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Downloaded by [31.185.98.131] at 13:16 23 June 2016 Ringing & Migration (2000), 20,125-128

Some aspects of the population structure of Storm Petrels
Hydrobates pelagicus breeding on a Mediterranean island

F. LO VALVO and B. MASSA* Stazione di Inanellamento, c/o Istituto di
Entomologia agraria, V.le delle Scienze 13, 90128 Palermo, Italy

Between 1986and 1998 1,374 adults and 1,708 chicksof Storm Petrels Hydrobates
pelagicus have been ringed on Marettimo Is. (Sicily, Italy); 207 (15.1%) adults and
31 (1.8%) chicks were subsequently controlled. Only eight adults (0.6%) were
recoveredtwice in different years after ringing. Site tenacity within the study site
was observed, both of individuals ringed as adults and of those ringed as chicks,
together with high intrapopulational turnover (neither adults after more than six
years since ringing, nor individuals ringed as chicks aged more than seven years
were recovered). This helps to explain eight cases of individuals ringed as chicks and
recovered as breedingadults between one and threeyears after fledging.

The population of Storm Petrels breeding in The laying period is strongly asynchronous; first

the Mediterranean basin has been estimated arrivals to the colony occur in March and fledging

at 15-20,000 pairs, though decreasing since 1965, of last young in October. Storm Petrels lay their

due mostly to human disturbance (Massa & eggs on the ground, in crevices, burrows, and

Sultana 1991; Massa & Même in Hagemeijer & holes at the sides of the cave walls. Up to the

Blair 1997). Following recent censuses, 1970s this species was breeding inside different

Mediterranean islets holding the largest colonies caves along the western coast of Marettimo, but

are Filfla (off Malta, about 5-10,000 pairs) and in recent years these colonies were deserted, due

Marettimo (Egadi Is., off the west coast of Sicily, to human disturbance and prédation by rats; the

more than 1,000 pairs) (Massa & Catalisano only successful colony is inaccessible to terrestrial

1986a, 1986b). Some authors (e.g. Hemery & predators and does not suffer disturbance by

D'Elbée 1985;Catalisano et al.1988) consider the tourism and nautical sports during summer

Mediterranean subspecies H. pelagicus melitensis (Massa & Sultana 1991).

to be taxonomically valid; individuals are Nowadays Marettimo is included among the
characterized by greater size compared to Important Bird Areas of Europe (Grimmett &
Atlantic ones, H. pelagicus pelagicus. Jones 1989), among the Special Areas for
Consequently, the conservation of this Conservation in application of Habitats Directive
Mediterranean population is important. 92/43 and among the Nature Reserves of the

This paper presents some data from a long- Sicilian Regional Plan.

term study of Storm Petrels on the island of

Marettimo, which suggests important METHODS
parameters of the population's life-history

characteristics. Between 1986 and 1997 (with the exception of

1989 and 1995) we visited the colony at least once

STUDY SITE a year in mid July (in August in 1997), in order to
ring adults (brooding the egg or attending

The colony on Marettimo (37°58'N, 12°03'E) is recently hatched chicks) and chicks aged more

located within a wide cave accessible only from than 15 days. We were not able to ring both

the sea, about 250m long and consisting of four partners of each pair, since only one individual

sectors at different levels; the first of them (A) is was present at the nest. Individuals ringed in
a wide room, the second one is subdivided in one of the four sectors cited above were
two rather parallel corridors (B and C), and the recorded on a map of the cave; since we did not
third (D) is a narrow terrace about 15m long. ring within the entire cave, we know the precise

"E-mail: zoolappl@unipa.it

© 2000 British Trust for Ornithology