ENS BJ, VAN LEEUWEN M, OOSTERBEEK K, NIENHUIS J & ALLEN AM (2019) Wintering areas of Oystercatchers Haematopus ostralegus breeding in the Netherlands. LIMOSA 92 (2): 74-86.
In recent decades Oystercatchers have declined rapidly in
the Netherlands. As part of the Year of the Oystercatcher,
organized in 2008 to draw attention to the decline and
initiate research into its causes, volunteer ringing groups
were stimulated to colour-band Oystercatchers throughout
the country. Furthermore, a website was developed (www.
wadertrack.nl) where volunteer observers could report
observations of colour-ringed individuals and directly
gain access to their life histories. In the autumn of 2018
wadertrack contained approx. 200 000 observations of approx. 15 000
individual Oystercatchers. We analyzed connectivity, i.e.
the relationship between the breeding and non-breeding
(wintering) areas, for adult Oystercatchers, which shows
high site fidelity to both breeding and wintering areas.
We defined winter as the period between August 1 and
January 31 and summer as the period between March 1 and
June 30. Oystercatchers breeding in the northern part of
the country mainly wintered in the Wadden Sea, whereas
Oystercatchers breeding in the south mainly wintered in
the Delta area. However, there was no clear-cut demarcation
and some Oystercatchers breeding in the Delta wintered in
the Wadden Sea and vice versa. Furthermore, the wintering
area of a considerable number of birds remained unknown,
especially for inland breeders (on average 59%) and less so
for coastal breeders (on average 35%). We think these birds
winter in the Wadden Sea in areas rarely visited by observers
during winter, as well as estuaries along the coast of France
and the United Kingdom, where observation intensity may
be less or observations are not reported to Wadertrack.
Oystercatchers wintering in the Eastern Scheldt (containing
the largest area of intertidal mud flats in the Delta) suffer from
habitat loss due to erosion of the tidal flats. Oystercatchers
wintering in the Wadden Sea are confronted with hand
gathering of Cockles Cerastoderma edule, which increased
after mechanized cockle fishing was stopped. Though
Mussel Mytilus edulis beds returned after overfishing in 1990,
they are increasingly mixed with Pacific Oysters Magallana
gigas, which continue to increase. As a result of differences
in connectivity, Oystercatchers breeding in different parts
of the Netherlands will be affected differently depending
on whether they over-winter in the Wadden Sea, Delta or
outside the Netherlands.
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