Mortality of Wildlife on a Texas Highway

Abstract

Considerable interest has developed of late in the problem of wildlife mortality on our public highways (see Dickerson, L. M., the JOURNAL OF WILDLIFE MANAGEMENT, 1939, vol. 3, p. 104). In an attempt to gain some measure of the losses on the highways of Texas, I kept daily records (except for July and August) from February 1, 1938, to January 31, 1939, of mammals run down by motorists on the six miles of concrete highway between College Station and Bryan in Brazos County. Traffic on this section of highway is heavier than average, increasing the hazard to wildlife, but this factor is compensated for in part by the relative scarcity of most kinds of mammals in this section of the state. I consider my data as probably slightly less than average for a similarly constructed six-mile section of highway in some other part in Texas, as, for example, the TransPecos region. On unimproved highways, of course, the losses would tend to be much less, for it is common knowledge that the rate of mortality to wildlife, and man as well, increases directly with the degree to which a highway is improved for rapid transit. Disregarding the months of July and August in which no data were recorded, the average monthly loss of mammals was 5, or nearly 10 per mile-year. If my data be nearly average for similar sections of fast highway in other parts of the state, the total number of mammals (not counting man) killed each year on the 15,675 miles of hard surfaced highways in Texas is 156,750. If w assume that a reduction of average speed on the highway from 50 m.p.h. to 30 m.p.h. will reduce highway mortality of wildlife from 10 a mile-year to, say, 4, the yearly loss on the 5,790 miles of graveled and unimproved roads in the State would amount to 23,160. Add this to the figure derived for the fast highways, and we get a total of 179,910. This figure is for mammals alone. No r cord was kept of the birds, reptiles, and amphibians run down by motorist , but I gained the impression that during the ten months of observation the loss of birdlife was only about onef fth that of mammals; reptiles, however, especially the painted terrapin (Terrapene ornata), fared much worse than did the mammals.