SEEN - SE European Bird Migration Network
The raw data from Emlen`s cage experiments - what can they tell us?
Przemysław Busse
Bird Migration Research Station, University of Gdańsk, Poland

Dr Gudrun Hilgerloh who worked on directional preferences of migrants in Spain some years ago, using the Emlen's cage, was so kind and supplied us with the raw data that were the basis for her paper in 1989: “Orientation of Trans-Saharan Passerine migrants in Southwestern Spain.” Auk 106, 502-503. The data contain results of experiments performed on the Spotted Flycatcher, Willow Warbler, Pied Flycatcher, Nightingale, Whitethroat, Garden Warbler and Reed Warbler. In that analysis only experiments done under clear sky conditions were included into further analysis. Originally, the data were elaborated using the classic procedure based on standard circular statistics that included calculation of the total sample azimuth that was later tested for statistical significance using the Rayleigh's test. The results were rather obscure – except some species that showed significant directionality (the Pied Flycatcher, Spotted Flycatcher, Willow Warbler) some others showed directionality statistically insignificant and one of them was called as totally disoriented (the Garden Warbler).
To compare both methods the same data were elaborated using the ORIENT programme based on a new approach of the analysis of orientation cage experiments’ data proposed by Busse and Trocińska (1999) and developed later. Results confirmed directionality of the bird species that have shown high directional tendencies in the original study but gave interesting insight into behaviour of other species and even “disoriented” Garden Warbler gave reasonable directional pattern. That means that classic method gives correct results in simple, unimodal, directionality while it cannot cope successfully with more complicated patterns. On the contrary, the new elaboration method can be successful with complicated directional patterns.
One of questions discussed nowadays within our group is whether eight sectors used in our cage give results precise enough or the number of sectors should be higher, let’s say sixteen. The answer, based on Hilgerloh's data (she has given the original data counted in 24 sectors) is surprising...
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