Where do Palearctic migratory birds overwinter in Africa?
is a preprint version of: Walther BA & Rahbek C. 2002. Where do Palearctic
migratory birds overwinter in Africa Dansk Ornitologisk Forenings Tidsskrift
BRUNO A. WALTHER and CARSTEN RAHBEK
A new EU-funded project at the Zoological Museum, University of Copenhagen, is trying to establish a publicly accessible database on the geographical distribution of Palearctic migratory birds in Africa to guide conservation decisions.
Bird migration is one of the wonders of nature. The annual migration of millions of birds world-wide has enchanted humans for centuries. Some 200 species breeding in the Palearctic region migrate in numbers of an estimated 3000-5000 millions to their African wintering grounds (Moreau 1972, Curry-Lindahl 1981). Due to the work of scientists in conjunction with information gathered by thousands of bird-watchers and bird-ringers, we know today the principal migratory routes through Europe and the Mediterranean (Alerstam 1990, Berthold 1993). We also understand the flight mechanics (Pennycuick 1989) and the principal physiological regulators of avian migration and orientation (Gwinner 1990, Berthold 1996).
However, we still have a lot to learn
about the causes of the significant variation in migration among species,
populations, age groups and sexes, i.e. the ecological and evolutionary
bases of migration as well as the physiology of migration. The
European Science Foundation, supported by science-funding agencies in 13
different countries (including
Another area where knowledge is still
fragmentary concerns the geographical distribution of Palearctic migrants
The need to map the distribution
of Palearctic migratory birds in
So far, we know very little about
the geographical location of flyways, stop-over sites, and wintering areas,
or the seasonal movements between wintering areas. We
know even less about where, for example, the Danish populations of various
species occur in
While we have detailed knowledge
about the distribution of migratory birds in
The information that do exist on
the distribution of migratory species in
Therefore, as a supplement to these
efforts, a new 2-year EU-funded research project at the
History and rationale of the project
For the last six years, the
The aim of the project presented
here is to improve our knowledge of migratory bird distributions in
Data and distributional analysis
This project will only be feasible if a large number of colleagues are willing to share relevant data with us. We hope to accumulate two types of data, reflecting the two types of analysis we planning to perform.
Verified data. We
intend to dig up as much information from primary sources as possible,
starting with such classic references as Hall and Moreau (1970), Moreau
(1972), Zink (1975), Snow (1978), Curry-Lindahl (1981), and The birds
of Africa series (Brown et al. 1982, Urban et al. 1986, Fry et al.
1988, Keith et al. 1992, Urban et al. 1997, Fry et al. 2000). We
will also search all standard journals of African ornithology such as the
Bulletin of the African Bird Club, Ostrich, and many others. In
addition to relying on published sources, we also hope to be able to compile
a vast amount of unpublished data collected by ornithologists working in
Modelled distribution based on
verified data. The
most precise method for representing geographic distributions is by mapping
point-localities. The major drawbacks
of this approach are incomplete sampling and the enormous effort required
to compile such data (Petersen et al. 1998). To
circumvent the first problem, one can map point-localities into grid cells:
the atlas approach (Udvardy 1981). A
disadvantage of this method is that in poorly sampled areas (such as much
Since many of the Palearctic migratory
species are endangered, their conservation is of utmost concern (Salathé
1991, Crick & Jones 1992). We
intend to use the results from the above analyses to determine priority
sets of conservation areas for migratory birds within
The project will run until the summer
of 2003, by which time we intend to publish the database, making it accessible
through the internet and in scientific publications (possibly as an atlas). We
are fully aware that data sharing may imply problems, and that there exists
a widespread pressure to publish first, and therefore decided that it is
in everyone's interest clearly to state from the outset that we would like
to make data publicly accessible. We
hope this policy will not discourage possible collaborators. However,
contributions from collaborators who want us to withhold data, either indefinitely
or for a certain period of time, will only be used in our analyses, but
not made public in any form. Results
from our analyses on priority conservation areas will be disseminated in
scientific journals and among conservation agencies world-wide, but specifically
in Africa, for example through conservation workshops.
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Bruno A. Walther & Carsten
Fig. 1. Species richness of Palearctic migratory birds in sub-Saharan Africa. Red colours indicate high species richness, blue colours low species richness. Species richness is probably exaggerated for many areas because published range maps often overestimate true distributions. The figure was generated by use of the program WorldMap (Williams 1996).