breeding success. The results suggest that the distribution of Black-winged Stilt
between types of pond (feeders, evaporators and crystallizers) was not particularly
affected by the construction. The major disturbance took place in the crystallizers,
where the pillars were erected. However, as the results above show, these were the
areas less used by the species, even in the pre-construction phase, which may be the
reason why no impact was observed during the entire construction period and
afterwards. Concerning nest phenology, the interruption of construction probably
prevented an impact on the temporal distribution of nests. Likewise, this may
explain why we did not find any evidence that the railway affected hatching and
survival of the fledglings that used impacted saltpans.
During the wintering season, the usage of the saltpans can be conditioned by
their availability, particularly by unpredictable fluctuations in the water level. Thus,
the birds may be more limited in their choice of the saltpans, causing a high
variability in the counts. This effect is more restricted during the breeding season
due to the management of saltpans for the extraction of salt. During the last phase of
this study, two saltpans (one impacted) were transformed into aquacultures, conditioning the use of the saltpans even more. Additionally, many of the shorebird
species do not show a random distribution since they group for foraging or roosting,
even if there is enough area to spread (van de Kamp et al. 2004). Even taking into
account these sources of variability, the data suggest that the wintering community,
as a whole, did show a negative response to the disturbance caused by the railway,
since significant differences were found between the two types of saltpans over the
years, regarding the species’ abundance. Nevertheless, although the use of a pooled
number of individual birds allowed the analysis of data that is inherently
over-dispersed and zero-inflated, it restricts the full interpretation of the data. On the
other hand, the distribution of the main wintering species was not affected, while for
the wintering Dunlin, the number of birds in each activity did not show a response
to the disturbance caused by the railway. Disturbances can inhibit foraging activities in favor of vigilant behaviour, but since all saltpans are close to sources of
human disturbance (e.g., roads), the effect of the railway may have been buffered.
Final Remarks
As an overall conclusion, the data collected suggest that the construction and the
beginning of the operation of the new Aveiro railway showed mixed effects on both
the breeding and wintering communities of shorebirds using the Aveiro saltpan
complex. Additionally, it had indirect effects, as it probably accelerated the abandonment of salt extraction in one of the affected saltpans, and thus promoted its
transformation into an aquaculture during the last phase of our study. The net
consequence of this process was the loss of this saltpan for the breeding birds, and
also for feeding of the smaller shorebird species. At this point and with the present
data, however, it is impossible to evaluate the consequences of this loss of habitat,
12 Evaluating the Impacts of a New Railway on Shorebirds …
211
between types of pond (feeders, evaporators and crystallizers) was not particularly
affected by the construction. The major disturbance took place in the crystallizers,
where the pillars were erected. However, as the results above show, these were the
areas less used by the species, even in the pre-construction phase, which may be the
reason why no impact was observed during the entire construction period and
afterwards. Concerning nest phenology, the interruption of construction probably
prevented an impact on the temporal distribution of nests. Likewise, this may
explain why we did not find any evidence that the railway affected hatching and
survival of the fledglings that used impacted saltpans.
During the wintering season, the usage of the saltpans can be conditioned by
their availability, particularly by unpredictable fluctuations in the water level. Thus,
the birds may be more limited in their choice of the saltpans, causing a high
variability in the counts. This effect is more restricted during the breeding season
due to the management of saltpans for the extraction of salt. During the last phase of
this study, two saltpans (one impacted) were transformed into aquacultures, conditioning the use of the saltpans even more. Additionally, many of the shorebird
species do not show a random distribution since they group for foraging or roosting,
even if there is enough area to spread (van de Kamp et al. 2004). Even taking into
account these sources of variability, the data suggest that the wintering community,
as a whole, did show a negative response to the disturbance caused by the railway,
since significant differences were found between the two types of saltpans over the
years, regarding the species’ abundance. Nevertheless, although the use of a pooled
number of individual birds allowed the analysis of data that is inherently
over-dispersed and zero-inflated, it restricts the full interpretation of the data. On the
other hand, the distribution of the main wintering species was not affected, while for
the wintering Dunlin, the number of birds in each activity did not show a response
to the disturbance caused by the railway. Disturbances can inhibit foraging activities in favor of vigilant behaviour, but since all saltpans are close to sources of
human disturbance (e.g., roads), the effect of the railway may have been buffered.
Final Remarks
As an overall conclusion, the data collected suggest that the construction and the
beginning of the operation of the new Aveiro railway showed mixed effects on both
the breeding and wintering communities of shorebirds using the Aveiro saltpan
complex. Additionally, it had indirect effects, as it probably accelerated the abandonment of salt extraction in one of the affected saltpans, and thus promoted its
transformation into an aquaculture during the last phase of our study. The net
consequence of this process was the loss of this saltpan for the breeding birds, and
also for feeding of the smaller shorebird species. At this point and with the present
data, however, it is impossible to evaluate the consequences of this loss of habitat,
12 Evaluating the Impacts of a New Railway on Shorebirds …
211