WINDEN J VAN DER & SCHOBBEN HPM (2001) A new Black Tern Chlidonias niger night roost in the IJsselmeer region. LIMOSA 74 (3): 87-94.

One of the most important post-nuptial stopover areas in Europe for the Black Tern is the Ijsselmeer region , The Netherlands. The numbers staging in the area in the period June-August in some years exceed 100000. These birds use the area for moult and pre-migration fattening. Until the mid-eighties, at least three night roosts were present around the feeding areas, but afterwards these locations were abandoned, due to habitat changes and disturbance (Fig. 1). The last 15 years only the Balgzand reserve in the western Wadden Sea area was used as a regular night roost. Every year Black Terns in the Ijsselmeer region are counted weekly in the evening near the Balgzand night roost. In August 2000 the total numbers present at this roost were surprisingly low and at 6 August a suitable new night roost location was found near Enkhuizen . Black Terns were counted weekly in the evening in 15-minute periods simultaneously with the counts near Balgzand (Vatrop) until 1 September (Fig. 2)
     Up to 15000 Black Terns used the roost at Enkhuizen and in total 38000 Black Terns were present on 18 August on both ternaries. On ave rage 45% of all regional Black Terns used the Enkhuizen night roost. It remains unclear if the roost was used already on 1 August when the largest numbers were present at Balgzand. Black Terns arrived mainly around sunset at the Enkhuizen roost, but in general somewhat earlier than at the Balgzand roost. In the period after 8 August, Black Terns clearly arrived later in the evening (Fig. 3).
     In the situation with one night roost at Balgzand the most distant feeding areas are situated up to 90 km from the roost. With the new roost, the birds may save flying 50 km (one hour) per day, which corresponds to about 5% of their daily needs of Smelt Osmerus eperlanus. It is discussed whether the loss of this roost will limit the number of terns in years with low abundance of Smelt. The late arrival of birds at the roost by the end of August, already points towards a limitation in the feeding period (daylight). For this reason it is recommended to con serve this new area as a suitable night roost or to create comparable new areas in the Ijsselmeer region. Black Tern Chlidonias niger

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