LENSINK R, OTTENS G, & HAVE VAN DER T (2013) Alien bird species in the Dutch avifauna: a story of colonisation and expansion. LIMOSA 86 (2): 49-67.

In this paper the population development of non-indigenous species in the breeding avifauna of The Netherlands is described. Four categories of non-indigenous species are distinguished: (1) invasive alien species, which successfully breed, increase in numbers and expand their range; (2) other (non-invasive) alien species, which have established (successful) breeding attempt(s), but do not increase nor spread; (3) introduced geese and ducks, that are native as migrant and wintering species, but whose establishment as breeding birds is not natural, and (4) feral species, domesticated forms now successfully breeding in the wild, of which some are increasing and spreading.
Presently 19 invasive species are recognized, of which 17 breed annually in the Netherlands, and two species of flamingo breed just across the Dutch-German border (table 1). Since the first invasive species were noticed in the1960s, the number of species involved has risen (Fig. 2). All species involved are residents and censuses of breeding and nonbreeding birds yield similar estimates of annual increase (Tables 1, 2, Fig. 2). Most have increased with more than 10% per year over the past decades, but rates of increase have slowed down for most species in the last 10 years (Fig. 1). More than 20 other non-indigenous species have made at least one breeding attempt in recent years (Fig. 3). The number of species involved is increasing per decade.
In de past 30 years several geese and ducks that were hitherto known only as native winter visitors started to breed in the Netherlands. The first was Barnacle Goose (considered to have escaped from waterfowl collections), followed by Greater White-fronted Goose (released birds formerly used as hunting decoys). In recent years a few more species have followed (Tab. 3, Fig. 1). Among domesticated forms, a few decades ago only three species had significant feral populations: feral pigeon, feral duck and Mute Swan. An increase was noticed mainly among domesticated waterfowl (Table 4, Fig. 1).
The increasing and expanding species share certain features: they are originally residents, and mainly herbivorous (Fig. 4). Piscivore or granivore feeding habits are less common, but some species with these habits have been successful. Migratory species and insectivores are lacking among the successful non-indigenous birds. Many successful species are common in the bird trade and hence well-represented in collections from which they can escape. In the near future more species can be expected to become successfully established in the wild. The ongoing climate change (Fig. 5) may help invasive species with a (sub)tropical origin. More detailed information about exotic species in The Netherlands can be found in Lensink et al. (2013b), at www.buwa.nl.

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