Falco 28 - International Wildlife Consultants Ltd.

Notes from the field in 2006
Andrew Dixon
International Wildlife Consultants (UK) Ltd, P.O. Box 19,
Carmarthen, SA33 5YL. UK
falco@falcons.co.uk
Introduction
The Environment Agency of Abu Dhabi has continued
to fund research on wild Saker Falcon populations in
2006 with projects being carried out in several regions
across the extensive Eurasian breeding range of the
species. What follows is a brief resume of the work
that has been undertaken this season on a country-bycountry
basis. Much of the data has only just been
collated and has yet to be analysed, whilst at the time
of writing radio-tracking studies are still underway.
Mongolia
Research in Mongolia is undertaken in collaboration
with Dr. Gombobaatar Sundev of the National University
of Mongolia. The university field team included Prof.
Sumiya and students from the Faculty of Biology:
Odkhuu, Zaya (both post-graduate masters students),
Tulga and Amraa (both under-graduate students). This
year research was again based in one large study area
in the central Mongolian steppe.
Work continued on the use of artificial nesting sites
by Sakers. The artificial nest platforms have now been
in place for four breeding seasons but unfortunately
the Brant’s Voles in the area were poisoned with
Bromodialone prior to the 2003 breeding season.
Consequently the small mammal population of the area
was decimated and has yet to recover. The artificial
platforms provide a substrate for ‘founder species’ such
as Upland Buzzard and Raven to build nests, which can
then be usurped by Saker Falcons. In 2006, the number
of breeding Sakers using the artificial platforms dropped
to a single pair, whilst the number of Upland Buzzards
has crashed from 29 breeding pairs to 3 over the four
years of study. In contrast the number of breeding Ravens
has remained relatively constant. Despite the fact that
the Brandt’s Vole densities have been consistently low
over the study period the level of artificial platform
occupancy suggests that there is a strong relationship
between vole density and the number of breeding
pairs of Upland Buzzards. Whether the breeding
Saker Falcons exhibit such a strong relationship is
not so clear from the small number of pairs that have
occupied the platforms over the study period; there are
other factors that could have influenced the number of
Sakers breeding at the artificial platforms such as nest
availability and the use of alternative sites on a nearby
electricity line.
Figure 1. Young Saker Falcons at a nest on an artificial
platform.
Upland Buzzards are specialist predators that feed to a
large extent on small mammals such as Brandt’s Voles,
whereas Saker Falcons can exploit a wider range of
prey species from mammals to birds and Ravens are
true generalists. In autumn 2003 we established a new
grid of 99 artificial nests that did not require a founder
nest to be built before they were suitable for occupancy
by Sakers. At these artificial nests 19 were occupied
by Upland Buzzards that built nests, 2 were occupied
by Sakers and 7 were occupied by Ravens that built
nests; the number of pairs that actually laid eggs was
7, 2 and 5 respectively. The breeding rate of Upland
Buzzards shows the classic response to food supply of a
vole specialist feeder such that only a small proportion
of birds that formed pairs and built nests actually
attempted to breed. The 99 artificial nests cover an area
of 324 km 2 and could easily accommodate more than
two breeding pairs of Saker Falcons. Clearly, some
factor other than nest site availability limited the level
of occupancy at these artificial nests and the most likely
explanation is that food supply was the limiting factor.
Across the extensive plains of the Mongolian steppe it
is likely that many, if not most, areas it is food supply
that will limit Saker Falcon breeding densities at a low
level and the provision of artificial nest sites is unlikely
to increase these densities significantly.
We still do not know how the breeding population of
Saker Falcons responds to changes in Brandt’s Vole
numbers. Intuitively we predict that an increase in
prey biomass will result in an increase in the breeding
population in our artificial nest area. Unfortunately,
the factors that regulate population explosions in the
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