How do migratory birds find their way

Bird migration is a fascinating phenomenon. Each autumn, millions (if not billions) of birds migrate through our country to spend the winter in more southern regions. After months of absence, they then return the next spring to breed and raise their young in our country or further north.

Introduction

How do inexperienced birds, that are still to make their very first migration, know where to go? Is the route (the direction and distance) coded in their genes, or do birds learn the route by following experienced adults. Very little is known about this. Yet, finding an answer to this question is very important when we want to understand how fast migratory birds can adjust their migration routes when their environment changes. Change may mean that areas that they once used during migration or in winter, become unsuitable, but change may also be positive, when areas become more suitable because of improved protection.

Why is this important to know?

The extent to which migration routes are shaped by genetic versus environmental factors will determine how fast migratory species can adjust their migration routes to a changing world. If migration routes are primarily shaped by genes, the rate of adaptation depends on the amount of genetic variation as well as generation time. For long-lived species with long generation times, like spoonbills, natural selection of suitable 'migration-genes' through 'survival of the fittest' is a rather slow process. If young birds learn the migration routes from adult conspecifics, the rate of adaptation is expected to be relatively quick, as young birds will not follow migration routes that are no longer suitable, since the adults that followed these routes will not have survived. Besides using social information, young birds also experience food availability and weather conditions themselves, at stopover sites and during migration, which may affect their decision to continue migration or stay at a site, or to change the course of migration, which may lead to faster adaptation of migration routes.

Implications for conservation

This study will teach us about the factors that shape migration routes of young spoonbills, which will affect the capacities and constraints of spoonbills in particular, and migratory birds in general, to adjust their migration routes to changes in their environment. In addition, tracking spoonbills with transmitters, as well as with colour-rings, gives us more insight into (changes in) the key areas that are used by spoonbills throughout the annual cycle and how site use is associated with survival. This information can be used to better protect the wetlands (e.g. estuaries, tidal basins, ricefields, salt ponds) that are of key importance for spoonbills, and likely also for many other water- and shorebirds.

Aim of the project

Until now, the genetic basis of migration distance and direction has only been studied in the lab, while the importance of environmental factors has been studied in populations with unknown genetic variation in migration distance and direction. Therefore, we do not know to what extent the individual variation in migration routes that we observe in the wild is shaped by genetic variation or by variation in the environment that young birds experience during their first southward migration. Environmental variation includes the role of social information from experienced adults, food availability, geographical barriers (many birds avoid crossing large water bodies and mountain ranges) and weather conditions. This VENI project aims to contribute to closing this knowledge gap by studying in concert the role of genetic and environmental factors in shaping individual migration routes, using the Eurasian Spoonbill as a model system.

You can find a more detailed version of this VENI project here. Including more information on the methods we use to follow young spoonbills on their first southward migration.