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EURING Newsletter - Volume 2, December 1998



By Andrea Pilastro


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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