Demographic patch size thresholds from a wader population guide optimal management areas for grasslands

Habitat management alone is often unable to reverse wader population declines because it doesn't address high predation rates of eggs and chicks. Focusing restoration on habitat features that reduce predation may be the key for successful management. Breeding patch size may be crucial for the reproductive success of waders, but very few studies have considered all important demographic variables when estimating patch size thresholds. We used long-term life-history data from an endangered Southern Dunlin ( Calidris alpina schinzii ) population breeding on Baltic coastal meadows to find optimal patch sizes for management. We tested for patch size effects on nest survival, nest predation, juvenile survival (from hatching to age one) and adult survival. We then used matrix models to examine patch size thresholds on predicted population growth rates and give guidelines on management decisions regarding patch size. Nest survival increased strongly with patch size among early nests from 24 % (10 ha) to 62 % (200 ha), but the effect became smaller as the breeding season progressed. Nest predation rates were the main determinant of the nest survival pattern. Juvenile survival was highest among chicks originating from medium sized meadows (120-150 ha) whereas adult survival showed no response to the natal patch size. Predicted population growth rates summarizing these responses showed clear patch size thresholds: population growth rates were < 1 among patches smaller than 90 ha. Hence, we recommend that managed grassland habitat patches for breeding birds should be an absolute minimum of 90 ha but preferably 120–150 ha in size to maintain population viability. • Grassland species such as waders are declining. • More efficient management is needed to halt the decline of grassland species. • Landscape characteristics may be linked to demographic rates. • Demographic rates of dunlins are positively linked to patch size. • Management should create habitat patches that are a minimum of 90 ha in size.