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JUNE 2010 WESTERN MARSH HARRIER MIGRATION 139
Panuccio et al. 2005b). This latitudinal segregation of crossing was higher during tail and lateral winds if the
sexes in some populations of Western Marsh Harriers latter provided at least partial tail-wind support
may be explained by Bergmann’s rule, which predicts (Meyer et al. 2000). Meyer and colleagues suggested
that larger individuals are better adapted to survive in that this strategy resulted in shorter crossing times
colder climates. Other hypotheses, based on social and thus lowered risk of unpredictable weather
dominance theory, are less supported by available da- changes. However, the probability of changing weath-
ta, including similar proportions of juveniles and er (wind) conditions increases with the length of the
adults in Italy (Panuccio et al. 2005b). crossing (see also Meyer et al. 2003). In the case of the
central Mediterranean, the flight strategy of Western
Water Crossings During Migration. The limited Marsh Harriers, moving hundreds of kilometers over
data available from satellite telemetry suggest that water in weak or no wind and using islands as stop-
Western Marsh Harriers can make nonstop cross- over sites (Panuccio et al. 2002, Panuccio and Agos-
ings over water of 300–550 km or more. For exam- tini 2010), might be seen as a conservative strategy.
ple, one adult male summering in the Ukraine and
studied with satellite telemetry crossed the central During autumn migration, large numbers of
Mediterranean Sea either via Corsica and Sardinia Western Marsh Harriers are seen each season leav-
or directly over water (R. Strandberg et al. 2008; ing the coasts of Tuscany (central Italy) heading
Fig. 1). Although locating birds using satellite te- southwest apparently en route to Corsica via the
lemetry produces large gaps in information in the islands of Elba and Pianosa (Fig. 1; Paesani and Po-
area around Italy because of an unknown interfer- liti 2002, Vanni and Paesani 2007). In contrast,
ence (R. Strandberg pers. comm.), it was known Western Marsh Harriers leaving central Italy from
that the male passed through central Italy and the Circeo Promontory (Fig. 1; Latium), south of
crossed the Tyrrhenian Sea from a starting point Tuscany, are expected to cross the sea en route to
north of Rome, continuing either to the east of or Africa, flying about 500 km nonstop over water be-
across the island of Sardinia, reaching northern Tu- cause they face the open sea when heading south-
nisia, and heading southwest through north Africa west (Agostini et al. 2001, 2003, Panuccio and Agos-
toward the Sahara Desert. Thus, this male either tini 2010). If the simplified plotted flyway reported
made a nonstop powered flight over water of ap- by Strandberg et al. (2008) is correct, the male from
proximately 550 km, avoiding the passage through the Ukraine expended a large amount of energy
Corsica and Sardinia, or traveled via the islands, and maximized its risks relative to the long sea cross-
likely with at least one night of rest. When crossing ing. However, based on the timing of the sea pas-
the central Mediterranean during both spring and sage, it appears that this bird might have used the
autumn, Western Marsh Harriers use several small Corsica-Sardinia route to Tunisia.
islands to enable soaring flight or as stopover sites
for roosting (Sammut 2005, Panuccio and Agostini In the western Mediterranean, birds leaving
2006) and/or hunting (Thake 1983, Frost 1994, Re- northeastern Spain apparently passed via the Balea-
bassa 1995, Agostini and Logozzo 1998, Jonze´n and ric Islands. These birds likely make ,300 km of
Pettersson 1999, Agostini et al. 2003, Panuccio et al. nonstop, powered flight over water during the sec-
2004, Sammut and Bonavia 2004, Panuccio and ond stage of that crossing, between the Balearic Is-
Agostini 2006). Western Marsh Harriers are able lands and northern Africa.
to cross water bodies during the night and tend to
cross the large body of water between western Sicily SPRING MIGRATION
and central Italy (.300 km; Fig. 1) during weak
rather than strong winds, without regard to wind Migration Route. There are fewer data on spring
direction, or during windless periods (Panuccio et migration than on autumn migration. However, avail-
al. 2002, Panuccio and Agostini 2010). However, a able visual observation data indicate that Western
study made simultaneously with radar and direct Marsh Harriers cross the Mediterranean on a broad
observations during autumn migration on the front during spring migration (Gensbol 1992, Handri-
southern coast of Spain (Fig. 1) showed that the nos and Akriotis 1997, Gustin and Pizzari 1998, Zalles
number of harriers undertaking a shorter sea cross- and Bildstein 2000, Agostini 2001, Ferguson-Lees and
ing (approx. 150 km) was similar for all wind direc- Christie 2001, Panuccio et al. 2002, Pandolfi and So-
tions during periods of weak winds. Conversely, dur- net 2003), as they do during autumn migration.
ing strong winds (.15 km/h) the number of birds
Migration of Different Sex and Age Classes. Stud-
ies in the central Mediterranean (Gustin and Pizzari
1998, Pandolfi and Sonet 2003, Panuccio et al.
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