Breeding Shorebird Abundance
For the three focal species, we recorded the number of individuals per saltpan on a
weekly basis during the breeding season. We tested for the effects of time (year) and
type of saltpan (impacted vs. control) on the weekly number of individuals using
GLMM with negative binomial distribution, controlling for overdispersion
(Crawley 2013). The saltpan and the week of census were used as random factors.
An offset variable was always specified to account for variation in the area (hectares) of the saltpans. The models’ fitness was assessed graphically (residuals
inspection), and they were compared with null models to test their significance
(Zuur et al. 2009).
Spatial Distribution of Black-Winged Stilt Nests
Each saltpan was divided into three pond categories (feeders, evaporators, and
crystallizers), according to their position, size, and microhabitat characteristics,
such as water level (Rodrigues et al. 2011). Black-winged stilt nests are not distributed randomly among these categories (Tavares et al. 2008), and we expected
that the disturbance caused by the construction and operation of the railway would
affect the distribution of nests. For this reason, we recorded the spatial distribution
of all Black-winged stilt nests according to type of pond. We then tested for
differences in the number of nests and the type of pond, time of year, and type of
saltpan (impacted vs. control) using a GLMM with a negative binomial distribution,
controlling for overdispersion and saltpan area (Crawley 2013), and specifying the
saltpan and week of visit as random factors.
Black-Winged Stilt Nest Phenology and Breeding Success
Black-winged stilts incubate 3–4 eggs for 4 weeks, and chicks remain in the same
saltpan while not yet able to fly and are protected by their parents. Five weeks after
hatching, chicks are no longer restricted to the saltpan where they were born,
because they can already fly and follow their parents (del Hoyo et al. 1996). We
recorded the timing of deployment of nests during the breeding season on a weekly
basis (see above) in all saltpans (impacted and control). We tested for differences in
the temporal distribution of the nests with time of year and type of saltpan (impacted vs. control), using Kolmogorov–Smirnov tests (Griffin 1999) with the ks.test
procedure (R Core Team 2015). Following nest identification (see above) we
recorded, on a weekly basis, the number of chicks and their ages. This allowed
estimation of two binomial parameters of breeding success: nest and fledgling
success. A nest was considered successful if at least one chick up to one week old
was observed, while fledging success was considered for each clutch when at least
one chick reached the age of fledging (4–5 weeks). We tested for differences with
time of year and saltpan (impacted vs. control) on nest and fledging success, using
12 Evaluating the Impacts of a New Railway on Shorebirds …
203
For the three focal species, we recorded the number of individuals per saltpan on a
weekly basis during the breeding season. We tested for the effects of time (year) and
type of saltpan (impacted vs. control) on the weekly number of individuals using
GLMM with negative binomial distribution, controlling for overdispersion
(Crawley 2013). The saltpan and the week of census were used as random factors.
An offset variable was always specified to account for variation in the area (hectares) of the saltpans. The models’ fitness was assessed graphically (residuals
inspection), and they were compared with null models to test their significance
(Zuur et al. 2009).
Spatial Distribution of Black-Winged Stilt Nests
Each saltpan was divided into three pond categories (feeders, evaporators, and
crystallizers), according to their position, size, and microhabitat characteristics,
such as water level (Rodrigues et al. 2011). Black-winged stilt nests are not distributed randomly among these categories (Tavares et al. 2008), and we expected
that the disturbance caused by the construction and operation of the railway would
affect the distribution of nests. For this reason, we recorded the spatial distribution
of all Black-winged stilt nests according to type of pond. We then tested for
differences in the number of nests and the type of pond, time of year, and type of
saltpan (impacted vs. control) using a GLMM with a negative binomial distribution,
controlling for overdispersion and saltpan area (Crawley 2013), and specifying the
saltpan and week of visit as random factors.
Black-Winged Stilt Nest Phenology and Breeding Success
Black-winged stilts incubate 3–4 eggs for 4 weeks, and chicks remain in the same
saltpan while not yet able to fly and are protected by their parents. Five weeks after
hatching, chicks are no longer restricted to the saltpan where they were born,
because they can already fly and follow their parents (del Hoyo et al. 1996). We
recorded the timing of deployment of nests during the breeding season on a weekly
basis (see above) in all saltpans (impacted and control). We tested for differences in
the temporal distribution of the nests with time of year and type of saltpan (impacted vs. control), using Kolmogorov–Smirnov tests (Griffin 1999) with the ks.test
procedure (R Core Team 2015). Following nest identification (see above) we
recorded, on a weekly basis, the number of chicks and their ages. This allowed
estimation of two binomial parameters of breeding success: nest and fledgling
success. A nest was considered successful if at least one chick up to one week old
was observed, while fledging success was considered for each clutch when at least
one chick reached the age of fledging (4–5 weeks). We tested for differences with
time of year and saltpan (impacted vs. control) on nest and fledging success, using
12 Evaluating the Impacts of a New Railway on Shorebirds …
203