Radar studies of bird migration

Observations of bird migration with NASA radars were made at Wallops Island, Va. Simultaneous observations were made at a number of radar sites in the North Atlantic Ocean in an effort to discover what happened to those birds that were observed leaving the coast of North America headed toward Bermuda, the Caribbean and South America. Transatlantic migration, utilizing observations from a large number of radars is discussed. Detailed studies of bird movements at Wallops Island are presented

Experimental Approaches in Migration Studies

The decision of whether or not to migrate has far-reaching consequences for the lives of individuals and their families. But the very nature of this choice makes identifying the impacts of migration difficult, since it is hard to measure a credible counterfactual of what the person and their household would have been doing had migration not occurred. Migration experiments provide a clear and credible way for identifying this counterfactual, and thereby allowing causal estimation of the impacts of migration. We provide an overview and critical review of the three strands of this approach: policy experiments, natural experiments, and researcher-led field experiments. The purpose is to introduce readers to the need for this approach, give examples of where it has been applied in practice, and draw out lessons for future work in this area.Migration, Remittances, Experiment, Identification, Self-Selection

Experimental approaches in migration studies

The decision of whether or not to migrate has far-reaching consequences for the lives of individuals and their families. But the very nature of this choice makes identifying the impacts of migration difficult, since it is hard to measure a credible counterfactual of what the person and their household would have been doing had migration not occurred. Migration experiments provide a clear and credible way for identifying this counterfactual, and thereby allowing causal estimation of the impacts of migration. The authors provide an overview and critical review of the three strands of this approach: policy experiments, natural experiments, and researcher-led field experiments. The purpose is to introduce readers to the need for this approach, give examples of where it has been applied in practice, and draw out lessons for future work in this area.Population Policies,Access to Finance,Remittances,Anthropology,Debt Markets

Adaptive long-range migration promotes cooperation under tempting conditions

Migration is a fundamental trait in humans and animals. Recent studies investigated the effect of migration on the evolution of cooperation, showing that contingent migration favors cooperation in spatial structures. In those studies, only local migration to immediate neighbors was considered, while long-range migration has not been considered yet, partly because the long-range migration has been generally regarded as harmful for cooperation as it would bring the population to a well-mixed state that favors defection. Here, we studied the effects of adaptive long-range migration on the evolution of cooperation through agent-based simulations of a spatial Prisoner's Dilemma game where individuals can jump to a farther site if they are surrounded by more defectors. Our results show that adaptive long-range migration strongly promotes cooperation, especially under conditions where the temptation to defect is considerably high. These findings demonstrate the significance of adaptive long-range migration for the evolution of cooperation.Comment: 7 pages, 9 figure

Orbital Migration Models under Test

Planet-disk interaction predicts a change in the orbital elements of an embedded planet. Through linear and fully hydrodynamical studies it has been found that migration is typically directed inwards. Hence, this migration process gives natural explanation for the presence of the 'hot' planets orbiting close to the parent star, and it plays a mayor role in explaining the formation of resonant planetary systems. However, standard migration models for locally isothermal disks indicate a too rapid inward migration for small mass planets, and a large number of massive planets are found very far away from the star. Recent studies, including more complete disk physics, have opened up new paths to slow down or even reverse migration. The new findings on migration are discussed and connected to the observational properties of planetary systems.Comment: 8 pages, Review talk at IAU Symposium 276, to appear in: The Astrophysics of Planetary Systems, Eds.A.Sozzetti, M.G.Lattanzi & A.P.Bos

Impacts of planet migration models on planetary populations. Effects of saturation, cooling and stellar irradiation

Context: Several recent studies have found that planet migration in adiabatic discs differs significantly from migration in isothermal discs. Depending on the thermodynamic conditions, i.e., the effectiveness of radiative cooling, and the radial surface density profile, planets migrate inward or outward. Clearly, this will influence the semimajor axis - mass distribution of planets as predicted by population synthesis simulations. Aims: Our goal is to study the global effects of radiative cooling, viscous torque desaturation and gap opening as well as stellar irradiation on the tidal migration of a synthetic planet population. Methods: We combine results from several analytical studies and 3D hydrodynamic simulations in a new semi-analytical migration model for the application in our planet population synthesis calculations. Results: We find a good agreement of our model with torques obtained in a 3D radiative hydrodynamic simulations. We find three convergence zones in a typical disc, towards which planets migrate from the in- and outside, affecting strongly the migration behavior of low-mass planets. Interestingly, this leads to slow type II like migration behavior for low-mass planets captured in those zones even without an ad hoc migration rate reduction factor or a yet to be defined halting mechanism. This means that the new prescription of migration including non-isothermal effects makes the preciously widely used artificial migration rate reduction factor obsolete. Conclusions: Outward migration in parts of a disc makes some planets survive long enough to become massive. The convergence zones lead to a potentially observable accumulations of low-mass planets at certain semimajor axes. Our results indicate that further studies of the mass where the corotation torque saturates will be needed since its value has a major impact on the properties of planet populations.Comment: 18 pages, 15 figures. Accepted for A&

Internal Migration and Regional Population Dynamics in Europe: Switzerland Case Study

This paper reports on internal migration and regional population dynamics in Switzerland. It examines briefly the main population trends in the last century and then turns to more detailed examination of internal migration patterns and trends in three years, 1984, 1994 and 1996 and compares them. First, inter-cantonal migration is investigated in the context of the life course. On the communal level population change patterns and underlying in-, out- and net migration are examined. An attempt is made to link migration with such variables as population density, level of unemployment, prevailing language and with a functional classification of the urban system. The methodology used is the same as in a number of other studies, making the results as comparable as possible with the results of other studies of migration in European states (Rees and Kupiszewski 1999)