strikes would vary spatially along with differences in these variables, even if wildlife
abundance were constant. There are at least three theoretical mechanisms that could
alter the spatial probability of strike occurrence. These mechanisms, based on
wildlife behavior are: (1) constrained flight paths—some design features, such as
bridges, may restrict wildlife movements on the rail bed surface instead of out of the
path of oncoming trains; (2) reduced detectability—some design features may
impede the sight and/or sound of oncoming trains, so that wildlife are less likely to
detect trains resulting in increased strike rates; and (3) reduced reaction time—higher
train speeds may reduce the time available to wildlife to successfully cross or flee
before being struck. These mechanisms likely interact. For example, with increasing
train speeds both the time to detect and flee may be reduced.
There is evidence that these mechanisms affect the rate of train strikes with
ungulates and bears along railroads. Previous studies have shown that bears were
struck at bridges and rock cuts (constrained flight paths) and in locations where the
sound of oncoming trains was reduced (reduced detectability) (Van Why and
Chamberlain 2003; Kaczensky et al. 2003). Moose have been observed to not flee
off the railroad tracks in Alaska, with the suggestion that deep snow alongside the
railroad restricted their ability to flee down the track (Andersen et al. 1991;
Modafferi 1991). Similarly for bears, engine-mounted video footage suggested that
some bears were struck while fleeing from trains where track-side slopes or other
design variables appeared to obligate flight paths on the tracks instead of off and out
of danger. Other associations are unclear, for example bighorn sheep (Ovis
canadensis) strikes have been associated with rock cuts and may be a result of
fine-scale habitat selection or multiple design mechanisms acting concurrently (Van
Tighem 1981). As a result, it may be difficult to determine the exact mechanism(s)
driving strike rates. However, identifying the animal, train or railroad variables
associated with strikes and the direction of the effect (e.g., increased mortality at a
particular design feature) may be a more tractable approach and could indicate ways
to reduce strikes along the CPR and railways more broadly.
The purpose of this research was to identify locations where species-specific
mitigation solutions are needed, and to identify the variables associated with those
locations along the CPR. Four ungulate species (elk, mule deer [Odocoileus
hemionus], white-tailed deer [O. virginianus] and two bear species (grizzly and
black bear) were used for this analysis). We tested whether strike rates were correlated with the relative abundance and nine railway variables that could alter the
flight path, detectability or reaction time of animals present.
Methods
Study Area
The study was conducted along a 134 km section of the CPR running from the western
boundary of Yoho National Park, British Columbia (116° 39′W, 51° 14′N) to the
9 Relative Risk and Variables Associated with Bear and Ungulate …
137
abundance were constant. There are at least three theoretical mechanisms that could
alter the spatial probability of strike occurrence. These mechanisms, based on
wildlife behavior are: (1) constrained flight paths—some design features, such as
bridges, may restrict wildlife movements on the rail bed surface instead of out of the
path of oncoming trains; (2) reduced detectability—some design features may
impede the sight and/or sound of oncoming trains, so that wildlife are less likely to
detect trains resulting in increased strike rates; and (3) reduced reaction time—higher
train speeds may reduce the time available to wildlife to successfully cross or flee
before being struck. These mechanisms likely interact. For example, with increasing
train speeds both the time to detect and flee may be reduced.
There is evidence that these mechanisms affect the rate of train strikes with
ungulates and bears along railroads. Previous studies have shown that bears were
struck at bridges and rock cuts (constrained flight paths) and in locations where the
sound of oncoming trains was reduced (reduced detectability) (Van Why and
Chamberlain 2003; Kaczensky et al. 2003). Moose have been observed to not flee
off the railroad tracks in Alaska, with the suggestion that deep snow alongside the
railroad restricted their ability to flee down the track (Andersen et al. 1991;
Modafferi 1991). Similarly for bears, engine-mounted video footage suggested that
some bears were struck while fleeing from trains where track-side slopes or other
design variables appeared to obligate flight paths on the tracks instead of off and out
of danger. Other associations are unclear, for example bighorn sheep (Ovis
canadensis) strikes have been associated with rock cuts and may be a result of
fine-scale habitat selection or multiple design mechanisms acting concurrently (Van
Tighem 1981). As a result, it may be difficult to determine the exact mechanism(s)
driving strike rates. However, identifying the animal, train or railroad variables
associated with strikes and the direction of the effect (e.g., increased mortality at a
particular design feature) may be a more tractable approach and could indicate ways
to reduce strikes along the CPR and railways more broadly.
The purpose of this research was to identify locations where species-specific
mitigation solutions are needed, and to identify the variables associated with those
locations along the CPR. Four ungulate species (elk, mule deer [Odocoileus
hemionus], white-tailed deer [O. virginianus] and two bear species (grizzly and
black bear) were used for this analysis). We tested whether strike rates were correlated with the relative abundance and nine railway variables that could alter the
flight path, detectability or reaction time of animals present.
Methods
Study Area
The study was conducted along a 134 km section of the CPR running from the western
boundary of Yoho National Park, British Columbia (116° 39′W, 51° 14′N) to the
9 Relative Risk and Variables Associated with Bear and Ungulate …
137