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Article Source and Acknowledgments

  • The article is available online at: http://dx.doi.org/10.1016/j.cub.2013.02.015.

  • Acknowledgments to Drs. T. Namikawa, Y. Matsuda, M. Mizutani, and Y. Atsumi for providing PNP roosters.

  • Takashi Yoshimura received funding from the NEXT Program initiated by the Council for Science and Technology Policy (CSTP).

  • Tsuyoshi Shimmura is supported for JSPS fellows under reference 22-4942.

  • WPI-ITbM is backed by the World Premier International Research Center Initiative (WPI), MEXT, Japan.

  • Authors declare no financial interest in the research.

References

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  4. Shaw, B.K. and Kennedy, G.G. (2002). Evidence for species differences in androgen receptor distribution related to androgen-dependent behavior. J. Neurobiol. 52, 203–220.

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Research Overview: Cliff Swallows and Road Mortality

  • Key Topics: Road kill, natural selection, cliff swallows (Petrochelidon pyrrhonota), social behavior, and coloniality.

  • Context: Estimated 80 million birds die from vehicle collisions in the U.S. annually; millions more in Europe and other regions. Common concern over roadway design to minimize wildlife fatalities.

Decline in Road-Killed Cliff Swallows

  • A 30-year study on cliff swallows in southwestern Nebraska demonstrated a significant decline in road-killed birds correlating with their inhabitation of roadside sites.

  • Observation of a marked change in wing length regarding the road-killed population compared to the broader population.

  • Research Site: Cedar Point Biological Station, Keith County, Nebraska (Coordinates: 41°12.591′ N, 101°38.969′ W).

  • Nesting Behavior: Cliff swallows nest in clusters on walls beneath overhangs, utilizing highway infrastructure (bridges, overpasses, culverts) for habitation.

Research Methodology

  • Each year, researchers counted road-killed swallows and compared the counts retrospectively to prepared specimen records.

  • Assessment involved comparing road kills to birds caught during mist-netting. No significant differences found between mist-net fatalities and living birds caught contemporaneously.

  • Key Findings:

    • Decline in annual salvageable road kills from 1983 to 2012.

    • Population size around roads remained stable or increased, while road kill numbers decreased significantly.

    • Decrease in road kills is independent of changes in avian scavenger populations.

    • Vehicle traffic volume trends showed no statistically significant reductions; rather, vehicle sizes shifted towards larger models, which typically increase collision risks for birds.

Wing Length Variation

  • Road-killed cliff swallows exhibited longer wings compared to the general population, with a trend towards increasing wing length over the study span.

  • Long-term studies suggested a decline in average wing length across the population while road kill individuals demonstrated the opposite pattern.

  • Statistical Analysis:

    • Road kills showed significantly longer wings (F1,229 = 7.06, p = 0.007, ANCOVA).

    • Average wing length increased for road-killed birds over time (rs = 0.78, p < 0.0001, n = 20 years) against a significant decline for the population (rs = 0.63, p = 0.002, n = 21).

    • General Observation: Indicates a possible adaptive response to avoid collisions due to morphological changes in wing structure potentially favoring escape dynamics (lower wing loading, ability to take off more vertically).

Evolutionary Implications

  • Natural selection may favor cliff swallows with morphological traits that enhance avoidance of vehicles.

  • Other factors contributing to decreased road mortality may include behavioral adaptation observed through social learning, as well as the removal of risk-taking individuals from the population.

  • Future Research Insights: Suggests potential for changes in road mortality patterns in other avian species over time, reflecting ongoing evolutionary pressures.

Supplemental Information

  • Additional data, including experimental procedures and detailed figures, available online (http://dx.doi.org/10.1016/j.cub.2013.02.023).

  • Acknowledgments for support from the University of Nebraska-Lincoln and funding bodies like the National Science Foundation and National Geographic Society.

  • References cited regarding broader impacts of anthropogenic influences on bird mortality.

    • Contact Email: charles-brown@utulsa.edu for further correspondence regarding the study.