Repeatability and heritability of migratory traits in Alpine swifts

 

How flexibly can Alpine swifts (Tachymarptis melba) adjust their migration behaviour to a changing environment?

Migration is one of the most spectacular phenotypes in vertebrate biology — and one of the most sensitive to global change. To predict how migratory birds will cope with climate change, we need to know how flexibly individuals can adjust their migration from year to year (repeatability), and how much of the among-individual variation has a genetic basis on which selection can act (heritability). For most wild species, both quantities remain very poorly known.

This project takes advantage of the long-term Alpine swift study system at the Swiss Ornithological Institute, where adults from several Swiss colonies (Solothurn, Biel, Baden, Luzern) have been equipped with light-level geolocators and miniaturised GPS tags since the early 2010s. Combined with the long-term, multigenerational pedigree available in these colonies, this gives us a rare opportunity to study both individual flexibility and the genetic architecture of migration in a fully wild, free-living population.

 

Background

Alpine swifts are extreme aerial migrants, spending up to 200 consecutive days on the wing between the breeding grounds in Europe and the non-breeding grounds in sub-Saharan Africa. They rely almost exclusively on aerial insects and are therefore strongly dependent on weather conditions — both at the breeding sites and along the migration route — for food and for safe flight. As the climate continues to warm and weather patterns become more variable, key migration decisions (when to leave, where to spend the non-breeding season, when to come back) are likely to become increasingly costly to get wrong.

Studying migration in long-lived species like Alpine swifts is particularly powerful because the same individuals can be tracked across many consecutive years and across major events of their reproductive life. This makes it possible to ask:

  • How consistent is an individual’s migration from one year to the next?
  • Does this consistency depend on the trait considered (e.g. timing of departure vs. choice of non-breeding location)?
  • How much of the variation among individuals is heritable, and therefore amenable to evolutionary change?

 

Aim

The project pursues two complementary main outputs:

  1. Repeatability of migration traits, using repeated tracks of the same individuals across years, to quantify within-individual consistency in migration timing, route choice and non-breeding distribution.

  2. Heritability of migration traits, using a Bayesian quantitative-genetic (“animal model”) framework on a multigenerational pedigree, to estimate the additive genetic variance underlying individual differences and assess the evolutionary potential of migration phenotypes.

 

Approach

Data. The project combines:

  • Long-term tracking data from light-level geolocators deployed on breeding adults across several Swiss Alpine swift colonies.
  • A long-term social pedigree for the same colonies, validated by very low rates of extrapair paternity, that enables formal quantitative-genetic inference.

 

Expected outcomes and impact

This work will deliver one of the first integrated estimates of repeatability and heritability of migration traits in a long-lived, free-living aerial migrant. By quantifying both individual flexibility and the genetic potential for change, it will help us understand how much of the response to climate change can come from plastic adjustments within individuals, and how much from microevolutionary change across generations — a question with direct relevance for forecasting migratory bird populations under global change.

 

Collaborators

  • Dr. Pierre Bize, Swiss Ornithological Institute, Switzerland
  • Dr. Christoph Meier