European cranes shift their wintering area northwards:
new evidences from radiotagged birds

Juan C. Alonso,
Museo Nacional de Ciencias Naturales, CSIC, José Gutiérrez Abascal 2, 28006 Madrid, Spain
Javier A. Alonso, José H. Martínez,
Facultad de Biología, Universidad Complutense, 28040 Madrid, Spain
Serge Avignon
Office National de la Chasse, Réserve Nationale de Chasse et de Faune Sauvage d’Arjuzanx, 40110 Morcenx, France
and Pierre Petit
7, av. de Genève, F-33600 Pessac, France


( Published in Proceedings IV European Crane Worshop, Verdun, France, November 2000)  

Abstract.  During the last two decades an increasing number of Common Cranes using the western route have spent the winter in northern Spain (Gallocanta) and France, probably in response to the increasing agricultural food resources and protection mesures at these areas. Our results on radiotagged cranes confirmed this trend: the percentage of marked cranes wintering in France increased from 12% in 1998-99 to 23% in 1999-2000. Four of these cranes spent their frst winter in Spain as juveniles with their parents, but remained in France as immatures in subsequent winter seasons, while no bird shifted southwards. These changes in wintering sites suggest that part of the northward shift observed during the last decades in the winter range could be due to the higher mobility of immature birds, which tend to aggregate at areas with more cranes and, thus more abundant food resources, while most adult pairs would probably tend to remain faithful to their traditional wintering areas in southwestern Iberia and Morocco.


Introduction

During the last two decades the numbers of cranes staging during migration and wintering at areas of northern Spain and France have increased (Alonso et al. 1987, 1994, Riols 1987, Bautista et al. 1992, Salvi et al. 1996). This northward shift of the traditional winter range of the species has probably been favoured by recent increases in agricultural food resources at these areas (Bautista et al. 1992, Génard et al. 1992, Alonso et al. 1994). In this paper we summarize the evidences supporting this trend and report on new data on internannual shifts of radiotagged cranes.


Methods

Between 1995 and 1999, a total of 93 Common Cranes were captured as flightless young (89 birds) or moulting adults (4 birds) at their breeding territories in Mecklenburg-Vorpommern, northern Germany, in an area comprising 690 km2 centered at 53º 36’N, 12º 00’Esee . All birds were provided with individual combinations of three colour-rings for visual identification, and 67 of them (63 young and 4 adults; 5 in 1995, 18 in 1996, 18 in 1997, 15 in 1998 and 11 in 1999) were additionally provided with backpack (47 birds) or leg-mount (20 birds) TW-3 radiotransmitters from Biotrack Ltd., United Kingdom. For details on capture and marking see Nowald et al. (1996).

During the winter seasons October to March 1995-96 to 1999-2000 we performed monthly surveys both with telescopes and radiotracking receiversof the area of  at Laguna de Gallocanta in northeastern Spain, and in the last two winters also at Arjuzanx and Camp de Captieux in southwestern France. In the two winters 1996-97 and 1997-98, in addition to the monthly surveys we installed an Automatic Location System (ALS; Radiolocation AB, Sweden) at 2 km from the main roost. The ALS recorded the presence or absence of all the radiomarked birds every 5 minutes continuously from mid October to mid March. In January, from 1996 to 2000 we made aerial searches with a Bonanza E-24 aircraft of the Spanish Air Force, of all radio-frequencies over the region Extremadura in SW Spain, which together with Gallocanta comprises about 85% of the estimated 70000 cranes wintering in the Iberian Peninsula (Alonso & Alonso 1990, 1996). To study the repeated use of the same wintering sites by adult cranes we used the sample of four radio-tagged adults and the locations of radio-tagged young of families where adults were not marked but their young were marked in consecutive years. We assumed that parents of the latter bred every year in the same nest (confirmed through pers. obs. at various nests with banded adults). The location of the offspring of these adults on subsequent winters enabled us to know the parents’ wintering site, since the family remains together until at least the initiation of spring migration (Alonso et al. 1984).


Results

Only one (20%) of 5 adults that could be tracked on two consecutive winters changed the wintering site in the second winter with respect to the first one. Both of these adults with data for three winters remained faithful to the same winter site. In contrast, 8 of 18 (44%) immature birds shifted their wintering site in the second winter, and 3 of 5 (60%) immatures with data for three and four consecutive winters shifted at least once (Fig. 1). The differences between adults and immatures were not significant due to the small sample sizes.

 

The number of radiotagged cranes located wintering in France increased from a 12% in 1998-99 (4 of 34 radiotagged birds) to 23% in 1999-2000 (9 of 40 radiotagged birds). Four of these cranes spent their first winter in Spain as juveniles with their parents but remained in France in subsequent winter seasons (Table 1). One bird (BuWBk ) shifted from France in its first winter to Gallocanta in its second winter, and again back to France. Another bird (GBuY) was not found during the first and second winters, and later located in France during the third and fourth winters. The parents of this bird spent the winter 1999-2000 at Gallocanta (see note 3 in Table 1). Finally, four birds which changed their wintering site within Spain showed a tendency to shift eastwards (YBuW, RBuW and RWBk within Extremadura) or northeastwards (WBuY between Extremadura and Gallocanta). None of the marked birds shifted southwards.

Discussion

Recent studies have documented the increases in numbers of Common Cranes staging or wintering at areas north of the traditional winter range of the species in soutwestern Iberia and nortwestern Morocco (Alonso et al. 1987, 1994, Riols 1987, Bautista et al. 1992, Salvi et al. 1996).  Figures 2 and 3 summarize these increases, respectively for Gallocanta (northern Spain) and France.  

In earlier studies we suggested that this northward shift observed during the last decades in the winter range of the species had probably been favoured by (a) recent increases in agricultural food resources at some areas, and (b) prohibition of hunting activities at feeding and, specially, roosting sites in these areas (Alonso et al. 1987, 1994, Bautista et al. 1992; see also Génard et al. 1992, for southwestern France). For example, Alonso et al (1994) showed that numbers of cranes counted at Gallocanta on a given fortnight during midwinter through a series of nine years were correlated with food availability during the previous fortnight (see Fig. 4).  

The interannual changes of radiotagged birds between wintering sites suggest that part of this northward shift could be due to a lower winter site fidelity of immature cranes. Immatures showed a higher mobility than adults, and a tendency to stay at areas with temporary abundant food resources and higher numbers of cranes, whereas adult pairs were more faithful to their traditional wintering areas in southwestern Iberia. We recorded four radiotagged cranes shifting from Spain in their first winter to France in subsequent winters, while no crane shifted southwards.

The higher mobility of immatures and non-breeders is supported by the negative relationship between numbers of cranes at a wintering area and the percentage of juveniles (Fig. 5). This negative relationship means that families tend to use smaller, more traditional wintering sites, whereas immatures and non-breeders tend to aggregate at sites with more birds, which offer more abundant food resources (Fig. 5a). A similar negative relationship was obtained between fortnightly censuses at Gallocanta, the main staging area in Spain, and percentage of juveniles (Fig. 5b). This relationship suggests that high increases in numbers at wintering areas are mainly due to the aggregation of immatures and nonbreeders.  

Two other studies have shown a higher mobility of immature cranes. In the first one, adult dominant birds foraging in flocks remained more faithful to their most preferred feeding zones within a wintering area, while subordinate birds, including both adults and immatures, switched among zones frequently (Alonso et al. 1997). Finally, some families showed a marked site fidelity, defending the same winter territories in consecutive years (Alonso et al. 1999, and in prep.).


Acknowledgements

G. Nowald, T. Fichtner, V. Günter, W. Mewes and many other helpers collaborated in crane radiotagging. Lufthansa, NABU, and WWF-Deutschland sponsored the marking campaigns. We are specially grateful to the Spanish Airforces (42 Group of the Getafe Air Base), who offered their aircraft to locate radiotagged cranes during winter. We thank J. Sampietro for his census data at Gallocanta 1992-2000, and C. Riols, A. Salvi, and personnel from LPO Aquitaine, Office National de la Chasse, Parc Naturel Régional des Landes de Gascogne and Réserve de Puydarrieux for counts in France.


References

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ALONSO, J.C., L.M. BAUTISTA & J.A. ALONSO. 1997. Dominance and the dynamics of phenotype-limited distribution in common cranes. Behavioral Ecology and Sociobiology 40: 401-408 

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GÉNARD, M., D. LANUSSE & T. BÉREYZIAT. 1992. Ressources en maïs et stationnement hivernal des grues cendrées (Grus grus) dans le soud-ouest de la France. Canadian Journal of Zoology 69: 2295-2299

NOWALD, G., W. MEWES, J.C. ALONSO & J.A. ALONSO. 1996. Colour-ringing of Cranes Grus grus in Germany: an interim report. Vogelwelt 117: 119-125

RIOLS, C. 1987. Wintering of Common Crane in France. Aquila 93/94: 123-136

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© Javier A. Alonso (1998-2002)
http://www.ecwg.org/
mailto:jaalonso@bio.ucm.es