Long-term surveillance of bird migration on Col de Bretolet

Each autumn thousands of migrants cross the Col de Bretolet, a pass located in the Swiss Alps. In the year 1958 a ringing program was started to monitor the migration of birds across Switzerland on a long-term basis.


The aims of the ringing program at Col de Bretolet are:

  • long-term surveillance of autumn migration in the Swiss Alps
  • investigation of the energy metabolism of migrants
  • investigation of changes in the seasonal migration patterns in relation to global climate change
  • documentation of invasions of tits, jays and finches
  • comparison with other ringing sites within and outside Switzerland
  • studies of the moult of passerines
  • education of ringers


Each autumn, between the beginning of August and the end of October, migrating small passerines are caught, ringed, measured and afterwards released. Of each bird, ring number, species, sex, age, date and time of capture, moult, fat score, muscle score, wing length and body mass is recorded. During foggy nights the birds are attracted with lights.


Col de Bretolet offers the unique possibility to catch birds out of their nocturnal flight in high numbers. Ringing data from 1958 onwards allow to analyse migration patterns and possible changes in these patterns over the last decades. Moreover, on Col de Bretolet it is possible to record species, which are rarely reported from other ringing sites.

At Col de Bretolet not only birds are caught. Bats are a common "by-catch". The investigation of insect migration has long attracted researchers from various countries. Millions of moths and hoverflies (Syrphidae) migrate across Col de Bretolet.

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