The Short-eared Owl Asio flammeus phenology in Italy
Marco Mastrorilli via Carducci 7 Boltiere (BG) 24040 Italy flammeus@libero.it
Luciano Festari via S.Antonino 12/d Capergnanica (CR) Italy

The Short-eared Owl Asio flammeus is a circumpolar Holarctic Strigiforme. In Italy, the species is regarded as regular migrant and partial wintering (Brichetti & Massa 1998), and is the poorliest investigated among nocturnal raptors (Benussi, 1997), only one paper dealing with its phenology - even if on a local scale - (Mastrorilli & Festari, in press).

Materials and methods 
The Italian museums provide researchers with a large amount of information, optimal for studying rare and elusive species, such as the Short-eared Owl. In order to carry out this work, museums have been contacted and catalogues of collections have been consulted. 295 data have been selected from 48 private and museum collections. The following data have been taken for each subject: date and place of provenance, sex, additional notes. The study gave space-time relationships enabling new and unpublished analyses of the Short-eared Owl occurrence in Italy. As in Winkler (1999), the data have been divided into ten days' spans, in order to show migratory fluxes.

Results and discussion
The data enabled us to to identify the areas most frequented by Short-eared Owls. 59.8 % of the birds considered were recorded in 5 Regions (Tuscany, Sicily, Piedmont, Lombardy and Emilia Romagna). Sicily (14.2%) and Tuscany (12.2%) gave the largest amount of data. In Lombardy, the species turned out to be more frequent in the first decades of the time span considered, showing subsequently a marked decrease; this evolution is likely to be related to the radical environmental changes which affected the Po Plane. The autumn passage (Fig. 1) concentrates between the first ten days of October and the third ten days of November (50.8% of the data), with a peak in the last ten days of October (13.3%). The long autumn migration is related to local movements of subjects wintering in Italy, whereas the Short-eared Owl moves as fast as possible to the breeding areas in spring. During winter, the Short-eared Owl occurs more rarely (11.55%) and locally, while the spring passage reaches a peak between the third ten days of March and the second ten days of April (17.3%).

Figure 1 The Short-eared Owl phenology in Italy. The data are divided in ten days' span

After April 20th, the number of Short-eared Owls decreases. This trend lasts till September. The Swiss passage migration (Winkler,1999) is linked with the Italian spring one, a peak occurs in the third ten days of April. The data collected point out that the Short-eared Owl can be regarded as regular passage migrant in Italy. During winter, the raptor looks for areas characterized by abundance of Microtidae, especially Microtus arvalis (Michelat & Giraudoux, 2000), and an estimate of the individuals occuring is difficult because of its movements, althought the species is not abundant. During the breeding season, the Short-eared Owl becomes extremely rare in Italy. Data concerning June, July and August date back to the first decades of the time span investigated, when the species used to be regarded as occasionally and locally breeding.

References
Benussi E., 1997. Avocetta 21:86
Brichetti P. Massa B. 1998. Riv. Ita.Orn. 68 (2):129-152
Mastrorilli M., Festari L., in stampa. Atti III Conv. Faunisti Veneti
Michelat D.,Giraudoux P.2000. Rev Ecol. (Terre vie) 55:77-92
Winkler R., 1999. Nos Oiseaux Supplement n°3

Acknowledgements
Special thanks to P. Brichetti and P. Galeotti for the unpublished data and for their thoughtful suggestions.

< articoli