|Monitoring van kustbroedvogels in de SBZ-V ‘Kustbroedvogels te Zeebrugge-Heist’ en de westelijke voorhaven van Zeebrugge tijdens het broedseizoen 2018|Stienen, E.; Courtens, W.; Van de walle, M.; Vanermen, N.; Verstraete, H. (2019). Monitoring van kustbroedvogels in de SBZ-V ‘Kustbroedvogels te Zeebrugge-Heist’ en de westelijke voorhaven van Zeebrugge tijdens het broedseizoen 2018. Rapporten van het Instituut voor Natuur- en Bosonderzoek, 2019(4). INBO: Brussel. 40 pp. https://dx.doi.org/10.21436/inbor.15947343
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This report describes the fluctuations in the numbers of breeding pairs in the Special Protected Area under the Bird Directive ‘Kustbroedvogels te Zeebrugge-Heist’ and in the adjacent western port of Zeebrugge during the period 1985-2017. Until recently, this was by far the most important breeding site for coastal breeders in Belgium and of high importance (> 1% of the biogeographic population) for the European tern populations as a whole. The conservation targets that were set in 2004 (being 22 ha of suitable nesting habitat without significant impact by land predators) for terns breeding in the Special Protected Area were never met since. The populations of the 3 tern species (Sandwich, Common and Little Tern) and of Black-headed Gulls breeding in the Special Protected Area have strongly declined after 2008 and the reproductive output has been extremely poor ever since. The decline is due to the presence of land predators, initially cats and rats, and from 2009 onwards also fox. The maximum number of breeding pairs amounted to respectively 4,067, 3,052 and 425 for Sandwich, Common and Little Tern,, but in 2016 these species no longer bred in the SPA. In 2017, fox was not present and the area again attracted Common Terns, although in lower numbers than before. In 2018, the SPA hosted 560 pairs of Common Tern, 23 pairs of Little Tern, 52 pairs of Black-headed Gull and 2 pairs of Mediterranean Gull, next to 60 pairs of Herring Gull and 354 pairs of Lesser Black-backed Gull. Considering the SPA conservation targets, the nests of the latter two species were systematically cleared. About 60% of the tern population chose to breed in the areas that were electrically fenced to prevent fox predation and disturbance. Eventually almost all tern chicks outside the fence were predated by fox, leading to a poor breeding success of Common Terns of 0.2 fledglings per pair. Inside the electric fence breeding success was not measured, but seemed somewhat higher. Also, in the non-protected western part of the Zeebrugge port, breeding numbers are in strong decline due to fox disturbance and predation and deterioration of the habitat. This area used to host large numbers of Herring Gulls (max 2,433 pairs in 2010) and Lesser Black-backed Gulls (max 4,760 pairs in 2011), but after 2013 both species strongly decreased in numbers as foxes frequented the breeding site. In 2018, 375 pairs of Herring Gull and 852 pairs of Lesser Black-backed Gull bred in the western part of the port, all on fox-free rooftops or in electrically fenced areas. The total population in Zeebrugge (SBZ-V included) amounted to 472 and 1,390 pairs, respectively. After 2013 the numbers of Herring and Lesser Black-backed Gull have increased elsewhere in Flanders and especially along the coast the number of breeding sites is rapidly growing. This suggests that part of the Zeebrugge colony has moved to both new and existing breeding sites. Indeed, recoveries of colour-ringed individuals revealed that there is a strong connection between Zeebrugge and other breeding sites along the Flemish coast. Other ringed gulls moved to existing colonies in the north of France, the south of the Netherlands and the south-east of the UK. Colour ring sightings further suggest that the gulls that colonised the SBZ-V most likely originate from the western part of the Zeebrugge port.