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For dem, der jævnligt forundres over trækfuglenes orienteringsevne, eller dem, der blot fascineres af trækkende fugle vil der måske være nyt at hente, når Kaper Thorup den 25. november forsvarer sin Ph.D afhandling omhandlende ”The migratory orientation programme in birds”.

Som en appetitvækker til forsvaret kan afhandlingens ”abstract” læses til sidst.

Ifølge Kasper Thorup er alle velkomne og nærmere information om tid og sted er:

Zoological Museum

Defence of Ph.D. thesis by Cand. scient. Kasper Thorup

Public defence of the submitted dissertation:

The migratory orientation programme in birds
(Thesis containing 11 original papers)

will take place at 13:00-15:00, Thursday 25 November 2004, at the Zoologisk Auditorium B, Biologisk Institut, Universitetsparken 15

Opponents are:
Professor (Chair) Jon Fjeldså, Zoological Museum, University of Copenhagen

Professor Franz Bairlein, Institut fuer Vogelforschung (Institute of Avian Research) Vogelwarte Helgoland, Germany

Professor Martin Wikelski, Department of Ecology and Evolutionary Biology, Princeton University

Supervisors are:
Professor Thomas Alerstam External Ph.D.-supervisor, Lund University

Professor Carsten Rahbek Internal Ph.D.-supervisor, Zoological Museum


Abstract

This thesis summarise my work on the migratory orientation programme in birds. This programme brings migratory naïve bird migrants from their breeding to their wintering area often thousands of kilometres apart, and in many species without guidance from experienced conspecifics. In general, birds are believed to use a so-called clock-and-compass strategy or vector navigation to reach the wintering area: the migration direction and period of time migrating are controlled by an endogenous circannual clock. The thesis presents results investigating the suitability of such a programme for explaining observed migration patterns and the interplay between internal and external factors in the birds? migration programme.

Three papers compare predictions from a model simulating the clock-and-compass strategy. The migration of raptors from Europe to Africa as observed using satellite telemetry and ring-recoveries was compared to the simulation model. Observations on honey buzzards fitted the simple model well, but ospreys showed a large initial scatter in orientation. Furthermore, the data indicated some variation between individuals in mean migration direction, which would imply a rather high proportion of birds orienting outside the normal winter range. In another paper I investigated the influence of geometric constraints on observed migration patterns. Comparing modelled data with an empirical data set on pied flycatchers Ficedula hypoleuca, removing non-terrestrial points improved the variation explained the variation in ring-recoveries. However, the qualitative fit of the model was rather poor. Several modelling studies have indicated a crucial influence of variation between individuals in migration direction. In one paper I used the simulation model to estimate the amount of variation between individuals in published cage tests and indeed found variation between individuals that will cause an unexpected large scatter in migration directions.

Four papers investigate how external factors influence the migration programme and how birds interact with these factors. The existence of an ability of compensating displacements in birds has long been controversial and is not generally accepted. A meta-analysis approach on published displacement experiments, indicate that young birds are able to detect and compensate displacements, possibly also detecting passive displacements. A paper investigating the influence of wind on migration of satellite tracked European raptors shows that juvenile birds do not compensate side-wind displacement, whereas adults to a large extent do. For the same data no evidence was found that birds selectively choose tailwinds for migration, but some tendency to avoid migration in rain was seen. Including American raptors to the data set showed that migration routes of raptors generally are in closer accordance with constant geographic courses than constant geomagnetic courses.

One paper investigates the possibility that Nearctic wheatears Oenanthe o. leucorhoa migrate a distance of more than 4,000 km direct across the Atlantic to wintering areas in West Africa. We argue that this may very well be the case. This proposed flight route is among the longest found in passerines. Another paper tests whether range size is restricted by the migration programme. Looking at non-breeding ranges, migrant species are more likely than resident species to occur in more than one wintering region, indicating that the migration programme does not constrain range size.

The last two papers test the orientation of caged migrants to reveal the influence of cue use on migrants. We had difficulties confirming the generally accepted inclination compass, but did find evidence of magnetic orientation. Furthermore, we found that young migrants apparently are able to find their specific migration direction without having access to geomagnetic cues in the pre-migratory period.