Here we provide a case study on bird collisions in a railway that crosses a
wetland of international importance, the Sado Estuary (Portugal), which is a
RAMSAR site and a Special Protection Area for birds classified under the European
Union Directive 79/409/EEC. Especially from autumn to mid-spring, this wetland
is home to thousands of waders, wildfowl, flamingos Phoenicopterus roseus, and
other aquatic birds, which use a diversity of wet habitats including open water, mud
flats, rice fields, and salt pans (Lourenço et al. 2009; Alves et al. 2011). These birds
were expected to cross the railway area on a daily basis, particularly the bridge
crossing the Sado River, due to movements from roosts to feeding areas, and among
feeding areas (e.g., Dias et al. 2006). Therefore, it was feared that they were
exposed to a high risk of collision, with the possibility of mass mortality events
occurring due to the collision of large flocks with bridge structures and circulating
trains. Our study was designed to clarify this issue, aiming at: (1) quantifying bird
mortality patterns due to collisions associated with the presence of the railway;
(2) characterizing the movements of wetland birds crossing the railway bridge along
the circadian and the annual cycles; and (3) estimating the seriousness of the risk of
wetland bird mortality associated with this railway, as well as which bird species
are most at risk. To the best of our knowledge, this is the first published study
documenting the impacts of railways on wetland bird mortality.
Methods
The study was carried out in Portugal, focusing on the “Variante de Alcácer”
railway, whose construction started in February 2007, with train circulation
beginning in December 2010 (Figs. 7.1 and 7.2). This is a single-track electrified
railway extending over 29 km, that is part of the network connecting Lisbon to the
south of the country. It crosses the Natural Reserve of the Sado Estuary (Portugal)
in a section of about 2.6 km (38° 24′N, 8° 36′W), most of which is occupied by
wetland habitats including the Sado River, rice fields and salt pans (1.6 km), while
the rest is dominated by cork oak Quercus suber and stone pine Pinus pinea
woodlands. The crossing is made through a bowstring bridge built between 2007
and 2010, with a length of 2735 m and three 160 m high arcs (Fig. 7.2). Another
viaduct of this railway (about 0.8 km) crosses a small wetland outside the Natural
Reserve, which corresponds to the São Martinho stream and the adjacent rice fields
(Fig. 7.2). During the period of observations conducted over one year (see below),
the bridge was crossed by 26 ± 4 [SD] trains/day. The train speed ranged from
44 km/h (charcoal trains) to 170–200 km/h (passenger trains).
Bird mortality due to collisions with trains and railway structures was estimated
at three sections of this railway, with a total length of 16.3 km. One of these
sections (Section 1: 6.3 km) included the sectors crossing the Sado (2.6 km) and
São Martinho (0.8 km) wetlands, while the rest (2.9 km) crossed forested habitats.
The other two sections (Section 2: 5.8 km; Section 3: 4.2 km) crossed only
forested habitats, and they were used as controls to estimate how the presence of
wetlands affected bird collision rates. The railway tracks and the surrounding areas
were thoroughly surveyed for vertebrate corpses in the three sections, between
7 Bird Collisions in a Railway Crossing a Wetland …
105
wetland of international importance, the Sado Estuary (Portugal), which is a
RAMSAR site and a Special Protection Area for birds classified under the European
Union Directive 79/409/EEC. Especially from autumn to mid-spring, this wetland
is home to thousands of waders, wildfowl, flamingos Phoenicopterus roseus, and
other aquatic birds, which use a diversity of wet habitats including open water, mud
flats, rice fields, and salt pans (Lourenço et al. 2009; Alves et al. 2011). These birds
were expected to cross the railway area on a daily basis, particularly the bridge
crossing the Sado River, due to movements from roosts to feeding areas, and among
feeding areas (e.g., Dias et al. 2006). Therefore, it was feared that they were
exposed to a high risk of collision, with the possibility of mass mortality events
occurring due to the collision of large flocks with bridge structures and circulating
trains. Our study was designed to clarify this issue, aiming at: (1) quantifying bird
mortality patterns due to collisions associated with the presence of the railway;
(2) characterizing the movements of wetland birds crossing the railway bridge along
the circadian and the annual cycles; and (3) estimating the seriousness of the risk of
wetland bird mortality associated with this railway, as well as which bird species
are most at risk. To the best of our knowledge, this is the first published study
documenting the impacts of railways on wetland bird mortality.
Methods
The study was carried out in Portugal, focusing on the “Variante de Alcácer”
railway, whose construction started in February 2007, with train circulation
beginning in December 2010 (Figs. 7.1 and 7.2). This is a single-track electrified
railway extending over 29 km, that is part of the network connecting Lisbon to the
south of the country. It crosses the Natural Reserve of the Sado Estuary (Portugal)
in a section of about 2.6 km (38° 24′N, 8° 36′W), most of which is occupied by
wetland habitats including the Sado River, rice fields and salt pans (1.6 km), while
the rest is dominated by cork oak Quercus suber and stone pine Pinus pinea
woodlands. The crossing is made through a bowstring bridge built between 2007
and 2010, with a length of 2735 m and three 160 m high arcs (Fig. 7.2). Another
viaduct of this railway (about 0.8 km) crosses a small wetland outside the Natural
Reserve, which corresponds to the São Martinho stream and the adjacent rice fields
(Fig. 7.2). During the period of observations conducted over one year (see below),
the bridge was crossed by 26 ± 4 [SD] trains/day. The train speed ranged from
44 km/h (charcoal trains) to 170–200 km/h (passenger trains).
Bird mortality due to collisions with trains and railway structures was estimated
at three sections of this railway, with a total length of 16.3 km. One of these
sections (Section 1: 6.3 km) included the sectors crossing the Sado (2.6 km) and
São Martinho (0.8 km) wetlands, while the rest (2.9 km) crossed forested habitats.
The other two sections (Section 2: 5.8 km; Section 3: 4.2 km) crossed only
forested habitats, and they were used as controls to estimate how the presence of
wetlands affected bird collision rates. The railway tracks and the surrounding areas
were thoroughly surveyed for vertebrate corpses in the three sections, between
7 Bird Collisions in a Railway Crossing a Wetland …
105