Orientation experiments with displaced juvenile barn swallows (Hirundo rustica) during autumn migratory season

Abstract

In a previous paper, we reported that juvenile barn swallows (Hirundo rustica)trapped during the autumn migratory season and tested in modified Emlen funnels under overcast conditions can use magnetic information for compass orientation, although they did not orient toward the expected migratory direction. To further investigate this behaviour, in the present paper, we report the results of two series of displacement experiments performed on ju- venile barn swallows belonging to two different roost sites (Massaciuccoli Lake (ML) and Terzo Cavone (TC)) and tested using the same protocol as that previously adopted. On the whole, the outcome of the ML and TC experiments was quite different with respect to (a) the degree of bird activity within the funnel (substantially lower for TC) and (b) the effect of the experimental displacement on the directional preferences of the tested subjects (not detectable in TC, while evident in ML swallows). Taken together, these results suggest that migrating swallows could react differently to the experimental tests depending on the roost site where they were caught. Indeed, TC swallows, trapped in southern Italy, close to the seacoast, and characterized by fairly large amounts of fat stores, mainly broke off their migratory activity or reoriented their directional prefer- ences toward inland sites, possibly in search of more prof- itable habitats. On the other hand, ML swallows, trapped about 660 km to the north and characterized by lower amounts offat stores, apparently tried to compensate for the experimental displacement.