Distribution and Numbers of Three Globally Threatened Waterbird Species Wintering in Morocco: The Common Pochard, Marbled Teal, and White-Headed Duck

Morocco plays a key role in the life of many migratory birds and their survival, thanks to the diversity and richness of its ecosystems. &e International Waterbird Census (IWC) has been regularly implemented in Morocco since 1983. &anks to this program, a large database on wintering waterbirds’ populations has been collected. In this article, we summarize the wintering data of three globally threatened waterbirds: Aythya ferina, Marmaronetta angustirostris, and Oxyura leucocephala. &e population of Aythya ferina, which is declining, is largely distributed in the country, in over a hundred wetlands, 26 of which verify the national importance criteria.Marmaronetta angustirostris has a stable trend over the years even though its population can know high annual fluctuations; it winters in more or less 50 wetlands, among which 18 host more than 1% of its regional population and 16 verify the criteria for national importance. On the contrary,Oxyura leucocephala, a globally endangered bird only encountered in a dozen wetlands, shows a moderate increase in its numbers; only two wetlands verify the Ramsar criterion 6, while a total of six can be considered of national importance. Furthermore, given the conservation statuses of these waterbirds and according to the Ramsar criterion 2, all their hosting sites are of international importance. &e results presented in this paper are a crucial step for the adoption and implementation of adequate conservation measures for the species and their key sites. Nevertheless, comprehensive research and coordinated efforts on the factors (ecological and anthropogenic) influencing the species, at the national and international levels, are required for a better understanding of their populations’ dynamics.


Introduction
Morocco is a North African country, with highly diversified ecosystems and coastlines along both Atlantic Ocean and Mediterranean Sea [1,2]. It is located at the crossroads of many bird migration routes between Europe and Tropical Africa, and its wetlands play a crucial role for thousands of birds as stopover, wintering, and breeding areas [3,4]. e country has ratified almost all international and regional agreements for the conservation of these birds and their habitats. In the context of the Ramsar Convention and the African-Eurasian Migratory Waterbird Agreement, the country undertakes regular waterbird censuses that provide an appropriate basis for effective decision-making in their conservation. In fact, Morocco has been regularly participating, since 1983, in the International Waterbird Census (IWC), one of the largest biodiversity monitoring programs in the world, thanks to the coordination of the Study Centre of Bird Migration (in the Scientific Institute) and the collaboration of GREPOM/BirdLife Morocco, which provides the majority of field volunteers.
e White-headed Duck is the only Palearctic species of the Oxyurini tribe [26]. Breeding birds are usually found in freshwater and brackish or eutrophic lakes with dense emergent vegetation [22,27], shallow and permanent or semipermanent [9], while wintering birds can be found in deeper and larger wetlands, alkaline or saline, and with less vegetation [28]. In Morocco, it is a winter visitor, resident breeder, and suspected passage migrant [11]. It used to breed in Morocco until the 20 th century, before becoming scarce and disappearing, due its habitats' loss by agricultural development and droughts [25]. Since the 1990s, the species reappeared in "Plan d'eau de Dwiyate" [4,29] and then expanded progressively to several other breeding sites [30,31]: "Merja de Sidi Bou Ghaba," "Merja de Fouwarate," "Barrage 'Arabat'," "Barrage El Mehraz," "Merja Bargha," cumulating about 60 couples. It is still vulnerable in Morocco [12].

Counting Procedure.
Our study is based on the dataset of the waterbirds' winter census, between 1983 and 2019. e counting procedure was adopted according to standard bird monitoring techniques [32], and the protocol was refined over the years [14,[33][34][35]. e censuses are conducted annually, usually during January, to avoid recounts.
Nevertheless, given the large number of wetlands to be censused, some missions can start in late December (especially in the Saharan region). Moreover, in some rare cases, data from censuses during the 1 st week of February were accepted; they were conducted in some sites (Atlas lakes) that were not accessible, during January, because of heavy snow. e number of wetlands censused, at least once, in the context of this program is 272 (IWC wetlands network). However, not all of them are visited every year, depending on the availability of human, financial, and logistical resources. e priority is always given to the wetlands with the highest waterbirds' numbers and specific richness.
During each visit, the observers (Table S4) counted all waterbirds on the grounds, in the water, and even those flying inside the site, using binoculars and telescopes. Counting points and transects are determined for each wetland, depending on its configuration and accessibility. When some wetlands are close to one another, in a way that allows frequent bird exchange between them, they are considered as complex sites and are covered during the same visit. Over the years (especially since the 1990s), most wetlands have been censused by the same group of observers, using the same protocol; this makes the obtained data more homogenous, comparable, and reliable. e observers participating in the IWC program are ornithologists, qualified and trained for bird identification. New observers can join the program after going through training sessions on bird identification and counting methods, both theoretical and practical. During their learning phase, they can join the established observers' teams during their census campaigns to strengthen their training.

Data Analysis.
e wintering waterbirds' numbers are entered in an information system, which generates automatically tables per species and sites.
To calculate populations' trends, we used the TRIM (TRends and Indices for Monitoring Data) freeware [36] (version 3.54). TRIM generates estimations for missing counts and can analyze data for 4000 sites, over 100 years; this makes it very suitable for our large dataset, especially since not all sites are visited every year (Table 1). e missing data imputations take into account a site effect and a time effect, assuming the counts in a year depend on those of the year before (serial correlation). e counts are assumed to be Poisson distributed and are converted into annual indices to simulate the missing data and calculate trends, based on the completed dataset (with the first year as base year, to which the index 1 is attributed. e overdispersion (when the variance is larger than expected for a Poisson distribution) and the serial correlation can be estimated by TRIM, through a generalized estimating equation (GEE) approach. e recommended overall slope by TRIM is based on the imputed data and given with the results of the additive slope and the multiplicative slope, which reflects the magnitude of annual change, as well as their standard errors. It is converted into one of six trend categories: (i) strong increase: an increase significantly greater than 5% per year; (ii) moderate increase: a significant increase, but not significantly more than 5% per year; (iii) stable: no significant increase or decline, and it is certain that trends are less than 5% per year; (iv) uncertain: no significant increase or decline, but not certain if trends are less than 5% per year; (v) moderate decline: significant decline, but not significantly more than 5% year; (vi) steep decline: decline significantly greater than 5% year. A significance threshold is also provided for the increasing and declining trends: (i) highly significant: p < 0.01 (i.e., confidence level of 99%); (ii) significant: p < 0.05 (i.e., confidence level of 95%).
For the Common Pochard and the Marbled Teal TRIM analyses, three periods were considered: long term To better understand the species evolution, we used different parameters, mainly as follows: (i) e average number of a species in each site is calculated for the long term and short term and corresponds to the arithmetic mean.  to determine the deviation of the numbers observed annually from the average.
where x i is the observed number in site i, x is the arithmetic mean, and N is the number of observations. To prioritize future conservation measures, we have identified for each species, categories of key sites, based on recent data (2010-2019): (i) Sites of international importance, priority 1 (SII1): wetlands verifying the 6th Ramsar criterion (the species' numbers reach or exceed regularly (5 winters or more) 1% of its regional population. (ii) Sites of international importance, priority 2 (SII2), verifying the 2nd Ramsar criterion (sites supporting vulnerable, endangered, or critically endangered species). (iii) Sites of national importance (SNI): the species' average number, in those sites, equals or exceeds the 1% of the national average. (iv) Sites of potential national importance (SPNI): they hosted, during at least winter, more than 1% of the national average.

Populations' Size and
Trend. e national average of the Common Pochard's wintering population is 11.158 in the long term, the total annual numbers varying between 1.710 (in 2012) and 20.458 ducks (in 2002) ( Figure 1). During the last decade (2010-2019), the national average is lower (7.496 individuals), but it represents 1.25% of the regional population "Central and NE Europe/Black Sea and Mediterranean" [37]. e Common Pochard was present in 809 counts and absent in 991 counts (no observed birds during visits), while 2.640 data are missing (the unavailable records relative to the species' known wintering sites, which have not been visited during certain years) (Table S1). Its population trend ( Figure 1) is stable in the long term (additive slope � −0.0101 ± 0.0057; multiplicative slope � 0.9900 ± 0.0057), a significant moderate decline in the medium term (additive slope � −0.0727 ± 0.0117; multiplicative slope � 0.9299 ± 0.0109; p < 0, 01), and uncertain in the short term (additive slope � −0.0226 ± 0.0279; multiplicative slope � 0.9776 ± 0.0273), but with a declining tendency. is decline is more evident during the last decade (2010-2019) even though the census effort has significantly increased.
e Marbled Teal's national average is almost the same, in the long term (3.071) and short term (3.070).
e White-headed Duck's national average is 445 between 2005 and 2019 and 542 individuals during the last decade (2010-2019). Morocco hosts 22% of the regional population "Spain and Morocco" [37]. e observed total annual numbers varied between 1 and 1.730 ( Figure 3). e species was observed, in the context of IWC, during the period 2005-2019 and was present in 29 counts and absent in 58 counts (no observed birds during visits), while 45 records are missing (Table S3). e population's trend ( Figure 3), for the 2005-2019 period, is a moderate increase (additive slope � 0.2749 ± 0.1181; multiplicative slope � 1.3164 ± 0.1554; p < 0, 05). In the short term, it is uncertain (additive slope � 0.3899 ± 0.4609; multiplicative slope � 1.4768 ± 0.6807), but with an increasing tendency.

Spatial Distribution.
e Common Pochard was observed in a total of 118 wetlands (43% of the surveyed wetlands) (Table S1), mostly in the Northern half of the country, along the Atlantic coast and Atlas region ( Figure 4). However, from year to year, the species was reported in 9 to 39 sites ( Figure 1). Between 2010 and 2019, the northwest (31 sites) and northeast (16 sites) regions hosted the highest concentrations (37% and 33%, respectively). Amongst the sites visited at least 19 winters over the 37 years study period, the species occurrence percentage was the highest in five of them (>85%): "Aguelmam Abekhane," "Aguelmam Afennourir," "Merja de Sidi Bou Ghaba," "Dayet Ifrah" and "Barrage de Smir." e highest total numbers (between 1983 and 2019) were cumulated as follows: "Barrage Mohammed V," "Barrage Al Massira," and "Embouchure de Wad Massa." In the short term (amongst the sites visited at least 5 years out of 10), the highest average numbers were recorded in "Barrage Mohammed V" and "Merja de Sidi Bou Ghaba" ( Table 2). Some wetlands have known a decline in the species' wintering numbers, such as "Embouchure de Wad Massa;" others such as "Merja de Fouwarate" have hosted increasing numbers in recent years. e highest concentration ever recorded in Morocco (15.600 birds) was observed in the reservoir of "Barrage Mohammed V" in 2002.
is site has known high fluctuations of the Common Pochard's numbers (zero to thousands), which is clearly reflected by its high standard deviation (Table 2).
e Marbled Teal was observed in a total of 50 wetlands (18% of the surveyed wetlands) (Table S2), mainly distributed north and west to the Atlas Mountains and in the northern part of the Sahara ( Figure 5). Annual distribution varied between 2 and 19 sites ( Figure 2). In the short term, 67% of the national average was observed in the southern region (in 15 wetlands), with particularly high concentrations in 2013 (95%) and 2018 (62%). e other regions hosted 8% to 15% of this number. e highest occurrence of the species was recorded in "Merja de Sidi Bou Ghaba" (97% of the visits), "Lagunes de Sidi Moussa-Walidia" (83%), and "Embouchure de Wad Massa" (81%). ree sites hosted each, more than 10% of the total numbers recorded between 1983 and 2019: "Lagunes de Sidi Moussa-Walidia," "Wad As-Saqia Al Hamraà La'youn," and "Merja de Sidi Bou Ghaba." e highest standard deviations were recorded in two sites (Table 3): Since its reappearance in Morocco in the early 2000s, the White-headed Duck was observed in 12 wetlands (17% of the surveyed wetlands), mainly in the north of the country (Table S3;  species was most regular in "Merja de Sidi Bou Ghaba" (75% of the visits) and "Merja de Fouwarate" (45%). ree wetlands ("Merja de Fouwarate," "Merja de Sidi Bou Ghaba," and "Barrage Mohammed V") hosted more than 10% of the wintering individuals. It is worth mentioning that the wetland "Plan d'eau de Dwiyate" is hard to access, since it is part of a royal domain. Except for a temporary lake on the east (suffering from some disturbance, overgrazing, and recurrent droughts [29]), it is fenced and well-guarded and hence with no disturbance, which makes it a site of great importance for the species. e highest standard deviation was recorded in "Merja de Fouwarate" (Table 4), where the species was not observed before 2014 (Table S3)

Sites of International and National
Importance. e Common Pochard is a globally vulnerable species, which makes all the sites hosting it of international importance (SII2 as we have defined in Methodology). None of the Moroccan wetlands verify the Ramsar criterion 6 for the species. Nevertheless, it is worth mentioning that "Barrage Mohammed V" could be of potential international importance. In fact, in 2002, this site hosted a high concentration of 15.600 ducks, which exceeded the estimated 1% of the regional population at the time (10.000) [37]. e reported species' numbers in this wetland can be highly underestimated due to a difficult access to many parts of the reservoir, depending on the conditions. erefore, it can, more than likely, host regularly at least 1% of the Common Pochard's regional population. is could also be the case for "Barrage Al Massira," a reservoir often partially censused and which hosted, in 2008, 5.500 ducks. Among the 118 wetlands where the species was observed, 26 have average numbers equal or superior to 1% the national average (7.496) ( Table 2), which makes them of national importance. On the contrary, 15 others hosted wintering numbers exceeding that threshold, during at least one winter (Table 2), which makes them of potential national importance. e Marbled Teal is a globally vulnerable species, which makes all the sites hosting it of international importance as well (SII2). Moreover, 18 wetlands hosted, at least once, more than 1% of the regional population [5], three of them regularly: "Lagunes de Sidi Moussa-Walidia," "Merja Zerga," and "Wad As-Saqia Al Hamraà La'youn;" they are thus of international importance for the species (SII1) ( Table 3). On the contrary, 26 wetlands have average numbers equal or superior to 1% of the national average (Table 3), which makes them of national importance. Among them, 11 hosted wintering numbers exceeding that threshold during at least one winter (Table 3), which makes them of potential national importance.
Because it is endangered, the White-headed Duck attributes an international importance to all the 12 sites hosting it (SII2). e 1% of the regional population [37] was exceeded, at least one winter, in five wetlands, but regularly in "Merja de Sidi Bou Ghaba" and "Merja de Fouwarate." On the contrary, seven wetlands hosted, at least once, more than 1% of the national average, cumulating 99.8% of this number. Among them, 6 are of national importance and one is of the potential national importance (Table 4).
For the three species, some sites need to be monitored more regularly to verify and/or confirm their national/international importance since they have been visited less than 5 winters (Tables S1-S3).

Current Conservation Measures in Morocco towards the ree
Species. An efficient legal conservation way consists in classifying a bird in an official list of protected species. Two main lists exist in the Moroccan legislation: a list of species for which hunting is banned (published through the "Annual Hunting Order") and a list of species in which trade and transport is conditioned by a special governmental authorization (through the CITES Law "N°29-5"). e hunting of the White-headed Duck and Marbled Teal is prohibited in Morocco, whilst the Common Pochard can still be hunted [38].
National action plans for species can also be efficient tools for the conservation of birds and their habitats. In Morocco, only the White-headed Duck has a national action plan [18].
In situ conservation mechanisms represent another important measure for the conservation of the three species. In addition to two international statuses for the conservation of wetlands: (i) Ramsar Sites and Important Bird and Biodiversity Areas (IBA), these mechanisms also consist, in Morocco, in the creation of three national statuses for which a high number of wetlands have been designated for. Several bird species, including the three ducks subject of this article, have been targeted by these statuses: (i) national parks (NPs); (ii) Sites of Biological and Ecological Interest (SBEI), defined in 1996 [39], with at least 84 wetlands, partly assessed using waterbirds; and (iii) permanent hunting reserves (PHRs).
e Common Pochard is found in 44 wetlands, with at least one conservation status (

Population Size and Trend.
e global population of the Common Pochard is considered to be decreasing [8]. Even though regional populations' trends differ from stable to unknown [8], the European population, which represents 35% to 40% of the global population, has decreased by 30-49% over three generations [8,40,41]. e Moroccan wintering numbers show a significant decline, especially during the two recent decades, which could be directly linked to the declining trend of the regional population "Central and NE Europe/Black Sea and Mediterranean" [37,[42][43][44], from which the wintering individuals in Morocco originate. In fact, according to the IUCN [37], the species' decrease is mainly due to the loss of its breeding habitat in Eastern Europe. In Central Europe, it appears that the major factors responsible for its decline are nest predation [37,45] by natural (Vulpes vulpes and Sus International Journal of Zoology scrofa) and alien mammal species (i.e., Neovison vison, Nyctereutes procyonoides, and Procyon lotor) and a decline of Dreissena polymorpha, the zebra mussel which is the preferred food of this duck [46][47][48]. Furthermore, Fox et al. (2016) [41] have summarized multiple factors influencing the breeding population in the old continent; they are mostly related to loss or changes in habitats, food availability, predation, alien species, hunting [9,49,50], fishing, disturbance, and lead poisoning [51]. On the contrary, Folliot et al. (2018) [52] suggest that decreasing wintering numbers in Western Europe can also be due to the decline of the breeding population in the southwest Asian flyway (especially in Siberia). In fact, analyses of ringing recoveries data showed that large wintering numbers in the northwest European flyway originate from the southwest Asian flyway, which brings to evidence the interactions and exchange between the different regional populations beyond the determined limits of the flyways. In addition to the aforementioned factors that are possibly contributing to the decline of the Common Pochard in Morocco, climate change can also play a crucial role in the species' populations changes [53][54][55][56][57][58] at a larger scale, as well as the direct threats faced by the species in Moroccan wetlands. e evolution of the Marbled Teal's wintering population in Morocco is consistent with the trend of the regional population (West Mediterranean/West Mediterranean and West Africa), which is stable [42], but with a possible declining tendency [37]. e global population of the species has decreased rapidly overtime [7]; only the southwest Asian population knows a possible increase [37], albeit it may be due to an improvement in census coverage instead of actual changes within the population [7].
In Morocco, the Marbled Teal's population often showed a lot of fluctuations from one year to another. In fact, the species can have extreme fluctuations in its population's size depending on rainfall's annual variation [18]. It can therefore relocate to other areas that may be unmonitored and vice versa and hence giving the impression of an increase or decrease in numbers. is relocation could occur between wetlands of the same country as well as at a larger scale, between wintering areas of different countries. Moroccan wintering individuals can come from breeding sites in Europe (e.g., Spain) and North Africa [59] (especially Algeria, which hosts important numbers of the species [60][61][62]). Nevertheless, the high records observed sometimes are not necessarily caused by an influx from Spain but could be explained by the presence of unknown breeding sites of great importance in the country or in North Africa [59]. e sometimes declining numbers of the species in Morocco and other regions can also be function of the habitats' quality and availability. In fact, the global population's decrease was a Wetlands surveyed (with no Marbled Teal) Hydrographic network Regional boundaries direct consequence of habitats' loss and degradation [7,59,63] due mainly to drainage of wetlands for agricultural purposes and hydrological work [7]. In our country, for example, one of the most important breeding sites, the Iriki Lake (where the Marbled Teal used to breed in high numbers (hundreds of couples in the 1960s)), has disappeared because of the construction of a dam (Barrage Al Mansour Ad-Dahbi) [24]. Although this vulnerable duck is legally protected in Morocco [24], it still faces many threats affecting negatively its population. ese threats are mainly related to human activities, disturbing, degrading, or destructing its habitats, and changes in water levels (caused by low precipitations, drainage, and hydraulic work). In fact, the species' wetlands occupancy in our country, especially in the breeding season, is closely dependent on habitat-related factors, such as the number and diversity of emergent vegetation species [22,64,65], which are more predominant in Ramsar sites close to the coastline [65]. Since its return in Morocco, the White-headed Duck's population has known a moderate increase. Notwithstanding, the global population of the species is thought to be decreasing [6]. is decline is estimated to be 50-79% in three generations [6] even though many subpopulations are not thoroughly recorded, which may lead to an underestimation of the species counts [6,66]. e increase in this endangered duck's population in Morocco, especially the high numbers recorded in "Merja of Fouwarate" during the 2018 winter (1.430 individuals) [30], could have different potential explanations and combined factors: (i) A flow of migrants from Spain: the conservation and protection efforts undertaken by Spain, over more than 30 years [29], have had a strong positive effect on the White-headed Duck's population in Spain and may have contributed to its return to Morocco and its increasing numbers in the country [29]. (ii) A flow of individuals from the regional population of "Algeria and Tunisia," which hosts significant breeding numbers of the White-headed Duck [66]. ere are, currently, insufficient data to decide if there is any exchange between the West Mediterranean and North African subpopulations [66] that could also contribute to the species increase in Morocco. Nevertheless, our country is at an advantageous position between the increasing Spanish population and the Algerian one, which hosts high numbers of the species during the breeding season and throughout the year [66][67][68][69][70], but faces many threats in the country, especially illegal killing [71]. (iii) e decline in the population of the ruddy duck and its hybrids due to campaigns for its eradication in Spain, Europe [29,72], and Morocco [73]. (iv) e presence of favorable breeding sites in Morocco, thanks to wetlands conservation efforts and suitable climate conditions that contribute to good water levels [74] and more developed vegetation cover.
In Morocco, many factors have contributed to the former disappearance of this endangered duck and halted its expansion. Overgrazing and repeated cutting of reed beds caused a regression of emergent vegetation in permanent wetlands [29], which is crucial for this duck's breeding. According to El Hamoumi et al. [31], the species still faces many other threats; the most imminent one is the hybridization with the ruddy duck. In fact, this introduced species has been observed in Morocco on many occasions, and the last documented observation was in 2013, where 2 individuals were observed in Merja Al Halloufa [75]. Never- Wetlands surveyed (with no White-headed Duck) Hydrographic network Regional boundaries   12 International Journal of Zoology  Inland lake  Atlas  --X  --X  --Aguelmam Afennourir  Inland lake  Atlas  X  -X  I 12  X  X  X  -Aguelmam Azegza  Inland lake  Atlas  --X  -- Wad As-Saqia Al Hamraà La'youn River South X X ---X X - Morocco is the excessive pumping [31], from artificial and natural wetlands, as well as groundwater. is leads to lower water levels or even the drying-out of the wetlands, making it difficult for the species to thrive in such conditions. e other threats are mainly related to different disturbances that can affect the species population directly (illegal or accidental hunting and stray dogs that feed on ducklings or eggs) or indirectly (recreational activities and inadequate management policies).
Most of the key wintering wetlands of the three waterfowls benefit from at least one conservation status. e attribution of these conservation statuses represents an important step in their conservation. In fact, some of these sites also have management plans that allow enhanced land and water management and the protection against anthropogenic threats. is begs the following question: if the most important sites for the species benefit from conservation statuses and measures, on what scale should we also focus to improve the populations' size?

Conservation Stakes.
For each of three species presented in this article, the population changes are often multifactorial and can be in situ or ex situ. In fact, these ducks are highly dependent on their habitats, especially during the breeding season. As we have discussed above, any negative change, be it natural (e.g., drought and flood) or anthropogenic (e.g., drainage, vegetation cutting, and hydraulic work) can potentially result in their decrease or redistribution to other sites. e designation of Ramsar and important bird and biodiversity sites is one of the important measures for the waterbirds and wetlands conservation and among the good indicators of its success. In Morocco, 49 wetlands are important bird biodiversity areas, 38 are Ramsar sites, and at least 84 are Sites of Biological and Ecological Interest (SBEI), among which many are part of national parks and/or permanent hunting reserves. While these statuses are important, if no ensuing effective management plans are developed and implemented, their degradation, thus their biodiversity's decline, is an inevitable consequence, especially for those subject to many anthropogenic pressures. e Moroccan Department of Water and Forestry has developed management plans for many wetlands: some are finalized, and others are still in progress. e implementation of these plans can face many challenges inherent to the multiplicity of actors involved and the cooperation of the local populations, whose livelihoods may depend on the ecosystem services those wetlands provide. e designation of SBEI in Morocco was a strategic measure and a starting point to prioritize the conservation of the ecosystems with the highest biodiversity indices and hosting the most endangered, rare, or endemic species. But as we have pointed out above, the implementation of management and conservation action plans remains crucial.
On the species' level, the adoption of the National Law N°29-05, enforcing the CITES Convention, is a particularly successful measure deterring all illegal actions threatening endangered species. Furthermore, the national action plan for the White-headed Duck [31] is a crucial step to the conservation of this endangered waterbird and the restoration of a viable population on the long term. Similar actions should be undertaken for the marble teal and the Common Pochard, as well as all globally threatened birds in Morocco, targeting the specific threats for each species in each site. However, efforts must be deployed for a rigorous implementation of these conservation action plans and their evaluation on a regular basis. While the hunting of the White-headed Duck and the Marbled Teal is prohibited, the Common Pochard can still be hunted. Given the current trend of this duck's population, at the national and international levels, more restrictions should be placed on its hunting.
So far, we have discussed the populations' changes inherent to factors at the national level. However, some of these changes can be related to factors at a larger scale and outside the national territory (e.g., threats and conservation measures in other countries). Furthermore, climate change and meteorological conditions can also have an impact on the national population. Kleijn et al. [76] have, for example, reported a positive correlation between waterbirds' population trends in Morocco and precipitations in the Sahel zone that may have a potential impact on birds' migratory strategies. erefore, some populations' changes are probably more related to shifts in migratory routes and wintering areas than actual changes in birds' numbers [76].
More thorough research could lead to the exact reasons behind the three studied ducks' populations' trends. Comprehensive studies should be conducted to understand the effects of ecological and anthropogenic factors on the distribution, abundance, and population dynamics of waterbirds' species [12], such as water quality, food availability, predation, weather, and conservation statuses. Furthermore, with the increasing challenges that may hinder our monitoring programs [77] and the effectiveness of conservation plans, we must develop new effective methods for waterbirds' census (wintering and breeding populations) with more precision and coverage, coupled with other programs such as ringing-recovery/capturerecapture, continent/flyway, or region-wide series of aerial survey transects as has been suggested by Fox et al. (2019) [77].
is is crucial since the movements occurring within and between the regional populations of the species are still not well understood. Large-scale information on birds' populations' trends and habitats' use is insufficient, which affects negatively the conservation process [78]. Cooperative and coordinated efforts, such as the Mediterranean Waterbirds Network [79], are the key to improve data quality and quantity and to successful and adequate conservation measures, for both waterbirds and wetlands.

Conclusions
rough this article, we presented the current status of three globally threatened waterfowls' populations in Morocco. While the White-headed Duck's numbers are increasing and the Marbled Teal's are mostly stable, the Common Pochard has known a decline in its wintering population and its breeding range is very limited in the country.
Another important result of this synthesis is the identification of the Moroccan wetlands that play a major role as hosting key sites of the three species. ese results can direct and focus the short-term conservation efforts on these key sites, to enhance the survival and thriving of these species in Morocco.
A better understanding of these ducks' populations' dynamics, which is crucial to prevent their decline, requires further studies on the ecological and anthropogenic factors influencing them. Furthermore, cooperative efforts, coupled with more effective census methods, should be carried out to enhance the knowledge on the species on the flyway/regional levels. ese threatened waterbirds' survival depends, in fact, on concerted large-scale conservation measures.

Data Availability
All data generated or analyzed during this study are included in this article and its supplementary information files. Disclosure e funders and supporting organizations were not involved in this study's proposal, decision to publish, or writing, editing, and approval of the manuscript. e field data used in this study come from the database originating from the yearly campaigns of the waterbirds winter census in Morocco. ese campaigns are conducted in the context of the IWC (International Waterbirds census), coordinated by Wetlands International. At the national level, these campaigns and the research studies (on bird species and wetlands), based on the collated data, are conducted as part of the work of the authors at the Study Center for Bird Migration, in the Scientific Institute of Mohammed V University in Rabat, Morocco. e annual campaigns have been coordinated, since 1983, by the Scientific Institute, and in recent years, the NGO "GREPOM/ BirdLife Morocco" has been providing financial and technical support for the field campaigns.

Conflicts of Interest
e authors declare that there are no conflicts of interest regarding the publication of this paper. Acknowledgments e authors would like to acknowledge the consistent efforts of the observers, national and international, who have relentlessly participated in the waterbirds' winter census that has been conducted regularly in Morocco since 1983. eir commitment is the key that has contributed to a better knowledge for the conservation of waterbirds at the national and international level. e authors greatly appreciate the moral, technical, and financial support of GREPOM/Bird-Life Morocco, the Department of Water and Forestry and the Medwaterbirds Network (coordinated by la Tour du Valat). A substantial financial contribution was provided by the ONCFS, through "la Tour du Valat," which coordinates the IWC at the Mediterranean level, and from VBN/Birdlife Netherlands, as a support for GREPOM. Table S1. National counts of the Common Pochard's wintering individuals per year and per site. Table S2. National counts of the Marbled Teal's wintering individuals per year and per site. Table S3. National counts of the White-headed Duck's wintering individuals per year and per site. Table S4. List of observers who contributed to the IWC program in Morocco between 1983 and 2019. (Supplementary Materials)