1. Orientation cage tests: application in bird migration studies
Orientation cage tests: application in bird migration studies
Agnieszka Ożarowska, Krzysztof Muś
Bird Migration Research Station
University of Gdańsk

2. Orientation cage tests Migratory restlessness (Zugunruhe)
(night; video rec. in infrared light (Berthold et al. 2000))

3. „Cage tests (...) allow the study of population-specific differentiation with respect to migratory directions.
This method may not only allow us to obtain reliable directional estimates more quickly than ringing, but also yield results not biased by the uneven recovery
probabilities that affect ringing data so strongly.” Helbig (1992)
„While in theory directional information could be obtained from ring recoveries, in practice many years of data are needed, and geographical bias in ring reporting can distort the picture” Newton (2008)

4. „Cage tests (...) allow the study of population-specific differentiation with respect to migratory directions.
This method may not only allow us to obtain reliable directional estimates more quickly than ringing, but also yield results not biased by the uneven recovery
probabilities that affect ringing data so strongly.” Helbig (1992)
„While in theory directional information could be obtained from ring recoveries, in practice many years of data are needed, and geographical bias in ring reporting can distort the picture” Newton (2008)

5. „Cage tests (...) allow the study of population-specific differentiation with respect to migratory directions.
This method may not only allow us to obtain reliable directional estimates more quickly than ringing, but also yield results not biased by the uneven recovery
probabilities that affect ringing data so strongly.” Helbig (1992)
„While in theory directional information could be obtained from ring recoveries, in practice many years of data are needed, and geographical bias in ring reporting can distort the picture” Newton (2008)

6. Factors causing uneven recovery probabilities result in spatial and temporal variation in recovery rate of ringed individuals.
These factors are, e.g.:
human population density,
education of the society/public awareness,
political situation in a region,
ringers/birdwatchers activity,
several factors influencing birds’ mortality, esp. hunting.
(Payevsky 1973, Busse and Kania 1977, Perdeck 1977, Busse 1981,
Kania and Busse 1987)

7. Very low recovery rate in small Passerines is a very serious problem and limitation in analyses.
For example:
less than recoveries on Robins
were reported compared to over individuals
ringed at the Operation Baltic stations in ,
i.e. recovery rate of Robins was 0.46% (Busse 2000).

8. Bird migration studies
Basic method: ringing
Complementary methods, e.g.:
radar,
direct observations of migrating
birds,
stable isotopes/trace elements,
- molecular studies,
- parasite studies,
telemetry,
- orientation cage tests.
(Berthold et al. 1992)

9. Field method

10. Busse orientation cage
Screen
Cage

11. Migrants tested in two types of orientation cages
(dot - mean angle)
Day
Night
(α – mean angle, r – mean vector length, s – mean angular deviation; ns – difference not significant)
(Ożarowska and Yosef 2004)

12. Percentage of tested individuals showing Ten most numerous species
uni- and multimodal behaviour
(0, 1, 2, 3, 4 – number of directions shown by tested birds)
Ten most numerous species
were analysed
N =
N =

13. Multimodal behaviour of tested birds - calculation procedures
„The experimentally derived mean orientation or mean vector, often described as „the” population migration direction, calculated from the aggregate of (...) different individual directions, is in many cases by no means visually obvious from the wide scatter of points shown in the figures.” Phillips (2000)
„(...) when samples of migrants are caught and tested at particular localities, two or more migration axes frequently emerge, as birds migrating through the same locality but from different areas take somewhat different directions (Busse 2000). This is another reason for using a statistical method that can pick out the different directional preferences, rather than calculate a single amalgamated mean from all birds tested.” Newton (2008)

14. Orientation data evaluation
Nowadays, data evaluation procedure is based on the Bayesian statistics. A maximum posterior probability among tested models (isotropic, unimodal, bimodal, 3-, 4- modal etc.) is a criterion for model selection.
More details on a poster
Final result of the calculation procedure applied:
an individual showing three directions

15. over 54 000 Number of tests Orientation data set
on more than 100 species of nocturnal migrants

16. ? Directional preferences of the Lesser Whitethroat
and ringing/recovery locations of
individuals controlled/ringed at Eilat
49%
35%
lack of recoveries! ?
EILAT (Israel), spring migration 1999, Nt = 195

17. The Blackcap migration flyways (Mokwa 2004; ringing recovery analysis)

18. The Blackcap autumn migration pattern in Central/Eastern Europe
– orientation test results analysis

19. The Blackcap autumn migration pattern in Central/Eastern Europe
– orientation test results analysis

20. The Blackcap migration in eastern part of the Mediterranean region
Autumn
Spring

21. migration system in a given region,
Testing the directional preferences of nocturnal migrants offers a great potential for study of:
migration system in a given region,
population differentiation of migratory directions,
species/population-specific migration strategy.

22. Special thanks to the teams of the SEEN member stations
Thank You