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March 2005

Thesis on a specially studied subject

Predator-prey study of avian predators and African Mastomys mice – prey composition analyses
of avian predator pellets

The multimammate mouse, Mastomys natalensis is an important rodent pest in sub-Saharan Africa. It acts as natural reservoir in several human pathogens and cause severe damage to agricultural crops. Rodent management today mainly rely on the use of rodenticides but this control method in general suffers from lack of knowledge and has often resulted in large amount of chemicals being distributed in the environment without the desired control effects. Alternative control methods that are far more environmentally friendly are desirable. 

A few studies have indicated that predation is an important mortality factor in M. natalensis populations and this has opened up for an interest in understanding the biological effects of predators on M. natalensis populations. A recently terminated study in central Tanzania in East Africa therefore focused on the effects of applying different predation pressures to M. natalensis populations in small, cultivated fields. In this study a large amount of pellets regurgitated from avian predators were collected around perch poles and under trees in a 60 ha area of mixed cultivated and fallow land. The frequency of pellets collected over time shows that there is a markedly seasonal fluctuation in the avian predation pressure, but further analyses of the pellet material are needed to obtain more information on the prey animals. 

Avian predators may prefer certain hunting habitats to others according to which of their senses are involved in hunting. If sight is an important hunting sense, the predator may prefer sparsely vegetated and open areas for hunting, but if hearing is an important hunting sense, it may also hunt in more densely vegetated areas.

The social structure in a rodent population may imply that certain individuals are more exposed to predation risk than others. A social subordinate status, may force the individual to forage in areas with high predation risk. Predators may therefore selectively predate on such more exposed groups of prey individuals and thereby affect the population structure. Selective predation can be related to for example sex, age and size of the rodents. 

The master study should focus on the prey composition of avian predators through analyses of the pellet contents. The contents of the pellets should to be sorted into prey groups; i.e. insects, birds, shrews and rodents, and for rodents be identified to species when possible. Jaw measurements and tooth wear measurements should be taken on M. natalensis prey material. In order to determine whether predators selective predate on certain age or size classes of M. natalensis, both the jaw measurements and the tooth wear measurements may be correlated to M. natalensis size classes (body mass) and subsequently be compared to the size composition of M. natalensis in the surrounding habitat. 

If the project is of interest to you please contact:
Solveig Vibe-Petersen
Danmarks JordbrugsForskning
Skovbrynet 14
DK-2800 Kgs.
Email Solveig.V-Petersen@agrsci.dk     Tlf. 45 87 80 55, (reception) 89 99 39 01 (direkte)


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