Page 4 - Corso_Cardelli _2004

Migration of Pallid Harrier across the central Mediterranean

Fig. 3. The age distribution of Pallid Harriers Circus Fig. 4. The proportion of males and females
macrourus recorded in spring (April and May), Strait among adult (third-calendar-year or older)
of Messina, southern Italy, 1997-2000 (n=203). Note Pallid Harriers Circus macrourus recorded in spring
that % 3CY refers to males only as 3CY females (April and May), Strait of Messina, southern Italy,
could not be safely distinguished from older females 1997-2001 (n=160).
and so have been included in the % adult total.

were identified positively, but also to the more extreme difficulty of identification, the separa-
thorough and systematic survey protocol in tion of 3CY females from older females was not
later years. Indeed, an increase in numbers has attempted. In terms of the sex ratio, 37.5% of
also been shown by other migrating raptors the adults were males and 62.5% were females.
(Corso 2001). Nonetheless, looking simply at Juveniles were sometimes sexed using iris
the period 1996-2001, when survey effort and colour (exceptionally!) or by plumage charac-
identification expertise would have been fairly teristics/wing shape, but this is not considered
constant, a clear increase in numbers is still further here. A detailed breakdown of the
evident (fig. 2), suggesting that our data reflect age/sex composition in each year is given in
a genuine rise in numbers. table 1.
Detailed records of the age and sex composi- The timing of migration of different age/sex
tion of migrating Pallid Harriers were made classes in 1997-2000 is shown in fig. 5. This
during 1997-2001 (figs. 3 & 4; table 1). In this shows clearly that, in spring, males migrate
period, we observed 335 birds, of which 60 earlier than females, while adults tend to
(17.9%) were adult males, 100 (29.9%) were migrate earlier than 2CY birds. Similar findings
adult females and 175 (52.2%) were second-cal- have been reported for other harriers (Gustin &
endar-year (2CY) birds. Of the 60 adult males, Pizzari 1998) and raptors (e.g. Shirihai &
only seven (11.7%) were identified as being in Christie 1992, Yosef 1996). There is also some
their third-calendar-year (3CY). Because of the variation in timing between years. For example,

Table 1. Migrant Pallid Harriers Circus macrourus recorded in spring (April and May), Strait of Messina, southern
Italy: percentage of males, females and second-calendar-year birds in each year, 1997-2001.
Male Female 2CY n
1997 52 20 28 25
1998 7 31 62 58
1999 13 41 46 37
2000 35 34 31 83
2001 7 26 67 132

British Birds 97 • May 2004 • 238-246 241