SEEN - SE European Bird Migration Network
Orientation behaviour of long-distance migrants - sun and researcher influences
Mihaela Ilieva
Institute of Zoology, blvd. Tzar Osvoboditel 1, Sofia 1000, Bulgaria

In 2001, 2002 and 2003 long-distance migrants were tested at Kalimok station (NE Bulgaria) in two type orientation cages – Busse cages in the daytime and Emlen funnels in the night. Possible influences of the sun and the researcher are noticed, mainly in the daytime experiments.
Influence of the researcher on the directional preferences of tested birds is shown for two species – Acrocephalus arundinaceus and A. schoenobaenus in daytime experiments during two autumn seasons. The activity of the birds in directions opposite to the researcher’s side increases in all cases. Although main directions of the two species for the different years are almost opposite, reversed pictures show nearly equal main directions, confirmed also from the night experiments. Hence, reversing of directions in cases of researcher’s disturbance is useful method for comparison of different distributions.
Influence of the sun in experiments was also registered in some cases. Distributions of directional preferences of Phylloscopus trochilus in daytime and night experiments during the autumn are presented. In all cases when sunlight influence is possible, similar NNW directed “sun” vectors appear. We suppose that birds prefer this direction in two cases. First, when they are attracted from sun reflection on the screen of Busse`s cages in daytime tests and secondly in early night tests with Emlen funnels when sunlight from the sunset is still visible on the sky. Reversing all data in these cases might give a non-existing direction or to extend a weak one.
Detailed analysis of the orientation experiments reveals impact of different environmental factors on the results. Preliminary consideration of possible impact factors must precede reversing the results. Only after this preliminary stage, reversing pictures are useful tool for comparison of different cases. 
Created by Pronetix 2006