EURING Newsletter - Volume 2, December
THE EURING SWALLOW PROJECT IN ITALY
By Andrea Pilastro
DIPARTIMENTO DI BIOLOGIA, UNIVERSITÀ DI PADOVA, VIA TRIESTE,
75, I-35121 PADOVA. ITALY.
Since 1994, with the launch of the national Swallow Project, and
later of the EURING Swallow Project, a dramatic increase has been
recorded in the number of ringed Swallows in Italy (Fig. 1). During
the last years, a much higher number of roosts have been studied
over the entire peninsula, allowing to analyse various aspects of
Swallow moult and fattening strategy.
Two papers have been recently published on this subject. A first
one (Pilastro A. & Magnani A. 1997. Weather conditions and fat
accumulation dynamics in pre-migratory roosting Barn Swallows Hirundo
rustica. J. Avian Bio. 28: 338-344) dealt with the
effect of weather on the fattening rate in roosting swallows at
a site in northern Italy. The data used in this study have been
collected, over 5 consecutive years, from July until the beginning
of September, by Ariele Magnani, an amateur ringer, with the help
of numerous field collaborators.
The results of the correlative analysis between weather conditions
and fat accumulation showed that there are two distinct phases in
the fattening strategy during the post-reproductive season: during
the first phase, swallows probably hang around the roost, undergo
a partial moult (body feathers and less frequently 1-3 inner primary
feathers) and maintain a small amount of fat reserves which seems
to function as an emergence energetic reserve in case of prolonged
bad weather conditions. In fact, when weather conditions start to
deteriorate, swallows react by increasing their fat reserves.
From the end of August onwards, once completed the moult, swallows
start to accumulate fat apparently at their maximum rate. In this
phase, when weather conditions are sub-optimal for feeding, fattening
rate decreases. Another interesting result of this study is that
the fat reserves accumulated by swallows in Italy are compatible
with a direct crossing of the Mediterranean and Sahara desert towards
the wintering areas of sub-Saharan Africa. Maximum body mass values
observed were around 30 g, corresponding to a body mass increase
of about 70% of the estimated lean body mass, a figure similar to
what is observed among other long-distance migrant passerine (e.g.
Garden Warbler) in the same area.
In a second paper recently appeared on Ringing & Migration
(Pilastro A., Micheloni P. & Spina F. 1998. Geographical variation
in pre-migratory conditions of Barn Swallows Hirundo rustica
in Italy. Ringing & Migration 19: 67-74), a wide geographical
survey allowed to investigate swallow fattening strategies along
the Italian Peninsula. Within a larger Italian project on the species,
contemporary ringing activities during three focal days (September
6-8, 1996, named ‘The 3 days of the Swallow’) have been
carried on at 24 roosts scattered from Northern to Southern Italy
and the main islands.
A total of 8,771 Barn Swallows were ringed, out of which 81.8%
were juveniles and 18.2% adults. Among the latter, 28.3% were classified
as males and 71.7% as females. Most birds had already completed
their body moult; a higher fraction of birds still in active moult
was found among adults. The frequency of adults with active primary
moult was intermediate between the values reported for Northern-Central
and Southern Europe respectively.
Mean body mass values were higher in adults, which were also fatter
than juveniles. Both in adults and juveniles, fat score was significantly
lower in moulting birds. A high variability in mean body mass values
and frequency of fat birds was found between roosts. The mean body
mass of the 25% heavier birds corresponded to 24.1% and 30.5% of
the lean body mass for juveniles and adults respectively. The situation
observed in early September does not indicate a clear north-south
gradient in the average physical conditions of pre-migratory Barn
Swallows, suggesting the use of roosts as sites of concentration
of birds staging and fattening in the surrounding areas. The observed
latitudinal gradient in the frequency of adults at the roosts might
be related to earlier southward movements of more northern birds.
The importance of reed-bed conservation is further pointed out
by their role as swallow roost habitats, as derived from these first
results of the Swallow project. Roost sites are in fact used not
as simple stopover sites, but play a vital role during the whole
pre-migratory fattening phase, which is crucial for swallows to
be able to safely cross the Mediterranean and Sahara while heading
towards their African winter quarters.
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