Aliens Newsletter - ISSG

Figure 3. NARD Male Photo: Mark Hulme
The Ruddy Duck Oxyura jamaicensis (Fig. 3) is a
native of the Americas, where it has a stable population
of around 500,000 (Wetlands International
2006), but the species is an invasive non-native in
the UK and elsewhere in Europe. In 1948 four males
and three females were imported into a wildfowl
collection in the UK but by 1961 a number had escaped
or been released, and they had started breeding
in the wild. During the 1960s and early 1970s
the breeding range spread only slowly (Hudson,
1976). However, in the mid 1970s the UK population
began to grow much more rapidly, and its range
began to expand significantly. In 1983 the first feral
Ruddy Duck was recorded in Spain, raising concerns
about the risk of hybridisation with the Whiteheaded
Duck.
The risk to the White-headed Duck
The two species belong to the same stifftail genus
but have been geographically isolated without any
gene flow between them for between two and five
million years (McCracken et al. 2000). Ruddy
Ducks have been recorded annually in Spain since
1991, and the first Ruddy Duck x White-headed
Duck hybrids were observed in the same year
(Hughes et al. 1999). A total of 68 hybrids have
been recorded in Spain (Mario Saénz de Buruaga
pers. comm.), although the number has fallen in recent
years as a control programme for Ruddy
Ducks has become more efficient and fewer have
been arriving. At least 184 Ruddy Ducks have been
recorded (Fig. 4), in 19 provinces, since 1991 (Carlos
Gutiérrez and Mario Saenz de Buruaga pers.
comms.). It is known that Ruddy Duck x Whiteheaded
Duck hybrids are fertile to the second generation
in captivity, which poses an increased threat
to the survival of the White-headed Duck. However
almost all of these Ruddy Ducks have been
culled (as are hybrids) in order to prevent introgressive
hybridisation.
18 29/2010