LENSINK R (1996) The rise of exotic bird species in the Dutch avifauna; past, present and future. LIMOSA 69 (3): 103-130.

Netherlands is described. Birds are termed exotic when their breeding is facilitated through introductions or escapes from captivity. Reconstructions are presented of settlement and population development of exotic bird species in The Netherlands, based on published data, databases with results of standardized counts, and on questionnaires distributed among hundreds of birdwatchers. Three groups of species are distinguished. (a) Species originating from foreign areas, such as Egyptian Goose and Mandarin. (b) Species present in The Netherlands only in winter (White-fronted Goose, Barnacle Goose). 126 Their breeding here is facilitated by man; birds stay here all year and do not leave for arctic breeding grounds in spring. (c) Species partly originating from captivity, such as the Red-crested Pochard. At least 28 exotic bird species are known to have made at least one breeding attempt in The Netherlands in the last 25 years (Tab. 1). By 1994, about nine species had established self-sustaining feral populations. The Pheasant has the longest history of feral breeding, but is in decline at present. Egyptian Goose has been the most successful exotic in The Netherlands in the last 25 years. Following initial settlement, the rate of increase differs among species (Tab. 2); this depends on the number of release/escape sites, the initial number of breeding pairs and life history parameters. Among relatively successful species, herbivores dominate, followed by granivores (Tab 3.). Insectivores have had no success at all so far. A long life span, pair bond for life and year-round gregariousness seem to contribute to the success of feral breeding of exotic birds in The Netherlands. (1) The Chilean Flamingo (since 1983) and European Flamingo (since 1993) both breed in Germany at a few hundred meters from the Dutch border (Fig. 1,2, 3, 4). Nesting success was 47% in 1983-94. Currently the birds only breed in Germany and are present in The Netherlands the rest of the year. Up to 1983, flamingos mainly stayed in the SW-Netherlands, moving to Denmark in summer. Nowadays, birds leave the breeding colony in August and mostly stay along the Dutch Lake IJsselmeer up to October. In November they leave for the SW-Netherlands, returning to the colony from March onwards. It is calculated that since 1965, at least 120 flamingos have escaped from captivity and joined the feral flock. Starvation in severe winters was more intense than expected (70% instead of 95% survival). (2) The Black Swan nowadays breeds mainly in the SWNetherlands and along rivers in the central part of the country (Fig. 5, 6, 7, 8). Breeding was first reported in 1978. Since 1988 a marked increase has been recorded. Nesting success was 54%, with an average brood size of 6.4 at the time of first observation. In autumn, most birds stay in the SW-Netherlands, moving to the central floodplain in winter. Elsewhere no large numbers are observed. (3) The Canada Goose has been breeding in The Netherlands since the 1950s (Fig. 9, 10, 11, 12). Up to 1970, no feral population developed. In 1970 a few birds, escaped from a nearby Belgian site, started breeding successfully in the most southern part of the country. All birds were shot about 1976. Since 1981, however, breeding flocks established at several sites. In two areas, nesting success was 56%, with an average brood size of 3.4 fledglings per successful pair. A few birds remain near breeding sites in winter, the remainder gather along rivers in the central part of the country. In addition, an increasing number of Scandinavian birds winter in The Netherlands in severe winters, reaching their southwesternmost distribution in the riverine area. (4) In 1967, the Egyptian Goose successfully bred in The Netherlands for the first time (Fig. 13, 14, 15, 16). Since 1969, the number of breeding birds increased and the species spread over the country (Tab. 4). Today, the distribution extends to the German border. Two settlements are recognized, one near The Hague since 1967 and one in the province of Drenthe since 1981. Nesting success in the two areas was 40%, with an average of 5.4 and 3.8 fledglings for successful pairs, respectively. In July and August, flocks of up to 200 moulting birds are observed near breeding sites. In winter, birds behave as if sedentary, and are vulnerable to severe winters. (5) Breeding of the Ruddy She1duck was first recorded in the early 1970s (Fig. 17, 18, 19, 20). In subsequent years it was frequently found breeding, but the number increased very slowly. Nesting success reported is only 26%. Outside the breeding season, birds mainly gather along rivers in the central part of the country. Based on observed seasonal patterns, some migration occurs in spring and autumn. (6) In the early 1960s, first breeding of the Mandarin was recorded in coastal dunes near The Hague (Fig. 21, 22, 23, Tab. 5). In 1967, a pair bred along the eastern border of the Ve1uwe, a large afforested, hilly area with brooklets. Here, a large feral population established. Small numbers of breeding pairs are observed in a few other areas. Outside the breeding season, birds mainly gather near breeding sites. (7) The Ring-necked Parakeet first bred in The Hague at the end of the 1960s (Fig. 24, 25). A few years later a population settled in Rotterdam and thereafter in Haarlem and Amsterdam. These are probably all different escapes. Since about 1980, the number of birds increased, but the species is vulnerable to severe winters. Outside the breeding season, birds stay around their breeding site and use large communal roosts. In the first years after successful settlement of a species, the population grows exponentially. Later on, population size becomes more or less stable; this primarily due to density-dependent effects and habitat constraints. After this initial 5-10 year phase, only newly occupied areas account for further population growth. These phenomena are characteristic for species colonizing new areas. Most successful species are found in ecosystems disturbed by man, such as agricultural landscapes and parks in urban areas, where empty niches are probably available. It is expected that more species (groups 2 and 3 in Tab. 2,3) will show rapid population growth in the near future. For this reason, the list of successful species is likely to become longer. On the other hand, it is expected that some species will never be successful (group 4 in Tab. 2, 3). In general, negative effects of exotic species are not recorded, but many hybrids are observed, some of which are fertile. In winter, the number of arctic geese in The Netherlands is an important issue because of their (potential) damage to crops and pastures. The increasing number of successfully breeding exotic waterfowl is an unwelcome coincidence in current discussions on this topic. It is concluded that information about exotics in The Netherlands is incomplete (behaviour in the field, interactions with native species), since birdwatchers have not paid much attention to exotics. ##### Great Reed Warbler Acrocephalus arundinaceus Tufted Duck Aythya fuligula Greater White-fronted Goose Anser albifrons Canada Goose Branta canadensis Barnacle Goose Branta leucopsis Egyptian Goose Alopochen aegyptiaca Mandarin Duck Aix galericulata Common Pheasant Phasianus colchicus Rose-ringed Parakeet Psittacula krameri Chilean Flamingo Phoenicopterus chilensis Black Swan Cygnus atratus Bar-headed Goose Anser indicus Ruddy Shelduck Tadorna ferruginea Red-crested Pochard Netta rufina Greater Flamingo Phoenicopterus roseus Swan Goose Anser cygnoides Taiga Bean Goose Anser fabalis Magellanic Goose Chloephaga picta Muscovy Duck Cairina moschata Common Goldeneye Bucephala clangula Blue-and-yellow Macaw Ara ararauna Monk Parakeet Myiopsitta monachus Wood Duck Aix sponsa Ferruginous Duck Aythya nyroca Ruddy Duck Oxyura jamaicensis Red-legged Partridge Alectoris rufa Indian Peafowl Pavo cristatus Cockatiel Nymphicus hollandicus Common Waxbill Estrilda astrild Zebra Finch Taeniopygia guttata Chilean Flamingo Phoenicopterus chilensis Black Swan Cygnus atratus

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