Understanding the role that extrinsic processes play in shaping animal population dynamics and demography is a central tenet of population ecology and an issue of vital importance for conservation and wildlife management. The top-down impact of predation and bottom-up influence of food availability are thought to be two of the most important extrinsic processes affecting population dynamics and demography of species occupying middle trophic levels. However, many studies only focus on quantifying the impact of one of these processes in isolation and it is not clear whether the impact of one extrinsic factor on population dynamics and demographic rates is augmented or lessened by changes in other extrinsic factors. In this thesis I examine the extent to which both top-down and bottom-up processes shape population dynamics (population size, recruitment and immigration) and demography (survival, reproduction, life-history trade-offs and reproductive strategies) in a long-lived species, the tawny owl, by taking advantage of a natural increase in predation risk (goshawk abundance) and a decline in food availability (field vole densities). Despite the increase in predation and the decline in food availability, the owl population remained stable, which we posit is due to goshawk predation being selective on individuals with a low reproductive value (juveniles and old individuals) and an increasing number of immigrants entering the population. Selective predation on older owls had a negative impact on the survival of this age class and appeared to be shaping the pattern of actuarial senescence and influencing the strength of the intrinsic trade-off between survival and reproduction. As food availability declined and predation risk increased owls appeared to be switching from an 'eggs in one basket strategy' of saving resources to invest more in fewer breeding attempts in the future, to a 'bet-hedging' strategy of reproducing more often, but investing less per breeding attempt.

Naminės pelėdos mitybos tyrimai yra atliekami siekiant nustatyti sugaunamas grobio rūšis. Šilutės rajone iki šiol tokio pobūdžio tyrimai nebuvo atlikti. Šie tyrimai svarbūs aiškinantis pelėdos mitybą ir vienas iš geriausių būdų nustatyti smulkiųjų žinduolių rūšinę įvairovę. Darbo tikslas – atlikti naminės pelėdos mitybos tyrimus Šilutės rajone, remiantis atrajose rastomis grobio liekanomis. Darbo tikslui įvykdyti buvo iškelti uždaviniai: pagaminti ir įkelti inkilus naminei pelėdai. Surinkti pakraikus iš inkilų ir atrajas šalia inkilų, drevių ir dienojimo vietų. Ištirti atrajų fizinius parametrus, išskirti iš atrajų grobio skeleto fragmentus, įvertinti grobio kiekį. Atrajose rastas grobio liekanas apibūdinti iki šeimos/rūšies remiantis kraniometriniais skirtumais. Atlikti rūšinės įvairovės ir biomasės skaičiavimus. Šilutės rajone buvo iškelti 3 inkilai, viename iš jų perėjo naminė pelėda. Iš šio inkilo buvo surinkti pakraikai, bei 66 atrajos iš įvairių dienojimo vietų. Surinktų atrajų vidutinis ilgis 3,9±0,93 cm, svoris 2,4±0,88 g, bei vidutinis grobio kiekis vienoje atrajoje 2,1±0,82 vnt. (max. 4). Atrajose identifikuotas 141 individas. Iš visų surinktų mitybos liekanų buvo identifikuoti 166 individai. Priklausantys 11 smulkiųjų žinduolių rūšių. Naminės pelėdos mityboje didžiausią dalį sudarė smulkieji žinduoliai 89,2%, o mažiausiai mitybą įtakojo paukščiai 6%, vabzdžiai 4,2%, ir varliagyviai 0,6%. Pelėdos mityboje dominuojanti rūšis buvo paprastasis pelėnas 28,3%, o... [toliau žr. visą tekstą] / Nutrition studies of the towny owl are carried out to ascertain the kinds of prey of the towny owl in Silute region. Such studies have not been done in this region so far. They are important to clear out the nutrition pecularities of the towny owl and one of the best ways to find out the variety of species of small mammals. The aim of the research is to carry out the nutrition studies of the towny owl in Silute region on the ground of the remains of the prey in the owls pellet. There were tasks for the work: to make and put up the bird houses for the towny owl, to collect the litter from the bird houses and the rumination near the bird houses, tree holes and dawn places, to investigate the physical parametres of the rumination, to separate fragments of the prey skeleton from the rumination, to estimate the amount of the prey, to describe the remains of the prey on the basis of the cranometric differences, to make the calculations of the variety of the species. Three bird houses were put up in Silute region. The towny owl was hatching in one of them. The litter from the bird house and 66 rumination parts from the dawn places were collected. The averrage length of the rumination is 3,9±0,93 cm and the weight is 2,4±0,88 g. The averrage amount of the prey in one pellet is 2,1±0,82 units ( max. 4). 141 individuals were identified in the rumination. 166 individuals which belong to small mammals were identified from all nutrition remains. The biggest part in the towny owls... [to full text]

This Master thesis deals with diet of the Tawny Owl (Strix aluco) and reproductive parameters. Muridae rodents dominated diet composition and Arvicolidae rodents and birds were alternative preys. Clutch size positively correlated with proportion of rodents in diet.