Segregation, that animals of different sex and/or age do not spend time together all year round, is a common phenomenon. One example is that males and older individuals in migratory birds wintering further north. Migration time also affects the distribution of birds in the wintering area. European Robins that migrate in late autumn tend to winter farther east. Another factor that affects wintering areas is global warming. Today wintering birds do not migrate as far as they used to. The aim was therefore to investigate if Robins segregate during winter and if they segregate by sex, age and/or migration time and to see if the wintering area has changed since 1950. Analysis of Robins ringed at Ottenby Bird Observatory that has been recovered during winter was conducted. To obtain an indication on what influences Robins in their choice of wintering area, an analysis was done with migration year, age, and migration time (sex was excluded in this analysis) to analyse what effects migration distance. The geographical centroid was used for representing the wintering area. The difference between the group’s centroid was tested with a permutation test. The result indicated that migration time best explains the distribution of Robins in the wintering area. Robins that migrate late migrate shorter and winter further northeast, this is probably due to sequential migration of different populations. No effect of age or migration year was observed. The wintering area appears to have moved north, which indicates that Robins are affected by global warming.

Magnetic fields influence the rate and/or yield of chemical reactions that proceed via spin correlated radical pair intermediates. The field of spin chemistry centres around the study of such magnetic field effects (MFEs). This thesis is particularly concerned with the effects of the weak magnetic fields B₀ ~ 1mT relevant in the ongoing debates on the mechanism by which animals sense the geomagnetic field and on the putative health effects of environmental electromagnetic fields. Relatively few previous studies have dealt with such weak magnetic fields. This thesis presents several new theoretical tools and applies them to interpret experimental measurements. Chapter 1 surveys the development and theory of spin chemistry. Chapter 2 introduces the use of Tikhonov and Maximum Entropy Regularisation methods as a new means of analysing MARY field effect data. These are applied to recover details of the diffusive motion of reacting pyrene and N,N-dimethylaniline radicals. Chapter 3 gives a fresh derivation and appraisal of an approximate, semiclassical approach to MFEs. Monte Carlo calculations allow the elucidation of several "rules of thumb" for interpreting MFE data. Chapter 4 discusses recent optically-detected zero-field EPR measurements, adapting the gamma-COMPUTE algorithm from solid state NMR for their interpretation. Chapter 5 explores the role of RF polarisation in producing MFEs. The breakdown in weak fields of the familiar rotating frame approximation is analysed. Chapter 6 reviews current knowledge and landmark experiments in the area of animal magnetoreception. The origins of the sensitivity of European robins Erithacus rubecula to the Earth’s magnetic field are given particular attention. In Chapter 7, Schulten and Ritz’s hypothesis that avian magnetoreception is founded on a radical pair mechanism (RPM) reaction is appraised through calculations in model systems. Chapter 8 introduces quantitative methods of analysing anisotropic magnetic field effects using spherical harmonics. Chapter 9 considers recent observations that European robins may sometimes be disoriented by minuscule RF fields. These are shown to be consistent with magnetoreception via a radical pair with no (effective) magnetic nuclei in one of the radicals.