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16/02/2022

Maximum historical number of hibernating aquatic birds in the Delta de l’Ebre

This winter, 317,425 water birds, corresponding to 96 species, were counted in the annual census of the Delta del Ebre Natural Park. This was explained on Tuesday by the director of the park, Francesc Vidal, and the coordinator of the census, Toni Curcó, who described the number as a historical maximum.

Increase in ducks

The most numerous group has been that of the anatidae (181,333 specimens, 57.1% of the effective), represented mainly by the mallard Anas platyrhynchos (105,157 specimens), and the northern shoveler Spatula clypeata and the eurasian teal A. crecca, both with quite similar values ​​(29,889 and 29,740 specimens, respectively). Overall, this group has shown a much higher value (+51%) compared to the average of the reference period (2005 – 2010), when the winter flooding of the rice paddies was at its peak. Most of the species (northern shoveler, mallard, gadwall) have shown quite remarkable increases, over 20%, and the exceptionally high value of the mallard (+84%) stands out.

Other species, on the other hand, have shown much lower winter populations: common pochard (-69%), red-crested pochard Netta rufina (-38%) and northern pintail A. acuta (-25%). The eurasian coot, on the other hand, with 18,621 specimens, has presented a rather low value (-34%), a far cry from the 30,000-40,000 coots that were counted between 2010 and 2017.

Variability in waders

Waders are the second best represented group of water birds, with 73,069 specimens (23% of the total). In general terms, the global population during this winter has been higher (+13%) than the reference level. However, there is great variability between species. The majority of waders that show a marked preference for natural wetlands have presented normal or very high values, such as the dunlin Calidris alpina (37,939 specimens, +39%) or the pied avocet Recurvirostra avosetta (3,591 specimens, +219%) ), while those most dependent on flooded rice paddies have shown very significant decreases, such as the northern lapwing Vanellus vanellus (-51%, with 7,242 exs.) or the european golden plover Pluvialis apricaria (-55%, with 1,750 exs.), made which has been repeated in recent years.

Flamingo record

The heron population (6,470 exs.) has presented a very low contingent (50% below the reference level) and has particularly affected the most abundant species in winter, such as the western cattle egret Bubulcus ibis (-73% ), the little egret Egretta garzetta (-64%) and the grey heron Ardea cinerea (-51%). Other particularly notable data correspond to the significantly low numbers of great cormorant Phalacrocorax carbo, with only 2,011 specimens (-46% in relation to the reference level). In the opposite direction, records have been achieved for the entire historical series of glossy ibis Plegadis falcinellus (with 11,358 specimens) and flamingo Phoenicopterus roseus (21,146 specimens).

The winter drying of the rice paddies is a measure to combat the apple snail, a tool implemented since 2011 in the Delta del Ebre, and which has led to the loss of winter flooding as an agro-environmental measure since the 2014-2020 Rural Development Program. Even so, the annual surface flooded during these last years has fluctuated a lot (15.5-100%), including winters in which even large areas have been flooded with sea water.

Loss of reception capacity

Within this great variability, the flooded surface of rice paddies in January 2022 was 57.9%, a figure that has not been reached since 2016. The data obtained from the winter censuses of waterfowl in the delta del Ebre provide a good indicator of the loss of reception capacity that the delta del Ebre has suffered as a wetland.

The time series of data between the period of widespread flooding (2005 -2010) and the period with flood limitations (2011-2022) is beginning to be sufficiently long to start analyzing statistically the consequences of this agronomic change, although it is necessary to take into account the high variability of the annual flooded surface that has occurred recently. Similarly, there are other factors, of an external type, that also have a high influence on the number of birds that winter each year in the delta del Ebre, such as the winter harshness in the areas of origin (north and center of Europe) or the annual breeding success.

Although this year has reached a historical maximum population in general, the difference between the global values ​​(including all species) of the two periods with different levels of flooding, is very small (+4%), given which would lead one to think that the changes haven’t been quite significant. Despite everything, the differences are quite evident if we consider separately the values ​​of those species that use flooded rice paddies as an almost exclusive wintering habitat from those species that preferentially choose natural habitats.

Thus, birds such as the common shelduck Tadorna tadorna, the flamingo Phoenicopterus roseus, the dunlin Calidris alpina or the pied avocet Recurvirostra avosetta, species highly dependent on brackish or saline wetlands, continue to experience very significant growth (+21-133 %). Conversely, those species that make more intensive use of flooded rice paddies as feeding areas have suffered rapid declines of great magnitude, such as the western cattle egret Bubulcus ibis (-57%), the little egret Egretta garzetta (-53%) , the eurpean golden plover Pluvialis apricaria (-40%) and the northern lapwing Vanellus vanellus (-34%).

Preservation commitment

From a global and long-term perspective, a significant decrease in the carrying capacity of the delta del Ebre, the main wetland in Catalonia and one of the most important in the western Mediterranean, is expected, and a decrease in many of waterfowl populations. Some of these species (european golden plover, little egret, wood sanpiper Tringa glareola) have been declared elements of conservation in the scope of the Natura 2000 Network and, therefore, there is a commitment to the European Union to maintain them in a state of favorable conservation.

On the other hand, there is also, under the umbrella of the AEWA (Agreement on the Conservation of Afro-Eurasian Migratory Waterbirds, derived from the Bonn Convention), a commitment to conserve the populations of migratory waterbirds.

Data on a global scale

The winter count of waterbirds in the delta del Ebre is part of the International Waterbird Census (IWC), which annually quantifies the number of waterbirds (anatidae, waders, ardeids, coots, etc.) that winter in more than 80 countries in Europe, Asia and North Africa. The data obtained makes it possible to know on a global scale the state of conservation of these species and, on a local scale, to evaluate the hosting capacity of each wetland. In the delta del Ebre, this census was carried out this year thanks to the participation of 27 observers, mainly technicians from the natural park and agents from the Rural Agents Corps.

This winter, unfortunately, volunteer participation has again been quite limited due to the containment measures of COVID-19. The census period (January 3-24) has developed normally, as anti-cyclonic weather conditions have prevailed. Carrying out this count involves great complexity, both in terms of the diversity of species and habitats (rice fields, lagoons, rivers, salt flats, bays and wetlands) and the large concentrations of birds that they contain.

Source: Generalitat de Catalunya - Climate Action, Food and Rural Agenda