Population Trends Of Waterbirds Research Articles

Anthropogenic bottom-up and top-down impacts on boreal breeding waterbirds.

Wetland habitats are changing under multiple anthropogenic pressures. Nutrient leakage and pollution modify physico-chemical state of wetlands and affect the ecosystem through bottom-up processes, while alien predators affect the ecosystems in a top-down manner. Boreal wetlands are important breeding areas for several waterbird species, the abundances of which potentially reflect both bottom-up and top-down ecosystem processes. Here, we use long-term national monitoring data gathered from c. 130 waterbird breeding sites in Finland from the 1980s to the 2020s. We hypothesised that the physico-chemical state of the waters and increasing alien predator abundance both play a role in steering the waterbird population trends. We set out to test this hypothesis by relating population changes of 17 waterbird species to changes in water chemistry and to regional alien predator indices while allowing species-specific effects to vary with foraging niche (dabblers, invertivore divers, piscivorous divers, herbivores), nesting site, female mass and habitat (oligotrophic, eutrophic). We found niche and nesting site-specific, habitat-dependent changes in waterbird numbers. While the associations with higher phosphorus levels and browning water were in overall positive at the oligotrophic lakes, the numbers of invertivore and piscivore diving ducks were most strongly negatively associated with higher phosphorus levels and browning water at the eutrophic lakes. Furthermore, increased pH levels benefitted piscivores. Invertivore diving duck species nesting on the wetlands had declined most on sites with high alien predator indices. Large herbivorous species and species preferring oligotrophic lakes seem to be successful. We conclude that the large-scale breeding waterbird decline in Finland is closely connected to both bottom-up and top-down processes, where negative associations are emphasised especially at eutrophic lakes. Niche-, nest site- and habitat-specific management actions are required to conserve declining waterbird populations. Managing wetlands on catchments level together with alien predator control may provide important approaches to future wetland management.

Effects of aquaculture on the maintenance of waterbird populations.

The global aquaculture industry has expanded rapidly and is increasingly important for maintaining food security while also providing alternative artificial habitats for many waterbirds. Clarifying how waterbirds use aquafarms and how aquafarm use affects waterbird population maintenance can be useful for improving management of the artificial landscape that can also provide waterbird habitat. Here, we investigated aquafarm use by waterbirds in China, the world's largest producer of aquaculture products, supported by literature review and questionnaire survey. We used Bayesian phylogenetic generalized linear mixed models to analyze the relationship between the degree of aquafarm use and population trends of waterbirds. The results showed that 69% of waterbird species in China have been recorded at aquafarms. Approximately one-quarter of all waterbird species and about the same proportion of threatened species were found to forage at aquafarms, consuming either cultured aquatic products or other food types. In general, species with a high degree of aquafarm use were unlikely to exhibit a population decline over the past two decades, when rapid loss of natural habitats occurred in China. This relationship was not detected in threatened species, despite there being no significant difference in the degree of aquafarm use between threatened and non-threatened species. Our study suggests that the large and expanding aquaculture industry is important for maintaining waterbird populations in China. However, aquafarms are not a replacement for natural habitats, because threatened species benefit less from aquafarm use. Given that aquafarms often come at the expense of natural wetlands, the degree to which aquafarms compensate for natural habitat loss probably depends on the quality of aquafarm habitat. We recommend an integrated ecological and economic analysis for formulating management policies that help conserve wildlife within the constraints and opportunities associated with maintaining human livelihoods. This article is protected by copyright. All rights reserved.

Invasive catfish in northern Italy and their impacts on waterbirds

Predatory fish have occasionally been observed preying on birds, sometimes repeatedly, but few studies were able to unravel the overall significance of avian prey in fish diet and the predation impacts on bird populations. We used a control/impact study setup, using a Nature Reserve in northern Italy and a nearby control area, to determine: 1) the contribution of waterbirds to wels catfish diet in the Reserve, 2) the population density of wels catfish in the Reserve and control area and 3) the potential impacts of waterbird depredation by wels catfish on waterbird population trends. Our stable isotope Bayesian mixing model indicated that birds contributed 12.2% (5–27.9%, 50% confidence interval) of the diet of large wels catfish (> 98 cm in total length). Large individuals constituted the majority of the population in the shoreline areas of the reserve in 2013–2019, where the population was stable despite control efforts. Numbers were below detectable levels in the control area. Large wels catfish consumed an average of 224, 148 and 187 kg of birds during the 2019 chick growing period, as estimated through three different bioenergetic models. Compared to the control area, mallard reproductive success was diminished in the Reserve, likely due to higher rates of fish predation, although effects were variable in different years. Overall, our data suggest that high densities of invasive wels catfish might impact waterbird reproductive success through predation on bird chicks, but further studies would be needed to reduce uncertainties related to the intrinsic variability of field ecology data. Our study constitutes a preliminary attempt to assess the potential of introduced wels catfish to affect the conservation value of waterbird protection areas, and should be repeated at broader spatial and temporal scales.

Diversity and population trends of waterbirds at Lake-2, the Ballavpur Wildlife Sanctuary, West Bengal State, India

Diversity and population trends of waterbirds at Lake-2, the Ballavpur Wildlife Sanctuary, West Bengal State, India

Population Trends of Waterbirds in Purulia Saheb Bandh in Response to Habitat Degradation

Population Trends of Waterbirds in Purulia Saheb Bandh in Response to Habitat Degradation

Trends in savannah waterbirds: protected area effect and influence of global threats on differing guilds

Understanding species threats is underpinned by information on their population trends. We investigated the contribution of population drivers associated with 86 waterbird species’ trends at a local scale, Hwange National Park (HNP) and a national scale (Zimbabwe). We used logistic regression models to test whether waterbird population trends differed across migration types, seasons, species traits (guild, weight, index of diet variety, social foraging and breeding systems), scale of use by humans (whether the waterbird species utilisation is documented at local or international scale) and susceptibility to hunting and diseases. In HNP during the wet season, waterbird population trends were mostly stable or increasing. During the dry season, larger species were more likely to be recorded, more so for those threatened by hunting, compared with the species limited by diseases. Colonial resident waterbirds had more increasing population trends in HNP in comparison to the solitary ones. At the Zimbabwean scale, records for 35% of species decreased during the wet season, and the declines were more pronounced in large birds. During the dry season, species threatened by habitat disturbances were more likely to decrease. Habitat disturbances and/or use of waterbirds at the international scale are more associated with declining trends than ecological and life history traits. We have shown that HNP, a protected area with mostly a pan wetland-system is supporting growing waterbird populations despite the species facing global negative population trends.

Community structure, abundance variation and population trends of waterbirds in relation to water level fluctuation in Poyang Lake

Poyang Lake is China's largest freshwater lake, and it has been an internationally important wintering ground for migratory waterbirds. Based on waterbird censuses from 2001 to 2016, community structure and abundance trends of waterbirds were analyzed, as well as the potential correlations with the water level of Poyang Lake. The results showed that the annual average number of waterbirds in Poyang Lake was 426,707 ± 150,170, with 111 species from 17 families. Waterfowl was the most abundant family accounting for 74.4 ± 8.8% of all individuals, followed by shorebirds (14.8 ± 8.5%), wading birds (6.5 ± 1.8%) and open-water/waterbirds (4.4 ± 1.9%). Although waterbird abundance fluctuated dramatically, there were no significant trends in the abundance of most guilds or in total waterbird abundance; only geese significantly increased among the eight groups. Analysis of trends of 37 relatively abundant or regularly occurring species indicated that population trends appeared to be species-specific. As for the correlations between water level and waterbird abundance, only shorebirds showed significant correlations with average July water level, average water level, and high water level duration in wet season among four guilds, i.e. waterfowl, wading bird, shorebird and, open-water and waterbird. At the group level, abundances of swans, geese, and ducks were significantly correlated with monthly average water level during the wet season, and wader abundance was significantly correlated with average water levels and high water level duration during the wet season. Correlations between population abundance and monthly water level also exhibited species-specific patterns.

Reversible effects of fertilizer use on population trends of waterbirds in Europe

Nutrients are often limiting primary productivity, and fertilizer use by agriculture increases primary and secondary productivity in marine environments. High levels of eutrophication due to fertilizer use can have negative effects on the distribution and the abundance of many organisms including waterbirds inhabiting freshwater and marine wetlands. Because nutrients, in particular phosphorus, can be stored in sediment, reversal of effects of eutrophication can take considerably longer time than the period during which effects of eutrophication build up. We quantified the effects of fertilizer use on 50 species of freshwater and coastal waterbirds monitored across Europe during 1982–2008 during the increase and the decrease phase of fertilizer use. More species were negatively affected by fertilizer use, and use of marine habitats during winter was the single-most important predictor of negative trends. The relative effect of fertilizer use on abundance of waterbird species was consistent during the increase and the decrease phase of fertilizer use. The effects of fertilizer use were statistically independent of the effects of climate change. Reversal of the effect of fertilizer use on population trends of waterbirds was almost three times as slow as the build-up of effects of nutrients on population size. These findings have management implications for the extent and the duration of fertilizer policies at local, national and international levels since these policies will partly determine the population trends and the population sizes of waterbirds.

Long‐term declines in multiple waterbird species in a tidal embayment, south‐east Australia

AbstractWorldwide, local extinctions and severe declines in waterbird densities are being reported from many important waterbird sites. Waterbird sites often exist as a network, collectively providing crucial habitat for different life history stages of different species. Therefore, population changes at one site may strongly influence others. In Australia, many waterbird species are highly mobile, and move rapidly over long distances in response to rainfall. Large tidal wetlands often serve as drought refugia or alternative breeding habitat for these species. These sites are also the migration terminus of many species of shorebirds that spend their non‐breeding season in Australia. One such site in south‐eastern Australia is Western Port, a Ramsar‐listed tidal embayment forming part of the East Asian–Australasian Shorebird Site Network. We measured waterbird population trends over nearly 40 years in Western Port to see whether changes showed consistent trends over time across multiple species. Thirty‐nine species were recorded often enough to allow an analysis of trends over time using dynamic linear models and, where appropriate, piecewise linear regression. Twenty‐two species had declined, including four species of duck, five species of fish‐eating bird (cormorants, terns and pelicans), one species each of grebe, gull and heron, and 10 species of shorebird. Only two species (Australian pied oystercatcher Haematopus longirostris and straw‐necked ibis Threskiornis spinicollis) increased significantly over the same time period. Patterns of decline in non‐migratory waterbirds may reflect diminishing wetland availability, local reductions in fish prey, increased predation pressure and changes in inland wetland resources. Declines in migratory shorebirds are most likely related to loss of habitat elsewhere in their trans‐equatorial migration routes. These trends in waterbirds that use Western Port reflect widespread impacts on populations elsewhere in Australia and overseas, necessitating more than simply local management of this tidal embayment.

Fertilizer Leakage to the Marine Environment, Ecosystem Effects and Population Trends of Waterbirds in Denmark

Leakage of nutrients from farmland to freshwater and marine environments results in fertilization that increases primary production with cascading effects in the ecosystem. Leakage of fertilizers may initially increase availability of food for primary and secondary consumers, although part of this effect may subsequently be followed by a reduction in food abundance caused by hypoxia. We hypothesized that leakage of nutrients from farmland increased primary and secondary production and subsequently the population size of waterbirds. The amount of phosphorus in the marine environment in Denmark during 1975–2010 increased with fertilizer use on farmland and this effect was stronger when winter precipitation was high. Leakage of fertilizer had ecosystem effects on phytoplankton, zooplankton, and ultimately biodiversity in the marine environment. We found linear relationships between fertilizer use and population size of breeding and wintering waterbirds, with additional quadratic relationships with fertilizer use and linear effects of temperature. The linear effect of fertilizer use depended on the diet of waterbirds with stronger effects in herbivorous and piscivorous species than in species eating benthos. These findings have implications for management of waterbird populations because a reduction in fertilizer use should result in increasing populations of herbivores and piscivores.

Waterbirds increase more rapidly in Ramsar‐designated wetlands than in unprotected wetlands

Summary There is a general lack of information on how international conservation treaties affect biodiversity. The Ramsar convention on the protection of internationally important wetlands is such an international conservation policy. It initiated the world‐wide establishment of over 2000 protected areas currently covering more than 200 million ha. The convention came into force in 1975, but to date, it remains unknown whether it actually produces biodiversity benefits. We analysed 21 years of survey data from a wide range of waterbird species in over 200 Moroccan wetlands and examined whether Ramsar designation as well as a national protected areas programme Sites d'IntérêtBiologique et Ecologique (SIBE) positively affected bird abundance. Furthermore, habitat characteristics of wetlands in protected areas and control sites were compared and bird abundance was related to habitat characteristics. After designation, waterbird species richness and abundance increased more rapidly in Ramsar wetlands than in non‐designated wetlands. In SIBE sites, increases in bird abundance were intermediate. Waterbird abundance was significantly related to habitat characteristics, most importantly cover of water or bare ground. Compared to control sites, Ramsar sites had significantly higher cover of habitat types favoured by most waterbird species. It remained unclear, however, whether these differences were caused by conservation management or were already present prior to conservation designation. Surprisingly, waterbird population trends in Moroccan wetlands were markedly positive. Trends were found to be related to precipitation levels in the Sahel which may have caused changes in migratory strategies. Synthesis and applications. This study demonstrates a powerful approach to systematically evaluating biodiversity responses to major international conservation policies. The results highlight that data on management and habitat quality are critical for reaching general conclusions about the effectiveness of conservation instruments. Site managers or conservation authorities should be encouraged to collect standardized data on conservation actions to help interpret the mechanisms behind population responses and thus extrapolate findings beyond the study system. These findings represent a first small step towards unravelling the contribution of international conservation tools towards global policy objectives of halting the biodiversity decline.

Unraveling the importance of rice fields for waterbird populations in Europe

Rice fields are an alternative habitat for waterbirds and provide food and shelter for many avian species, but there is a lack of information about how the use of rice fields translates into population level effects. The aim of this study was to test the relationship between the use of rice fields by European waterbirds and trends in their populations. We tested this relationship during the autumn migration season and during the breeding season. Based on counts conducted over the last 23 years in natural marshes and areas of rice fields in Doñana (SW Spain), an index of rice field use was constructed for 76 bird species, which was then compared to these species’ European population trends obtained from the literature. A positive relationship was found between waterbird population trends and the use of rice fields during autumn migration season. Our study suggests that changes in the Common Agriculture Policy in Europe leading to reductions in areas of rice cultivation may have important effects on waterbirds. The restoration of former marsh areas and the maintenance of rice cultivation would seem to be more environmentally friendly approaches than the use of these areas to grow alternative crops or solar farms.

A Review of Human Disturbance Effects on Nesting Colonial Waterbirds

-We reviewed 64 published investigations concerning effects of human disturbance on nesting colonial waterbirds. We summarized and reviewed articles, based on taxonomy, examining investigator, ecotourist, recreator, watercraft, and aircraft activity effects on physiology, reproductive behavior, reproductive success, and population trends of waterbirds. Though most studies found significant negative effects, taking careful measures minimized impact on some species. Guidelines for minimizing investigator and visitor disturbance are outlined. Little practical information for visitor management is available. Increasing pressure from the ecotourism industry to visit waterbird colonies makes research that develops scientifically-defensible tourism policies imperative. Received 27 December 1997, accepted 27 April 1998.