Variation in behavioural responses of ewes towards predator-related stimuli

 

Introduction

 

The article I read was written by Inger Hansen, of Tjøtta Rural Development Centre, Frank Christiansen from Nord-Trøndelag Research Institute, Hanne S. Hansen of Nord-Trøndelag College, and Bjarne Braastad and Morten Bakken from Agricultural University of Norway. The purpose of their work is to see for variation in behavioural responses of ewes towards predator-related stimuli, and if the response variation comes from breed, size or stimuli. The methods they are using is a simple test.

 

The Test

 

They use an enclosure of 25x60 metres, with two camouflage-coloured tents in the middle of the longest sides.

 

Between these tents they pulled a trolley manually with 3 mm transparent fishing line. On this trolley they placed the different stimuli. The stimuli were: empty trolley, big plastic ball (75 cm diameter) with painted eyes and mouth on the trolley, a stuffed lynx (Felis lynx) on the trolley, a stuffed wolverine (Gulo gulo) on the trolley, a stuffed bear (Ursus arctos) on he trolley, and a man in green rain poncho walking with or without a domestic dog (Norwegian elkhound, grey).

These seven stimulies was introduced to the grazing flock for about 45 s in intevals of less than 30 min between each stimuli. The recorded behavior of the sheep was: approaching stamping, approaching investigating, stamping immobile, attentive immobile with eyes focused on the stimuli, standing immobile and eyes not focused on the stimuli, no reaction e.g. lying down or grazing and paying no attention to the stimuli, walking away, cantering away and fleeing among others.

 

The sheep, a total of 32 groups of six ewes from 11 different farms, were divided into three main groups according to their weight:

-        Light, containing only the Old Norwegian sheep; a small and long legged, slim, shy, but well flocking and of good condition. They are not selected for economical traits, such as meat and wool, and are more of a niche product. Most often they give only one lamb annualy, which are of high survival.

-        In the medium class they used Spælsau and Norwegian fur sheep, which are to some extent heavier, with slightly better slaughter qualities, and with good maternal instincts.

-        The heavy class contained Suffolk, Steigar and Dala, which all have good slaughter qualities, but is said to have poorer flocking and maternal behavior than the lighter breeds.

 

The Results

 

The data registered during the tests indicated that the lighter breeds have a longer recovery time than the heavier. In extreme cases even three times longer. The medium and heavier had almost similar reaction for all the stimulies.

The average flight distance also decreased by weight, and while 3.9 % of the heavy reacted by running to the net furthers away, 35 % of the light breed reacted the same way. On the other hand bleating was less common among the light, than others. One of the reason for this may be that the heavier sheep more often lost control of their lambs when fleeing.

The light breeds showed the best flocking behavior, as well as the longest recovery time, and longest flight distance. The heaviest breed was ranked bottom in these comparisons. This support the researchers assumptions that the antipredatory behaviors are weakend by the selection of economical traits, like slaughter quality and higher avarage of offspring.

 

Conclusion

 

Reactions would obviously been different towards real, live predators – the way they responded towards the domestic dog is an indication for this. As a live domestic dog, on a leash, gave longer recovery time than a stuffed predator on a trolley, they clearly differentiated between the stimulies.

 

While working with this article I searched the web for other related articles. On www.sheep-isle.dk I found some other interesting information. One of the researchers of the discussed  article, Inger Hansen, had also written a historical background article on the domistication of sheep. In this, she stated that the sheep is one of the earliest animals to be domisticated by man. This happened approxmately 11000 years ago, in ancient Iraq. The domistication, and search for the optimal economicly breed, have removed some of the instincts towards predators. But since behaviour is a trait found and controlled by several genes, and the specialised breeding for production is on a singel gen level, the domesticated sheep have kept remarkable many of their behavioral traits and instincts towards the herd, offspring and predators (Goddard 1980).

 

The reason why I choose this topic for this assignment was my interest for sheep. Home at my family farm we have both sheep from the medium, and the heavy class. I have personal experience with their behavioral patterns towards dogs, and the way they are flocking when collecting them from the mountains in the fall, is just like predicted from these experiments. Our medium size breed, Spælsau, are much more gathered than our heavy breed, Dala, and I can see the have better maternal qualities by the way they look after their offspring.

 

By Vidar Nedrebø