Syftet med den här studien var att undersöka om revirstorleken påverkar den reproduktiva framgången hos lövsångarhanar. Datan samlades in i södra Sverige mellan 1984 och 1988 och består av etableringsdatum av revir, revirstorlek, antal partners (en eller ingen), datum för parning, antal ägg i kullen och antal flygga ungar. Det fanns inget samband mellan revirets storlek och de olika variablerna. Inte heller fanns det något samband mellan revirstorlek och hanens ålder när samma individ följdes över tid. Det fanns inget samband mellan revirstorlek och huruvida hanarna parades eller inte. Sammanfattningsvis påverkar inte revirstorleken hanens reproduktiva framgång. Istället finns det andra faktorer som troligtvis påverkar, som revirets kvalitet (t.ex. föda och predatorskydd), hanens ankomsttid, hanens sångrepertoar, hanens ålder samt föräldrarnas kondition. / The aim of this study was to examine if territory size of Willow Warbler males affects reproductive success. The data were collected in the south of Sweden between 1984 and 1988 and consist of date of establishing territory, territory size, number of partners (one or none), date of pairing, number of laid eggs and number of fledglings. There were no relationships between territory size and the different variables, nor was there a relationship between age of the male and territory size when following the same individual over time. There was also no relationship between territory size and whether or not the males reproduced or not. In summary, I could find no relationship between territory size and male reproductive success. Instead, other factors are likely to affect reproductive success, such as territory quality (i.e., abundance of food, safety from predation), male time of arrival, male song repertoire, male age and the body condition of the male and his partner.

This study shows the importance of the basic spectro-temporal song parameters in territorial contests between male songbirds. Chiffchaff and willow warbler were selected as model species for their phylogenetic and ecological similarity, strong territorial behaviour, but very different singing styles. We found that bigger males of both species sing lower pitched songs and that males of both species adjust their behaviour according to song pitch of their rival simulated by playback. Thus, it seems that both species use song pitch to acoustically assess the body size of their rivals. We also show that song length and syllable rate are important features of the song, probably signalling short-term motivation to escalate territorial conflict.

Recent global climate change is influencing the behaviour and ecology of species worldwide. Birds are typical systems to study in this context, as they are often migratory and thus subjected to a variety of environmental effects. This thesis employs the use of long-term ringing records, field observations, historical maps and historical volunteer observations with the aim of describing behavioural and ecological responses of birds to the current environmental change. An investigation into the spring arrival, reproduction and autumn departure in willow warblers (Phylloscopus trochilus) breeding at a southern study site in Sweden (65°N 18°E) showed that all three phenological events had advanced in parallel. Thus birds arrive earlier, start breeding earlier and leave Sweden earlier, with the breeding period staying the same in length. By teasing apart the migratory responses of different individuals, it became clear that particularly early arriving males and early departing juveniles had advanced migration. However, willow warblers migrating past a northern study site in Sweden (65°N 23°E) displayed no change in autumn departure. When migration in the two regionally separate populations were analyzed in relation to climatic variables, the results indicated that foremost a combined effect of growing season onset and the North Atlantic Oscillation influenced migratory timing, and only in individuals that had advanced migration. As growing season onset had advanced at both regions, but only elicited migratory change in southern willow warblers, it is proposed that intra-specific difference between populations prepare them differently to climate change. Willow warblers breeding at northern latitudes were also displaying absence of an otherwise common behaviour of the species: philopatry. It is suggested that the climate induced change in onset of the growing season, coupled with an increase in available territories, could have enabled a southern influx of dispersal-prone birds adopting a less philopatric breeding behaviour. Availability of territories was also studied in southern Sweden, in relation to 100 years of land use change and future climate change effects on forestry. The mass-conversion of grazed forest into coniferous sylvicultures that has occurred in Sweden 1900-2013 was shown to have negatively affected territory availability for willow warblers. The second most common bird species in Sweden, the chaffinch (Fringilla coelebs), was however shown to be largely unaffected. In a future scenario where rising temperatures will increase growth rates of trees, harvest rotation will be faster and both sylvicultures and logged areas will increase in coverage, favouring both species. Thus commonness in terms of landscape and species occurrence has altered historically and is dynamically linked. Historic perspectives were also applied to observations of spring arrival of 14 migratory bird species. A relative comparison of two data sets, collected over 140 years, revealed that short-distance migrants have changed their spring arrival more than long-distance migrants in southern Sweden. In conclusion, the results of this thesis provide insights into climate change effects on avian behaviour and ecology, document unique observations and contribute with a great spectrum of knowledge, from exact details on responses by individual birds, through long-term changes in populations to historical perspectives on shifts in entire landscapes / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.</p>