Change of breeding localities

Ring recoveries also lend support to the view that individual Common Crossbills have bred in widely separated areas in different years, taking the main breeding season in Norway Spruce areas as January-April inclusive. Movements of Common Crossbills that were ringed in the January-April of one year and recovered in the same period in a later year are shown in Figure 18.12. They include 10 recoveries of birds ringed as adults (representing breeding dispersal) and three of birds ringed as juveniles and recovered as adults (representing natal dispersal). These various birds were reported up to four years after ringing; their successive capture sites were between 28 and 3170 km apart, and included eight birds that had moved more than 2000 km. The main interest in these records lies in the great distances that separated the breeding areas of different years, which are thoroughly in line with the long and irruptive movements of the species. None of these birds was reported as nesting at the time of ringing or recovery, but they were all

Figure 18.12 Ringing and recovery sites of Common Crossbills Loxia curvirostra that were both ringed and recovered in different breeding seasons (taken as January-April in areas of Norway Spruce Picea abies). Continuous lines - ringed as adults (representing breeding dispersal); dashed lines - ringed as juveniles (representing natal dispersal). Compiled mainly from information in Schloss (1984); also from Danish Ringing Report (1931-1934), Swedish Ringing Report (1965), Swiss Ring recoveries provided by Dr L. Jenni, and Russian ring recoveries provided by Dr K. Litvin. Details listed in Newton (2006b).

Figure 18.12 Ringing and recovery sites of Common Crossbills Loxia curvirostra that were both ringed and recovered in different breeding seasons (taken as January-April in areas of Norway Spruce Picea abies). Continuous lines - ringed as adults (representing breeding dispersal); dashed lines - ringed as juveniles (representing natal dispersal). Compiled mainly from information in Schloss (1984); also from Danish Ringing Report (1931-1934), Swedish Ringing Report (1965), Swiss Ring recoveries provided by Dr L. Jenni, and Russian ring recoveries provided by Dr K. Litvin. Details listed in Newton (2006b).

within the usual breeding season from within potential breeding range. Moreover, no records have emerged of individuals in the same spruce locality in successive spruce years, which is not surprising as good crops seldom occur in the same locality two years running. This contrasts with the situation in Pyrenean Mountain Pine Pinus uncinata forests, where seed crops are relatively stable from year to year, and where Common Crossbills are more sedentary, with many individuals trapped in the same place in successive years (Senar et al. 1993). These findings from a pine area again imply that the frequent movements in spruce areas are driven by the huge annual fluctuations in regional crop sizes. Similarly, colour-marked Scottish Crossbills L. c. scotica were re-sighted in the same pine areas in successive years, or had moved over distances of at most a few tens of kilometres (Marquiss & Rae 2002). The same presumably holds in other pine areas in Europe, most of which hold local races of large-billed crossbills (Box 18.3).

The return of crossbills after an outward movement is analogous to the 'homing' of other migrants, but unlike most other species, crossbills sometimes breed before returning. This means that, if they are to reach their ancestral home, young raised in invasion areas have to make their first migration in a direction opposite to the first migration of their parents and of all other individuals raised on the regular range. Several ring recoveries of birds from Germany to northern Russia, and another from south Sweden to northern Russia, are consistent with such a movement. All these birds were hatched in breeding seasons following invasions. Perhaps the juveniles simply travelled with returning adults (as reported by Weber 1971-72). An alternative possibility is that the directional preferences of Crossbills differ according to geographical location, with birds leaving northern Russia moving mainly southwest, and those leaving central Europe moving mainly northeast. In one respect, this would be no different from other migrants, which head in one direction from their breeding areas and in the opposite direction from their non-breeding areas. But it differs in that Common Crossbills would need to take different directions at the same time of year, and both times after breeding, rather than at markedly different seasons, as in twice-yearly migrants. To judge from recent east-west displacement experiments on other bird species (Chapter 9), this might be expected, but it would be interesting to test at migration time the directional preferences of young Crossbills raised in the two regions.

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