LENSINK R, VAN TURNHOUT, C., BAKHUIZEN JJ, BOELE A, VAN DONGEN R, FOPPEN R, HULSEBOS B, LANJOUW R, RADEMAKER J & WOUDA S (2023) Increase and expansion of Middle Spotted Woodpecker Dendropicos medius in the Netherlands in 1995-2020: a textbook example of an invasion. LIMOSA 96 (1): 2-16.

The Middle Spotted Woodpecker re-established itself as a breeding bird in the Netherlands in 1995, after decades of absence and only a handful of confirmed breeding cases earlier in the 20th century. This was the start of a process of fast increase and expansion. In 2020 the population is estimated at 1900-2100 pairs, breeding in 11 of the 12 Dutch provinces, whereas colonisation has not yet come to an end.
The first part of the colonisation occurred in the southeast of the country (Limburg), near the German and Belgian border. From 2004 onwards breeding was noted in the east of the Netherlands (Twente, Achterhoek), and gradually other regions in the south and east were occupied (Fig. 2). Around 2010 the species reached the coastal region. In the first years after initial establishment increase and expansion were relatively slow, but between 2002 and 2006 it accelerated. Thereafter, the speed of colonization slowed down again. Between 1995 and 2020 population growth averaged around 10% per year and the rate of range expansion 6.4 km/year. Between 2002 and 2006 increase and expansion were twice as high. Most pairs breed and highest densities are reached in old broadleaf forests with a strong dominance of Oak species. Densities in the south (2 pairs/10 ha) seem to have stabilized, whereas in the east these are higher (4 pairs/10 ha) without any signs of saturation. Recently also broadleaved woodlands dominated by other tree species than Oak were occupied, as well as small woodlots and broad, old hedgerows.

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