birds that cross the railway by flying between or below the catenary wires face the
mortality risk from train-kill.
In the HSR stretch analyzed here, surveys of birds flying over the infrastructure
were carried out between 2010 and 2015, with a total of approximately 270 h of
observation at nearly 1100 observation points. Sampling structure varied,
depending on the objectives of particular studies, but in all cases observations were
made from fixed stations for 10 min or 20 min. Bird flight was recorded from these
points, with HSR crossing flight height estimated with respect to the rails.
Therefore, for all crossing events over the railway (N = 3313 records and 10,776
individuals), it is known whether the birds crossed within the collision risk area
(train path or catenary), allowing a risk index to be calculated for each species.
Additionally, data obtained within 120 m of the observer have been used to estimate HSR crossing rates throughout the year (birds h
−1 km
−1 ). Furthermore, spatial
and temporal sampling patterns are informative for elucidating interactions of
various factors, such as whether track crossover frequency is independent of HSR
geometry, astronomical season, or environmental conditions such as wind speed.
Complementarily, data available on birds from surrounding areas, such as parallel
sampling of flight behavior, can be used to determine whether birds change their
usual flight trajectories in the presence of the HSR. To ensure consistency of the
results, the data presented are restricted to species for which, in at least one sampling station, 10 crossing records were obtained.
Our analysis showed that birds cross the HSR frequently, with an average HSR
crossing frequency of 246.7 birds km
−1 h
−1 (experiment range, 160.2–514.0 birds
km
−1 h
−1 ). No consistent seasonal pattern was observed across the trials. However,
our data analysis did reveal alterations in bird flight patterns in the vicinity of the
HSR. An experiment conducted between June and July of 2011 at 237 observation
stations along the HSR and 85 remote control sites showed that birds of any species
fly, on average, almost 5 m higher near the HSR than in control sites (9.9 vs. 5.2 m
over the ground). This increase in flight heights reflects some avoidance of the
infrastructure, with an added energy cost. The average flight height of birds over the
HSR was lower in areas where the railway runs along embankments relative to
sections of railway that are level with the surrounding landscape. In fact, several
experiments showed that birds reduced their crossing railway height between 1 m
and 4 m for every 10 m of embankment height. However, these general patterns
were found to vary greatly across different species, and all of them combine
observations of birds both inside and outside the cross-section of collision risk.
Although the birds fly higher over the infrastructure than over an open field, the
frequency with which they cross the railway within the risk area is high. For the 33
analyzed species, almost half of railway crossings (combined average, 46.5%)
occurred less than 8.5 m above the ground (Table 8.4). More than two-thirds of
these low crossings were under the catenary, and the remainder were through the
catenary wires. In fact, birds of 21 species crossed within (rather than over) the risk
area for at least 33% of their HSR crossings, and 14 species did so for at least 50%.
The partridge (100%), Eurasian tree sparrow (Passer montanus, 90%), hoopoe
(Upupa epops, 88.5%), and northern wheatear (Oenanthe oenanthe, 83%) stand out
126
J.E. Malo et al.
mortality risk from train-kill.
In the HSR stretch analyzed here, surveys of birds flying over the infrastructure
were carried out between 2010 and 2015, with a total of approximately 270 h of
observation at nearly 1100 observation points. Sampling structure varied,
depending on the objectives of particular studies, but in all cases observations were
made from fixed stations for 10 min or 20 min. Bird flight was recorded from these
points, with HSR crossing flight height estimated with respect to the rails.
Therefore, for all crossing events over the railway (N = 3313 records and 10,776
individuals), it is known whether the birds crossed within the collision risk area
(train path or catenary), allowing a risk index to be calculated for each species.
Additionally, data obtained within 120 m of the observer have been used to estimate HSR crossing rates throughout the year (birds h
−1 km
−1 ). Furthermore, spatial
and temporal sampling patterns are informative for elucidating interactions of
various factors, such as whether track crossover frequency is independent of HSR
geometry, astronomical season, or environmental conditions such as wind speed.
Complementarily, data available on birds from surrounding areas, such as parallel
sampling of flight behavior, can be used to determine whether birds change their
usual flight trajectories in the presence of the HSR. To ensure consistency of the
results, the data presented are restricted to species for which, in at least one sampling station, 10 crossing records were obtained.
Our analysis showed that birds cross the HSR frequently, with an average HSR
crossing frequency of 246.7 birds km
−1 h
−1 (experiment range, 160.2–514.0 birds
km
−1 h
−1 ). No consistent seasonal pattern was observed across the trials. However,
our data analysis did reveal alterations in bird flight patterns in the vicinity of the
HSR. An experiment conducted between June and July of 2011 at 237 observation
stations along the HSR and 85 remote control sites showed that birds of any species
fly, on average, almost 5 m higher near the HSR than in control sites (9.9 vs. 5.2 m
over the ground). This increase in flight heights reflects some avoidance of the
infrastructure, with an added energy cost. The average flight height of birds over the
HSR was lower in areas where the railway runs along embankments relative to
sections of railway that are level with the surrounding landscape. In fact, several
experiments showed that birds reduced their crossing railway height between 1 m
and 4 m for every 10 m of embankment height. However, these general patterns
were found to vary greatly across different species, and all of them combine
observations of birds both inside and outside the cross-section of collision risk.
Although the birds fly higher over the infrastructure than over an open field, the
frequency with which they cross the railway within the risk area is high. For the 33
analyzed species, almost half of railway crossings (combined average, 46.5%)
occurred less than 8.5 m above the ground (Table 8.4). More than two-thirds of
these low crossings were under the catenary, and the remainder were through the
catenary wires. In fact, birds of 21 species crossed within (rather than over) the risk
area for at least 33% of their HSR crossings, and 14 species did so for at least 50%.
The partridge (100%), Eurasian tree sparrow (Passer montanus, 90%), hoopoe
(Upupa epops, 88.5%), and northern wheatear (Oenanthe oenanthe, 83%) stand out
126
J.E. Malo et al.