Ferrer i Parareda, Xavier

Revistes Catalanes amb Accés Obert

S C I E N C E  
"THE ROLE PLAYED BY THE WETLANDS IN THE REST AND 
FEEDING OF MIGRATORY BIRDS IS OF MAJOR IMPORTANCE IN 
THE CASE OF THE EBRO DELTA". 
XAVIER FERRER RESIDENT LECTURER OF THE DEPARTMENT 
O F  ANIMAL BIOLOGY U N I V E R S I T Y  O F  BARCELONA 
he seaboard of Catalonia is 
orientated in an approximately 
NE-80 directian, just the same 
direction as that in which the migrations 
of European birds circulate in the spring 
and autumn, when they use this coast as 
a guide line. The contingent of migrants 
which pass through this territory is also 
important quantitatively, among other 
reasons because the orographic barrier 
which the Pyrenees are for the migrants, 
can be more easily negotiated in its 
Catalan part, where the passes of low- 
er altitude are situated. This migratory 
route was marked out traditionally by a 
series of wetlands; estuaries, enclosed 
coastal bays, littoral lagoons, etc, which 
served as feeding- and resting-grounds 
for the travellers. Many of these wet- 
lands are today completely dried up, or 
greatly deteriorated, because of the in- 
tense human activity which our sea- 
board has experienced. There still exist 
today some very important ones which, 
in spite of their legal status as natural 
parks, do not escape the serious dan- 
gers of partia1 disappearance or rapid 
transformation which threaten them. 
Even though all these wetzones are 
of international importance because of 
their role in migration, one of them 
stands out from the others in impor- 
tance: the Ebro Delta. 
Covering approximately 320 square ki- 
lometres, the Ebro Delta is hydrologi- 
cally conditioned by the cultivation of 
rice, which occupies half its surface, and 
which by its action on the waters, regu- 
lates the life of a large part of the com- 
munity of wild organisms there. The 
9,300 hectares of horticulture and fruit 
growing are increasing progressively, 
in contrast to the natural resources, 
which, situated on the coastal fringe, 
occupy 7,500 hectares of land and 
5,100 hectares of coastal bays. Al- 
though there are some coastal lagoons, 
the bulk of the natural resources is 
made up of salt-water surroundings: 
beaches, spits, salt-mines, salt-marshes, 
etc. The reedbeds also take up a not 
very large part, and the rest is occupied 
by small areas of landscape such as 
dunes, river branches, and the large 
lake formed by the mouth of the Ebro. 
Two large, shallow and enclosed bays 
of great biological activity close the 
delta on the north and south, giving it a 
peculiar appearance. These bays also 
play an important role in supplying food 
for many organisms there, especially 
birds and fish. The result is surprising 
because, despite the reduced extension 
of its natural zones in comparison with 
others in Europe, here the delta posses- 
ses a wide variety of landscapes and 
supports a high animal density, which is  
maintained largely because of rice culti- 
vation and the presence of these pro- 
ductive coastal bays. 
From the international point of view, 
apart from the value of diversity in a 
reduced area, its importance must be 
argued chiefly on the basis of ictiolo- 
gical and especially ornithological 
wealth. For instance, the fish community 
of the continental waters is rich and va- 
ried, being composed of 39 species. Of 
these, only 5 are of limnetic origin or 
are migratory (the eel), whereas the 
rest come from the sea and only enter 
those zones of brackish waters with a 
definite marine influence. Apart from 
the wide diversity of fish, the Ebro Delta 
is important because it possesses well 
conserved populations of Aphanius ibe- 
rus, a ciprinodontid endemic to the Ibe- 
rian peninsula which is  in danger of ex- 
tinction in a great many of its original 
locations. 
The birds in the Ebro Delta, with more 
than 275 known species, of which 75 
are nest-building, have here a location 
of maior international importance. This 
is demonstrated by the fact that in all 
the conventions for the protection of 
wetlands of international importance, 
the delta appears catalogued in the first 
category, that is to say in urgent need 
of protection. This has been the case 
both in the MAR project (Camargue) in 
1962, in the RAMSAR convention (Iran) 
in 1971, and more recently in the first 
symposium of Mediterranean sea- 
birds held in Sardinia in 1985. 
At the time af nest-building, the delta is 
important because of the presence of 
interesting Mediterranean breeders 
S C I E N C E  
such as the pratincole (100 pairsl, the 
black-winged stilt, the black tern, the 
red-crested pochard, the squacco he- 
ron (200 pairsl, and the moustached 
warbler. The colonies of herons, terns 
and gulls, with 20 species, make up a 
total of approximately 9,000 pairs 
which are distributed evenly among the 
three groups. Also of maior importan- 
ce are the 650 pairs of little terns, the 
Bengalese tern which has heie one of 
the very few enclaves of breeding in 
Europe, and the slender-billed gull. 
During the rest of the year too, the Ebro 
Delta plays an important role in Euro- 
pean bird fauna. For instance, the num- 
ber of non-passerines wintering here is 
calculated at between 100,000 and 
150,000 individuals, but in the case of 
severe cold weather in central and 
Northern Europe, this number can double. 
The wildfowl, with 50,000 to 90,000 
birds from 15 to 20 species, make up 
the largest group, followed by the gulls 
with approximately half that number, 
and the waders with about 15,000. 
Once again the diversity is remarkable, 
and there are many interesting species 
such as the black-tailed godwit, the 
avocet, the flamingo, the Mediterra- 
nean guli' and the red-creasted po- 
chard. As a colophon, we may add that 
in a study made by the lnternational 
Wildfowl Research Bureau on European 
localities of international quantitative 
importance for the wintering of wild- 
fowl, the Ebro Delta was selected for 
two species: the wigeon and the sho- 
veler. • 


The Ebro Delta

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