Tringa glareola - Gruppo Inanellamento Limicoli (GIL, Napoli)

Migration pattern and weight changes of Wood Sandpiper Tringa glareola in a stopover site in southern Italy

Sergio Scebba & Giancarlo Moschetti

from: Ringing and Migration (1996) 17: 101-104.

SUMMARY

408 Wood Sandpipers were examined at a stopover site in the central Mediterranean near the southern Italian coast during the pre- and postbreeding migration. Some details about the timing of passage of adults and young birds are given. The weight changes are examined; birds arriving in the spring had very low mean body mass and could well have overflown non-stop across the Mediterranean as well as perhaps the whole or part of the Sahara. Summer migrating birds use the artificial ponds both as a resting area and as a refuelling site to accumulate fat.

INTRODUCTION

The Wood Sandpiper Tringa glareola is a common migrant in Campania (south Italy) but its migration dynamics and weight changes are undescribed. Little is known about the utilization of food resources and the changes in body mass during periods at stopover sites.
Birds ringed within breeding range in Fenno-Scandia moved predominantly in direction S-SSW; in fact, most of these were recovered in France and Italy (Cramp & Simmons 1983). Scebba (1993) reported that 8 birds ringed mostly in Scandinavia were recovered during post-breeding migration in the Volturno plain (south Italy) from 6 to 55 days after ringing. Usually in this area in spring daily aggregations of up to 100-200 are observed together. Similar numbers have been reported from Sicily (Iapichino & Massa 1989).
In this paper we describe the studies that have been carried out on migrant Wood Sandpipers and their mass changes in a stopover area in southern Italy.

STUDY SITE & METHODS

The work was carried out at four sites in the Volturno plain (Caserta). One was situated near the mouth of the river Volturno, another near the inflow of a channel of waste water; the other two were small artificial ponds used as decoys for hunting ducks. Birds were ringed in the spring of 1992 and 1993 and in the summer of 1991 and 1992; in total, 408 Wood Sandpipers were ringed during pre- and post- breeding migration (241 and 167 respectively). Mist-nets and tape lures were used at night at the roosting sites, which coincided with the feeding sites. Body mass was measured with a 100 g Pesola spring balance to the nearest 0,1 g. On capture, the birds were put in cages, ringed and measured within one hour; therefore, corrections on body mass values were not made. Birds were aged following the characters given by Prater et al. (1977) (categories: juveniles and adults, i.e. older than first-year birds).
Trapping was carried out twice-weekly during the first two years (extremes: 8 April-13 May and 10 July-3 September), while in spring 1993, with the collaboration of the Wader Study Group and the "Roccolo Ganda" Bird Observatory ringing was continuous from 1 April to 20 May.
The samples from the three years were pooled and fitted into standard 5-day periods (pentades) (Berthold 1973).

RESULTS AND DISCUSSION
Migration patterns

In spring, birds were caught between 8 April to 13 May (pentades 20-27) with a peak between 21-30 April, periods in which 56% of trapping occurred (Fig. 1a). Post-breeding migration occured from July 10 to early September (pentades 39-50) (Fig. 1b); in this season, unlike in spring, there was no migration peak and the period of migration exceeded that during spring.

Fig. 1. Trapping patterns per pentades of Wood Sandpipers on the Volturno plain during (a) pre-breeding migration (spring 1992 and 1993, pentades 20= 6-10 April; 27= 11-15 May) and (b) during post-breeding migration (summer 1991 and 1992, pentades 39= 10-14 July; 50= 03-07 September.

Age class distribution in summer showed that adult movements begin early July, while juvenile movements begin early August (Fig. 2). Similar patterns were reported by Cramp & Simmons (1983).

Fig. 2. Age class distribution of Wood Sandpipers during post-breeding migration. Pentades 39= 10-14 July; 50= 03-07 September.

Analysis of body mass

The variation in body mass per pentades is shown in Figs. 3a (spring) and 3b (summer). Mean body mass of birds ringed in spring was 57.2 g (SD = 7.2, n=240), ranging between 42.5 g and 81.0 g. In summer the mean was 70.3 g (SD = 10.6, n=166, min 46.0 g, max 94.0 g). The difference between the means is statistically significant (t-test=13.1 P<0.001).

Fig. 3. Variation in body mass per pentades of Wood Sandpipers trapped during (a) spring 1992 and 1993, pentades 20= 6-10 April; 27= 11-15 May and (b) during summer 1991 and 1992, pentades 39= 10-14 July; 50= 03-07 September (b).

In spring, the frequency distribution of body mass showed a bimodal distribution with a peak at 50 g and another one at 60 g (Fig. 4a). Even in summer the distribution was bimodal with a peak at 64 g and another one at 76 g (Fig. 4b). These patterns could be due to two age classes. In fact, in summer adult body mass was higher than in juveniles: mean adult body mass was 72.5 g (SD = 9.3, n=98), vs. the juvenile mean of 66.9 g (SD = 11.5, n=68). The difference between the means is statistically significant (t-test=3.39 P<0.01). Apart from age effects, the bimodal distribution may also refer to different populations passing the area.

Body mass variation of retrapped birds
Only 6 birds out of 408 which were ringed between 1991-1993 were caught and weighed more than once within the same period; there were 7 recapture occasions (Fig. 5). No recaptures were made during spring. There was a substantial change in body mass: four birds recovered in summer after 6-16 days showed a mean daily body mass gain of 1.4 g, while the others 2 birds showed a little decrease, albeit of 0.2-0.3 g, after 13-23 days.
On the basis of the days which elapsed between ringing and recapture during post-breeding migration, a mean stopover duration of 12.3 days was ascertained.

CONCLUSION
An examination of body mass of Wood Sandpipers at two different Mediterranean stopover sites during their pre-breeding migration shows a mean weight of 62.6 g (SD = 7.1, n=77) in April and 61.6 g (SD = 6.4, n=180) in May in Camargue (Glutz et al. 1977) and a mean weight of 58.1 g (SD = 6.0, n=178, min 45.0, max 76.0) in South-eastern Greece (Akriotis 1991). In this study the samples caught in Campania showed the lowest mean: 57.2 g (SD = 7.2, n=240, min 42.5 g, max 81.0 g); this value is statistically different from those of Camargue (t-test=5.8 P<0.01 and t-test=6.6 P<0.01, respectively), but is statistically not significant if compared with that of Greece (t-test=1.4 P>0.1). Thus, birds arriving in the Volturno plain in the spring could well have overflown non-stop across the Mediterranean as well as perhaps the whole or part of the Sahara, reaching the stopover sites with low fat reserves.
In this season the level of brackish water in the artificial ponds was sufficiently constant; it allowed the presence of numerous Crustacea (ex. Gammarus sp.) where the water was clear and the concentration of aquatic insect larvae (Chironomidae) in innumerable puddles. In fact, frequently in spring observations were made, also during day-time, large flocks of Wood Sandpiper feeding actively in small ponds (about 2 ha).
During summer migration, Glutz et al. (1977) reported a mean weight of 65.1 g (SD = 8.8, n=87) in July and 63.6 g (SD = 8.8, n=193) in August for adults and a mean weight of 60.3 g (SD = 7.2, n=31) in Juli and 61.2 g (SD = 7.8, n=898) in August for juveniles caught in Camargue. In this season in the Volturno plain the mean weight were 72.5 g (SD = 9.3, n=98) for adults and 66.9 g (SD = 11.5, n=68) for juveniles.
In summer, mean body mass of juveniles and adults was significantly different and individuals weighed more than once during the same refuelling stop have show a significant mass increase. Our results indicated that a considerable number of Wood Sandpipers stop over on the Volturno plain during their northward spring migration and that summer migrating birds use the artificial ponds both as a resting area and as a refuelling site to accumulate fat.

ACKNOWLEDGEMENTS
The following people helped with field work: Rodney West, Paul Newton, Michael Wright, John Glazebrook and Alan Miller of Wader Study Group, Phil Ireland of Wash Wader Ringing Group, Zsolt Karcza of Hungarian Ornithological Society, Andrea Vitolo, Marta Lancini, Rosanna Esposito and Stefano Laurenti of Gruppo Inanellamento Limicoli (Naples), Roy Hughes and Jan Spence. We would like to thank Gabor Lövei for reading and criticising the manuscript and Mark Walters for the stylistic amendments. We are pleased to acknowledge Daniele Anesa and "Roccolo Ganda" Bird Observatory (Aviatico-Bergamo) which provided financial assistance.

REFERENCES
Akriotis, T. (1991) Weight changes in the Wood Sandpiper Tringa glareola in south-eastern Greece during the spring migration. Ringing and Migration, 12, 61-66.
Berthold, P. (1973) Proposals for the standardization of the presentation of annual events, especially of migrating data. Auspicium, 5 (suppl.): 49-59.
Cramp, S. & Simmons, K.E.L. (1983) The Handbook of the Birds of the Western Palearctic. Vol. III, Oxford.
Glutz von Blotzheim, U.N., Bauer, K.M. & Bezzel, E. (1977) Handbuch der Voegel Mitteleuropas. Vol. 7. Akademische. Verlagsgellsschaft, Wiesbaden.
Iapichino, C. & Massa, B. (1989) The Birds of Sicily. British Ornithologist's Union.
Prater, A.J., Marchant, J.H. & Vuorinen, J. (1977) Guide to identification and ageing of Holarctic waders. B.T.O. Guide 17, Tring.
Scebba, S. (1993) Gli Uccelli della Campania. Ed. Esselibri, Napoli.

Paper n.18 of Gruppo Inanellamento Limicoli (G.I.L.), Naples-Italy.