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Seabirds and Late Pleistocene Marine Environments in
the Northeast Atlantic and the Mediterranean
ABSTRACT
The technique of reconstructing Pleistocene environments by
finding present-day areas of sympatry for the taxa occurring in
paleofaunas has been extensively used with micromammals in
North America. For a number of reasons the method is not generally
applicable to birds; however, most of these objections do not
apply to obligate seabirds. This paper treats 31 West Palearctic late
Pleistocene faunas from 22 sites containing two or more species of
obligate seabirds. The analysis suggests that the waters around the
British Isles during the last (Eemian) interglacial were slightly
warmer than during the present interglacial, that conditions in the
western Mediterranean during much of the last glaciation were
similar to those found in the Bay of Biscay and around the British
Isles at the present time, and that conditions in the Norwegian Sea
during the warmest part of the mid-Weichselian interstadial were
similar to those found off the west coast of Spitzbergen today. The
stratigraphic position of a number of undated avifaunas containing
seabirds is discussed based on the species composition of the seabirds.
Intoduction
Reconstructing Pleistocene environments by identifying
present-day areas of sympatry for the taxa occurring in paleofaunas
is a method that has been extensively used in North
America, particularly as applied to micromammals on the
Great Plains (e.g., Graham et al., 1987). The theory and procedures
used are summarized by Graham and Semken (1987).
The same method of analysis was independently applied by Olson
and Rasmussen (1986) to the Oligocene avifauna of Fayum
in Egypt, but otherwise this technique does not seem to have
been applied to birds.
The method has been little used in Europe for several reasons.
The concept works best in large blocks of relatively homogenous
territory without dispersal barriers, where taxa can
migrate freely in response to climatic changes. This applies to
Tommy Tyrberg, Kimstadsv. 37, S-610 20 Kims tad, Sweden.
Tommy Tyrberg
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central North America but not to large parts of Europe, where
mountain ranges and marine barriers strongly affect the distribution
of terrestrial animals. Most European Pleistocene faunas
also are "disharmonious," that is, they contain taxa that are allopatric
at the present time, either because there are no good
modern analogs of the relevant Pleistocene habitats, or because
the modern ranges of taxa have been affected by humans. European
Pleistocene mammalian faunas also frequently contain a
fairly large proportion of extinct taxa, the habitat requirements
of which cannot be determined with certainty.
These and similar factors also affect avifaunas. Although the
proportion of extinct taxa is quite low in late Pleistocene European
avifaunas, and dispersal barriers affect birds less than
mammals, a large proportion of the European avifauna consists
of long-distance migrants with total annual ranges so large that
their occurrence provides very little constraint on environmental
conditions. The high vagility of birds also means that there
is always a risk that a fossil record may be from a vagrant and
is outside the species' normal range.
There is, however, one group of birds to which most of these
problems do not apply, namely, strictly marine seabirds. These
birds use a continuous habitat (the sea), without any dispersal
barriers. Although their modern range has certainly been influenced
by humans, this would be more likely to result in the
decimation or extirpation of breeding colonies than in changes
in the total annual range of species.
Late Pleistocene European avifaunas contain two extinct
species of seabirds {Puffinus holei Walker et al. (the incorrect
original spelling "holer used herein was emended to "holeae"
by Michaux et al., 1991) and Pinguinus impennis), but this
does not seriously compromise the usefulness of the sympatry
method, particularly because it is possible to reconstruct the
"present-day" range of Pinguinus impennis with fair precision
from historical data and subfossil records (Figure 1). The range
of Puffinus holei cannot be reconstructed, although it is known
to have bred on Fuerteventura, Canary Islands (Walker et al.,
1990). The composition of a local fauna of obligate seabirds
should therefore be a reasonably good indicator of the condition
of the nearshore waters off the site.