Recoveries by Condition for Common Merganser

Game species in Fennoscandia, Denmark, Iceland, and Russia. Most encounters obtained during the breeding season in late spring and early summer – ca. 65% in May-Jun. In total, the encounters based on alive birds form about 62% of all cases; however, their share fluctuates from 12% pre-1960s, about half (ca. 52%) during 1961-1990 to ca. 77% after 1991. Inversely, the share of recoveries based on dead birds largely decreased from about 74% before 1960 to ca. 21% after 1991. Shooting’s share dropped from ca. 56% of all cases pre-1960 to ca. 6% after 1991.

Drowning in fishing nets can be an important negative factor – ca. 10% pre-1960, 4.5% after 1991 (39% of all dead birds in Finland) (Saurola et al. 2013).

Most encounters obtained between 1975 and 2000, mainly in N Europe (ca. 76%).

Annual Movements for Common Merganser

The species undergoes a flightless wing-moulting period in late summer and autumn (Aug-Sep), either moving large distances to secluded moulting/staging sites (mostly males) or staying on/ close to the breeding grounds (Pearce et al. 2020). Tana River mouth and adjacent fjords in N Norway are considered the most important moulting site in Europe – biggest concentrations recorded in Sep (Wernham et al. 2002). The number of birds wintering in the Black Sea region increases from mid-Oct to mid-Dec (Scott, Rose, 1996). Birds breeding in N Europe overwinter mostly in the coastal waters of Baltic and North Seas, which are considered species’ main wintering areas in Europe. Return movements are evident from Jan to Mar and the breeding sites are occupied in Apr-May. Breeding sites in W & C Europe are usually reached back in Mar. Cases of abmigration are known (Bairlein et al. 2014).

Connectivity by Month by Region for Common Merganser

Post-breeding movements of the birds breeding in Fennoscandia and NW Russia start in late summer; they are later on encountered from mid-autumn until mid-winter or early spring (depending on the season) primarily in the region of Baltic and North Seas. Few birds move S to the Black Sea. Local breeders on the British Isles take short within-region movements for wintering; most males undertake long-distance moult migration in late summer and early autumn to N Norway where they form big concentrations joining other males originating from Fennoscandia and Russia. They are back on British waters in late autumn – early winter.

Most wintering sites are left by mid-spring. Breeding sites in W & C Europe are reached back in early spring, while those in N Europe – in mid- or late spring.