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Speed kills: ineffective avian escape responses to oncoming vehicles - PubMed

  • ️Thu Jan 01 2015

Speed kills: ineffective avian escape responses to oncoming vehicles

Travis L DeVault et al. Proc Biol Sci. 2015.

Abstract

Animal-vehicle collisions cause high levels of vertebrate mortality worldwide, and what goes wrong when animals fail to escape and ultimately collide with vehicles is not well understood. We investigated alert and escape behaviours of captive brown-headed cowbirds (Molothrus ater) in response to virtual vehicle approaches of different sizes and at speeds ranging from 60 to 360 km h(-1). Alert and flight initiation distances remained similar across vehicle speeds, and accordingly, alert and flight initiation times decreased at higher vehicle speeds. Thus, avoidance behaviours in cowbirds appeared to be based on distance rather than time available for escape, particularly at 60-150 km h(-1); however, at higher speeds (more than or equal to 180 km h(-1)) no trend in response behaviour was discernible. As vehicle speed increased, cowbirds did not have enough time to assess the approaching vehicle, and cowbirds generally did not initiate flight with enough time to avoid collision when vehicle speed exceeded 120 km h(-1). Although potentially effective for evading predators, the decision-making process used by cowbirds in our study appears maladaptive in the context of avoiding fast-moving vehicles. Our methodological approach and findings provide a framework to assess how novel management strategies could affect escape rules, and the sensory and cognitive abilities animals use to avoid vehicle collisions.

Keywords: animal–vehicle collisions; antipredator behaviour; disturbance; escape response; flight initiation distance; video playback.

© 2015 The Author(s) Published by the Royal Society. All rights reserved.

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Figures

Figure 1.
Figure 1.

Response metrics of animals avoiding oncoming vehicles.

Figure 2.
Figure 2.

Reactions of brown-headed cowbirds to virtual oncoming vehicles approaching at apparent speeds of 60–360 km h−1. Panels (a) and (b) represent alert and flight behaviours, respectively, expressed as time-to-collision (s); panels (c,d) represent the same behaviours expressed as distance to collision (m). Two vehicle sizes (standard and extended) are combined for apparent speeds 60–210 (n = 20 cowbird groups for each), but only standard vehicles were used for approaches at 240 and 360 km h−1 (n = 10 groups for each). Bars represent means ± 1 s.e. The horizontal dotted line in the time-to-collision panels represents the time necessary (0.8 s) for cowbirds to travel 3 m from a resting position (i.e. successfully escape the oncoming vehicle; see the electronic supplementary material).

Figure 3.
Figure 3.

Scatterplots depicting the ratio of FID to AD versus AD across vehicle speed treatments. Circles represent trials using the standard truck size; triangles represent trials using the extended truck size. Regression lines, equations and r2 values are shown where relationships are significant (p ≤ 0.05). A second-order polynomial term was included in all models to account for potential asymptotic relationships characteristic of that expected from a fixed spatial margin of safety (see also electronic supplementary material, figure S4).

Figure 4.
Figure 4.

Proportion of trials, by vehicle speed, for which FID divided by AD = 1 (i.e. trials for which no alert behaviour was apparent).

Figure 5.
Figure 5.

Bar chart of high-quality assessment (HQA) time (time difference between alert and flight behaviours) of brown-headed cowbirds in response to virtual vehicles approaching at apparent speeds of 60–360 km h−1. Two vehicle sizes (standard and extended) are combined for apparent speeds 60–210 (n = 20 cowbird groups for each), but only standard vehicles were used for approaches at 240 and 360 km h−1 (n = 10 groups for each). Bars represent means ± 1 s.e.

Figure 6.
Figure 6.

Proportion of trials for high-quality assessment time in which the estimated minimum time threshold for a successful escape was (enough time) or was not (not enough time) met. See text for details.

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