region; 10,000 in the Black Sea; and 26,000 in the Caspian Sea region of the 

 U.S.S.R. 



Migration Like Old World birds (Cramp et al. 1977), North American Common 

 Mergansers may make either short local migrations or more extensive ones (Palmer 

 1976b), and migratory pathways are still poorly known. Palmer (1976b) noted 

 that this species usually moves singly, in pairs, and in small groups that tend 

 to remain close to shore along coasts. Timken and Anderson (_in Johnsgard 1975) 

 indicated that groups of 8 to 9 birds are usually seen, and that flocks never 

 contain more than 30 birds. Apparently females and young migrate farther than 

 do most adult males (Palmer 1976b); this accounts for the preponderance of 

 sightings of the former in southeastern waters. 



In fall this species migrates later than most other ducks. Young and adult 

 females precede adult males by several weeks. On the Atlantic coast, migration 

 peaks in November; in Florida it does not peak until after mid-December (Palmer 

 1976b). Birds wintering from Mobile to Galveston Bay do not arrive until late 

 December (Bellrose 1976). The spring migration is relatively early, and the age 

 difference in migration is reversed from that found in fall. The spring migra- 

 tion of more southerly wintering birds may begin as early as mid-February (Pal- 

 mer 1976b), but the peak is in March and may continue into April. Data summa- 

 rized by Cramp et al. (1977) suggest that these migratory phenomena are similar 

 in Old World birds. 



HAB ITAT 



Breeding Palmer (1976b) regarded the Common Merganser as a species that 

 nests primarily in cool, clear waters of northern forests and western mountains. 

 Johnsgard (1975) believed that the preferred nesting habitat was ponds near the 

 upper portions of rivers in forested areas and clear freshwater lakes with for- 

 ested shorelines. He indicated that Common Mergansers prefer to nest on islands 

 in such situations. 



Nests are usually found in holes and concealed recesses. Holes in trees 

 are frequently used (Palmer 1976b). Other sites used include recesses beneath 

 boulders, dark spaces under the roots of fallen trees, crevices in cliffs, areas 

 under dense shrubbery, and hollows in stream cutbanks (Bellrose 1976, Palmer 

 1976b). Most nests are situated near water (Palmer 1976b) and may be found as 

 much as 50 ft (15 m) up in tree holes (White 1957 ^n Bellrose 1976). 



Common Mergansers also have used a wide variety of artefactual cavities as 

 nest sites. Nest boxes have been used in both the New and Old Worlds. Since 

 the availability of suitable nesting holes is believed to limit distribution 

 (Palmer 1976b), breeding populations of this species in some areas could presum- 

 ably be increased by providing such sites. Grenquist (1953 in Palmer 1976b) in- 

 dicated that as many as 63 of 100 nest boxes were occupied during one breeding 

 season in the Finnish Archipelago, and young hatched in 53. Other nest sites 

 provided by man include an abandoned lighthouse tower, bales of hay in an aban- 

 doned icehouse, and a stone pier supporting a covered bridge (Bellrose 1976). 



Feeding Johnsgard (1975) summarized preferred feeding habitat as fairly 



441 



