than any reproductive variable. Life stage analyses corroborated this result. At baseline values, survival of adults and juveniles may be the main determinants of growth in these populations, and reproduction may not be adequate to compensate for these losses. Therefore, population growth above baseline levels may be regularly needed to restock these populations. Researchers have hypothesized that population dynamics may differ between mixed mesopytic and oak-dominated sites due to differences in forage quality and quantity. Thus, a potential mechanism for the increases in λ needed to sustain populations on mixed mesophytic forest sites is the greater fecundity observed during years with high oak or beech (Fagus grandifolia) mast abundance. The availability of this high quality forage allows hens to enter the breeding season in better condition and realize higher fertility. Alternatively, on oak-dominated sites, population growth increases may also be a product of higher non-breeding survival of birds in mast years, when birds do not need to range as far to forage and can limit their exposure to predators. 相似文献
7.
The flesh-footed shearwater (Puffinus carneipes) is a migratory seabird that ranges widely across the Pacific and Indian Oceans. The principal breeding populations are in Australia and New Zealand. The only breeding site in eastern Australia is on Lord Howe Island. Despite it being afforded a high level of legislative protection, the population on Lord Howe Island has declined substantially during the last few decades. The total extent of nesting habitat in 2002 was 24.3 ha, a reduction of 13.4 ha (35.6%) since 1978. Loss of nesting habitat was associated with increased urbanisation, the adverse impact of which extended beyond the footprint of buildings and gardens. In 2002, overall burrow density was 0.123 per m2 and the total number of burrows was estimated to be 29,853 ± 5867, a decline of about 19.0% since 1978. A substantial decline in burrow density was evident in the colony where loss of habitat to urbanisation had been greatest. In 2002, 58% of burrows were occupied by breeding birds, and the total population size was estimated to be 17,462 breeding pairs. Breeding success (the proportion of eggs that produced fledglings) was 50%, but was lowest in the most urbanised colony. To avert further declines in the population of flesh-footed shearwaters on Lord Howe Island major changes in land use practices, enforced through appropriate legislation, are needed, together with reductions in the level of seabird bycatch in fisheries operations and in the amount of plastics that litter the world’s oceans. 相似文献
8.
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. 相似文献
9.
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. 相似文献
10.
The recent history, current status and prospects in the immediate future of the seven species of the Pelecanidae are reviewed. As a consequence of pesticide poisoning, Pelecanus occidentalis suffered severe population declines in the 1950s and 1960s in portions of its range in the United States. However, since the ban on use of DDT in 1972 the species is again laying eggs of near normal thickness, reproductive success appears to be normal and populations are stable or increasing. Similarly, available data indicate that the world populations of P. rufescens, P. conspicillatus, and P. erythrorynchos remain stable, although local population fluctuations do occur. Data for P. onocrotalus show a stable population in Africa but a decline in Asia and Europe, both in numbers of birds and breeding colonies. More seriously, only very small populations of P. crispus and P. philippensis exist. Fewer than 1000 pairs of P. crispus next in 19 colonies in eastern Europe and Asia. Fewer than 1200 pairs of P. philippensis nest in four colonies in eastern/southern India and 23 colonies in Sri Lanka. The populations of both species have declined considerably in the past few decades. The causes for the declines are not documented but are thought to result from a combination of human disturbance in nesting colonies; destruction of nesting and roosting-loafing areas; declines in fish availability; and pesticide contamination. Only immediate action and concerted efforts at stabilizing the populations in the wild, in conjunction with the establishment of captive breeding populations, will preserve these two species from extinction. 相似文献
11.
Large-scale declines of grey partridges (Perdix perdix) since the 1980s have led to local extinctions in the species’ range. As part of a UK recovery programme, we aimed to identify the best methods of re-establishing grey partridges through releasing in areas of extinction where a suitable environment has been restored. In East Anglia and southern England we followed the fates and breeding success of radio-tagged (one site per region) and colour-ringed birds (12 sites per region) of individuals released using five different techniques. The average resighting rate after the first 6 months post-release was 20% for bantam-reared and artificially-reared fostered young, 7% for unfostered young, 10% for full-grown birds in autumn-released coveys and 9% for spring-released adults. For birds that survived the first 6 months, the percentage resighted after a second 6-month period averaged 35%. Across both regions, 65% of grey partridge losses were due to predation of which 58% were killed by mammalian predators and 37% by raptors. Of birds still alive during the breeding season, 88% established their breeding territory within 1.5 km of the release location. There were no detectable differences in breeding success between release methods, but the proportion of females with broods among released birds was a third lower than among wild birds. We recommend re-establishing grey partridges by first releasing autumn coveys, followed by fostering. However, where wild birds are still present, the conservation focus should be on habitat improvements and predation control. 相似文献
12.
Sang-Don Lee Elizabeth R. Ellwood Se-young Park Richard B. Primack 《Biological conservation》2011,(9):2182-2187
Barn swallows (Hirundo rustica) are arriving later in the spring than they did 30–40 years ago at numerous sites in Korea. In some cases their arrival times are later by more than 1 month. This result is perplexing as spring activities of plants and animals are generally getting earlier due to warming temperatures. The first arrival dates of swallows are not related to temperature, suggesting that another factor is involved. On the basis of a questionnaire, a large majority of long-term observers are confident that there has been a moderate to severe decline in swallow populations at their field site over the study period. The greatest delays in arrival times are associated with sites with more severe reported declines in population size. Simulations using trapping data of large migratory bird populations from the United States, consisting of hundreds of individuals, suggest that severe population declines of 99% can result in delays of 10–12 days in arrival times. In summary, our results suggest that the large delays in arrival time of Korean swallows are due, at least in part, to severe reductions of more than 99% in what were formerly very large populations. Significant delays in spring phenology over time during a period of climatic warming may indicate population decline, though alternative explanations, such as changes in range or migration path or changing number of broods per season, should also be investigated. Delays in first arrival data can provide a valuable new tool to conservation biologists by indicating declines in a population that would otherwise go unnoticed. This can, in turn, lead to efforts by researchers to verify the dynamics of a population and draw attention to the conservation needs of the species. 相似文献
13.
鸡的马立克氏病(MD)抗病育种是防制 MD 的一个新方向。经三年多的研究,采用马立克氏病病毒(MDV)强毒株攻击霞烟鸡1日龄雏鸡,选留幸存者进行繁殖,其后代未经MD 疫苗接种,以自然感染进行选择,并结合后裔攻毒测定法进行抗 MD 的选育。至三世代时,鸡抗 MD 的能力已大为提高。三世代雏鸡1日龄攻毒后,10周龄时 MD 总保护率为74%,与对照组的35%有非常显著的差异(P<0.001),其中自然死亡鸡的 MD 肿瘤阳性率为16%,与零世代的48.1%有非常显著的差异(P<0.001).与对照组的37.5%亦有显著差异(P<0.05);1日龄经火鸡疱疹病毒(HVT)疫苗免疫,14日龄以 MDV 强毒攻毒后,三世代10周龄时对 MD总保护率为96.9%,而对照组为87%。抗病核心群目前已有基本种鸡500羽。 相似文献
14.
Evidence for food limitation in the declining hen harrier population on the Orkney Islands, Scotland
The hen harrier (Circus cyaneus) population on the Scottish Orkney Islands has declined dramatically since the end of the 1970s. We postulate that the cause of this decline was due to a reduction in the amount of available prey and predict that if this was the case the population would currently be limited by food. The evidence for this hypothesis is explored by examining the rates at which males deliver prey to their females in relation to breeding performance both among individuals within the declining population and also between this declining population and another, non-declining population in southern Scotland. Breeding performance within the Orkney population was related to male provisioning rates: males that provided more food to their females were more likely to initiate a breeding attempt and there was a tendency for males with the highest provisioning rates to breed with more females. Comparisons between the two populations revealed that harriers on Orkney had a lower breeding performance and also a lower rate of food provision. Changes in agriculture, in particular decreases in rough grazing and increases in sheep densities are thought to be the most likely cause for a reduction in food supply. Conservation measures should be aimed toward increasing the areas of rough grass habitat. 相似文献
15.
Habitat fragmentation is thought to create a barrier to individual movements particularly for area-sensitive species which, by definition, prefer to breed in large tracts of forest. For two breeding seasons, we radio-tracked an area-sensitive species, the scarlet tanager Piranga olivacea, in a fragmented landscape in northeastern PA. We found that scarlet tanagers made extensive and frequent movements among fragments. Paired males were less likely to leave their capture fragment, and traveled shorter distances. Unpaired males in fragments had two distinct tactics we labeled: “Sedentary” and “Mobile”. Sedentary males stayed at one fragment and sang at high rates, while mobile males spent 58% of the total time tracked off their capture fragment and traveled over a kilometer away from the capture site over open fields and through forests. Mobile males were not floaters per se because they were territorial (i.e., singing) in multiple sites. Habitat structure of a fragment did not correlate with the percent time a male spent off the capture fragment. Males in fragments experienced lower pairing success and were more likely to be first time breeders compared to males in continuous forest. Our results suggest that movements by scarlet tanagers in fragmented landscapes are not restricted during the breeding season, and that these movements are related directly to pairing status and indirectly to population density. 相似文献
16.
Oriol Lapiedra Anna Ponjoan Anna Gamero Gerard Bota Santi Mañosa 《Biological conservation》2011,144(12):2882-2890
Cereal pseudo-steppes hold the largest proportion of declining bird species in Europe. Understanding how this process of decline is driven is essential for designing adequate management practices. The little bustard (Tetrax tetrax) is one of such threatened steppe-land bird species, which has suffered recent dramatic range constrictions and population declines. Although low breeding success has been claimed to be the main threat for the viability of future little bustard populations, the surprising lack of studies dealing with ecological requirements of broods hinders the implementation of efficient conservation practices. We studied the ranging behaviour and the reproductive success of a little bustard population by means of female radio-tracking conducted during 2006–2008 breeding seasons in the Ebro basin (NE Spain). We recorded an average breeding success of 0.27 chicks/hen, which is not enough to sustain a viable population according to the demographic models for the species. Early-laid clutches showed more probabilities to hatch and to fledge. This was associated to two different ranging patterns (i.e. sedentary versus wandering respectively) which depended on the ability of the hen and its chicks to settle in suitable areas harbouring enough arthropods and shelter for chicks. Such resources decrease drastically as the breeding season progresses. Overall, data suggest that agricultural practices associated to agricultural intensification, particularly early harvest, reduce breeding success both directly by nest destruction and indirectly through a decrease on resource availability for broods. Based on our findings on the characteristics and structure of the home range of little bustard broods, we propose the creation of a network of permanent vegetation plots interconnected by high-quality field margins as a management practice to raise the breeding success of little bustards and other ground-nesting birds on cereal farmland. 相似文献
17.
The flesh-footed shearwater (Puffinus carneipes) is a medium-sized seabird (ca. 700 g) that is incidentally killed during longline fishing operations. We examined the levels of bycatch in Australia’s Eastern Tuna and Billfish Fishery and developed a model to examine the impact of this fishery on the eastern Australian population of flesh-footed shearwaters, which breeds at only one site, Lord Howe Island. Observed bycatch rates for flesh-footed shearwaters were 0.378 birds/1000 hooks for night sets, and 0.945 birds/1000 hooks for day sets. The mean number of birds killed from 1998 to 2002 was estimated to be 1794-4486 birds per year, with the estimated total killed over this period ranging from 8972 to 18,490 birds. Models incorporating both density-independent and density-dependent scenarios were applied to levels of bycatch representative of that observed in the fishery. Density-independent scenarios showed that fishing mortality levels caused declines in the majority of simulated populations. In contrast, density-dependent scenarios produced populations that were more resilient to fishing mortalities. Although some modelling scenarios led to population growth, under most stochastic simulations median population halving and quasi-extinction times were less than 55 and 120 years, respectively. We conclude that the level of bycatch observed in the fishery is most likely unsustainable and threatens the survival of the Lord Howe Island population. This situation can be improved only with the development and implementation of mitigation measures that will halt or greatly reduce the level of bycatch currently observed. Improved knowledge on a range of demographic parameters for the species, combined with a clearer idea of the at-sea distribution of breeding and non-breeding shearwaters, will greatly assist in improving understanding and the management of this population. 相似文献
18.
Animals use environmental cues, social information and behavioural decision-making rules moulded by natural selection to decide where to breed. We assessed whether the presence of an alien nest predator, the Black Rat (Rattus rattus) is used by a colonial seabird, the Cory’s shearwater (Calonectris diomedea), as an environmental cue in the selection of breeding sites. We compared potential habitat preference using quality of breeders and nest fidelity as response to nest predation between two sub-colonies with different habitat characteristics, breeding success and predation pressure. Quality of individuals was better in the predated habitat and birds did not perceive the presence of predators signalling differences in predation risk and in turn of breeding success. This failure of perception could be at two levels: in the selection of habitat for first breeding and in the breeding dispersal following a reproductive failure. Preference for the sub-colony with higher predation risk suggests the presence of an evolutionary trap. In fact, the introduction of alien predators probably transformed the behaviour of shearwaters in a maladaptive response due to a mismatch between the new environmental factors and their behavioural and evolutionary algorithms. This can be a common pattern in other species with little behavioural plasticity, evolved in stable environments free of predators. 相似文献
19.
This study investigated the relationship between the current size of endangered bullhead (Cottus gobio) populations and microsatellite genetic variability. Additionally, the microsatellite data were used to evaluate whether a genetic test for population bottlenecks was able to provide evidence of recent severe population declines. Finally, our results were used to develop conservation priorities and measures. Population size appears to be a crucial parameter in determining the amount of genetic diversity that can be preserved in bullheads, since a significant positive correlation was observed between both variables. Furthermore, in some populations we were able to detect genetic signatures of the documented decline in population size. We suggest that the most immediate goal for bullhead conservation should be to increase the size and the range of the populations, and in doing so minimise or even reverse further genetic erosion. Potential management actions like habitat quality improvement, reduction of river fragmentation and supplementation programmes (translocation, supportive breeding) are discussed. 相似文献
20.