peaks in the migration of the five kinds of spotted thrushes generally 

 do not coincide. Dates of departure in these species have evolved so all 

 the individuals of these closely related birds do not converge on one 

 area at the same time and subsequently exhaust the food supply. By 

 selection of staggered peak migration dates, evolution has distrib- 

 uted the members of this family more or less evenly throughout the 

 entire season. Likewise, in the eastern Mediterranean area, we find a 

 similar situtation in spring migration for three closely related 

 buntings; Cretzschmar's bunting comes through first, followed a few 

 weeks later by the Ortolan bunting and, at the tail end of the 

 migration period, the blackheaded bunting appears (Fig. 8). 



By Age 



The adults of most birds leave the young when they are grown. This 

 gives the parents an opportunity to rest and renew their plumage 

 before starting for winter quarters. The young are likely to move 

 south together ahead of their parents. This has been documented in a 

 number of species including our mourning dove, the common swift of 

 Europe, and storks. Mueller and Berger (1967) found an age-specific 

 migration pattern in sharp-shinned hawks passing through 

 Wisconsin. The immatures were much in evidence during 

 mid-September while the adults came through a month later. Far to 



Species Captured 



March April 



Figure 7. Average number of species captured daily in mist nets during spring migra- 

 tion at Eilat, Israel, in 1968. The number of species passing through an area on 

 migration will rise and fall similar to the number of birds counted in the area. In this 

 case two major movements came through about 1 month apart. 



36 



