15 June 2007

16 dead in Ohio

A small scraper or putty knife was an indispensable tool to loosen and remove squashed specimens from the highway surface.
Seibert & Conover, 1991

Untold numbers of animals perish while crossing highways. We notice mostly the larger vertebrates, but the majority of the casualties are probably invertebrates. During my childhood in Turkey many, many years ago, after every night drive thru the country side, the grille in front of our car would be filled with all sorts of dead insects. Alas, I never thought of removing those casualties to start a collection. Many of those species have probably become rare since then.

A study reported in the Ohio Journal of Science1 in 1991 claimed to be the first to tally invertebrate casualties attributable to collisions with vehicles. The authors, Seibert & Conover, collected all the dead invertebrates they found along a 1-mile stretch of a highway in Ohio during an approximately 14-month period.

They ended up with 1162 invertebrate specimens, of which 1069 were insects. Hymenopterans (bees, etc.), lepidopterans (butterflies and moths) and dipterans (flies) constituted the majority of the victims. Some of the collected specimens had been absent in the Ohio University insect collections. The authors, therefore, suggested that collections of roadkills should be included in faunal surveys.

Among the relatively small number of non-insect casualties were 16 polygyrid snails (family Polygyridae). I am sure many more snails as well as insects had been killed but not accounted for, because they either remained on the tires or windshields of the vehicles or were squashed beyond recognition.

In the half a billion-year old history of life, death by motorized vehicles came into play less than 200 years ago with the introduction of steam locomotives. Have any animal groups evolved defensive mechanisms to lessen their chances of getting hit by motorized vehicles since then? Collisions with vehicles may be a strong enough selective force to have affected the behaviors and agilities of animals, for example, squirrels, that live alongside busy roads.

1Seibert, Henri C. & Conover, James H. 1991. Mortality of Vertebrates and Invertebrates on an Athens County, Ohio, Highway. Ohio Journal of Science. 91:163-166. pdf


umit said...

Crested larks along with severla other species around here evolved a behavior of picking up dead insects crashed and boiled due to summer hot.

Even so that the larks tend to wait along the main roads, even to risk their lives, for any chance of delivery.

I think many snails collected by the team should be accepted as vicitims to sun light and heatened surface rather than cars


They made the same argument for the dead earthworms, some of which might have died from exposure. Even though they also made the point that the latter were still "highway victims", they excluded earthworms from the total.

Ralph Hartley said...

My wife swears that at least some of the deer on the NIST grounds in Gaithersburg MD look both ways before crossing a road.

Motor vehicles are essentially their only cause of mortality.

You still see a lot of them on the roadside in suburban areas, so the behavior is not universal yet.

I know first hand that rural deer do not do this. A friend of mine has hit about a dozen. His wife bought him one of those whistles that is supposed to scare them away. It didn't work, and was eventually broken off by hitting a deer.

K said...

I've never seen this for myself, but I hear tell that an armadillo in imminent danger of being run over will actually jump vertically, rather than hunker down or try to run off to the side. It seems a behavior selecting them for easy roadkill. Can anyone verify this unfortunate behavior?


I don't know much about armadillos, but squirrels have this undoubtedly detrimental habit that I've witnessed many times. If they are in the middle of the road & see a car coming, they run towards one side, stop before reaching the curb, turn around & run towards the other side of the road. That sort of direction changing might confuse a predator, but it usually has fatal consequences in front of an approaching car.

Anonymous said...

Not sure about insects but with birds and mammals assume behaviour learned from parents would be the major factor. Pretty sure all the young squirrels currently raiding our bird table did not chance upon this source of food completely by accident.

monado said...

I have seen squirrels waiting by the side of the road for cars to go by, braced like runners in the starting blocks.

Sadly, I also see dragonflies buzzing the windshields of cars on sunny days, apparently mistaking the glitter for water.

Frank Anderson said...

I wonder how strong the selection for automotive avoidance behavior actually is. It seems like it would be substantial, but it probably is only great for 1) creatures that live very close to high-traffic, high-speed areas (it isn't hard to avoid squirrels, etc., on suburban streets when you're only driving 25 mph, though snails are a different story) and/or 2) creatures that have high vagility. A squirrel a couple hundred meters from a state highway may never encounter it. Also, standard (and, perhaps, more generally useful) anti-predator behavior may be exactly not what is needed to avoid a car, as noted above, so there might be a trade-off -- learning to avoid cars may make a squirrel more likely to be eaten by, say, coyotes or something. Advantageous behavior in traffic areas may not be advantageous in most of the range of the species.

On another note, I bet lots of insects probably just get caught in the slipstream and end up just taking a disorienting tumble over oncoming vehicles, rather than getting pasted. I wonder what percentage of insects that encounter cars actually end up splattered on grills or windshields?