Tawny owl ( Strix aluco ) and its variation in diet between years

Inglés. The tawny owl resides in temperate forests in Europe and mainly hunts rodents but can also hunt other animals like birds,invertebrates and bats. In this study I examined how the diet of tawny owls varies during the span of 2018-2020, I also compared the diet found from nest boxes with footage obtained from cameras inside the nestboxes. The diet of the tawny owl can vary due to different reasons, other studies have shown that the diet is seasonal due to changes in snow cover and development of ground vegetation . Studies have also shown that different temperatures create different proportions of animals in the diet of the tawny owl. The biggest proportion of the tawny owl diet consists of mammals, more specified rodents which was shown in my study as well but the variation studied was only seen between the year 2019 and 2020. Surprising was how my result showed that birds were not the second most favoured prey item but instead a high proportion of invertebrates were found in the contents of the nestbox and no variation was found for invertebrates over the years. The lack of birds could be explained by different reasons but one is the lack of experience in identifying bones and therefore misjudging whether something is a bone of a mammal or a bird. Lastly the comparison between footage and the nest box contents showed that there was no difference in prey proportions between the two.

Inglés. Tawny owls cannot go shopping like us they are dependent on nature What was the reason for this study? Well to find out how the tawny owl changes its diet between 2018-2020 and what that might be because of. I also wanted to figure out whether two methods of detecting the diet of the tawny owl gives the same result or not. Tawny owls can be found in forests around Europe and Asia and are nocturnal hunters meaning that they hunt during the night. With the help of their good eyesight and hearing they can easily hunt rodents, birds, invertebrate, bats and amphibians. Rodents are the main prey of tawny owls and the population of these rodents can fluctuate from year to year. During 2019 one of these fluctuations occurred and is the main reason why I think that there will be a difference in the diet of tawny owls between the years. Method Firstly the contents of nest boxes were gathered and later gone through trying to find bones and feathers from rodents or birds, and exoskeleton from beetles. This was repeated for every nest box for each year that was analysed. Then these contents were compared between the years to obtain a result. When the contents of the nest boxes were done footage was analysed. Footage was gathered with the help of cameras setup in the nest boxes. This footage was gone through frame by frame to identify what type of prey the tawny owl brought back. These two methods were then compared to see if there was a difference between the results. Result The result showed us that there was less rodents eaten during 2019 then 2020 but no other years. Another difference was found for the bird proportions where more birds were eaten during 2019 than 2018 but again no other years. Lastly the same proportions of invertebrates were eaten during the 3 years. When comparing the two methods I found no difference between the two. This was an interesting result which means that for future studies these two methods can be compared with each other. It also means that the method that was the easiest and cheapest to execute, in this case going through the nest contents, should be the one used in future studies. Handledare: Hanna Watson and Johan Nilsson Examensarbete 15 hp i biologi 2021 Biologiska institutionen, Lunds Universitet