observed, and included black-headed gull Chroicocephalus ridibundus (21.9% of
birds observed), greater flamingo Phoenicopterus roseus (20.7%), northern shoveler A. clypeata (10.0%), black-tailed godwit (9.6%) and lesser black-backed gull
Larus fuscus (9.3%). Many more birds were recorded in autumn (47.3%) and winter
(22.0%), than in spring (11.9%) and summer (18.8%). This pattern of seasonal
occurrence was also observed for the most abundant species, except in the case of
flamingos, which were mainly recorded in winter and spring, and godwits, which
peaked in autumn and summer.
The distribution of birds was highly concentrated, with about 76% of individuals
counted on just eight of the 22 plots surveyed. Many more birds were counted in the
tanks of salt pans (64.5%), than in either rice fields (27.2%) or intertidal areas
(8.4%). This pattern was also found for most individual species, although there
were also several species with peak counts (>75% of observations) in rice fields
(e.g. cattle egret Bubulcus ibis, purple heron, white stork Ciconia ciconia, black
stork C. nigra, glossy ibis Plegadis falcinellus, and lapwing Vanellus vanellus).
Only a few species were most counted (>50%) in intertidal areas, including mallard
A. platyrhynchos, grey plover Pluvialis squatarola, common sandpiper Actitis
hypoleucos, and whimbrel Numenius phaeopus.
Effects of Distance to Railway
There were no statistically significant effects of distance to railway on species
richness, total bird abundance and the abundance of the 12 most abundant species
(overall counts >500 individuals) (Table 11.2). The observed patterns of bird distribution in relation to the railway varied markedly across species, and for each it
often varied in relation to the tidal cycle and the season (Fig. 11.2). For instance,
black-headed gull densities were highest close to the railway in winter, both at low
and high tides, while in both autumn and summer, densities were highest far from the
railway, particularly at high tide. Also, the densities of the shoveler were highest
close to the railway in autumn irrespective of tide, and in winter at low tide, while the
reverse was found in winter at high tide. A comparable variation in relation to tide
was found for pied avocets Recurvirostra avosetta, which in autumn, showed the
highest densities close to the railway at low tide, and far from the railway at high tide.
In white storks, densities in autumn and winter were always higher close to the
railway, while the reverse was found in summer, irrespective of the tidal cycle. Other
species had more consistent patterns, albeit not statistically significant, with larger
densities tending to be found either close to (e.g. flamingo, dunlin Calidris alpina) or
far from (e.g. godwit, great cormorant Phalacrocorax carbo) the railway.
Discussion
The bird assemblages recorded around the railway line crossing the upper Sado
Estuary were comparable to those occurring in other coastal wetlands in Portugal,
including a diversity of species such as herons, egrets, ibis, flamingos, gulls, waders,
184
C. Godinho et al.
birds observed), greater flamingo Phoenicopterus roseus (20.7%), northern shoveler A. clypeata (10.0%), black-tailed godwit (9.6%) and lesser black-backed gull
Larus fuscus (9.3%). Many more birds were recorded in autumn (47.3%) and winter
(22.0%), than in spring (11.9%) and summer (18.8%). This pattern of seasonal
occurrence was also observed for the most abundant species, except in the case of
flamingos, which were mainly recorded in winter and spring, and godwits, which
peaked in autumn and summer.
The distribution of birds was highly concentrated, with about 76% of individuals
counted on just eight of the 22 plots surveyed. Many more birds were counted in the
tanks of salt pans (64.5%), than in either rice fields (27.2%) or intertidal areas
(8.4%). This pattern was also found for most individual species, although there
were also several species with peak counts (>75% of observations) in rice fields
(e.g. cattle egret Bubulcus ibis, purple heron, white stork Ciconia ciconia, black
stork C. nigra, glossy ibis Plegadis falcinellus, and lapwing Vanellus vanellus).
Only a few species were most counted (>50%) in intertidal areas, including mallard
A. platyrhynchos, grey plover Pluvialis squatarola, common sandpiper Actitis
hypoleucos, and whimbrel Numenius phaeopus.
Effects of Distance to Railway
There were no statistically significant effects of distance to railway on species
richness, total bird abundance and the abundance of the 12 most abundant species
(overall counts >500 individuals) (Table 11.2). The observed patterns of bird distribution in relation to the railway varied markedly across species, and for each it
often varied in relation to the tidal cycle and the season (Fig. 11.2). For instance,
black-headed gull densities were highest close to the railway in winter, both at low
and high tides, while in both autumn and summer, densities were highest far from the
railway, particularly at high tide. Also, the densities of the shoveler were highest
close to the railway in autumn irrespective of tide, and in winter at low tide, while the
reverse was found in winter at high tide. A comparable variation in relation to tide
was found for pied avocets Recurvirostra avosetta, which in autumn, showed the
highest densities close to the railway at low tide, and far from the railway at high tide.
In white storks, densities in autumn and winter were always higher close to the
railway, while the reverse was found in summer, irrespective of the tidal cycle. Other
species had more consistent patterns, albeit not statistically significant, with larger
densities tending to be found either close to (e.g. flamingo, dunlin Calidris alpina) or
far from (e.g. godwit, great cormorant Phalacrocorax carbo) the railway.
Discussion
The bird assemblages recorded around the railway line crossing the upper Sado
Estuary were comparable to those occurring in other coastal wetlands in Portugal,
including a diversity of species such as herons, egrets, ibis, flamingos, gulls, waders,
184
C. Godinho et al.