A comparison of survey methods for monitoring crop damage by wild boar (Sus scrofa)

Abstract

Abstract

This paper compares three different survey methods for monitoring wild boar (Sus scrofa) damage to agricultural crops on the island of Mörkö, Sweden. The first method investigated was also the most conventional and involved walking through the fields on foot to locate and measure patches of wild boar damage. This method was compared to a second that involved the use of a remotely controlled aerial drone which took digital photographs of the fields. These photographs were then analyzed and observed damaged areas were recorded. The third method considered the theory that most wild boar damage to crops occurs on the edge of the fields, in order to determine if a relationship exists between the damage on field edges and the total damage in the whole field. The premise of this is based on the theory that using an edge index would increase efficiency since only the field edges needed to be physically inspected.

The methods were compared in regards to time and cost efficiency. The cost of the aerial survey method was calculated to be 285 SEK/ha whereas the ground method cost 85 SEK/ha. The aerial method took less time compared to the ground method with a time cost of 0.28 h/ha compared to 0.34 h/ha. The edge index for the third method did not show any consistent relationship between fields so could not be further utilized. In conclusion, the aerial method was too costly to provide a suitable alternative to the ground method, and evidence suggested that the ground method was more accurate in distinguishing wild boar damage from that caused by other game species.

Abstract

Popular science summary

Are aerial drones the future for wild boar crop damage surveys?

The wild boars are back, and they have returned in force. This is a rather recent trend since wild boars were extinct in Sweden until the 1970s and since then they have multiplied explosively, spreading all over central and southern Sweden. Their re-appearance has led to conflicts with human interests, namely the damage they cause to agricultural crops and forests. Anyone who has visited the countryside of central and southern Sweden would have witnessed the effects that the destructive rampage of foraging wild boars can have on forests and agricultural crops. Naturally it is of interest to the farmers to know the extent of the damage and the economic loss they suffer from wild boar activity and in order to find out, surveys have to be undertaken. The conventional method for conducting such surveys involves walking through the fields on foot to detect and measure any patches of damage caused by wild boars. This is of course highly labour-intensive and also takes a fair amount of time.

In an attempt to find more efficient survey technique, the classic method was compared with two other methods in wheat, barley and oat fields on the Swedish island of Mörkö. One of these alternatives involved the use of a remotely controlled aerial drone not unlike the military drones often seen in warzones around the world. The drone would take very detailed pictures of the fields which were then further evaluated. The third method was based on the theory that wild boars mainly caused damage on the outskirts of the fields since they are able to quickly retreat into the forest if danger approaches. The survey method would still be carried out on foot but would only concentrate on the outskirts of the field where the results would be used as an index for the damage extent of the entire field, in theory at least.

Depending on the region wild boar damage may be very severe and result in large economic loss. In the case of Mörkö, where the wild boar population is strongly regulated, the results showed that wild boars caused damage to the wheat fields equalling 1.5% of the total area used for wheat cultivation, which led to a loss of income surpassing 80 000 SEK. This may be considered acceptable to farmers if the economic loss caused by wild boars can be mitigated by the economic gain from hunting, as occurs on Mörkö.

The use of the aerial drone proved to be much more convenient than the conventional method, as expected, since the operator could sit and relax while the drone flew its pre-defined path, taking pictures along the way. The analysis of the aerial pictures on the other hand took some time and needed considerable computer power to put all the aerial pictures into one giant image covering the entire field. The big drawback of this method however was the price tag. It was more than double the cost of the conventional method, which may make it too expensive for the farmer to be of any use. Unfortunately, the third method – the edge index – was too inconsistent to be of any practical use even though it could be confirmed that the majority of the wild boar damage is indeed caused on the outskirts of the field.

Wild boars will continue to use agricultural fields for foraging and nesting, so unless farmers and land owners are willing and able to pay the price for aerial surveys, it would seem that they will have to continue with the conventional method, or investigate other methods to survey the wild boar damage in their fields.

Supervisors: Jan-Åke Nilsson, Gunnar Janson & Jonas Nordström
Master’s Degree Project 30 credits in 2013
Department of Biology, Lund University

• author: Steinbrücken, Bastian
• supervisor: Jan-Åke Nilsson; Gunnar Jansson; Jonas Nordström
• organization: Degree Projects in Biology
• course: BIOM32 20122
• year: 2013
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 4123606
• date added to LUP: 2013-10-24 14:41:32
• date last changed: 2013-10-24 14:41:32