Area Wanted For Birds, Pests Studies

Press, Volume CVIII, Issue 31659, 20 April 1968, Page 8

Area Wanted For Birds, Pests Studies

There are conflicting opinions about the part that birds play in the control of grass grub and porina in pasture lands. Some people place considerable importance on them and some farmers even put out nesting boxes to encourage the birds round and do not use insecticides.

Studies are being initiated at Lincoln College which it is hoped will determine, by measurement, the role of birds, and in particular starlings as the commonest bird, and also of other vertebrate predators such as hedgehogs and mice. The work is being undertaken by Mr K. East, a Christchurch student who recently completed a bachelor of science honours degree at the University of Canterbury with first class honours in zoology. He is now continuing his studies at Lincoln for a doctorate of philosophy and will be working under Dr R. P. Pottinger, in the agricultural zoology department at the college, who is himself engaged in long-term ecological studies of grass grub and porina to determine what regulates the populations of these pests. For his studies, Mr East is looking for an area in Canterbury, preferably handy to Lincoln, which has both a high bird population, of starlings in particular, and also magpies, and also of grass grub and porina. He said that he would be trying to study intensively a small area to determine the effect of bird and mammal predators on these pasture pests. Persons who believe that their country would suit these requirements should contact Dr Pottinger or the agricultural zoology department at the college. Mr East said that quite a lot of work of this nature had been done in North America, on such subjects as defoliating pests of spruce forests in Canada, but prac-

tically nothing had been done on pasture pests. In North America it had been found that birds appeared to exercise significant control where pest populations were at low densities. Where pest populations existed under an undisturbed natural environment, he said that there were a series of natural controlling factors such as birds, mammals, insect predators such a carabid beetles and parasitic insects like wasps, but in Canterbury, the natural order had been largely or almost entirely replaced by improved pastures, which provided a super-abundance of feed for grass grub and porina, but conditions to which the natural enemies of these pests had not adapted themselves so well. Mr East, however, noted that all the vertebrate predators of these pests were introduced. He said that some 25 years ago entomologists and others had noted the pressing need for basic investigation of the biology and ecology of these pests, but the introduction of D.D.T. for their control had seemed to be the complete answer and interest in such studies had waned until the emergence of residue problems and resistance to D.D.T. had indicated that it was perhaps not the full answer, so that there had been a revival of interest in these basic studies. Mr East believes that eventually the control of these pests may well be approached through a system of integrated control which involves the selective use of insecti-

cides to support natural control and this requires a detailed knowledge of the biology and ecology of the pests and their natural enemies. In the course of his studies Mr East will be sampling populations of grass grub and porina at frequent intervals to follow changes in the incidence of the pests and at the same time he will be seeking to determine causes of mortality in them. He will also be working to fix the part of grass grubs and porina in the diet of birds and how many they may eat in a day or season. While he is working at Lincoln Mr J. Coleman will be working under the supervision of Dr E. C. Young in the zoology department at the University of Canterbury on the broader aspects of birds of pasture lands, and particularly the starling, looking at the relationship of their numbers to feed supply, and Mr East said it was hoped that between the two of them it would be possible to determine just how important such things as starlings and hedgehogs were in keeping these insect pests under control. While ecological studies would take much longer, Mr East said he was hopeful that it would be possible to show the importance of vertebrate