Australasian Science: Australia's authority on science since 1938

Where Has All the Roadkill Gone?

By Magdeline Lum

Some birds are evolving shorter wings to help them avoid cars, and the stress of combat training leads to gastrointestinal issues.

Swallows the world over have slender, streamlined bodies and long, pointed wings, allowing them to hunt and eat insects while flying. They are incredibly efficient at flight and are capable of reaching speeds in the range of 50–65 km/h with great manoeuvrability. Despite their speed and mobility, they do make up a proportion of roadkill each year.

The American cliff swallow (Petrochelidon pyrrhonota) migrates between North and South America. Prof Charles Brown of the University of Tulsa and his wife, Dr Mary Bomberger Brown of the Tern and Plover Conservation Partnership at the University of Nebraska, have studied this migration and associated roadkill carefully. The data they have collected shows that roadkill exerts a selective advantage on swallows with shorter wingspans.

“Evolution is an ongoing process, and all this – roads, SUVs and all – is part of nature or ‘the wild’; they exert selection pressures in a way we don’t usually think about,” Prof Brown says.

The couple travelled the same roads every year for three decades, stopping to collect dead birds. They observed a decrease in mortality of the cliff swallows over this period.

In 1982, 20 dead birds were collected compared with up to four dead birds collected in the past 2 years even though the swallows being studied have nests near major roads, bridges, overpasses and culverts. The population of the swallows increased during the period of the study.

The research team then compared the measurements of 104 collected birds that had been preserved and a group of 134 swallows that had died accidentally. Using data from the 2012 season, they found that the average wingspan of swallows is 107 mm while the average wingspan of the roadkill birds is 4–5 mm longer than this. The longer wings are harder to flap, and this slows take-off and manoeuvring, making the swallows less agile.

However, what has not been excluded as a possible reason for the decrease in bird mortality is that the swallows may be learning to avoid traffic.

Battle of the Bowels

The most frequently reported symptoms unrelated to trauma among soldiers in high pressure operational situations are gastrointestinal. These can range from abdominal pain, diarrhoea, constipation, nausea and a range of cognitive changes.

Singapore researchers have reported in the journal Alimentary Pharmacology & Therapeutics that combat training can trigger stress, anxiety and depression, as well as a range of gastro­intestinal symptoms.

Apart from being inconvenient, diarrhoea in the battlefield can be viewed as infectious but often the cause behind the infection is not documented.

Recent data from defence forces in the Gulf, Iraq, and Afghanistan conflicts does highlight significant gastrointestinal effects on manpower and military efficiency. While there is much evidence about the long-term consequences of combat stress and anxiety among veterans, there is less known about the effect of ongoing stress during conflict.

The Singaporean study involved 37 soldiers aged 19–23. Soldiers had no significant gastrointestinal symptoms but after 4 weeks of combat training, 26 soldiers reported abdominal pain or discomfort, constipation, and alternating constipation and diarrhoea. During the rest period, only 11 soldiers reported these symptoms.

While the Singaporean study looked at a small number of people, it builds on a 2008 American study that found excessive exercise caused rapid onset of gastrointestinal dysfunction.