1. Colonies of wild Rattus norvegicus Berkenhout were kept in closed rooms containing nesting sites. The conditions permitted breeding.2. Seventy-six experiments, each lasting 6–35 days, were done to test the rats' food preferences. In each experiment except two, a choice was given between two foods, both available in excess. In the two exceptional experiments a choice between three foods was given.3. Although marked preferences were shown, a food was rarely quite rejected in favour of an alternative.4. Among cereals, wholemeal was preferred to wheat grains, but wheat grains were preferred to white flour; little or no white flour was eaten if wholemeal was available. Wheat germ was eaten only in small quantities when an alternative cereal was available, but in larger quantities if the alternative was sugar or a sugar-cereal mixture.5. The addition of sugar or saccharin to cereals increased acceptability; sugar was preferred to saccharin.6. The addition of arachis oil to wholemeal or wheat increased acceptability.7. Cod-liver oil at 2·4 % acted as a deterrent.8. Total calorific intake remained steady over short periods, but over several weeks rose as the mass of the rat colony increased. The higher the mean weight of the rats in a colony, the lower the calorific intake per unit weight of rat.9. The amount of food eaten was partly determined by its calorigenic capacity: in particular, wet foods were eaten in much larger quantities than dry foods.10. The food preferences of wild rats differ in several respects from those of white Rattus norvegicus.11. Apart from palatability or flavour, the main factors influencing food preference were (a) previous experience and probably (b) the nutritional value of the food. The effect of previous experience was often observed when rats, accustomed to one food, gradually changed from the accustomed food to another. The stages of a change to a new food, or the establishment of a particular preference, varied, and are discussed in detail.
With Plates 12 and 13, 9 Text-figures and z Maps)Rat (Rattus nmvegirus Berkenhout) populations have been studied in two villages in Devonshire. One village had a human population of 266, the other, of 364. The main activity in each village is mixed farming, with poultry and pig keepingon a small scale.From spring 1947 to spring 1950 visits were made to both villages at six-monthly intervals. At each visit a relative census of the rat populations was taken. This was done either by test baiting, which records only the visits by rats to bait points ; or by census baiting, in which a surplus of wheat is laid each day until the amount taken levels off. The level so reached is a measure of the rat population. Test baiting was found to be less reliable, as an index of changes in the rat populations, than census baiting. In some instances treatments, consisting of one, two or three strikes, i.e. poisonings after prebaiting, were carried out after the census.Complete clearance of a whole village was not achieved on any occasion. Lasting reductions of the rat populations were achieved only by comprehensive double or triple strikes. After such treatments the rat populations took more than a year to recover; probably the recovery to the maximum rat population would often have taken 2 years or more had it been allowed to take place.In each village the rats were distributed in discrete colonies, most of them in farms or chicken runs. Poor hygiene and dilapidation of buildings were important factors in promoting rat infestation. When a new source of food became available near an existing infestation, e.g. as a result of the setting up of a new chicken run, rats soon appeared.Apart from rats five species of small mammals visited the bait points : Mus musailus, Apodetnus sylcatinrs, Microtits agrestis, Clethrionornys glareolus and Sorex araneus. Their presence was detected by their droppings, by characteristic nibbling of the grain, and by trapping. Allowance was made for their presence in recording the results of census baiting.Mouse activity at the bait points was greatest when the rat population was low, but there is no certam evidence that mouse numbers greatly increased when the rats were reduced. I t is suggested that, for effective control and the economical use of manpower, treatments in rural areas should always consist of at least two strikes. It may be expected that such treatments, if carried out with a high degree of thoroughness and efficiency, need normally be carried out only once a year; and it might often be possible to leave an area for 18 months or 2 years.
1. A preparation containing 0·7% scilliroside (the glucoside of red squill) had been tested as a poison for Rattus norvegicus and R. rattus.2. The preparation has been found to be effective in the field against norvegicus but not against rattus.3. Assayed against a strain of white rats, the preparation had an LD 50 for males of about 25mg./kg., and for feamales of about 5 mg./kg.4. The LD 50 for adult Rhode Island Red fowls was greater than 400 mg. /kg. Pigs, dogs and cats were treated with doses up to 16mg./kg. without fatal results.5. Silmurine was unpalatable to pigs, dose and cates, but fowls readily consumed a mash containing 1% Slimurine.
1. Sodium fluoracetate (1080) has been tested in the field as a poison for Rattus norvegicus and R. rattus.2. Direct poisoning (without Prebaiting) was used in thirteen tests on R. norvegicus. In eight of these tests censuses showed kills of at least 89% in three tests the poison failed, and in two the results were equivocal.3. Of three similar tests against R. rattus two were successful and one was a failure.4. Six tests of 1080 after prebaiting gave five successes (including one against R. rattus), and one in which the estimated kill was about 82%.5. In five out of six tests populations of R. norvegicus which had survived baiting with 1080 showed shyness (refusal) of the poison when it was given in a new bait base.6. The LD 50 of 1080 for a strain of white rats was found to be 3·8 mg./kg. (approx. range 2·8–5·2).7. A number of wild brids and some domestic animals were accidentally killed during the tests despite stringent precautions taken in laying the bait and in warning occupiers.8. It is concluded that: (a) although 1080 is probably more effective in direct poisoning than other poisons used in the past, it does not give as consistent results as the standard poisons do after prebaiting; (b) 1080 is too dangerous for general use.
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