Migration is a widespread phenomenon seen across diverse taxa. Species show much variation in migration traits, including the distance covered, social interaction and degree of participation. Migration is particularly interesting in birds because of the large variation in traits and vast geographical distribution of the birds that migrate. Avian migration is thought to have played a crucial role in shaping current avian biodiversity. Most research on avian migration has focused on understanding the causes and mechanisms underlying the evolution of migration. However, the evolutionary history of migration and its evolutionary correlations with associated factors have not been studied comprehensively. Tracing the evolutionary changes in migratory behaviour and its correlations with other factors can help us understand the evolutionary processes that led to the current distribution of migration in extant birds. For understanding such patterns, one needs to reconstruct the ancestral diversification of migratory behaviour using the phylogenetic relationships among extant birds. With around 10000 extant bird species in the world, examining such relationships poses a great challenge. The existing ancestral reconstructions of migratory behaviour have remained limited to a genus or family level and have used methods that do not assess gains and losses of the migratory behaviour over time. We, thus, lack a comprehensive and complete reconstruction of migration across all bird species. Therefore, during my PhD, I gathered data on all extant bird species globally and reconstructed the ancestral trajectory of migratory behaviour on a global phylogeny. For this, I used ancestral character state reconstruction (ACSR) methods in a likelihood framework. Since the efficiency of such methods for large datasets has not been tested systematically before, as a part of my thesis research, I also examined the robustness of ACSR to sampling and dataset properties. Hence, for the first chapter of my thesis, I examined the effect of taxon sampling and character evolution rate on ancestral character state reconstruction efficiency under a likelihood framework. For doing this, I used a simulation approach. I simulated phylogenies with a wide range of taxa, starting from 16 taxa to 16000 taxa. I also examined an extensive range in character evolution rate. The results show that ancestral character state reconstruction under a likelihood framework works best for large datasets and a low character evolution rate. In the second chapter of my thesis, I focused on understanding the evolutionary trajectory of migration. I also tested the effect of uncertainties and biases due to the behavioural data classification, phylogenetic topologies and ascertainment biases on inferences. I used the migratory behavioural data gathered for 9993 bird species and used ancestral reconstruction techniques to determine how migration evolved. The results suggest that migration is an old trait that over time has declined; that is, the rate of loss of this trait is substantially higher than the rate of gain, suggesting overall loss of migration. These results support the idea of a migratory drop-off. This result is robust to data uncertainty, phylogenetic uncertainty and ascertainment biases. In the third chapter, I aimed to understand the evolution of a common form of migration, namely, migrating in groups. Since social interactions are an important part of group migration, I tested whether another key behaviour that involves social interactions, namely foraging in groups, might facilitate the evolution of group migration. I first examined the evolutionary trajectory of group migration. I then tested for an evolutionary correlation between group foraging and group migration to check if group foraging could be one of the facilitators for the evolution of group migration. I extracted data on foraging for each species and used ancestral reconstruction and Pagel's correlation method to test my hypotheses. I found that group migration has evolved early among birds, similar to migration and shows a pattern of losses over time. There is a strong evolutionary correlation between group foraging and group migration, and additionally, there is weak support to show that group foraging may precede and, therefore, facilitate group migration. By comprehensively sampling all extant bird species, using ancestral character state reconstruction methods, and incorporating diverse sources of uncertainty, my thesis contributes towards understanding the evolutionary patterns of migration in birds.