Animal orientation and navigation

In 1960 I started up studies on visible, diurnal migration at Knudshoved near Nyborg (my home-town).

In 1964 I became a bird-ringer, and in 1967 - the year after the publication of Emlen & Emlen of the funnel/inkpad-method - I carried out my first funnel orientation experiments on Hesselø. In the end of the sixties I also became involved in radar-studies of bird migration.

My first geographical displacements of migrant passerines with subsequent funnel-tests were in 1968 (Ottenby/Blåvand). In the seventies I carried out various manipulations in the funnel-tests including application of bar-magnets and prisms (tilting the starry sky).

In the nineties funnel experiments under the artificial starry sky of the Tycho Brahe and Steno planetariums were carried out. In 1998 I published "Star-navigation in Pied Flycatchers Ficedula hypoleuca and Redstarts Pheonicurus phoenicurus. - Dansk Ornithologisk Forening Tidsskrift 92, 283-289".

In the following the focus will be on orientation experiments.

In course of the years I carried out many thousands of such experiments - in particular at Blåvand and on Christiansø, and I displaced migrant passerines to many parts of Denmark and several part of the world including the Canary Islands, Kenya and the Czech Republic.

In the middle of the nineties I felt a need for a sceptical attitude and repetition of several of the classical experiments and the generalizations of the results/interpretations of these.

I am sceptical about the interpretation in the classical case of vector orientation (Gwinner & Wiltschko 1968). See the document Gwinner2 (submitted).

I was sceptical too about the magnetic inclination compass, and during 1992 to 1999 more than 500 funnel experiments were carried out focusing on this issue. The results are published in Rabøl, J., S. Hansen, L. Bardtrum & K. Thorup 2002: Orientation of night-migrating passerines kept and tested in an inverted magnetic field. - Ital. J. Zool. 69, 313-320. In short, we found no evidence for a magnetic inclination compass in the sense of the Wiltschkos. On the contrary, the responses to an inversion of the magnetic field sometimes found were indicative of a change in the motivational state of the birds and not in the compass mechanism as such.

In the summer and autumn I raised and tested 23 local juvenile Whitethroats (and 8 Lesser Whitethroats) on Endelave in order to confirm the hypothesis of the Wiltschkos and co-workers that the starry sky needed setting from the magnetic compass in the pre-migratory period in order to establish a migratory course deviating from due S. The results are published by Rabøl, J. & K. Thorup 2006. Migratory direction established in inexperienced bird migrants in the absence of magnetic field references in their pre-migratory period and during testing. - Ethology Ecology & Evolution 18, 43-51. We could not confirm the hypothesis, as a migratory course deviating significantly from due S was found in tests under the starry sky and in the absence of meaningful magnetic information.

In autumns 2001 and 2002 three samples of long-distance passerine migrants were trapped on Christiansø and displaced to Endelave where the birds were caged and tested for several days/weeks within homogeneous magnetic fields where magnetic N was deflected W (4 fields) or E (another 4 fields). The main purpose of the experiments was to investigate the hypothesis of the Wiltschkos and others that the magnetic compass in the sunset/early night phase calibrated the stellar compass for the rest of the night. The results are presented in the document Magnet2 (submitted) (now published, Rabøl, J. 2010. Dansk Orn. Foren. Tidsskr.), and in short no such calibration was observed. However, the orientation of the deflected birds tested in the deflected fields on some starry nights was steered by the magnetic compass but then always in about the reverse of the normal/standard direction.

In the autumns of 2006, 2007, and again in 2011 and 2012 such conflict experiments were taken up again - this time on Christiansø and with "fresh" migrants trapped on the same or the preceding day. The results are presented in the documents ChrøDOFT and Cø2012a (submitted) and again no signs of calibration in the sunset/early night phase of the magnetic- or the sunset compass were observed.

During autumns 2004 and 2005 three samples of long- and medium-distance passerine migrants were trapped on Christiansø and displaced to Endelave. Here the birds were caged and tested within homogenous magnetic fields simulating magnetic conditions on Earth far to the North or far to the South, i.e. we simulated geographical displacements in order to reveal whether compensatory orientation in particular in the birds "displaced" S were carried out. The experiments were inspired of the Fischer et al. (2003) experiments with Tasmanian Silvereyes. The results are published in Dansk Orn. Foren. Tidsskr. 108 (2014): 232-250, and in short there was no sign of a magnetic navigation system, but the treatment seems to induce some increased sample scatter and - in the sub-sample "displaced" N - some reverse orientation.

In the document LarsB (submitted) we have summarized four series of funnel experiments.

The first two were carried out on Endelave in autumn 1999 with samples of Pied Flycatchers + Redstarts and Robins + Blackcaps, respectively. Both samples were trapped at Blåvand. We carried out conflict experiments under a starry or an "overcast" sky when magnetic N was deflected towards 250º (WSW), or 270º (W), respectively. There were indications of steering or calibration by a stellar (or sunset) compass.

The third series - migrants trapped and tested on Christiansø in a magnetic field deflected towards 60º (ENE) - already was published by Rabøl (1979: Magnetic orientation in night-migrating passerines. - Ornis Scand. 10, 69-75). On starry nights there were no difference in three samples between the orientation of the controls and the exp.s, and clearly the orientation was steered by a compass in reference to geographical N (stellar N?). On "overcast" nights the orientation in five samples out of seven was seemingly steered by a magnetic compass.

The fourth series was a sample of Pied Flycatchers trapped on Christiansø and transported to Endelave in autumn 2001. We compared the "overcast" orientation of outdoor controls (often experiencing the sunset and the starry sky) and indoor controls (never experiencing the sunset nor the starry sky). On four nights there were profound differences between the two groups - which there should not be according to the simple vector orientation hypothesis.

Some of the results in the four series are indicative of a mysterious third kind of compass (in a straightforward relation to geographical N) not yet recognized.

Finally, the document Jable (submitted) reconsiders - and "integrates" - the two concepts compass orientation and gradient navigation. In order to understand what is going on we have to leave the dichotomy in the Kramer-model of a compass (vector orientation) separated from the navigation process (gradient navigation).

In connection with the publication Thorup, K. & J. Rabøl 2007: Compensatory behaviour after displacement in migratory birds. A meta-analysis of cage experiments. – Behav Ecol Sociobiol 61: 825-841 the following documents should be consulted: a) Displacement2 (submitted) with supplementary notes to 1) the method used for demonstrating compensatory orientation following geographical displacements. 2) Notes on the concept of pseudo-navigation. 3) Notes on the influence of stationary “stellar skies”, and 4) Clockshifts. b) Forflytning (submitted) with unpublished orientation experiments following geographical displacements. c) Mouritsen (submitted) with commentaries and supplemental notes to Mouritsen, H. & O.N. Larsen 1998: Migratory young Pied Flycatchers, Ficedula hypoleuca did not compensate for geographical displacements. – J. Exp. Biol. 201: 2927-2934.

Prisme2 (submitted) is about simulated geographical displacements in birds looking through a prism on the starry sky. Significant compensations for a simulated displacement 4º towards S were found. Prisme3 (submitted) is about prism experiments performed during autumns 2011 and 2012 in order to elucidate whether the thin edge of the prism influenced the orientation in a spurious way.

In addition to the document magnav2 the document JohnPhil presents and comments on the presumed magnetic homeward orientation in the North-american Eastern Red-spotted Newt.