NIJLAND F (2012) Breeding birds of winter-flooded grassland reserves in Friesland. LIMOSA 85 (1): 29-38.

In the Dutch province of Friesland, historically about 100,000 ha of grasslands outside the main dike systems were regularly flooded in winter. Nowadays, only about 3,000 ha of these 'summer polders' remain. This papers compares the breeding bird assembly of grasslands managed as nature reserves in summer polders with that of similarly managed reserves that are not flooded during winter. The study is based on territory mapping in 540 plot-years in the period 1984- 2009. Based on a comparison of breeding densities (table 1), 5-6 out of 19 species showed a significant preference for summer polders: Blue-headed Wagtail Motacilla flava, Ruff Philomachus pugnax, Common Quail Coturnix coturnix, Eurasian Curlew Numenius arquata and Eurasian Skylark Alauda arvensis. Common Shelduck Tadorna tatorna tended to prefer summer polders as well. Three or four species reached significantly higher densities in winter polders: Meadow Pipit Anthus pratensis, Oystercatcher Haematopus ostralegus, Northern Shoveler Anas clypeata, and, marginally significant, Black-tailed Godwit Limosa limosa. It is suggested that habitat conditions in summer polders such as a delay of the breeding season due to the inundation until early spring, low densities of soil invertebrates and presence of long, rough grasses in the breeding season underlie these differences in preference.

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