Effects on Wintering Shorebirds
Shorebird Abundances
The total number of shorebirds counted per winter varied between 9331 (2008) and
2166 (2009). Dunlin was the most abundant species, followed by the Black-tailed
Godwit Limosa limosa. The full GLMM was significantly different from the null
model without the interaction term, thus pointing out the presence of impacts from
the railway (Table 12.1). The number of birds counted in the impacted saltpans
during the operation phase (2011) was significantly lower than expected given the
temporal trends observed at the control saltpans (Table 12.1).
Spatial Distribution and Activity Within Saltpans
The use of a specific type of pond (feeders, evaporators and crystallisers) in winter
did not show significant differences with type of saltpan (impacted or control).
Although the full GLMM was significantly different from a null model
(Table 12.1), none of the variables presented significant interactions between the
type of pond and the combined interaction between time of year and the type of
saltpan. Likewise, although the full GLMM for activity differed significantly from
the corresponding null model without the interaction term, none of the interaction
terms was statistically significant (Table 12.1). This suggests that shorebirds did not
change significantly their spatial distribution and activity within impacted saltpans
during the construction and operation phases.
Discussion
During the breeding season, we detected significantly negative impact of the railway on the average abundance of Black-winged Stilt and Kentish plover. But,
during the construction phase, it is likely that the interruption of the construction
during the breeding phase in the whole area of the railway viaduct corridor,
imposed by legal authorities, was crucial to reduce the impact of the construction
phase and in the case of the Kentish plover (2008) and the Little tern (2008 and
2009) this had a positive impact on the average abundance in impacted saltpans.
However, our data does not discriminate between birds that failed to breed from
breeding individuals. These birds can be present at different saltpans in different
sampling dates, and this increased the dispersion of the data and could have masked
to some extent the real pattern.
In the case of the Black-winged Stilt, assumed to be the key indicator species to
assess the impact of disturbance caused by the railway, we did not find significant
evidence for any impact on the spatial distribution of nests, breeding phenology and
210
T. Múrias et al.
Shorebird Abundances
The total number of shorebirds counted per winter varied between 9331 (2008) and
2166 (2009). Dunlin was the most abundant species, followed by the Black-tailed
Godwit Limosa limosa. The full GLMM was significantly different from the null
model without the interaction term, thus pointing out the presence of impacts from
the railway (Table 12.1). The number of birds counted in the impacted saltpans
during the operation phase (2011) was significantly lower than expected given the
temporal trends observed at the control saltpans (Table 12.1).
Spatial Distribution and Activity Within Saltpans
The use of a specific type of pond (feeders, evaporators and crystallisers) in winter
did not show significant differences with type of saltpan (impacted or control).
Although the full GLMM was significantly different from a null model
(Table 12.1), none of the variables presented significant interactions between the
type of pond and the combined interaction between time of year and the type of
saltpan. Likewise, although the full GLMM for activity differed significantly from
the corresponding null model without the interaction term, none of the interaction
terms was statistically significant (Table 12.1). This suggests that shorebirds did not
change significantly their spatial distribution and activity within impacted saltpans
during the construction and operation phases.
Discussion
During the breeding season, we detected significantly negative impact of the railway on the average abundance of Black-winged Stilt and Kentish plover. But,
during the construction phase, it is likely that the interruption of the construction
during the breeding phase in the whole area of the railway viaduct corridor,
imposed by legal authorities, was crucial to reduce the impact of the construction
phase and in the case of the Kentish plover (2008) and the Little tern (2008 and
2009) this had a positive impact on the average abundance in impacted saltpans.
However, our data does not discriminate between birds that failed to breed from
breeding individuals. These birds can be present at different saltpans in different
sampling dates, and this increased the dispersion of the data and could have masked
to some extent the real pattern.
In the case of the Black-winged Stilt, assumed to be the key indicator species to
assess the impact of disturbance caused by the railway, we did not find significant
evidence for any impact on the spatial distribution of nests, breeding phenology and
210
T. Múrias et al.