Oil Palm Rat Infestation - Field Control by Field Investigation

摘要

Rat damage in oil palm plantations can be persistent and costly, and it has been a target of much investigation. The potential for heavy crop losses was clearly identified from the 1960s, through field ecology study techniques. That work included thedevelopment of poison baiting methods through investigating the effects on actual rat population size, in turn showing techniques that could eliminate economic populations for several months. Barn owls were noted from the 1970s as sporadic residents of oil palm plantations, and they are known to be voracious predators of rats. Thus in the last three or four decades, there have been two general approaches to rat control on estates, namely by baiting programmes, or by providing nesting boxes to support abroadly distributed owl population. Published comparisons of the two approaches are scarce. Further, there are no reports of them being tested, at the necessary extensive scale, against no application of control measures, to see how population sizes might settle over a period of time.Two recent issues are the increasing difficulties in achieving control by baiting, and a lack of any objective evidence that owls can directly reduce losses to rats. Actual rat numbers in relation to owl populations have not been further studied since the early investigations on establishing the birds. What can be said with certainty at present is that in some localities where owls are established, there are places with low rat populations, but in other places with owls, rat numbers remain high. Equally, there are localities with no owl establishment in which there are some places with low rat numbers, but others with high incidence.For some years now, there has been increasing emphasis on investigating the field ecology of the pests. Increasing knowledge in this aspect forms a sound basis for economic assessment, and for devising sustainable control methods. Applied specifically tooil palm, there is need of full comparison of rat populations and crop losses on areas of estate scale size, respectively with baiting programmes, with owl establishment, and with no specific control measures. Ecologically based trials along these lineshad been initiated, providing interesting findings (summarised in the reproduced article below), but they were not persisted with. Great economic benefit to the industry as a whole would come from implementing such comparisons over an adequate time period. In addition, systematic trials could be done to investigate the real effect of field environment differences in the regulation of rat population size. Such trials would show why numbers can vary so greatly between different fields where no control measures have been applied. Further, they could lead to more reliable long term control within economic limits by means of environmental manipulation.Developing and encouraging skills in investigating the ecology of rat populations would pay dividends, j both for assessing current control approaches, and in developing newer sustainable and economicallyw reliable methods.