COUNTS OF ANIMAL CORPSES ON EAST SUFFOLK ROADS BETWEEN SEPTEMBER, 1966 â€” SEPTEMBER, 1968 PETER N I C H O L S O N
Introduction and Methods This work was stimulated by the appearance of apparently abnormal numbers of animal corpses, mostly casualties of motor traffic, on the roads of East Suffolk du ring 1966. Although it was of interest to speculate on the possible causes of the carnage, without any past data available for East Suffolk it was impossible to know whether the observations were abnormal or not. Since the Author had to make daily journeys into different parts of East Suffolk, a census was started in which the number and species of animal corpses passed whilst travelling were noted together with a record of the distance covered. T h e results of these counts from September, 1966, to September, 1968, are presented and discussed here. DĂźring the two years, a motor journey was made nearly every day with an average daily mileage of 19-7 miles. T h e journeys were confined to East Suffolk, most of them being made from Cookley, near Haiesworth, to Westleton, Walberswick, Orford, and Redgrave villages. Most major towns or villages were visited at least once during the survey. Whilst travelling, all fresh animal corpses were counted, but badly flattened or obviously nonrecent casualties were not included. Results In two years, 477 casualties were observed whilst travelling a distance of 14,615 miles. A complete list of species and casualty numbers in given in T A B L E 1. Rabbits ( 2 7 - 3 % ) , rats (23-3%), and birds (21-2%) were the most frequently encountered, but hedgehogs (9-2%) and hares (5-9%) were common. Because of high travelling speeds it was not possible to identify accurately all mammal or bird species although these were noted as casualties and included in the total. No reptiles or amphibia were observed during the survey. In order to compare results for different seasons and years the counts were grouped to give three four-monthly seasons in each year: July-October = summer; November-February = winter; March-June = spring. T h e results for each season were calculated as casualties per thousand miles travelled (see FIG. 1). Four main groupings are presented: 1. Rabbits 2. Rats 3. Birds (all species) 4. All other animals.
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Rabbit casualties reached peak values of 34-1 and 17-2 per thousand miles for the summers of 1966 and 1967, whilst winter figures were low at 2-8 and 1 -6 for 1966/7 and 1967/8, respectively. A further peak was indicated in summer 1968. Rat counts showed peak values of 22-3 for summer 1966 but thereafter more or less declined and counts from the summer 1967 to summer 1968 remained between 2 â€˘ 3 and 5 â€˘ 8. Bird counts varied between 5 â€˘ 1 and 7 - 7 for summer 1966 to summer 1967 but feil to 0-5 in winter 1967/8 and then rose to reach peak values of 15-5 by summer 1968. Counts of other species showed peak values of 33-0 for summer 1966 but thereafter varied little between 4-7 and 12-2.
Discussion T h e survey indicates that the counts of dead mammals on the East Suffolk roads during the summer 1966 were exceptionally high when compared with the counts for the two summers following. At any one time the numbers of animal corpses on the road must be the result of an interaction of many factors, e.g., population size, activity (see Haugen, 1944, Brockie, i960),' traffic volume and speed. However, it is noteworthy that the high counts for rats of summer 1966 coincided with reports and complaints of rat plagues in both Suffolk and Norfolk. T h e pest division of the Ministry of Agriculture, Fisheries and Food reported that 1966 was an exceptionally 'bad' year for rats, so much so that a special training scheme was devised to teach farm staff how to cope with them. It seems quite likely that in this instance the high mortality was related to high population level. If this was also true for the other counts, it would appear that 1966 was a year that favoured the breeding of mammals but not of birds. It would be most interesting to know what factors were responsible. Mole corpses were only encountered during June, 1967, when it is thought that the exceptionally dry spring had made the soil dry and hard and therefore difficult for burrowing and catching food. Dead moles could be observed in most gardens and fields on high land during this period. Hodson (1966), investigating animal road deaths on a two mile Stretch of a road in Northamptonshire, recorded six mole corpses during the summer of 1959 (three during June and three in September), but none at all during 1960. It will be remembered that the summer of 1959 was a record one for both high sunshine and low rainfall values and it seems probable that a hard dry soil was also the cause of this mole mortality. T h e absence of records for amphibia and reptiles is a marked contrast to the results of Hodson in Northamptonshire, who found that 70-8% of all animal casualties were frogs (Rana temporaria). I have on rare occasions found the corpses of
ANIMAL CORPSES ON EAST SUFFOLK ROADS
frogs a n d grass s n a k e s (Natrix natrix) whilst W a l k i n g on East Suffolk roads and it is probable that the type of survey described in this paper, with its lack of careful searching, is not suitable for the smaller animals. Cuthbert (unpublished data), counted eighty small bird corpses in June and July, 1965, over a three mile Stretch of r o a d between Theberton a n d Leiston, most of which were found by careful searching of the grass verges. Nevertheless, if the results of my survey are treated as a daily search of a regulĂ¤r 19-7 mile road length, a total animal mortality of 23,800 animals per year can be estimated for East Suffolk alone (allowing that the total mileage of all classes of road in East Suffolk is 1,956 miles). References Brockie, R. (1960). Road mortality of the hedgehog (Erinaceus europaeus, L.) in N e w Zealand. Proc. Zool. Soc. Lond. 134, 505. Haugen, A. O. (1944). Highway mortality of wildlife in southern Michigan. J. Mammal. 25, 177. Hodson, N . L . (1966). A survey of road mortality in mammals (and including data for the grass snake and common frog). J. Zool. Lond. 1966, 148, 576.
P. Nicholson, Carmel Cottage, Cookley, Haiesworth, Suffolk.