Study Design
The study was based on a Before-After-Control-Impact (BACI) designed to test for
the impacts of railway construction and operation in shorebirds using saltpans.
Sampling was carried out on three time periods (Fig. 12.1) six years: one control
year before the construction (2006); two years during the phase of construction
(2008 and 2009); and one year in the post-construction (i.e., operation) phase
(2011). Each “treatment” phase (i.e., construction and post-construction) was
compared with the control phase (i.e., pre-construction) using as sampling units
three impacted (those under the viaduct) and six control saltpans (Fig. 12.1). The
presence of significant interactions between year and type of pond (i.e., control vs.
impact) was understood to indicate significant railway impacts-either positive or
negative-depending on the sign of the interaction term. We used saltpans as sampling units because they were the most important shorebird habitats affected by the
project, and because they form discrete units where it is possible to make absolute
counts both of all birds and their nests. Moreover, they have easy access and they
were the only nesting areas used by shorebirds close to the railway corridor.
Periodical winter counts in the surrounding saltmarshes did not reveal a substantial
usage of these areas by shorebirds, with the exception of a small number of Dunlin
(Calidris alpina) and common sandpiper (Actitis hypoleucos), which seemed to be
largely insensitive to the construction of the pillars (personal observation).
We focused the impact assessment on breeding and wintering seasons, which are
the two most critical periods in the phenology of shorebirds. During the breeding
season (April–July), data were gathered from visits carried out at weekly intervals
to all saltpans. During the winter season (January–February) we made regular, but
interspersed visits (at least 1-week intervals) to all saltpans to obtain a suitable
number of sampling occasions. In each sampling visit, selected parameters (see
below) were estimated in all saltpans based on pre-established transects and
observation points, by a team of two researchers using binoculars and telescopes.
Detailed maps of bird distribution in each saltpan were produced at each visit.
Statistical analysis was carried out in the R 3.2.6 statistical environment (R Core
Team 2015), using packages lmer4 (Bates et al. 2015), glmmADMB (Fournier et al.
2012), and lsmeans (Lenth 2016; Bates et al. 2015).
Evaluating Effects on Breeding Shorebirds
Shorebirds are mobile animals and can thus avoid potential impacts by moving
away from impacted saltpans (Cayford 1993). When they remain in the impacted
saltpans, however, they may still change their spatial distribution (individuals or
nests), which may eventually affect their phenology or breeding success, through
reduced nest or chick survival (Sansom et al. 2016; Pearce-Higgins et al. 2007). We
tested these ideas by focusing on the three main breeding shorebird species:
12 Evaluating the Impacts of a New Railway on Shorebirds …
201
The study was based on a Before-After-Control-Impact (BACI) designed to test for
the impacts of railway construction and operation in shorebirds using saltpans.
Sampling was carried out on three time periods (Fig. 12.1) six years: one control
year before the construction (2006); two years during the phase of construction
(2008 and 2009); and one year in the post-construction (i.e., operation) phase
(2011). Each “treatment” phase (i.e., construction and post-construction) was
compared with the control phase (i.e., pre-construction) using as sampling units
three impacted (those under the viaduct) and six control saltpans (Fig. 12.1). The
presence of significant interactions between year and type of pond (i.e., control vs.
impact) was understood to indicate significant railway impacts-either positive or
negative-depending on the sign of the interaction term. We used saltpans as sampling units because they were the most important shorebird habitats affected by the
project, and because they form discrete units where it is possible to make absolute
counts both of all birds and their nests. Moreover, they have easy access and they
were the only nesting areas used by shorebirds close to the railway corridor.
Periodical winter counts in the surrounding saltmarshes did not reveal a substantial
usage of these areas by shorebirds, with the exception of a small number of Dunlin
(Calidris alpina) and common sandpiper (Actitis hypoleucos), which seemed to be
largely insensitive to the construction of the pillars (personal observation).
We focused the impact assessment on breeding and wintering seasons, which are
the two most critical periods in the phenology of shorebirds. During the breeding
season (April–July), data were gathered from visits carried out at weekly intervals
to all saltpans. During the winter season (January–February) we made regular, but
interspersed visits (at least 1-week intervals) to all saltpans to obtain a suitable
number of sampling occasions. In each sampling visit, selected parameters (see
below) were estimated in all saltpans based on pre-established transects and
observation points, by a team of two researchers using binoculars and telescopes.
Detailed maps of bird distribution in each saltpan were produced at each visit.
Statistical analysis was carried out in the R 3.2.6 statistical environment (R Core
Team 2015), using packages lmer4 (Bates et al. 2015), glmmADMB (Fournier et al.
2012), and lsmeans (Lenth 2016; Bates et al. 2015).
Evaluating Effects on Breeding Shorebirds
Shorebirds are mobile animals and can thus avoid potential impacts by moving
away from impacted saltpans (Cayford 1993). When they remain in the impacted
saltpans, however, they may still change their spatial distribution (individuals or
nests), which may eventually affect their phenology or breeding success, through
reduced nest or chick survival (Sansom et al. 2016; Pearce-Higgins et al. 2007). We
tested these ideas by focusing on the three main breeding shorebird species:
12 Evaluating the Impacts of a New Railway on Shorebirds …
201