WINDEN J VAN DER, HAGEMEIJER W, HUSTINGS F & NOORDHUIS R (1994) Vicissitudes of the Dutch Red-crested Pochard Netta rufina population. LIMOSA 67 (4): 137-146.

As part of a westward range expansion of the Red-crested Pochard, a breeding population established in The Netherlands in 1942. The species has remained a rare breeding bird ever since, with an estimated maximum population of 30-65 pairs (Tab. 1), but population size in the 1960s is likely to have been underestimated. This contrasts with population changes of Pochard and Tufted Duck in The Netherlands: formerly small breeding populations started to increase in the early 1940s as well, but then continued to increase to several thousand pairs nowadays. Breeding of Red-crested Pochards in The Netherlands is concentrated in a few lakes in the' Vechtplassen' area; this 'core area' holds at least 80% of the Dutch breeding population (Tab. 1, Figs.l, 2). The Dutch breeding population decreased during the 1970s and 1980s until no more than 6-15 pairs remained in 1989-1990. Breeding outside the core area was not recorded, and breeding success was poor. In 1991-1993 however, the Dutch population recovered to 20-30 pairs. Breeding was no longer confined to the core area and breeding success had improved. During the first period after settlement, the number of birds present outside the breeding season increased also. In the 1950s and 1960s relatively large numbers were recorded at lakes Zwarte Meer (650, September 1953), Veluwemeer (1600, October 1965) and Naardermeer (150, autumn 1970). The number of birds present in autumn during the 1970s and 1980s was considerably smaller. In 1992 and 1993 however, larger numbers were recorded (>100, Gouwzee lake, September-October). The total number of birds in The Netherlands in autumn 1993 was estimated at 120-150. This number corresponds with the estimated size of the Dutch breeding population, and virtually all birds present in autumn presumably are of Dutch origin. The fluctuations of sizes of both breeding population and autumn population in The Netherlands seem to be linked with changes in distribution and abundance of stoneworts, a major component of the birds' diet. This relationship is analysed in a paper elsewhere in this issue (Ruiters et at. 1994). Red-crested Pochard Netta rufina

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