Overwintering Cranes, Waders, and Shorebirds versus Ducks and Coots Showed Contrasting Long-Term Population Trends in Caohai Wetland in Guizhou Province, China

Abstract

The Guizhou Caohai Wetland plays a crucial role as a wintering site for migratory birds in the Yunnan–Guizhou Plateau and ranks among the largest wintering spots globally for black-necked cranes (Grus nigricollis). To better understand the factors influencing waterbird populations and ecosystem changes, we conducted a comprehensive analysis of historical waterbird population variations over a 30-year period spanning from 1992 to 2022. The current investigation revealed a downward trend in the abundance index curve of the total number of waterbirds during this observation period. Among the five waterbird guilds examined, dabbling ducks, diving ducks, and coots (Fulica atra) experienced declines in their populations, while wading birds and shorebirds saw an increase. Moreover, we observed a rise in species richness within the community over time, accompanied by smaller compositional changes. Additionally, the findings indicated positive growth trends in wintering endangered species such as black-necked cranes and common cranes (Grus grus) in Caohai. Furthermore, we observed an increase in the occurrence and persistence of rare species, such as Eurasian spoonbills (Platalea leucorodia), black-faced spoonbills (Platalea minor), and black storks (Ciconia nigra) wintering in Caohai. These occurrences suggest that the wetland environment provides favorable conditions for a diverse range of species. Despite the rise in species richness, these trends in the abundance and species composition of wintering waterbirds over the past thirty years are still of concern. This study serves as fundamental scientific support for waterbird conservation and the restoration of ecological wetlands in the Guizhou Caohai Wetland.

1. Introduction

Human activities have had a significant and multifaceted impact on wetland ecosystems. Factors such as climate change, biological invasion, land use changes, and pollution can greatly affect both global and local wetland biodiversity, leading to changes in wetland ecosystem stability and services [1,2,3]. Waterbirds, being vital components of wetland ecosystems, serve as important indicators for assessing the quality of and changes in the wetland ecological environment [4,5]. While the global waterbird population and diversity are generally declining [6,7], this is not always the case at the local level [8,9]. Hence, understanding the trends in population size and diversity is crucial to preventing biodiversity decline. Long-term monitoring data are especially valuable for comprehending the responses of local and global ecosystems to changes and formulating effective conservation measures to counteract such changes.

Species abundance and richness are key indicators that reflect changes in community structure and function and have been evidenced to be negatively affected by aspects such as water quality, hydrological regimes, food resource availability, habitat suitability, and climate change [10,11,12,13,14]. The composition and diversity of regional communities typically result from the interaction of species acting and interacting at different spatial and temporal scales with environmental variables [15]. By simultaneously examining changes in species number and diversity, we can gain deeper insights into wetland waterbird community dynamics and the reasons for their occurrence in specific situations [13], which is essential for the preservation of local and global biodiversity.

The Guizhou Caohai Wetland, situated in Southwest China, is a representative alpine shallow-water wetland. It serves as a crucial wintering site for rare waterbirds, particularly the black-necked crane (Grus nigricollis), and is an important stopover for migratory birds on the western migratory route in China. Each autumn, 50,000 to 100,000 migratory birds from Gansu, Qinghai and other regions migrate southwards to the Caohai Wetland for wintering [16]. Over the past 30 years, rapid socioeconomic development has led to a sharp increase in population and urbanization in Weining County. This has resulted in significant human-induced impacts on the wetland ecosystem, particularly in the northeast region of Caohai Lake, adjacent to the county’s town. As a result, waterbirds in the Caohai Wetlands are facing growing pressures. Previous studies on waterbirds in Caohai have mostly focused on community characteristics and changes within a single year or different seasons [17,18,19,20]. However, these studies have limitations in fully explaining the underlying causes of community changes. To address this gap, this study conducted a comprehensive analysis by reviewing the literature, compiling historical data, and conducting recent field surveys to examine the population dynamics and change patterns of wintering waterbirds in Caohai Wetland since its designation as a national nature reserve in 1992. This study aimed to understand the population trends of all waterbird species and different waterbird guilds over time, as well as the patterns of change in the waterbird structure within the wetland. Ultimately, the present study aims to provide scientific support for waterbird conservation and the restoration of ecological wetlands in Guizhou’s Caohai Wetland.

2. Materials and Methods

2.1. Study Area

The Caohai National Nature Reserve is positioned at coordinates 26°47′~26°52′ N, 104°10′~104°20′ E and is situated within the southwestern sector of Weining County in the northwestern part of Guizhou (Figure 1). This karstic lake, resulting from geological processes, occupies an average altitude of 2171.7 m above sea level. The locale encounters a chiefly mountainous subtropical humid monsoon climate. The mean annual temperature is recorded at 10.6 °C, accompanied by an average annual precipitation of 950 mm. The period without frost lasts for approximately 180 days. Within the flood season spanning May to October, there is a zenith of precipitation, constituting approximately 88% of the complete yearly rainfall [21]. The water expanse during this inundation phase covers around 26.05 km². The Caohai Wetland enjoys substantial sunshine, thereby yielding mild winters and temperate summers characterized by a dry winter season and a moist summer season. This wetland encompasses diverse habitats, with both profound and shallow waters, marshlands, and grasslands [19]. Consequently, it presents an optimal winter habitat for a multitude of migratory avian species, particularly those classified as endangered or scarce. A notable example is the black-necked crane, which assumes a flagship role within conservation endeavors.

2.2. Data Collection

Data spanning the years 1992 to 2012 were primarily gathered from books, reports, and papers. Conversely, data concerning wintering waterbird populations between 2012 and 2022 were predominantly acquired via field surveys (as documented in Table S1). However, the comprehensiveness of waterbird datasets for distinct ecological categories exhibited disparities, thereby leading to variances in the initial year of the datasets utilized within the analysis. In order to sustain a coherent analysis during periods featuring sporadic data gaps, interpolation techniques were implemented (for specific interpolation methods, please refer to the section on data analysis) prior to executing the overarching summary analysis.

2.3. Waterbird Surveys

Between the winters of 2013 and 2022, field surveys were undertaken from early December through late February of the subsequent year to appraise the constancy of waterbird populations over the wintering season. To prevent redundant tallies, 11 pivotal waterbird observation sites were designated as sample locations and routes, namely Wujiayantou, Miaojiayuanzi, Yangguanshan, Xihaimatou, Huyelin, Wenjiatun, Wangjiayuanzi, Gujiadixia, Kangjiahaizi, Liujiaxiang, and Baijiazui. For each survey site, no less than two adept observers were appointed, equipped with binoculars (SVAROVSKI EL10 × 42 WB) and telescopes (SVAROVSKI ATS80), facilitating the enumeration and recognition of waterbirds both upon the water’s surface and along the lake’s periphery. These observers duly documented the avian creatures’ spatial location, habitat category, as well as any potential factors that could impede accurate observations. Instances where identifying species from a distance posed challenges prompted the capture of photographs to aid in discernment. For the enumeration of black-necked cranes and common cranes (Grus grus), emphasis was placed on synchronized tallies executed as the birds took flight from their nocturnal roosting spots during the early hours. Should multiple counts be obtained during the same winter survey phase, the most substantial count from a given survey day was embraced as the definitive outcome.

2.4. Data Analysis

This research assesses the changes in the abundance of 61 recorded waterbird species from 1992 to 2022 (Table S2). Following the categorization by previous studies [17,22], the waterbird populations were classified into five groups based on their feeding ecology and habitat preferences: ① Dabbling ducks, which engage in shallow-water feeding; ② Diving ducks, renowned for their submersion into deep water for sustenance; ③ Wading birds, encompassing cranes, storks, moorhens, and herons; ④ Shorebirds, including sandpipers and plovers; and ⑤ Perennial dominant coots (Fulica atra). Additional waterbird species featuring limited data and relatively modest numbers were omitted from the analysis (as expounded in Table S2). To effectuate data interpolation for the diverse ecological guilds of waterbirds, the methodology delineated by Inger et al. was employed [23]. This interpolation protocol initially entailed the utilization of linear regression, exponential regression, and geometric mean techniques. Subsequently, generalized additive models (GAM) were applied to impart smoothness to the data derived from the three interpolation methodologies. The veracity of the data’s smoothing effects was gauged using R² and GCV values. Based upon these assessments, the dataset processed through exponential regression interpolation emerged as the most congruent fit within the generalized additive model (details available in Table S3). Ergo, this interpolation approach was adopted for all ensuing analyses.

2.5. Waterbird Population Trends

By utilizing interpolated data, matrices can be constructed for all species (abundance) and time (years), as well as matrices for the five guilds. To accurately identify population trends for these ecological groups of waterbirds, we can apply the method proposed by Fewster et al. [24], which is based on a generalized additive model (GAM). This method facilitates the estimation of smooth trends for the various ecological groups of waterbirds. The smoothness of the curve is determined to be 0.3 times the smooth spline of the time series. Subsequently, key years of changes in different ecological groups of waterbirds can be identified through the second derivative of the abundance index curve. The GAM employs additive predictors to represent the year effect, allowing population trends to follow any smooth curve. The construction of the generalized additive model (GAM) framework is as follows:

log(µ_it) = α_i + s(t)

(1)

where log() represents the linking function, µ_it stands for the expected value of waterbird taxon i in year t, α_i denotes the intercept of waterbird taxon i, and s(t) is a smoothing function representing time.

Using the estimated value (ŝ) of the smoothing function s(t), the population index I_t for year t is defined as follows:

$$\mathrm{I}(\mathrm{t})=\frac{\exp (\widehat{s}(t))}{\exp (\widehat{s}(1))}$$

(2)

where the overall annual effect of the base year for each guild of waterbirds is represented.

By analyzing the second derivative of the curve, we can detect noteworthy changes in the population of distinct groups of waterbirds. The confidence interval (second derivative) of the exponential curve allows us to pinpoint the pivotal years of population changes. If the confidence interval encompasses zero, the population trajectory is classified as a “non-significant change”; conversely, if the confidence interval excludes zero, the population trajectory is recognized as “significant growth or decline” based on the sign of the exponential. The definition of the second derivative of the curve (I″) is as follows:

I″ = I(t + 1) − 2I(t) + I(t − 1)

(3)

where the second derivative is significantly greater than zero for a specific year, it indicates a noteworthy increase in the population or a noteworthy decrease in the rate of decline. Conversely, if the second derivative is less than zero for a particular year, it suggests a substantial decline in the population or a reduction in the rate of growth.

2.6. Changes in Community Diversity

The α diversity of the community was assessed based on the variation in species richness (number of species). In contrast, the β diversity measured the changes in species composition and abundance across two or more time points [25]. To carry out these computations, we employed the “codyn” package in R, which facilitated the quantification of species richness, species turnover, and mean rank shift of species abundance [26]. The “turnover ()” function was used to determine the overall species turnover, species appearance, and disappearance, while the “rank_shift ()” function calculated the extent of species abundance reordering. These measurements were utilized to understand how the community is changing over time. Notably, the “rank_shift ()” function computed the mean species reordering only for species present in all years.

2.7. Dynamic Analysis of Rare and Endangered Species

Considering that the endangered crane species, namely the black-necked cranes and the common cranes, coexist in the Caohai Wetland area [27], we utilized a linear regression model to analyze the population trends of both species. Furthermore, we categorized other species listed in the IUCN Red List as critically endangered (CR) and endangered (EN) and other nationally protected species as rare and endangered species, as presented in Table S2. Subsequently, we statistically described their wintering frequency in Caohai. For this research, we established 1995 as the baseline and recorded the time and frequency of appearance for each rare species between 1995 and 2022.

3. Results

3.1. Long-Term Changes in Overwintering Waterbird Abundance

In relation to alterations in the abundance of waterbirds, the curve illustrating the index of abundance showed the trends for all the species and five categories from 1992 to 2022 (Figure 2). We noted a decline in the total population of waterbirds within the wetland setting (total population: −51.9%). Among the five categories, both dabbling ducks and diving ducks experienced parallel declines, while the most substantial decreases were observed in the case of coots (dabbling ducks: −57.9%, diving ducks: −59.8%, coots: −71.2%). Conversely, notable increments were observed for wading waterbirds and shorebirds (wading waterbirds: +536.1%, shorebirds: +741.3%).

The abundance of waterbirds within the five categories showed notable fluctuations over various wintering spans, as evidenced by the second derivative of the abundance index curve. Between 2005 and 2022, a pronounced downward trajectory became evident in the collective population of dabbling ducks, diving ducks, and coots. Dabbling ducks and diving ducks experienced a significant decrease over successive years (2013–2016), and their declining patterns were markedly curbed, with instances of population recovery (2007–2011, 2015–2020). Conversely, the Coot population exhibited a significant decline from 2009 to 2016. In contrast, there were noteworthy increases for wading birds between 1996 and 2006 and for shorebirds between 2018 and 2020. However, the increases during 2009–2015 and 2013–2017 were significantly suppressed.

3.2. Temporal Diversity of Overwintering Waterbird

The investigation unveils a prevalent upward trajectory in the wintertime diversity of waterbirds from 1995 through 2022 (α diversity, as illustrated in Figure 3A). Conversely, two metrics that gauge β diversity, specifically species turnover and mean rank shift, demonstrated notable fluctuations throughout the examined period (Figure 3B,C). The average rank shift of species exhibited a sustained descent prior to 2015, succeeded by a continuous ascent post 2016 (Figure 3B). Analogously, the species turnover mirrored the pattern of the mean rank shift, with an ongoing alternation between the disappearance and appearance of species from 1995 to 2015. However, subsequent to 2016, the count of the species appearing surpassed the count of the species disappearing (Figure 3C).

3.3. Population Dynamics of Cranes, Rare and Endangered Waterbirds

The crane populations in Caohai Wetland undergo significant changes during the overwintering period each year (Figure 4A,B). On average, the population of black-necked cranes was 1123, reaching a peak of 2385 in 2015 and with a minimum of 330 in 1992. Similarly, the average population of common cranes was 783, with a maximum of 1357 in 2014 and a minimum of 296 in 1992. The crane population has displayed considerable fluctuations over the years, with common cranes showing a gradual increase while black-necked canes increased significantly.

Regarding other rare and endangered species, the number of overwintering species has fluctuated over the years. The highest record was six species in 1995, while only three species were recorded for many years. However, since 2019, the number of rare species has started to rise (Figure 4C). Between 1995 and 2022, the highest recorded frequency was observed for the Eurasian spoonbill (Platalea leucorodia), followed by the purple swamphen (Porphyrio porphyrio), black stork (Ciconia nigra), black-faced spoonbill (Platalea minor), Eurasian curlew (Numenius arquata), tundra swan (Cygnus columbianus), and Baikal teal (Aythya baeri). However, the smew (Mergellus albellus) and slaty-backed duck (Sibirionetta formosa) were only observed once in 1996 in the Caohai Wetland (Figure 4D).

4. Discussion

Our investigation has brought to light substantial shifts in the population dynamics of waterbirds over the preceding three decades within the Caohai Wetland. On the whole, a discernible reduction in avian populations has been ascertained. Nevertheless, the trajectories of duck and coot populations contrast with those of wintering cranes, waders, and shorebirds. The diversity metrics indicate a modest rise in α-diversity, while the β-diversity has shown noteworthy oscillations between 1995 and 2022. Moreover, with the exception of cranes, the presence of other infrequent and at risk waterbirds during each winter at Caohai was not conspicuous, though it was augmented over time.

4.1. Population Trajectories in Wintering Waterbirds

The investigation disclosed a noteworthy decline in waterbird populations within the Caohai Wetland from 1992 to 2021, principally propelled by the swift decrease in two guilds—ducks and coots (details available in Table S2, depicted in Figure 2). This decline is aligned with the global trend of diminishing duck and coot populations reported by the Asian Waterbird Census [28]. The dwindling numbers of these waterbirds might potentially be ascribed to agricultural practices and anthropogenic disturbances. The proximate adjacency of the Caohai Wetland to the county has engendered an upsurge in agricultural activity, the excessive usage of pesticides and fertilizers, as well as the unregulated disposal of domestic refuse and sewage. These factors have engendered a prominent conflict between population expansion and environmental conservation, resulting in compromised water quality, extensive wetland area contraction, and the degradation of habitat. Notably, Caohai in Guizhou has recently undergone eutrophication, transitioning from a grass-dominated lake to an algal-dominated lake. This has been accompanied by a marked loss of submerged vegetation and a significant elevation in the chlorophyll-a concentration [29]. The decrement in herbivorous waterbird populations could be attributed to the scarcity of aquatic vegetation. Additionally, findings by Tománková et al. [13] demonstrated a correlation between the decline in macroinvertebrate biomass and long-term changes in phytoplankton biomass, as quantified by chlorophyll-a concentration. They also found that the dwindling macroinvertebrate population led to the collapse of the diving duck population. Hence, the diminishing duck and coot populations observed in our study area likely stem from limited food availability.

The temporal shifts among the three populations suggest that the downward trend in waterbird populations slowed after 2015–2016, with certain clusters displaying signs of recuperation. The escalating ecological predicament, shrinkage of wetlands, diminished biodiversity, and degradation of wetland ecological functions, influenced by augmented regional climate interference and human endeavors, have eroded the carrying capacity of the Caohai Wetland ecosystem [30]. These factors have contributed to the prolonged decline in waterbird populations. Since 2013, governmental focus has been on strengthening the preservation of the Caohai Wetland ecosystem and implementing comprehensive preventive and control measures, possibly accounting for the amelioration of population decline through habitat enhancement.

The study also unveiled a five-to-sevenfold increase in the populations of wading birds and shorebirds during the study. Prior research has suggested that diverse feeding requisites can have distinct effects on specific species or foraging guilds [31]. Owing to low winter rainfall [21], extensive zones of shallow marshes (<20 cm) take shape in Caohai, offering abundant nourishment for insectivores, piscivores, and certain omnivorous waterbirds. These areas aggregate invertebrates, juvenile fish, and shrimps [32,33].

The growth of the wading bird population hinges on the expansion of the crane population (as depicted in Figure 2D and Figure 4A,B). China’s ratification of the Ramsar Convention in 1992 [34], coupled with global upswings in the population sizes of both black-necked cranes and common cranes as a consequence of wetland restoration and rehabilitation efforts [35,36,37], has influenced the proliferation of crane populations within Caohai. Research underscores that over 80% of cranes rely on residual crops left in arable land during the wintering phase [38,39], and the encompassing arable land offers adequate sustenance during winter. As cranes assume a pivotal role in Caohai’s conservation endeavors, the reserve has implemented various preservation measures, encompassing restrictions on human and livestock ingress into the core zone, curtailed human activities, the cultivation of crops (such as potatoes and carrots) in proximity to Caohai Lake, the provision of regular maize feed during winter, and the establishment of a bird rescue center. These measures have effectively contributed to the upholding and expansion of black-necked crane and common crane populations. The investigation highlighted positive progress in both black-necked crane and common crane populations within Caohai Wetland. Nevertheless, the population sizes have annually oscillated within a specific range. The model fitting exhibited the most accurate predictive influence on the black-necked crane population (R² = 0.85), whereas the predictive precision for the common crane population was comparably lower (R² = 0.28) (as depicted in Figure 4A,B). These outcomes imply that the crane population numbers could be influenced by additional factors (such as landscape configuration, water levels, and temperature fluctuations) [37]. Unfortunately, direct evidence of population size variation in Caohai is currently lacking.

4.2. Temporal Diversity of Wintering Waterbirds

Fascinatingly, our study signifies an affirmative progression in species richness across time, while the collective waterbird abundance has experienced a decline within the Caohai Wetland. This discovery stands in contrast with other Chinese wetlands such as Poyang Lake, which exhibited no significant alterations in waterbird abundance and richness between 2001 and 2016 [22], while the Liaohe Estuary showed an increasing trend in both waterbird abundance and richness from 2010 to 2019 [40]. This disparity may arise due to the fact that waterbird abundance is more attuned to environmental shifts, responding with a lag compared to richness, which presents a delayed reaction [41]. Another contributing facet could be the annual incidence rate of rare species. Guizhou’s Caohai area serves as a prominent winter haven and repose site for waterbirds in Southwest China, often witnessing the sporadic presence of singular vagrant species, particularly among shorebirds. Our research found that variations in species representation during distinct winter spans could contribute to a rise in waterbird richness without significantly influencing the overall abundance (details in Table S2).

Furthermore, our study uncovered noteworthy alterations in the species composition of waterbirds throughout the study period (as depicted in Figure 3B,C), signifying that the waterbird community experienced constant turnovers in both composition and species quantity within the Caohai Wetland. Nevertheless, this alteration has gradually subsided over time, a phenomenon similarly observed within the waterbird community of the Liaohe Estuary [40]. Shifts in species richness and composition yield insights into broader temporal fluctuations in biodiversity [26,42,43]. In the grander scheme, while species richness of waterbirds has increased over time, the differences in species composition have diminished. This trend aligns with the findings of Dornelas et al. [8] and suggests that though local communities are becoming more intricate, the trajectory of community composition is steering toward heightened complexity albeit accompanied by increased uniformity, a prospect that could pose a substantial risk to wetland biodiversity.

4.3. The Status of Rare and Endangered Species in Caohai Wetland

Spanning the period from 1992 to 2022, our study identified positive advancements among rare and endangered waterbirds in the study area. While resident cranes with stable and sizable populations within Caohai consistently inhabited the area, other rare wintering waterbird species characterized by minute populations occasionally overwintered here. Certain species such as the Eurasian spoonbill, black-faced spoonbill, and black stork demonstrated pronounced clustering in their winter sojourns. The persistence of waterbirds hinges largely on suitable habitats [44], especially for rare and endangered species with specific habitat prerequisites. Habitats conducive to waterbirds are susceptible to degradation due to pollution, plant invasions, and hydrological modifications [45]. Fortuitously, wetland restoration initiatives launched by the Guizhou Province Forestry Department post 2015 have contributed to heightened sightings of rare and endangered waterbirds, underscoring the efficacy of these restoration endeavors. Moreover, transformations in the Caohai Wetland ecosystem might have fostered conditions for local waterbird populations to contract, thereby liberating more resources and ecological niches for rare and endangered waterbirds. This could elucidate the augmented sightings of these species.

To safeguard the wealth and variety of waterbirds on both global and regional scales, it is imperative to address the ongoing decline in waterbird diversity and abundance despite enduring historical conservation exertions [46]. Conservation management frequently targets augmenting the abundance of locally uncommon species, albeit this might offer insufficient shelter for more prevalent, widespread species [23]. Nevertheless, the diminishment in abundance of commonplace species often entails significant ecological ramifications [47,48]. Ubiquitous waterbirds play a pivotal role in upholding ecosystem structure and functioning, encompassing pest and ailment control as well as equilibrium maintenance within the food chain [49]. Hence, the preservation of rare and endangered waterbirds should be judiciously balanced with the safeguarding of common counterparts.

Over the past three decades, the ecological environment, waterbird abundance, and diversity of Caohai Wetland have experienced substantial changes. While we have speculated on the causative factors behind various waterbird shifts, further exhaustive experiments and studies are requisite to corroborate these hypotheses. To actualize the objectives of ecosystem services and biodiversity preservation within the Caohai Wetland, policymakers and conservation practitioners should endorse and enhance the waterbird monitoring system. This will foster a more comprehensive grasp of the dynamics of diversity changes within local communities. Furthermore, founded upon the findings of this study and the current circumstances in Caohai, we contend that restoration endeavors should persist as a prime focus. Urgent steps to enhance water quality and restore aquatic vegetation are particularly imperative to mitigate pressures on waterbird survival, given that copious food resources, water levels, and habitat structure are pivotal determinants of waterbird abundance and diversity [11,44]. Furthermore, waterbird conservation strategies can be recalibrated, as suggested by Campos-Silva et al. [50], to safeguard ‘umbrella species’ while concurrently generating ancillary benefits for other species, fostering an improved condition for a wider gamut of avian species, including incidentally protected non-targeted ones.

5. Conclusions

Our study underscores a substantial protracted wane in the abundance of wintering waterbirds within the Caohai Wetland over the past three decades. The drop in abundance is particularly notable among waterbirds that rely on plant material and macroinvertebrates for sustenance, such as ducks and Coots, reflecting inadequate food supply, a notion discussed in prior studies [13,29]. Conversely, there has been a remarkable surge in the abundance of shorebirds and waders, which might be explained by the presence of ample food resources created by extensive shallows facilitated by diminished winter rainfall [31,32]. Furthermore, the diversity indicators of waterbirds have displayed noteworthy temporal fluctuations on various scales, with a tendency toward homogeneity. This suggests that the stability of waterbird community structure could be at risk, warranting conservation attention. Additionally, our study identifies an increase in sightings of certain rare waterbirds, a noteworthy development given that these rare species are reliant on specific habitats and therefore face an elevated extinction risk. Strengthening the waterbird monitoring system is imperative for the preservation and safeguarding of waterbird diversity in the region. Furthermore, the restoration of wetland functions is now of paramount importance. Lastly, conservation strategies that balance the needs of rare and common species could offer the greater efficacy in preserving waterbird diversity.